Cucumber Breeding

North Carolina State University has had a breeding program on cucumber (Cucumis sativus L.) for more than half a century. The program was established by Warren Barham in 1948. Richard Lower was hired in 1968 to work on pickling cucumbers. Cucumber breeding was carried out part-time prior to 1968 by Frank Haynes and Johnny Jenkins. In 1979, Todd Wehner was hired to breed pickling and slicing cucumbers.

The main objectives of the program are to expand our knowledge of cucumber genetics and breeding, educate graduate students interested in vegetable breeding, do research on problems affecting the cucumber industry, and develop improved cultivars and breeding lines of pickling and slicing types for use in North Carolina and the U.S.

We are working on breeding and germplasm enhancement projects. These include improved yield, new plant types (dwarf-determinate, parthenocarpic, little leaf), early maturity, and resistance to diseases, insects and chilling. We also are involved in germplasm collection and exchange around the world.

One of our research areas was to incorporate nematode resistance from LJ 90430 (a wild accession of Cucumis sativus var. hardwickii collected from the foothills of the Himalayas in India) into an elite, adapted inbred line. A set of cultivars (Lucia, Manteo, and Shelby) released recently from the program shows the progress made. The wild accession has bitter fruit, dormant seeds, large seedcell, low yield, late maturity, small leaves, multiple branching habit, and mostly male flowers. From that, we produced resistant cultivars with high yield, early maturity, fast germinating seeds, high quality fruit with small seedcell, large leaf size, and monoecious flowering habit.

  • Cucumis sativus var. hardwickii (wild cucumber)
    • Cucumber has been improved by using accessions of the wild var. hardwickii. Traits such as resistance to nematode (Meloidogyne arenaria and M. javanica) have been transferred from LJ 90430, resulting in the cultivars Lucia, Manteo and Shelby.
    • Some traits of hardwickii, including littleleaf (ll-2), black spine (B-3, B-4) and multiple-branching are not the same (are non-allelic) compared with cucumber. For example, Arkansas Littleleaf, and black spined (B-1) Wis. SMR 18 have similar traits, but hardwickii has different genes for those traits. Cucumis sativus var. hardwickii (top) compared with Cucumis sativus (bottom) see image (JPEG).
  • Cucumis sativus var. sikkimensis (Sikkim cucumber)
    • Large, oblong fruit are also found among cultivars of Cucumis sativus var. sikkimensis Hook. f. (Sikkim cucumber). It has been reclassified as Cucumis sativus var. sativus. These cultivars are grown primarily in mountainous Nepal and India. The Sikkim cucumber has accessions that represent much variation, including high resistance to downy mildew, and five-carpellate fruit see image (JPEG).
  • Cucumis sativus var. xishuangbannanensis (Xishuangbanna gourd)
    • A distinct group of cultivars, known as Xishuangbanna gourd, is classified as C. sativus var. xishuangbannanensis Qi & Yuan. Grown by the Hani people of southwestern China at elevations of 1000 m or higher, these landraces are largely unknown outside of eastern Asia. The Xishuangbanna gourd has much variation and includes cultivars with five-carpellate fruit. It is more closely related to Cucumis sativus var. sativus than to C. s. var. hardwickii.
    • Vines of this variety are vigorous, reaching up to 7 m in length. The large mature fruit is oblong and weighs about 3 kg. The rind is white, yellow or brownish-orange, sometimes with distinct netting, but otherwise relatively smooth and without prominent warts. Because the yellow to orange flesh color is caused by provitamin A carotenes, researchers have transferred the trait (light orange mesocarp, orange seedcell) controlled by the ore gene from the Xishuangbanna gourd to cucumber cultivars see image (JPEG).
  • Cucumis hystrix
    • Cucumis hystrix is a wild species of Cucumis that can be crossed with C. sativus to produce, after chromosome doubling, an allotetraploid. The new species is C. hytivus, and lines have been developed that have characteristics of processing or fresh market cucumbers, along with other traits not present in cucumber. Introgression lines were produced by Chen and co-workers that have introduced disease resistance to cucumber.
