Cucurbit Conference 1992

Raleigh, North Carolina

North Carolina State University hosted a cucurbit conference in 1992 that represented many groups doing work on the cucurbit crops. Below are the abstracts from that conference.

Nematode Resistance in Cucumber

S. Alan Walters, Todd C. Wehner and Kenneth R. Barker

North Carolina State University &endash; Raleigh, NC 27695

Root knot, caused by (Meloidogyne spp.) is the most important disease of cucumber (Cucumis sativus L.) in North Carolina, causing an average annual yield loss of 12 %. Currently, there is no known resistance in cucumber, except to M. hapla, and many of the nematicides are being taken off the market.

In previous tests, best results were obtained when plants were grown from seed in 150 mm diameter clay pots and two-week old seedlings of C. sativus or C. metuliferus were inoculated with 5000 nematode eggs per plant and evaluated 8 weeks later. The U.S. germplasm collection of 900 cultigens of C. sativus (728 accessions, 36 breeding lines and 136 cultivars) and 24 accessions of C. metuliferus was evaluated for resistance to three root-knot nematodes, M. incognita r. 3, M. arenaria r. 2 and M. hapla. All cultigens evaluated were resistant to M. hapla and all accessions of C. metuliferus evaluated were resistant to all root-knot nematodes tested. Most cultigens of C. sativus evaluated were susceptible to all nematodes tested besides M. hapla. Only 113 cultigens possessed some level of resistance to M. arenaria r. 2 and 112 cultigens possessed some level of resistance to M. incognita r. 3. Considering both M. arenaria r. 2 and M. incognita r. 3, most cultigens of C. sativus tested were susceptible (834 of 884). Only 3 cultigens were found to be highly resistant overall, ‘Green Thumb,’ ‘Southern Pickler’ and LJ 90430.

A retest of the extreme cultigens (best and worst) was conducted involving 34 cultigens of Cucumis (14 accessions, 12 cultivars and 6 breeding lines of C. sativus and 2 accessions of C. metuliferus) for resistance to 4 root knot nematodes, M. incognita r. 1, M. incognita r. 3, M. arenaria r. 2 and M. javanica. The two accessions of C. metuliferus evaluated (PI 482452 and PI 482443) were highly resistant to all 4 root-knot nematodes. Most cultigens of C. sativus evaluated were susceptible to all 4 root-knot nematodes. None was highly resistant overall, and only LJ 90430 was moderately resistant overall with a gall index of 29. ‘Green Thumb’ was not resistant to any of the 4 root-knot nematodes. Several cultigens of C. sativus possessed some level of resistance to M. arenaria r. 2; those were ‘Mincu,’ LJ 90430, ‘Southern Pickler,’ ‘Producer,’ Ohio MR 17 and ‘Poinsett.’ LJ 90430 was the only cultigen of C. sativus that had resistance to M. javanica. None of the C. sativus cultigens evaluated had resistance to either of the M. incognita races tested.

Inheritance of resistance studies to M. arenaria r. 2 and M. javanica in LJ 90430 are currently being conducted. Resistance to M. javanica from LJ 90430 x Sumter appears to be a single recessive gene, mj. Resistance appears to be controlled by a few major genes, and could be incorporated into elite inbreds using backcross methods.

Ulocladium Leaf Spot of Cucumber Caused by Ulocladium cucurbitae

Thomas A. Zitter

Department of Plant Pathology, Cornell University, Ithaca, NY 14853-5908

Ulocladium cucurbitae (Letendre and Roumeguere) Simmons is responsible for a leaf spot disease of cucumber. Although attributed to other causal organisms, Ulocladium leaf spot has probably occurred in Europe (Czechoslovakia, 1972; glasshouse crops in England, 1974) and, more recently in breeding plots near Ithaca throughout the 1980s. The disease was first detected in commercial cucumber fields in western New York in 1988 (Zitter & Hsu, 1990).

Immature lesions are dark brown and measure 1-2 mm in diameter. As the lesions age, the central area becomes beige, surrounded by a dark brown ring and a circular brown halo measuring 6-7 mm in diameter.

U. cucurbitae produces dark conidia that measure 12-30 µ long x 12-21 µ wide. The conidia are usually borne singly or rarely in chains of 2 and are attached to the tip and closely along the sides of conidiophores, forming a cluster of conidia. That species, like other Ulocladium species, is unique in producing both ulocladioid-, intermediate- and alternarioid-type conidia in culture and on tissue depending upon age and temperature conditions (Zitter & Hsu, 1992). The alternarioid morphology dominates in an early culture at low temperatures (8 C), the intermediate and later (10 days) ulocladioid at 21 C, and the ulocladioid form dominates at 27 C. Examination of lesions from the field may show a mixture of conidial types. Additionally, Alternaria alternata (Fr.:Fr.) Keissl. can colonize the necrotic tissue produced by Ulocladium infections and further confuse conidial identification.

Attempts to infect other cucurbits were unsuccessful. The organism survives between crops on infected debris in the soil, probably as dormant mycelium or as Chlamydospores (thick-walled modifications of the mycelium) similar to Alternaria spp. Commercial cultivars vary in their susceptibility to Ulocladium leaf spot. Resistant cultivars developed by H.M. Munger including Albion 87, Marketmore 87, Dryden 87 and Poinsett 87-8 provide an excellent method of disease control.


Zitter, T.A. and L.W. Hsu, 1990. A leaf spot of cucumber caused by Ulocladium cucurbitae in New York. Plant Dis. 74:824-827.

Zitter, T.A. and L.W. Hsu, 1992. Influence of temperature and fungicide on germination, growth and virulence of Ulocladium cucurbitae on cucumber. Phytopathology 82:358-362.

Bacterial Seed Treatments for Induction of Systemic Disease Resistance in Cucumber

S. Tuzun and J. Kloepper

Department of Plant Pathology and Biological Control Institute, Auburn Univ. and Alabama Agric. Exper. Station, Auburn AL 36849-5409

Utilizing cucumbers as a model system, 96 isolates of confirmed plant growth promoting rhizobacteria (PGPR) were screened in planta to determine their ability to induce systemic resistance against Colletotrichum orbiculare, the causal agent of anthracnose disease. Seed treatment with four bacterial isolates significantly protected cucumbers against C. orbiculare in repeated experiments. The inducing strains did not produce antifungal compounds in vitro. Significant protection was also evident against cucumber mosaic virus (CMV), Fusarium oxysporum, a fungal wilt pathogen, and Pseudomonas lachrymans, a bacterial disease causing agent, by seed treatment with select PGPR strains. The protection against C. orbiculare and yield increases were also evident in two field studies performed during summer of 1992. In one field trial, indigenous cucumber beetles introduced bacterial wilt, caused by Erwinia tracheiphila. The incidence of wilt was significantly reduced in plots treated with the inducing bacteria, compared to controls. Studies probing mechanism(s) of protection indicated that bacteria enter roots of the treated plants. However, the bacteria appeared to be limited to this area. Macroscopic and microscopic studies indicated no evidence of necrosis. Protection is correlated with increases in peroxidase activity indicating host involvement, however, changes in chilinase activity did not appear to be correlated with protection. These results indicate that seed treatments with specific bacteria may enhance host defenses, leading to reduced plant damage by several pathogens.