    • Resistances obtained from crosses with C. hystrix include gummy stem blight and downy mildew. C. hystrix offers a way to increase the genetic diversity of cucumber, already known to be rather narrow. No other species has been crossed successfully with cucumber, although the two botanical varieties, C. sativus var. hardwickii (formerly C. hardwickii) and C. sativus var. xishuangbannanensis, will cross readily with cucumber. See hystrix x sativus hybrid (JPEG).
  • Cucumis sativus (Cucumber)
    • Overview
    • Origin and History
      • Cucumber is of Asiatic origin along with the closely related, wild Cucumis sativus var. hardwickii, which was first found in the Himalayan foothills of Nepal. Plants of this botanical variety are highly branched, daylength sensitive and prodigious producers of bitter fruit. The most closely related species to cucumber (2n=2x=14) is Cucumis hystrix (2n=2x=24). Both species are more closely related to the species of Australia and New Guinea, such as C. umbellatus, than to the African species, such as C. hirsutus, C. metuliferus, C. myriocarpus, C. anguria and C. sagittatus. Cucumber diverged from C. hystrix 4.6 million years ago, and the cucumber / melon relative diverged from its African relative 11.9 million years ago. Based on the recent sequencing of the Lagenaria genome, Lagenaria diverged from Citrullus 10.4 to 14.6 million years ago, from Cucumis 17.3 to 24.3 million years ago, and from Momordica 29.2 to 41.0 million years ago.
      • Cucumber remains in eastern Iran have been dated to the third millennium bc. Cucumber cultivation goes back at least 3000 years in India and 2000 years in China. China is considered a secondary centre of genetic diversification. Today, cucumber is one of the most important vegetable crops in that country, second only to Chinese cabbage in area cultivated.
      • Cucumber was probably not known to the ancient Egyptians, Greeks or Romans. The Latin cucumis, Greek sikyos and Hebrew qishu’im refer to the snake melon, Cucumis melo var. flexuosus. In English translations of the Bible, cucumber and melon are referred to in Numbers 11:5, but that probably should have been translated as snake melon and watermelon. Snake melon fruit can be distinguished by small hairs (fuzz) on the surface, whereas cucumber fruit are smooth, with ridges, warts, or spines.
      • Early travellers brought cucumber to Mediterranean countries from India through Iran, Iraq and Turkey in the 6th or 7th centuries. Cucumber probably reached Spain in the 9th century, and Tunisia in the 10th century. In the early 14th century, cucumber plants were cultivated in England. There, the fruit were known as ‘cowcumbers’. Portuguese explorers subsequently carried cucumber to West Africa. Columbus introduced this species to the New World, planting it in Haiti in 1494. Today, cucumber is grown throughout the world in patio containers, small gardens often using trellises, large commercial farms, unheated high tunnels and heated greenhouses.
    • Taxonomy and Wild Relatives
    • Uses
      • There are several non-food uses of cucumbers. White-skinned cultivars were grown in France in the 19th century for the production of cosmetics. Today, cucumbers are used in health and beauty products, including perfumes, lotions, soaps and shampoos. Indigenous practitioners create medical concoctions from the roots, leaves, stems and seeds.
      • The common use of cucumbers is as food, where it is classified as a warm-season vegetable. Cucumbers are most often consumed fresh or pickled. In China, India, Indonesia, Malaysia and some other countries, they may be cooked before eaten. The fruit are used in curries and chutney in India. Cucumber seeds are eaten, particularly in Asia, and the seeds can be crushed to produce an edible oil which is sometimes used in French cuisine. Young leaves and stems are cooked in southeastern Asia.
      • Cucumber cultivars are classified as slicers, usually served fresh in salads, or picklers, which are often fermented. However, in some areas, fruit of pickling cultivars are used like slicers in salads. Small-fruited pickling cucumbers are called gherkins in various countries, including India. Pickling cucumbers are also sold as pasteurized and acidified rather than fermented. Although, not technically pickles, the former are increasingly preferred by consumers (two thirds of the USA market).