Middle Eastern and Asian Cucumbers &endash; Cultivars, Cultural Conditions and Usage

Ken Owens

PetoSeed Company, Inc. &endash; Woodland, CA 95695

The Middle East (Beit Alpha) cucumber market is divided into two basic types &endash; those used in the open-field and those used in the greenhouse. The cultivars used in most cases are completely different for each growing method. The major open-field cultivars used are Dama, Miracross, Babylon and Celebrity. The open-field types are grown during the warmer times of the year on the ground. Powdery and downy mildew and many virus diseases are common problems. Greenhouse grown Beit Alpha cucumbers are primarily parthenocarpic and are grown year round in either loosely closed plastic houses or tighter, air conditioned fiberglass or glass greenhouses. The greenhouse area has grown rapidly in the past 10 years. There are many different cultivars used and the cultivar usage changes rapidly in the greenhouse market. The major parthenocarpic cultivars are Sahara, Rawa, Hana, Shams, Farah, Yazan and Hiba. Virus and mildew diseases are again major impediments to production in the greenhouse as well as insect and nematode problems. Most cucumbers in the Middle East are used fresh (whole, sliced, chopped) but there are some processed into pickles.

Several different types are used in the Far East (Asia), including long spiny Chinese types; smooth, large, dark green fresh market types used in Taiwan; petite burpless types used in Japan, Taiwan and some southern Asian countries; and very light green types (short and long) in Thailand, Malaysia, Indonesia, India; as well as a few American slicers used for the hotel trade and in Australia. Cultural conditions usually involve growing on trellises outdoors or in plastic houses. Primarily mildews and viruses are problems again. Pickles are used in some countries but primarily fruit are used fresh. The major hybrid cultivars come from Sakata, Takii, Known You, though much open-pollinated seed is still used.

Pickling Cucumbers in Europe

André Beekman

Royal Sluis &endash; Enkhuizen, The Netherlands

Pickling cucumbers are grown and eaten in almost every country in Europe. Data will be shown on the most important pickling cucumber growing areas. In many countries the acreage grown with pickling cucumbers is decreasing. Details on the cultivation (most important diseases, sowing, planting, forcing, hravesting, etc.) will be given. Attention is given to the (history of) machine harvest of pickling cucumbers in Europe. The last 10 years there has been a quick shift in the spectrum of pickling cucumber varieties grown in Europe. Most important is the change over to parthenocarpic varieties. Backgrounds of these changes are presented. Information on varieties grown in Europe is given.

On the one hand the data and examples in the lecture reflect the diversity in cultivation, harvesting, processing and consumption of pickling cucumbers in Europe. On the other hand general trends with respect to the above mentioned aspects of pickling cucumbers in Europe can be deduced. Comparisons with the situation in the USA will be made where possible.


Anonymous, 1992. KEN cijfers internationale markt van groenten en fruit. Commodity Board for Fruit and Vegetables, P.O. Box 90403, Den Haag.

Weichmann, J., 1987. Textur parthenokarper Einlegegurkensorten. Ind. Obst- u. Gemueseverwert. 72:94-95.

Identification and Development of High Carotene and Ascorbic Acid Breeding Stocks in Cucumber

J.P. Navazio and P.W. Simon

U.S. Department of Agriculture, Agricultural Research Service, Department of Horticulture

University of Wisconsin &endash; Madison, WI 53706

In a program to improve the nutritional quality of cucumber (Cucumis sativus L.), diverse genetic sources of high carotene (vitamin A precursor) and ascorbic acid (vitamin C) have been used to evaluate the expression and genetics of those important characteristics. An oriental cucumber (Cucumis sativus L. var. xishuangbannanesis) has proven to be a particularly useful source of high carotene content , with relatively simple inheritance of that trait. The timing of the development of yellow or orange pigmentation varied among genetic stocks derived from a combination of that oriental germplasm with adapted U.S. materials. Certain stocks exhibited color development in the mesocarp as early as the 2B stage, whereas pigmentation developed much later in other stocks. Orange color was very well retained in the overnight refrigerated product. Relatively high ascorbic acid levels were found in cucumber germplasm adapted for U.S. production. Retention of high carotene and high ascorbic acid levels is being evaluated in both the overnight refrigerated product and salt mediated fermentation pickles. The usefulness of nutritionally improved cucumbers will be discussed.

Grading/Handling Concepts

Ervin G. Humphries

Biological and Agricultural Engineering Department, North Carolina State University &endash; Raleigh NC 27695-7625

Most grading machines can perform at acceptable levels of accuracy if the product is fed onto the sizing slots or screens in a single layer. Unfortunately, that prerequisite is seldom met; poor feed conveyor design, modifications to existing systems to increase capacity, and improper operation can contribute to non-uniform product flow and subsequent errors in sizing. That work describes recent investigations of a simple mechanism for delivering cucumbers (or other similar items) to a sizing machine in a single layer. A series of stationary parallel rollers rotating in the same direction has the unique action of transporting product perpendicular to the rollers axes and reducing a bulk pile to progressively smaller depths. Thus the contents of a dry hopper can be uniformly fed and transported to a grading screen. Test results indicate that 1 3/4 inch diameter rollers on 2 1/8 inch centers can reduce pile depth by a factor of 3 for each roller the pile traverses. In addition, if a wider spacing between two or more successive rollers is introduced into the system, the mechanism also serves as a size separator. That concept also has potential to act as a “scalper” on the harvesting machine to remove oversize product when installed as part of an in-line conveyor.

Impact Damage on Pickling Cucumbers

Dale E. Marshall

U.S. Department of Agriculture, Agricultural Research Service, Agricultural Engineering Department, Fruit and Vegetable Harvesting Unit Michigan State University &endash; East Lansing, MI 48824-1323

The mechanical harvesting, transfer to transport truck, transfers in receiving and handling facilities, and vibratory grading operations in greenstock receiving and grading lines are where major impacts can occur which cause excessive fruit damage (broken or split fruit and visible internal damage).

To reduce this damage a number of reinforced vinyl “hammock” designs were suspended 0.6 to 0.9 m above the bottom of the container on rubber elastic springs. As the vegetables fell into and filled the hammock it settled to the floor. The hammock and spring system provided cushioning and significant damage reduction compared to when vegetables directly impacted on the floor. Another hammock design using a central slot permitted the vegetables to be cushioned by the hammock, but then flow through the slot onto the floor with less strain on the hammock.

Field studies showed a 46% to 55% reduction in broken or damaged cucumbers in the first 6 to 8 in. of cucumbers dropped onto the hammock compared to the first 6 to 8 in of cucumbers dropped onto the steel floor. When the slit hammock was used the average damage was reduced even more.

Compared to active systems such as those using an air-bag, the hammock design is more simple, relatively inexpensive, and a passive method that will reduce impact damage. The hammock can be easily and quickly removed if desired. A punctire will not prevent its use, and repairs can easily be made.

There are several separate handling operations required to move vegetables from the field to consumer package. Each individual handling operation must be examined to eliminate the severe impact damage now occurring. To maintain field level quality for the consumer, the impact damage encountered in field, packing- and processing-plants must be reduced.

The Re-firming Effect of Calcium on Thermally-Softened, Calcium-Depleted Cucumber Mesocarp Tissue

Jesse C. Mabellos and Roger F. McFeeters

U.S. Department of Agriculture, Agricultural Research Service, Food Science Department, North Carolina State University &endash; Raleigh, NC 27695-7624

A substantial amount of refirming was observed when calcium was added to thermally-softened, calcium-depleted cucumber mesocarp tissue. For instance, nonheated, firm tissue with a firmness of 12 Newtons (N) increased in firmness by about 8%. Addition of 20 mM calcium to tissue softened to 3 N increased the firmness by 35%. The tissue firming effect of calcium was greater at 25C than at either 4C or 37C. Barium and strontium had a greater firming effect than calcium, but magnesium did not cause an increase in firmness. The firming effect with calcium was constant from pH 3 to pH 8. That is different than the pH effect on calcium inhibition of softening rate previously investigated. The firming effect of calcium was prevented when as low as 200 mM sodium chloride was added with calcium. That work indicates that calcium may have two effects in blanched cucumber tissue. In addition to inhibiting the rate of softening, it also can increase the firmness of tissue to a limited degree.

Single Injection HPLC Analysis of Sugars, Alcohols and Acids in Cucumber Fermentations

Roger F. McFeeters

U.S. Department of Agriculture, Agricultural Research Service, Department of Food Science, North Carolina State University &endash; Raleigh, NC 27695-7624

The principal changes which occur in food fermentations, including cucumber fermentations, involve the degradation of sugars and certain organic acids and formation of organic acids and alcohols. The analysis of those compounds continues to be a difficult problem due to their similar chromatographic properties and lack of spectroscopic characteristics which allow differentiation and high sensitivity detection. For the first time an HPLC technique was developed to analyze glucose, fructose, glycerol, ethanol, n-propanol, malic acid, succinic acid, lactic acid, acetic acid, propionic acid, and butyric acid with a single injection. Those are the major compounds which disappear or form during normal or aberrant cucumber fermentations. A conductivity detector and pulsed amperometric detector were connected in series for the detection of those compounds. Good quantitation was obtained whether calculations were based upon peak area or peak heights. Either internal or external standardization may be used. The sensitivity of detection was improved for all compounds except ethanol and n-propanol as compared to refractive index detection, which has been the primary method used for the analysis of that group of compounds. Analysis of all of those compounds by refractive index detection requires at least two injections on two different chromatographic columns.

Non-Destructive Evaluation of Pickling Cucumber Using Visible/Infrared Light Transmission

A. Raymond Miller

Department of Horticulture, Ohio State University, OARDC, Wooster, OH 44691

A non-destructive method was developed which utilized a modified water-core tester to evaluate the internal quality of pickling cucumbers. The method involved measuring the relative amount of visible/infrared light passing through the longitudinal midsection of whole cucumber fruit. Light transmission was quantified on an unitless sigmoid scale from 1 to 10, transmission and scale values positively related. Immediately after hand harvest, size 3B cucumbers exhibited transmission values between 2 and 3, regardless of cultivar. Following a mechanical-stress treatment, which simulated bruising incurred during harvesting and handling of cucumbers, the internal quality of the fruit declined and was associated with an increase (up to a value of 6) in light transmission compared to non-stressed fruit. Light transmission increased as the severity of stress applied to the fruit increased, and high light transmission values were evident throughout a 48 h storage period at room temperature. Light transmission values also increased as fruit diameter decreased, but values within a particular size class were consistent. Machine-harvested fruit (size 3B) evaluated just prior to processing exhibited light transmission values from 2 to 8, but the majority of fruit fell within the transmission range of 2 to 3. When fruit exhibiting different light transmission values were speared, processed and then visually evaluated by panelists, spears prepared from fruit exhibiting high transmission values were judged to be of lower quality than those prepared from fruit exhibiting low transmission values. These data indicate that visible/infrared light transmission may be a valuable tool for detecting poor quality cucumbers prior to processing, and could allow the segregation of high and low quality fruit on a large scale basis.

Water and Heat Stress Effects on Cucumber Production

J. Staub and J.P. Navazio

U.S. Department of Agriculture, Agricultural Research Service, Department of Horticulture, University of Wisconsin, Madison, WI 53706

The most prevalent environmental stress affecting plants is lack of water. Worldwide losses in crop yields from water deficits exceed the losses from all other types of stress combined. Water stress can result not only in yield reductions, but also may adversely affect fruit quality at harvest and during post-harvest storage. For instance, the frequency and severity of pillowy fruit disorder (PFD) in cucumber (Cucumis sativus L.) is influenced by plant water stress and postharvest storage. That anomaly appears as brown water-soaked lesions in processing cucumber and can result in significant product loss. It is not known whether heat and humidity play a significant role in the production of PFD. The interaction of environmental factors may influence the response of cultigens to soil moisture deficits. Therefore, several experiments were designed to test the effects of humidity and temperature on pillowy development and the response of cultigens to water soil deficits. Four cultigens were grown in differing temperature (23 and 30 C) and relative humidity (35 and 75%), pollinated, and fruit were harvested and rated for the incidence and severity of PFD. Regardless of relative humidity, fruit matured under high temperature had more PFD symptoms than those matured in low temperatures. Results indicate that temperature is a factor that influences the development of PFD. Eight cultigens tested for their response to soil water deficits were ranked based on stomatal conductance (mol.m-2.s-1), plant dry weight, fruit number and weight. Based on those criterion cultigen differences were observed. ‘Flurry’, H-19, ‘Fancipak’, and ‘Regal’ were considered most resistant to water stress. H-19, however, produced fruit which were significantly more susceptible to the development of PFD when compared to other cultigens.

Weed Control Options for Cucumbers

John O’Sullivan and W. J. Bouw

Horticultural Experiment Station, Simcoe, Ontario, Canada

Poor weed control is a major factor limiting yield in commercial cucumber production. Seedling cucumbers compete poorly with weeds and throughout their growing period. In the absence of competition, weeds proliferate causing yield reduction and interference with efficient harvest. Herbicides are essential for weed control since the growth habit of cucumbers makes mechanical weed control difficult during much of the growing season. The sensitivity of cucumbers to chemical weed control limits the choice of herbicides. Currently, “Prefar”, “Alanap”, “Poast”, “Curbit” and “Dacthal” are registered. “Roundup” and “Gramoxone” can also be used, however, those are non-selective, post-emergence contact herbicides, suitable for use only prior to planting of the crop.

In recent years, several effective herbicides have been withdrawn from registration on cucumber. “Chloramben” and “Dinoseb”, both excellent grass and broadleaf herbicides, are no longer available. The removal of those products from use means that the cost of production, due to the increased requirement for cultivation and hand-hoeing, has increased by approximately l0%. The number of herbicides that can be safely and effectively used in the production of cucumbers is now severely limited and those herbicides that are available often give poor weed control.

The objective of that research was to develop information about the selectivity of new herbicides for use on cucumbers. Cucumbers are extremely sensitive to most herbicides. In addition, the production area of cucumbers in any one season is relatively limited and herbicide manufacturers express little interest in using their resources to develop the data required for the registration of new herbicides. Herbicides that have been tested for weed control in cucumbers include “Devrinol”, “Dual” and “Basagran”. Because of fairly significant crop injury, those herbicides have never been registered for use.

New herbicides that potentially could be used in cucumbers include “Fusilade” and “Assure” for grass control and “Command” for broadleaf control. Of those products, the registration of “Command” is by far the most important since it is a broadleaf herbicide, something that is currently lacking in the production of the cucumber crop. “Command” is currently registered for use on other vine crops such as Pumpkin and Squash. However, it is generally recognized that those crops have more tolerance to herbicides than do cucumbers. Research on cucumbers with “Command” shows that the rate of application must be between 0.25 and 0.50 kg/ha. Rates in excess of 0.50 kg/ha will cause significant crop damage. Injury symptoms observed have included white and variegated foliage, stunting and yield reduction. Crop injury was eliminated or drastically reduced in research trials by reducing the herbicide rate between 0.25 and 0.50 kg/ha. Control of susceptible annual weeds was acceptable at the lower rates evaluated. “Command” has the potential to be a useful new herbicide for use in processing cucumbers.