      • Generally, picklers have shorter fruit with more prominent warts than slicers. The length to width ratio, usually about three to one, is important for pickling cucumbers. Most cultivars have white-spined fruit, but older cultivars may have either white or black spines. Pickling cultivars with white spines became the standard because their fruit retain green color longer, and turn cream or yellow rather than orange or red when they get larger and more mature.
      • After harvest in commercial operations, slicers are usually graded, washed, cooled and waxed before being marketed. Greenhouse cucumbers have thin skinned fruit, so are wrapped in plastic before marketing. Picklers are prepared for fresh pack (unpasteurized, refrigerated dills) and for brined and fermented products.
      • Over 70% of the USA cucumber crop is pickled. Yield of pickling cucumbers has increased more than three-fold in the USA in the past 60 years, from 3.61 metric tonnes per hectare in 1930 to 11.61 in 1990, but yield improvement has slowed since then.
    • Breeding
      • Cultivar Types
        • Glasshouse cucumber cultivation is important in northern Europe, Asia, the Middle East and other areas. Glasshouse production of cucumber in the USA has declined in recent years, due to competition in winter from plants grown outdoors in Florida, Mexico and other warm regions. Slicing type cucumber cultivars are most commonly grown in glasshouses. Pickling cultivars have been grown in glasshouses in The Netherlands, but this practice is declining.
        • Glasshouse cucumbers have become popular in markets, commanding a premium price because of their excellent quality. They can often be identified by their very long, slender fruit, with constricted neck, thin skin, indistinct warts and spines, and crisp texture. Their crispness, tender skin and other quality attributes are primarily due to the cultivar, rather than to being grown in a glasshouse. Glasshouse cultivars include the original European gynoecious cultivar ‘Telegraph’ and the related, improved selections ‘Petita F1’ and ‘Superator’. The small-fruited versions such as ‘Hayat’ have resulted in a new type for the Middle East, the greenhouse Beit Alpha.
        • Some of today’s cultivars are known to be centuries old, having originally been developed in Europe or Asia. An example is ‘Early Russian’, which was described by Naudin in France in 1859. Many field-grown cultivars in Europe and the Middle East differ from American cultivars by having numerous fine spines and indistinct warts.
        • Cultivar selection in the USA began in the late 1880s, with emphasis placed on fruit shape and color as well as adaptation to local growing conditions. Many cultivars introduced before 1900 were developed simply by selecting superior plants from the heterogeneous cultivars grown at that time. American and English cultivars were crossed to develop ‘Tailbys Hybrid’, introduced in 1872, and controlled hybridization has subsequently become important in cucumber improvement. Some of the old cultivars that are still available today include ‘Early Cluster’ (1778), ‘Early Russian’ (1854), ‘Chicago Pickling’ (1897), ‘Snows Pickling’ (1905), ‘National Pickling’ (1924), ‘Double Yield’ (1924), ‘Producer’ (1945), and ‘Model’ (1946).
        • Older American cultivars of slicing cucumbers develop stippling at high temperature, i.e. the fruit develops light green spots at the location of the lenticels. Cultivars from Asia and most European glasshouse cucumbers have an allele for uniform green fruit colour (u), and Munger backcrossed this allele into ‘Marketmore 70’ and other breeding lines to produce cucumbers that retain their uniform, dark green fruit colour even at high temperatures. Most slicing cultivars marketed in the USA today have that trait.
        • ‘Maine No. 2’ (released 1939) was the first cucumber cultivar resistant to the scab disease. Its resistance is due to a single dominant allele. Scab is no longer an important disease in most cucumber crops because most current cultivars have that allele, which is linked to resistance to Fusarium wilt resistance, another important disease. Barnes developed ‘Pixie’ (released 1963) with resistance to diseases in the southern USA production areas: downy mildew, powdery mildew, and anthracnose. Resistance permitted a fall crop to be grown, expanding the useful production season. Later, ‘Sumter’ (1973) was released with additional disease resistances to angular leafspot, scab and cucumber mosaic virus.