Cucumber Mixture Effects on Yield in Multiple Harvest

Jonathan R. Schultheis and Todd C. Wehner

Department of Horticultural Science, North Carolina State University &endash; Raleigh, NC 27695-7609

In some U. S. production areas, seeds of different cucumber cultivars have been mixed before planting with the idea of improving or stabilizing yield. The objective of this study was to determine whether mixtures actually improve yield compared with monoculture. Treatments were 3 pairs of cultigens (Gy 14 + M 21, Gy 4 + WI 2757, Regal + Carolina) and 5 component mixtures (0, 25, 50, 75 and 100% of the first cultigen). Pollination was not limiting since borders were planted with ‘Sumter’ as the pollenizer. Fruits were harvested from 5 environments (spring 1989, 1991 and 1992, and summer 1989 and 1992). Fruits were hand harvested twice a week for a total of 4 to 8 times in each environment. Fruits were graded according to North Carolina standards. Data were collected on yield, earliness, vine size and disease resistance.

Environments differed. Early and total fruit weight, and dollar value were greatest when M 21 and WI 2757 were planted in pure stands (0% of the other cultigen). The combination of 25% Carolina and 75% Regal had slightly higher early and total fruit weight and dollar value than the other mixtures of that pair. Disease incidence was not significantly affected by the various mixtures evaluated in this study.

The practice of arbitrarily combining cultigens generally does not offer an advantage over monoculture. However, mixtures should be evaluated for overcompensation to determine whether specific combinations offer advantages.

Chilling Resistance in Cucumber

Todd C. Wehner and Lambertus Smeets

Department of Horticultural Science, North Carolina State University &endash; Raleigh, NC 27695-7609

Chilling damage occurs every few years in cucumbers planted early in the spring production season by growers wanting to take advantage of high prices for early production. Chilling was investigated in cucumber to determine whether genetic resistance was available, using a four stage approach: development of a seedling test, verification against field tests, screening the germplasm collection, and measurement of heritability.

A seedling test method was developed by running factorial experiments in the NCSU phytotron on growth temperature (30/26, 26/22 or 22/18°C), chilling duration at 4°C (0, 3, 5, 7 or 9 hours), light intensity during chilling (0, 150, 270 or 500 mmol.m-2.sec-1), chilling stage (cotyledon, 1st true leaf), and 9 cultigens chosen for diversity. Best results were obtained using growth temperature of 22/18°C, chilling seedlings at the cotyledon stage for 7 hours at 4°C under 500 mmol.m-2.sec-1, and rating damage 3 days after chilling. Little John, Pixie and Chipper were most resistant, and Marketmore 76 and Gy 14 were most susceptible.

The seedling test was checked against field performance for correlation using several planting dates. The 30 March planting received a light chilling and the field ratings were correlated with phytotron tests (0.86**). The 6 April planting was killed by a heavy chilling, and the 18 April planting received no chilling.

The germplasm collection of 884 cultigens was screened using the seedling test. Cultigens were planted in 2 replications with 3 plants each. Of 821 cultigens with good data, the most resistant were ‘Dual’, PI 379283, M 41, ‘Southern Pickler’, PI 171613, PI 267942 and PI 426629. Most susceptible were PI 342951, ‘Olympian’, PI 422183, PI 264665.

Heritability was measured in two populations (NCWBP and NCES1) using parent-offspring regression. The standard method was used to test 416 plants of each population, which constituted the parents. Parents were transplanted to isolation blocks for intercrossing to produce one half-sib family of each. The half-sib families were tested in the same way as the parents. Data were corrected for position in the phytotron chamber, and were transformed and scaled to improve normality. Narrow-sense heritability for cotyledon rating 3 days after chilling was estimated at 8% (9% scaled) for NCWBP and 22% (37% scaled) for NCES1. Rating in the 1st true leaf stage generally resulted in lower heritability. Correction for chamber position did not improve the heritability, nor did transformation.

Biological Control of Damping-off in Cucumber

M. Cubeta, R. Vilgalys and E. Echandi

Department of Botany, Duke University &endash; Durham, NC 27708, and Department of Plant Pathology, North Carolina State University &endash; Raleigh, NC 27695-7616

Selected nonpathogenic isolates of binucleate (BN) Rhizoctonia spp. were evaluated singly and in combination with seed treated with biocontrol bacteria, fungicides, or osmopriming agents in the greenhouse and the field for control of Rhizoctonia and Pythium damping-off of cucumber. Cucumber seed treated with different osmopriming agents (KNO3, NaCl or PEG8000) or strains of Enterobacter clocae and sown in soil alone or combined with BN Rhizoctonia spp., did not protect cucumber seedlings from Rhizoctonia and Pythium damping-off in the field. Amendment of BN Rhizoctonia isolate 232-CG to soil and combining it with seed treatment or soil application of metalaxyl resulted in decreased (P=0.05) levels of Rhizoctonia and Pythium preemergence damping-off in 12 naturally infested fields at five geographic locations when compared with the nontreated control or 232-CG alone. Seed treated with metalaxyl and sown in soil amended with 232-CG had less (P=0.05) Rhizoctonia and Pythium preemergence damping-off at 20 and 30% of the field sites when compared to seed treated with metalaxyl and captan, respectively. Additional studies to characterize isolates of Rhizoctonia solani which cause damping-off and root rot of cucumber in North Carolina were also conducted. Isolates of R. solani on infected hypocotyls and roots obtained from 10 major cucumber producing counties in North Carolina were characterized using hyphal anastomosis, RAPD and rDNA PCR fingerprinting, AG-4 subgroup specific probes and DNA/DNA hybridization. Of 100 isolates which were studied, 60% could be assigned to AG-4 homogeneous group 1 (HG1), 24% to AG-4 HG2, and 10% to AG-4 HG3, while 6% were unassignable to any anastomosis group. Experiments using BN Rhizoctonia spp. for biological control of damping-off caused by these genetically dissimilar subgroups of R. solani AG-4 will be discussed.

Weed Control and Competition

David W. Monks

Dept. Hort. Sci., North Carolina State University &endash; Raleigh, NC 27695-7609

Weeds interfere with cucumber growth by direct competition for light, nutrients and soil moisture. There is evidence that interactions involving allelopathic substances released from weeds may inhibit cucumber growth and development. One of the greatest problems with weeds is their ability to interfere with hand and mechanical harvest of cucumbers. The critical period of weed interference appears to be between 2 and 4 weeks after emergence. When as few as 5% of the weeds are allowed to remain in cucumbers longer than 3 weeks, yields are often reduced significantly.

In a 1991 North Carolina survey, 60% of growers responding to a survey use herbicides. Common lambsquarters, pigweed, annual grasses and common cocklebur are the most troublesome weeds in spring and fall crops. From the survey, cucumbers are mechanically cultivated 3 times and hand weeded twice. Ethalfluralin (Curbit) is used preemergence on 54% of the acreage and naptalam (Alanap) is used preemergence on only 10% of the acreage. Sethoxydim (Poast) is used postemergence on 9% of the cucumber acreage. Use of naptalam or sethoxydim on more acreage would lessen the negative effect from weeds on the total yield of cucumbers in North Carolina.

The objective of our study has been to evaluate new herbicides in cucumbers. Ethalfluralin has given the best (>90%) preemergence control of common lambsquarters, annual grasses and pigweed. Mixtures of ethalfluralin with naptalam have improved control of large seeded weeds such as common cocklebur and common ragweed over ethalfluralin alone. No negative interactions have occurred when these herbicides are mixed. Injury with ethalfluralin has been observed but only when cucumbers are seeded near the soil surface and when heavy rainfall occurs early in the season. Cucumber tolerance to ethalfluralin is improved when the soil environment is optimum for growth. Clomazone (Command), a non-registered preemergence herbicide, has been evaluated in our studies. Cucumber tolerance on Norfolk loamy sands varies with clomazone rate, with leaf whitening observed with rates over 0.17 kg ai ha-1. Ratings for common lambsquarters control are usually excellent at 0.17 kg for 2 weeks after emergence but cultivation and/or hand weeding may be necessary after 2 weeks.

Studies are also being conducted to develop new uses for older herbicides. Naptalam is registered to apply preemergence or postemergence in cucumbers. A study was conducted to evaluate the ability of adjuvants to enhance activity of naptalam postemergence. Induce, a surfactant manufactured by Helena, increased postemergence control of common lambsquarters by naptalam over naptalam alone. Crop oils concentrates were not as effective as nonionic surfactants in increasing naptalam activity. Liquid nitrogen was the least effective adjuvant in our study.

Diversity and Genetic Distance Among Seed Company Cucumber Cultivars Based on Isozyme Analysis

V. Meglic and J. Staub

U.S. Department of Agriculture, Agricultural Research Service, Department of Horticulture, University of Wisconsin &endash; Madison, WI 53706

The United States cucumber (C. sativus L.) germplasm collection was surveyed using fifty one enzyme systems. Within fifteen enzyme systems (AK, FDP, G2DH, GR, GPI, IDH, MDH, MPI, PGD, PEP-LA, PEP-PAP, PER, PGD, PGM, and SKDH), 21 polymorphic loci were identified and used to evaluate genetic diversity among 440 cucumber lines of eleven seed companies. Allelic frequency differed between and among the three populations examined. The frequency of the most common allele was Ù 0.45. Genetic diversity was characterized using Nei’s modified genetic distance approximations. Distance values were used to evaluate differences between seed companies and differences between lines within seed companies. Genetic relationships were visualized by analyzing genetic distance values using multidimensional scaling techniques. Seed company lines were “genetically distant” from each other such that they tended not to form clusters with respect to origin (European or American). Some companies appeared to be genetically more distant than others (e.g., Harris Moran vs. Nunhem). Other companies appeared to have a closer relationship (e.g., PetoSeed and Asgrow). No cultigen examined possessed a banding pattern that uniquely separated it from all other cultigens. Although those results confirm variation on the protein level, they do not imply static differences or similarities since germplasm diversity within seed companies can change dramatically. Moreover, results may be expressions of a non-random sample of privately owned germplasm. Those results, however, indicate that isozyme diversity can be useful for cultivar discrimination when used in conjunction with other descriptors.

Molecular Markers and Their Legal Relevance for Cultivar Identification

J. Staub and V. Meglic

U.S. Department of Agriculture, Agricultural Research Service, Department of Horticulture, University of Wisconsin &endash; Madison, WI 53706

In the last decade, there has been increasing interest and debate over ownership of intellectual property–patents, copyrights, trade secrets and plant proprietary rights in both the private sector and public universities. To the horticulturist involved in the technological development and protection of plant germplasm, patent issues are becoming more important and more complex. Interest in plant proprietary rights issues has arisen because the protection of research products is necessary to provide incentive for continued investments by private and in some cases, public institutions. Scientific disagreement about criteria for accurate classification of similar, if not seemingly identical, cultigens has lead to spirited debate. A lack of a universally acceptable working definition of genetic distance as well as insufficient data on genetic diversity has made it difficult to define a legal framework for cultigen discrimination. Increasingly, patent examiners must interpret novelty and distinctness in terms of molecular as well as morphological information. A key issue in that regard is agreement on an acceptable definition of “difference”, which must be unequivocally described in measurable terms. Information will be given on the U.S. patent law and genetic interpretation of distinctness using molecular markers. The importance of a genetic database (allelic frequency) and genetic distance will be discussed and examined as to their potential use in the plant patenting process.

Genetic Engineering of Zucchini Yellow Mosaic Virus Resistance in Cucurbits

Rebecca Grumet and Guowei Fang

Horticulture Department, Michigan State University, East Lansing, MI 48824

Three versions of the zucchini yellow mosaic virus (ZYMV) coat protein (CP) were engineered for expression in plants: the full length CP sequence (CP); the conserved core portion of the gene (Core) and an antisense version (AS). These constructs were introduced into muskmelon and tobacco; gene expression was verified by northern and western analysis. Transgenic R0 and Rl muskmelon plants expressing the Core or AS constructs and inoculated with ZYMV exhibited a delay in symptom development and a reduction in virus titer. R0 and Rl muskmelon plants expressing full length CP exhibited near immunity to ZYMV, there was no symptom development or virus accumulation as determined by ELISA. Core and AS constructs gave variable levels of protection. Preliminary tests are under way to determine if the ZYMV CP can confer protection against the heterologous cucurbit potyviruses watermelon mosaic virus-2 and the watermelon strain of papaya ringspot virus.

Underutilized Genes in the Improvement of Pickle Varieties

Henry M. Munger

Cornell University &endash; Ithaca, NY 14853

Cucumbers of pickling varieties are appearing in certain markets for use in salads at a much higher price per pound than traditional slicing varieties. In growing regions where cucumber mosaic virus is serious, the incorporation of genes from slicer cucumbers to pickling cucumbers could improve yields and lengthen the harvest period. Since that usage probably means multiple hand harvesting, the determinate gene can speed picking greatly by reducing vine size and increasing fruit concentration. It also tends to be associated with earlier fruit production. The non-uniform or stippled color of traditional pickling types leads to marked fluctuations in color between locations and picking dates, probably from temperature differences. More consistent color can be maintained by using the uniform color gene as found in most modern slicers. That gene has been transferred to a few pickling varieties.

Development and Use of an RFLP Map of Cucumber

M. Havey, W. Kennard, A. Dijkhuizen and J. Staub

U.S. Department of Agriculture, Agricultural Research Service, Department of Horticulture, University of Wisconsin &endash; Madison, WI 53706

Research completed to date includes development of genomic and cDNA libraries of cucumber, evaluation of diverse cucumber germplasm for RFLPs, and generation of two segregating families (the pickling inbred Gy 14 crossed to PI432860 of the cultivated cucumber and Gy 14 to an accession of C. sativus var. hardwickii). Segregation of molecular and classical genetic markers in two families will allow us to establish complimentary linkage groups and detect linkages where segregating markers are absent within cultivated cucumber. We have presently completed over 60 hybridizations to the DNA of the segregating families; approximately one-half of the RFLPs segregate as expected. The remainder do not segregate (parents were likely heterozygous) or show aberrant segregation ratios. DNA of 35 cucumber lines from 7 companies was included on the mapping blots and RFLP fingerprints determined. A majority of the RFLPs were shared among all lines, but a few probes distinguish lines from individual companies. Near-isogenic lines of cucumber differing for resistance to CMV (provided by Dr. Munger, Cornell University), PRSV-W, and ZYMV have also been included in the hybridizations. To date, one RFLP may detect a chromosome region conditioning resistance to CMV.