        • Cultivars resistant to CMV have been available for more than 50 years. Walker combined scab and CMV resistance in ‘Wisconsin SMR 18’ (released 1958) pickling cucumber. A higher level of resistance to CMV, combined with good horticultural type, was achieved in the ‘Marketmore’ series of slicing cultivars bred by Munger. He incorporated resistance to scab and additional diseases into this cultivar by backcrossing. Cucumber breeders continue to combine genes for resistance to different diseases. Peterson developed a breeding line, WI 2757 (released 1982), with resistance to 9 diseases.
        • ‘Burpee Hybrid’, the first F1 monoecious hybrid cucumber cultivar (released 1945), was bred by Shifriss at the Burpee Seed Company. The development of hybrid cultivars became important after gynoecious sex expression was obtained from a Korean cultivar. The genes for gynoecious expression (F F M M genotype) are dominant, and gynoecious hybrid cultivars have a high proportion of female flowers, resulting in early maturity and good yield. Gynoecious hybrids have early and concentrated fruit set, and are suited to mechanical harvest. ‘Spartan Dawn’, introduced in 1962, was the first gynoecious hybrid cultivar. Peterson developed the maternal parent of this hybrid by backcrossing the gynoecious trait (F F M M genotype) into ‘Wisconsin SMR 18 (f f M M genotype)’. The most popular pickling cultivars today are gynoecious hybrids.
        • ‘Lemon’ is a unique cultivar. It has andromonoecious sex expression, whereas other cucumber cultivars are monoecious or gynoecious. The small, round, yellow fruit, which have five placentae instead of the customary three, faintly resembles a lemon fruit, hence its name. Other improvements made by plant breeding include high yield, fruit with high vitamin A, fruit with small seedcell, fruit resistant to damage while in brine tanks (bloater resistance), concentrated fruit set for machine harvest (using gynoecious and multiple branching types), fruit with long length : diameter ratio for stressful environments, and parthenocarpic, seedless cultivars (usually made as hybrids from two parthenocarpic and gynoecious inbred lines) for open field production, thus eliminating the need for pollenizer plants or pollinating insects such as bees.
        • Cucumber breeders in China have developed improved inbred and F1 hybrid cultivars (e.g. ‘Ningqin’, ‘JingYan No. 2’) of the oriental trellis type for production in open field as well as greenhouse. New traits include gynoecy, earliness and multiple disease resistance. Breeders are also trying to improve various traits for autumn crop production. Parthenocarpy has been incorporated to reduce the need for pollination in the greenhouse. For oriental trellis cucumbers, the preferred type is long fruit with dark green skin and thick, prominent spines or ridges.
        • Breeders worldwide continue to select for a wide range of desirable characteristics, in addition to disease and pest resistance. Cultivars have been bred for tolerance to cold, heat, drought, herbicides, sulphur dioxide and soil salinity. Pickling cucumbers have been bred to withstand carpel separation in order to prevent bloating during the brining process. Cucumber cultivars differ in the time required for their fruit to develop from the optimal size for market to oversized fruit of little value, and ‘Marketer’ has become important because it produces a large proportion of fruit of marketable stage.
        • The littleleaf mutant (ll ll genotype) was discovered by Bowers and Goode. Its multiple branching and multiple fruit setting traits were desirable for once-over harvesting systems, but there were problems with slow fruit development (common to mutants having multiple fruit set) that led to fruit having tough skin, large seeds, and a watery (mature) seedcell. Currently, parthenocarpic (seedless fruit development without pollination) cultivars that promise high yield are being evaluated for machine-harvest systems of pickling cucumbers in the USA and Europe. Problems that need to be solved are unreliable fruit set, and tough skin in the larger fruit sizes. Littleleaf (front) vs. normal leaf (rear) JPEG image.