Linkage Analysis of Potyvirus Resistance Genes from the Chinese Cucumber Line TMG-1

Thanda Wai, Jack Staub and Rebecca Grumet

Dept. of Horticulture, Michigan State University &endash; E. Lansing, MI 48824-1323, and U.S. Department of Agriculture, Agricultural Research Service, Dept. of Horticulture, University of Wisconsin &endash; Madison, WI 53706

The Chinese cucumber line TMG-l is resistant to three potyviruses that infect cucurbits: zucchini yellow mosaic virus (ZYMV), watermelon mosaic virus-2 (WMV-2), and the watermelon strain of papaya ring spot virus (PRV-W). Resistance to ZYMV is due to a single recessive gene (Provvidenti, 1987); two recessive genes confer resistance to WMV-2 and a single dominant gene confers resistance to PRV-W (Wai et al, 1991). We sought to further characterize these resistance traits by studying possible linkage relationships with physiological, morphological, electromorphic, and phytopathological markers. TMG-l, WI2757 (an inbred line susceptible to both viruses), and their F2 progeny were screened for various single gene characters that differ between the two parents, including: bitterfree (bi), mannosephosphate isomerase (Mpi-l), phosphoglucomutase (PGM-l), female (F), numerous spine (ns), small spine (ss), tuberculate (Tu), scab resistance and fusarium resistance. Linkages reported in the literature were also observed in this study: (l) between bitterfree (bi) and female (F), and (2) between numerous spine (ns), small spine (ss), and tuberculate (Tu). New linkages detected were between: (l) resistance to WMV-2 and F, (2) resistance to WMV-2 and ZYMV, and (3) possibly resistance to ZYMV with fusarium and ns.

A RAPD Map of Cucumber

K. Poetter, W. Kennard, R. Fruth and J. Staub

U.S. Department of Agriculture, Agricultural Research Service, Department of Horticulture, University of Wisconsin &endash; Madison, WI 53706

DNA-based methods have been developed to assist in genetic analysis. One such technique, random amplified polymorphic DNA (RAPD) analysis, is attractive for use in genomic mapping and marker-aided selection because of its speed, power, and relatively low cost. A RAPD map of the cucumber genome has been developed using 98 F2 individuals from the cross Gy 14 x PI 432860. Those individuals were assayed for RAPD markers with 1060 commercially available 10-mer deoxynucleotide primers. Roughly 140 possible polymorphisms were identified in parental screening. After further parental screening and segregation checks of F2 subpopulations, 70 usable polymorphisms were identified. Approximately 40 of those markers segregated in an expected 3:1 ratio. An additional 11 markers segregated in 1:1 ratio, suggesting the possibility that the parents were heterozygous at those loci. Using a threshold of 32 cM, 8 linkage groups were identified containing a total of 37 markers. An additional 6 markers showed fairly strong association with a group, but could not be definitively placed. A ninth group comprising 3 markers was also identified. Although that group has distance values of 32.5 and 33.3 cM, the markers do not associate with others in the data set. Twenty-three markers in the data set showed no strong association with any group, nor with each other. Work is underway to find more markers in order to develop a more saturated map in cucumber.

Influence of CG 41396 on Acid Peroxidase Activity and Acquired Disease Resistance in Pickling Cucumbers under Controlled Environmental Conditions

Irvin Widders, Ray Hammerschmidt, and Lavetta Newell

Departments of Horticulture and Botany and Plant Pathology, Michigan State University &endash; East Lansing, MI 48824

Resistance to fungal, bacterial and viral pathogens can be induced in cucumber plants by limited inoculation of the foliage of young plants with localized necrosis inducing pathogens or by treatment with specific salt solutions. Numerous physiological changes have been shown to be correlated with increased resistance to pathogens, including higher levels of activity of acid peroxidases, beta-1,3-Glucanase, and of chitinases in leaf tissue. In the present study, the effectiveness of CG 41396, a proprietary naturally occurring compound of Ciba Geigy, in inducing disease resistance in cucumbers was evaluated under controlled environmental conditions.

A single foliar application of CG 41396 to ‘Flurry’ cucumber seedlings at the 1-2 true leaf stage significantly enhanced the acid peroxidase activity in extracts from leaf lamina tissue. The maximum activity was measured at 20 mg a.i./L with lower activity at 10 and 1 mg a.i./L CG 41396. Peroxidase activity was also found to increase with time following application. High levels were measured in leaves which emerged following foliar treatment, thus confirming the systemic nature of the hypersensitive response within plants.

The hypersensitive response in cucumber plants can be induced at different stages of plant development. Plants at the 6th true leaf stage were found to be equally or even more responsive to a single foliar application of 20 mg/L CG 41396 as compared to plants at the 2nd true leaf stage. In addition, a soil drench (50 ml of 20 mg a.i./L CG 41396 per plant) was found to elicit as large or a larger increase in peroxidase activity within leaf tissue than foliar treatments.

Multiple foliar applications of CG 41396 were beneficial and gave rise to higher peroxidase activity in leaf tissue as compared to a single application. Maximum peroxidase activity was found in plants receiving three applications.

The implications of those data to the development of application strategies for the use of compounds such as CG 41396 in the induction of acquired disease resistance in machine harvested pickling cucumbers under commercial production conditions will be discussed.

Field Trials for Belly Rot Resistance in Cucumber

Michael S. Uchneat and Todd C. Wehner

Department of Horticultural Science, North Carolina State University &endash; Raleigh, NC 27695-7609

In the Southeastern United States fruit rot caused by the fungus Rhizoctonia solani can cause significant loss in yield of cucumber (Cucumis sativus L.). If they could be developed, resistant cultivars would be an economical and effective method of control.

Multiple harvest trials were conducted in spring and summer seasons of 1992 to evaluate eight pickling and eight slicing cucumber cultivars. Trials consisted of randomized complete block designs with 3 replications. Plots were 20′ long and were inoculated with oat grains (4 grains/in2) colonized with R. solani. Yield, fruit quality, and fruit rot incidence were among the many variables evaluated. In the pickling cucumber trial, we were unable to detect differences among cultivars for disease incidence. There were significant differences among cultivars in the slicer trial. ‘Tablegreen 72’ was the most resistant with a disease loss of 26%, and ‘Poinsett 76’ was the most susceptible with a loss of 65%. The LSD (5%) for the tests was 23 and 21% for the pickle and slicer trials, respectively.

In a separate experiment, a parent-offspring regression was used to estimate narrow-sense heritability in two cucumber populations. The populations used were the NC Wide Base Pickle and NC Elite Slicer 1. The NCWBP population contained 273 families, and the NCES1 population had 252. Offspring values were the means of four replications. Estimates of heritability were 0.06 for the NCWBP population, and 0.04 for the NCES1 population. Thus, additive genetic effects were near zero in the two populations, and selection progress would be minimal.

There was significant difficulty in distinguishing between resistant and susceptible cultivars in the trials. This has also been the case for previous field and detached fruit tests, and recently conducted seedling tests. Along with the low heritability, this information suggests that there was much environmental variation during disease evaluation.

Biological Control of Pythium Fruit Rot and Damping-off of Cucumber

K. P. Smith, M. J. Havey, and J. E. Handelsman

U.S. Department of Agriculture, Agricultural Research Service, and Departments of Horticulture and Plant Pathology, University of Wisconsin &endash; Madison, WI 53706

Pythium aphanidermatum incites cottony leak, a rot of cucurbit fruit, and damping-off of seedlings. A strain (UW85) of Bacillus cereus, a natural soil-inhabiting bacterium, has been found to protect legume seedlings from damping-off and may be useful in controlling Pythium diseases of cucumber. The environmental conditions most conducive to the rotting of cucumber fruit were identified and a protocol for the inoculation of fruit developed. Experiments demonstrated that UW85 protected wounded fruit from infection and correlated well with in vitro fungal growth inhibition assay. Biocontrol was associated with the biological activity of the resting spores of UW85 and with an extracellular factor produced by the bacterium. UW85 may be an economical alternative to hydrocooling immediately after harvest to protect harvested cucumber fruit from cottony leak. In growth chamber experiments, treatment of seed with UW85 significantly suppressed damping-off of cucumber seedlings. Biocontrol activity differed among four diverse cucumber genotypes and these preliminary data may indicate that host genotype impacts biocontrol effectiveness.