      • Patio Cucumbers (Container Production)
      • Biogeography and Germplasm Resources
      • Germplasm Exploration and Evaluation
      • Environmental Sustainability
      • Flowering and Sex Expression
      • Qualitative Genetics
        • Gene List (Cucurbit Genetics Cooperative Report)
        • Many alleles conferring disease resistance have been found and incorporated into cucumber cultivars. Dominant alleles have been reported for resistance to bacterial wilt (Bw), scab (Ccu), target leaf spot (Cca), Fusarium wilt (Foc) and watermelon mosaic virus (Wmv and wmv-1-1). Linkage of scab resistance with Fusarium wilt resistance has resulted in many cultivars having both, even though they were only selected for scab resistance. A dominant allele (Cmv) at a single locus has also been postulated for resistance to cucumber mosaic virus, but alleles of additional genes are needed for a high level of resistance. Recessive alleles provide resistance to angular leaf spot (psl), zucchini yellow fleck virus (zyf) and zucchini yellow mosaic virus (zymv). Alleles Ar and cla reportedly confer resistance to different races of anthracnose. Resistance to papaya ringspot virus is provided by prsv or Prsv-2. Several genes have been proposed to govern resistance to downy mildew and powdery mildew, with the main ones being the closely linked dm and pm.
        • The bitterfree loci (bi and bi-2) inhibit biosynthesis of cucurbitacin, which is an attractant for cucumber beetles but a repellant for spider mites, aphids and various other insects. The bi genes are epistatic to the bitter genes (Bt and Bt-2) for increased cucurbitacin content.
        • Salinity tolerance is influenced by many genes, in addition to a single major gene (sa). A single gene (Sd) has also been suggested to control resistance to sulphur dioxide air pollution.
        • Dwarf plant habit, due to short internodes, is produced by alleles bu, by, cp, cp-2 and dw. Although these alleles are currently assigned to distinct loci, allelism testing is needed to confirm that none represent allelic variants of the same gene. Allele dw also retards the development of oversized, and hence unmarketable, fruit. Vine size is also reduced by the determinate habit allele (de), which is modified by the intensifier gene In-de.
        • The interaction of two major genes, m and F, influences sex expression. F is modified by In-F and alleles at other genes. Some cultivars heterozygous for F have only female flowers, due to the right combination of modifying genes, but others can be monoecious under some growing conditions. Cultivars homozygous for F have been developed because they are more dependably gynoecious than heterozygous cultivars. Additional genes have been reported to influence androecious (a), andromonoecious (m-2) and gynoecious (gy) sex expression.
        • Multipistillate alleles mp and Mp-2 and their modifiers at other loci increase the number of pistillate flowers per node. The gene for twin fused fruit (tf) results in 2 fruit at one node fusing into a single unit. The development of parthenocarpic fruit is governed by Pc and modifying genes.
        • Fruit spine color is governed by the putative genes B, B-2, B-3 and B-4, with black spines being dominant to white. Spine number and size is influenced by genes ns, ss, s-1, s-2 and s-3. Spines and warts are absent on fruit of plants with the gl allele for glabrous foliage, and more pronounced when possessing the tuberculate fruit allele, Tu.
        • European glasshouse cultivars have glossy fruit with a tender skin and uniform dark green color, without light green stippling. These are monogenic traits, governed by the D gene for dull versus glossy fruit and the tender skin (te) and uniform color (u) genes.
        • Green immature fruit color is dominant to white (w) and yellow green (yg). The interaction of alleles at two genes, wf and yf, reportedly determines white versus yellow or orange flesh color.
        • Six linkage groups were proposed for cucumber genes, but rigorous testing and recombination frequencies are generally lacking. Chromosome assignments of the linkage groups have now been made, along with the sequencing of the genome.
      • Quantitative Genetics
        • Inbreeding Depression and Heterosis
    • Cultivar Development History
    • Breeding Methods
      • Selection Methods
      • Breeding Objectives and Traits
      • Mechanization of the Breeding Program
      • Yield Improvement
      • Defect Resistance
      • Disease Resistance
      • Chemical Control (see NC Agricultural Chemicals Manual)
      • References on Resistance to Disease, Insects, Cold
      • Insect Resistance
      • Stress Resistance
        • Drought Resistance
          • Drought during the production of cucurbit crops can lead to shorter vines, cause delayed flowering, and shift the plant towards maleness (with more staminate, fewer pistillate flowers), and reduce fruit yield and quality.