Cucumber Disease Management Strategies in North Carolina

Charles W. Averre

Department of Plant Pathology, North Carolina State University &endash; Raleigh, NC 27695-7616

Diseases of commercial cucumbers have remained remarkably constant for over a decade with small year to year variations depending on environmental conditions, seed quality, cultivar resistance, crop rotations, and spray program. With few exceptions, foliar diseases in the spring crop require few or no sprays, while numerous sprays are needed for the fall crop. Damping-off, foliar and fruit rot diseases are serious during wet weather, while root-knot tends to be worse during dry periods. Diseases can be ranked according to estimated percent losses, especially in the fall crop: 5.0% downy mildew, 5.0% target spot, 4.0% belly rot, 4.0% gummy stem blight, 3.0% anthracnose, 2.5% cottony leak, 1.5% damping-off, 1.0% air pollution, 1.0% alternaria leafspot, 1.0% angular leafspot, and less than 0.1% or rarely observed include virus diseases, powdery mildew, and scab. The implication of Microdochium tabacinum cucurbit blight on cucumber is unknown. Most of the mentioned diseases have caused severe losses or crop failures on individual farms. These diseases must be considered in disease management strategies.

Current disease management and strategy recommendations for North Carolina to reduce the risk of losses due to disease include the following: 1- Use a one-year, or more, crop rotation. 2- Turn plow to cleanly bury crop residue. 3- Take soil samples for nutrition, pH, nematodes. 4- Treat soil with a nematicide if needed. 5- Select acceptable cultivars with high levels of disease resistance (e.g. viruses, powdery mildew, anthracnose, downy mildew). 6- Use high quality seed. 7- Keep plant lots separate. 8- Avoid sequential plantings in the same fields. 9- Survey fields at least weekly. 10- Have all problems diagnosed. 11- Select proper fungicide. 12- Use a high pressure (over 300 psi) hydraulic sprayer or a good mist blower. 13- Avoid harvesting and handling injuries to fruit. 14- Promptly move harvested fruit from the field to a cool place. 15- Use chlorine in wash water.

Currently available crop protectants must be used in the context of the Disease Management Recommendations and include: dichloropropene, chloropicrin, metam sodium, oxamyl, ethroprop, carbofuran, metalaxyl, maneb, mancozeb, chlorothalonil, thiophanate-methyl, and benomyl. Current and future work is emphasizing evaluation of crop protectants that are more effective, safer, and environmentally sound than existing ones, and assessment of cultural practices to reduce disease pressure.

Heritability Estimates for Resistance to Gummy Stem Blight in Cucumber

Paul C. St. Amand and Todd C. Wehner

Department of Horticultural Science, North Carolina State University &endash; Raleigh, NC 27695-7609

The narrow-sense heritabilities of leaf and stem ratings for resistance to gummy stem blight (Didymella bryoniae (Auersw.) Rehm) were estimated using parent-offspring regression for two cucumber (Cucumis sativus L.) populations differing in genetic diversity. Leaf and stem resistance were rated from 0 (no symptoms) to 9 (complete necrosis). Heritability estimates based on individual selection for leaf ratings ranged from 0.08 to 0.15 in the NCES1 population, and from 0.10 to 0.14 in the NCWBP population. Heritability estimates for stem canker ratings ranged from 0 to -0.02 for the two populations. Estimates were usually less than twice the standard error for that trait.

Estimates of gain per cycle using individual selection for leaf ratings ranged from 0.30 to 0.47 for the two populations. Heritabilities based on half-sib family selection were estimated using half-sib family analysis. Heritability estimates for family selection ranged up to 0.49 for leaf ratings. However, estimates based on family selection were biased upward because data were available for only one environment at the time the analysis was run. Additional experiments are being completed this fall.

North Carolina Survey of Pesticide Use in Cucumber

Stephen J. Toth, Jr., Charles W. Averre, David W. Monks, Jonathan R. Schultheis and Kenneth A. Sorensen

Departments of Entomology, Plant Pathology and Horticultural Science, North Carolina State University &endash; Raleigh, NC 27695

A mail survey of pickling and slicer cucumber growers in 15 North Carolina counties was conducted in January and February 1991 to determine pesticide use and pest control on the 1990 cucumber crop. Commercial cucumber growers in the participating counties received questionnaires mailed from the county extension offices. A total of 935 growers were sent surveys with 404 or 43% returned. The growers responding to the survey planted 9,574 acres of cucumbers in the spring and 4,092 acres of cucumbers in the summer, for a total of 13,665 acres in 1990. The largest portion of the pickling acreage was planted with the cultivar ‘Calypso’ (54%), while ‘Primepak’ (17%) and ‘Regal’ (15%) placed second and third, respectively. ‘Dasher II’ was the leading slicing cucumber cultivar, planted on 64% of the acreage. The majority of survey respondents grew cucumbers for processing (10,717 A) while 2,964 acres were for fresh market. According to the North Carolina Department of Agriculture, 6,100 acres of fresh market cucumbers and 24,600 acres of processing cucumbers were harvested in the state in 1990.

Cucumber growers reported the use of pesticides on both the spring and summer crops in 1990. Nearly 60% of the growers used herbicides to control weeds in their cucumber fields. The primary weeds listed by growers were grasses, lambsquarter, pigweed, ragweed, crabgrass, cocklebur and morningglory. Curbit and Alanap were the most commonly used preemergence herbicides while Poast was used for postemergence grass control. Cultivation and hand weeding were the most popular methods for controlling weeds. Insecticides and miticides were used by 34% of the survey respondents. Sevin and Asana were the primary insecticides used for the control of cucumber and flea beetles, aphids, cabbage loopers, cutworms, leafminers, thrips, wireworms and spider mites. Lannate was most often used for pickleworm control. Nematicides, including Furadan, were used by 22% of the growers returning questionnaires. Approximately 27% of the growers used fungicides to control diseases in their cucumbers in 1990. Ridomil was used to control damping-off, Benlate and Bravo to control leaf spots and Bravo and Ridomil to control belly rot and cottony leak.

Nonchemical pest management practices employed by cucumber growers in 1990 were also reported. Crop rotation was practiced by two-thirds of the growers who responded. Almost 85% indicated that they or a family member scouted their cucumber crop for insects, weeds or diseases, while 6% had an employee scout their crop. An additional 6% employed a professional scout. Soil tests were taken by 60% of the growers, nematode samples by 22% and a plant tissue sample by 4%. Less than 1% used a pickleworm pheromone monitoring system or planted squash as a trap crop for pickleworm.

Evidence for Acquired Disease Resistance to Angular Leaf Spot in Field Grown Pickling Cucumbers

Irvin Widders, Ray Hammerschmidt, Mark Uebersax and Lavetta Newell

Departments of Horticulture, Botany and Plant Pathology and Food Science and Human Nutrition, Michigan State University &endash; East Lansing, MI 48824

Cucurbit species are known to exhibit a hypersensitive response (HR) following inoculation with a foliar pathogen. The physiological changes associated with the HR are systemic within plants and have been shown to confer resistance against a broad spectrum of foliar pathogens. Currently, numerous laboratories are attempting to identify natural signals which might trigger the systemic induction of disease resistance and to understand their mode of action. In the present study, we evaluated the effect of foliar applications of a naturally occurring plant compound, CG 41396 (Ciba Geigy), on acquired disease resistance in field grown pickling cucumbers.

Pickling cucumbers, cultivars Flurry and Calypso (Asgrow Seed Co., Kalamazoo, MI) were direct seeded on 17 June 1992 into a sandy loam soil at the MSU Horticulture Research and Teaching Center, East Lansing, MI. Foliar applications of H2O (control), 100 mM K3PO4, and 15, 25 and 35 mg a.i./L CG 41396 were made at weekly intervals beginning at the 2nd true leaf stage and terminating following fruit set, for a total of 4 applications. The experimental design was a split plot with cultivars constituting the main plots and foliar treatments as subplots. All treatments were replicated 4 times. Each subplot was comprised of a bed of three rows 6.1 m long. Two days before the final foliar treatment and ten days prior to once-over destructive harvest, the foliage was spray inoculated with Psuedomonas lachrymans.

Acid peroxidase activity in leaf lamina tissue homogenates, which has been shown to be correlated with acquired disease resistance, increased by over 100% as compared to controls following CG 41396 applications, but was unaffected by 100 mM K3PO4 treatment. The higher the concentration of CG 41396 in solution, the higher the acid peroxidase activity. Although both cultivars responded similarly to CG 41396 application, the magnitude of the increase in peroxidase activity within leaf tissue following multiple foliar applications was greater in Flurry than in Calypso.

At harvest time, leaves (12 per subplot) from the 8th node from the shoot apex were excised from randomly selected plants and the number of lesions counted. The predominant foliar disease observed was angular leaf spot. The number of disease lesions per leaf (27) in Flurry from control plots was approximately double that of Calypso (12). Application of 35 ppm a.i. CG 41396 reduced lesion incidence to approximately 5 per leaf in both cultivars. That represented a >75% reduction in disease symptoms in Flurry and >50% in Calypso. No evidence of a phytotoxic response was ever observed from foliar applications of CG 41396. K3PO4 was found not to be effective in inducing disease resistance in cucumbers at the concentration applied.

Anthracnose Pathogen Diversity: Screening for Disease Resistance

J. C. Correll and T. E. Morelock

Departments of Plant Pathology and Horticulture, University of Arkansas &endash; Fayetteville, AR 72701

Isolates of the anthracnose pathogen, Colletotrichum orbiculare, collected from various cucurbit hosts from throughout the U. S., have been examined for genetic, molecular, and virulence diversity. The data indicate that there are two distinct groups in the contemporary anthracnose population. The first group, VCG1, is composed of isolates which originated from cucumber or cantaloupe and give disease reactions characteristic of race 1. The second group, VCG2, is composed of isolates which originated from watermelon or cucuzzi gourd and give disease reactions characteristic of race 2. Race determinations were conducted on 13 differential cucurbit cultivars. In general, VCG1 isolates are more aggressive on cucumber, whereas VCG2 isolates are more aggressive on watermelon. A disease screening program has been initiated to quantify anthracnose resistance in cucumber cultivars to these races. Initially, the cultivars H-19, Gy 14, SMR 58, Poinsett 76, Marketer, Pixie, and PI 197087 have been compared. Disease reactions are being measured on cotyledons or the first set of true leaves under greenhouse conditions as well as on more mature plants under field inoculations. Although many variables influence these disease reactions, a rapid and reliable cotyledon assay has been developed to compare levels of anthracnose resistance in cucumbers.

Survey of Pesticide Use by North Carolina Cucumber Growers in 1990

Stephen J. Toth, Jr. and Kenneth A. Sorensen

Department of Entomology, North Carolina State University, Raleigh, NC 27695-7613

A mail survey of cucumber growers in Duplin, Edgecombe, Franklin, Greene, Henderson, Hyde, Johnston, Lenoir, Nash, Pitt, Richmond, Robeson, Sampson, Wayne, and Wilson Counties was conducted in January and February 1991 to determine pesticide use on the 1990 cucumber crop in North Carolina. Commercial cucumber growers in the participating counties received questionnaires mailed from the county Extension centers. Of the 935 questionnaires delivered to growers, 404 or 43% were returned. The growers responding to the survey planted 9,574 acres of cucumbers in the spring and 4,092 acres of cucumbers in the summer, for a total of 13,665 acres planted in 1990. Calypso, Dasher II, Primepak and Regal were the most common cultivars planted. The survey respondents harvested 2,964 acres of cucumbers for fresh market and 10,717 acres of cucumbers for processing. According to the North Carolina Department of Agriculture, 6,100 acres of fresh market cucumbers and 24,600 acres of processing cucumbers were harvested in the state in 1990.

Cucumber growers were asked to report their use of all pesticides on the spring and summer crops in 1990. Insecticides and miticides were used by 34% of the survey respondents. Sevin and Asana were the primary insecticides used for control of cucumber and flea beetles, aphids, cabbage loopers, cutworms, leafminers, thrips, wireworms, and spider mites. Lannate was used most often to control pickleworms.

The cucumber growers were also asked to report their nonchemical pest management practices. Sixty-six percent reported that they rotated fields planted with cucumbers as a means of pest management. Approximately 85% responded that themselves or a family member scouted their cucumber crop for insects, weeds or diseases, while 6% claimed an employee scouted their crop. Another 6% reported that a professional scout provided this service. Cucumbers are scouted for early season cucumber beetles and late season foliar diseases. Less than 1% of the respondents used a pickleworm pheromone monitoring system or planted squash as a trap crop for these insects.

Agricultural Weather Program

Katharine B. Perry and Todd C. Wehner

Department of Horticultural Science, North Carolina State University &endash; Raleigh, NC 27695-7609

The ability to predict accurately the harvest dates and developmental stages of a crop has widespread application for improving management of a crop, e.g. scheduling labor and machinery. The concept of heat summation to achieve this for vegetable crops dates back to 1929 when it was found that peas flowered after receiving a particular amount of heat, regardless of the number of days involved. The work that followed focused on what we now call “growing degree days.”

Work at North Carolina State University has focused on cucumbers for pickling and slicing. The best heat unit accumulation method was to sum, over days from planting to harvest, the difference between the daily maximum and a base temperature of 15.5°C, but, if the maximum exceeded 32°C, replace it by 32°C minus the difference between the maximum and 32°C, before subtracting the base. In a test of this method it was found to be better than the standard method of counting days for pickling but not slicing cucumbers.

Any attempt to explain the entire developmental and maturation process of a crop using only a temperature model is a simplistic, but necessary approach. Still, results of current work showed that heat unit modeling has value for improvement of production systems. We are working to improve the model for accuracy and ease of use.

Cucumber Facts Database

Todd C. Wehner and Paul C. St. Amand

Department of Horticultural Science, North Carolina State University &endash; Raleigh, NC 27695-7609

In order to perform accurate, modern, and meaningful research, development or testing, today’s researcher or technician must keep abreast of the ever increasing body of literature spread across a myriad of journals, magazines, universities, meetings, and newsletters (some well-known and others obscure). To make this imposing task faster and more accurate, journal abstracting services have developed on-line databases for scientists. At NCSU we have access to the largest and most often used agricultural abstracting services: CAB, Agricola, and Dissertation Abstracts. So that we can keep abreast of the literature for cucumbers, we have developed a database of cucumber references and we are offering this database to all interested persons.