        • Flooding Resistance
          • In most cases, cucurbit crops are extremely sensitive to flooding, which is why they are often produced on well-drained soils, or in arid regions. Raised beds are useful in areas with rain during the production season, unless the soils are sandy. Flooding tolerance is important in humid regions such as southeast Asia and Brazil, but prolonged periods of heavy rain cause reduced fruit yield and quality.
          • Excess water causes reduced oxygen in the soil (hypoxia). Some cucurbits, such as bottle gourd, possess some genetic tolerance to hypoxia in the roots during periods of flooding. These may be useful as rootstocks for bitter gourd, watermelon and other flood-sensitive cucurbits. Some investigations into the mechanisms for flood tolerance among cucumber genotypes have identified the importance of adventitious roots in hypoxia tolerance. The most flood-tolerant genotype had numerous adventitious roots in the hypocotyl region, while susceptible genotypes did not. Major genes controlling adventitious root development have been identified in several crops, and development of molecular markers for such genes in cucurbits should be feasible.
          • Excess water can also reduce the nutrient content of the soil, reducing plant growth as a result. Cucurbits growing in flooded soil will be yellow and stunted. In response, aerial (adventitious) roots will develop at the base of the plant in cucumber and melon, but not watermelon or squash.
        • Heat Resistance
          • Heat tolerance is an important trait for sustainable vegetable production, considering that many countries in the tropics struggle with food security issues. Though cucurbits originated in tropical regions, not all are capable of producing a useful yield in lowland areas, especially in the warmer growing periods. Humans have improved the adaptation of cultivars to high temperature for many cultivated cucurbits. However, continued efforts are needed to improve fruit yield and quality.  The quality of heat tolerant cultivars is often inferior to crops grown at optimum temperatures.  Flower abortion and pollen sterility are common symptoms of heat stress in melon and cucumber. Reduced fruit size is another common response to excessively high temperatures.  Additionally, sunburn and desiccation of leaves and fruit may occur.
          • Dudaim and agrestis groups of C. melo have demonstrated high levels of heat tolerance in Texas, while cantalupensis and momordica types did not tolerate temperatures of 40°C as well. Inodorus types varied in response, with some honeydew cultivars exhibiting reduced fruit set and susceptibility to sunburn, compared to others. The cultivars ‘TAM Uvalde’ and ‘TAM Dew Improved’ were developed at Weslaco and have demonstrated improved heat tolerance, and fruit setting abilities under high heat and humidity than other cultivars trialed there.
          • Cucurbits grow well in tropical climates, since they are warm-season vegetable crops. However, they grow poorly at high temperatures (38-45°C), where growth is slowed, and leaf margins become yellow. At 42-45°C, young leaves become yellow-green, flowers abort, sex expression changes to more staminate, and yield is reduced.
        • Chilling Resistance
          • Cold tolerance in both cucumbers and melons has been achieved through traditional breeding as well.  Both recessive genes and a cytoplasmic factor are involved.
          • Temperature below 10°C causes chilling injury in cucurbits. Watermelon and squash have more chilling tolerance than luffa gourd and melon, which have more chilling tolerance than cucumber, which is the most chilling susceptible cucurbit. Chilling injury is greater under the following conditions: lower temperatures (below 10°C), longer chilling duration, higher light intensity during chilling, high air speed during chilling, higher growth temperature before chilling. There are cultivars with chilling tolerance genes in the cytoplasm (maternal inheritance) and chromosomes (single gene tolerance). Cucumbers resistant vs. susceptible to chilling injury (JPEG image).
      • Program Overview (diagram)
      • Seed Production
      • Biotechnology
    • Production
      • Cultural Practices
      • Seeding
      • Transplanting and Rootstocks
      • Growth Stages
      • Greenhouse Production
      • Weeds and Mulch
      • Irrigation and Fertilizer
      • Pest Management
    • Harvesting and Postharvest Physiology
    • Consumption
  • Cucumber Trials Summary
  • Trials correction factors
  • Wehner Publications
  • Extension Publications