Inheritance of parthenocarpy in the cucumber (Cucumis sativus L.)

Summary The inheritance of parthenocarpy in cucumber is conditioned by an incomplete dominant gene P. In the homozygous condition PP produces parthenocarpic fruits early, with the first developing generally by the fifth node. Heterozygous Pp plants produce parthenocarpic fruits later than homozygous plants and fewer in number. The homozygous recessive pp produces no parthenocarpic fruits.Trapping of pistillate flowers was effective in identifying homozygous PP plants but failed in accurately identifying heterozygous plants. Screened cages or field isolation of gynoecious lines are efficient means of accurately identifying all parthenocarpic plants.Journal Paper No. 4333 of the Michigan Agricultural Experiment Station, East Lansing, Michigan, U.S.A.     

Inheritance of waterlogging tolerance in cucumber (Cucumis sativus L.)

Flooding of vegetable crop fields along the Yangtze River basin in China has been an annual occurrence; therefore the cultivation of tolerant varieties has become one of the most promising control strategies. Our objective was to investigate the inheritance of waterlogging tolerance of cucumber at the early stage of growth with two cucumber parents consisting of PW0832 (tolerant) and PW0801 (susceptible). In 2006, 4-weeks-old potted plants of P₁, P₂, F₁, F₂, B₁ and B₂ generations were subjected to one week waterlogged stress, control plants were not flooded. The simple additive model explained the variations of tolerance score (TOL) adventitious root formation (ARF) and waterlogged root dry weight (RDW) while the additive-dominance model explained the control treatment of RDW. Non-allelic interactions were detected for waterlogged vine length (VLH) and root length (RLH). Complementary epistasis occurred in waterlogged VLH while additive × additive, additive × dominance and dominance × dominance epistastic effects were significant for waterlogged RLH. Transgressive segregation was also observed in most of the traits in the F₂ generation indicating some alleles are dispersed in the parents used in this study. The estimates of narrow-sense heritabilities for TOL and ARF were moderately high. Backcross of F₁ to both parents in ARF, waterlogged SDW and waterlogged RDW showed good convergence of genes in the B₂. These results suggest that it should be possible to develop varieties with high levels of tolerance by selecting transgressive segregants in this cross.     

Relation in the inheritance of resistance to Pseudoperonospora cubensis rost and Sphaerotheca fuliginea poll. in cucumber (Cucumis sativusl. L.)

Summary Among the genes for resistance against Sphaerotheca fuliginea, the gene s for resistance of the hypocotyl is linked to or identical with gene p for resistance to Pseudoperonospora cubensis. This gene s is present in the cultivars Ashley, Poinsett, Natsufushinari, Pixie, Taipei and in accessions PI 179676. PI 212233 and PI 234517.Although gene s initially brings about some resistance of the true leaf, it appears that when s is present. other genes are necessary for complete resistance to S. fuliginea.     

Inheritance of firmness in raw cucumber (Cucumis sativus L.) fruit

Summary Inheritance of raw cucumber fruit texture (Magness-Taylor Fruit Pressure Tester firmness) was investigated over a 4-year period from 1971–1974. Results from 2 separate but related experiments suggested that firmness was quantitatively inherited with sufficient additive effects to permit gain from selection. In a selection study within 4 F₂ populations derived from crosses between firm (Chipper and Gy3) and soft (Mincu and Green F) fruit type cultivars, variation among and within F₃ and F₄ families was significant but overall family means were not significantly higher than the high parent in any of the 4 crosses. Narrow sense heritability estimates for fruit texture were 0.80 in the Mincu × Chipper population and 0.77 in the Green F × Chipper, Mincu × Gy3, and Gy3 × Green F crosses. In a separate experiment, generation means analysis was used to assess the mode of gene action in 2 crosses: Green F × Chipper, and Gy3 × Green F. Additive genetic effects accounted for 98.8% and 99.3% of the total genetic variation within each cross, respectively.Scientific Journal Series Paper No. 9794.     

The inheritance of resistance to Cucumis virus 1 in cucumber (Cucumis sativus L.)

Summary In crosses between highly resistant and susceptible parents, the resulting segregation ratios indicated that three genes govern a high level of resistance to cucumber mosaic, caused by Cucumis virus 1. The F₁ between highly resistant and susceptible is intermediate. The present results were compared with the contradictory results in the literature.     

Polyploidy in the glasshouse cucumber (Cucumis sativus L.)

Summary An autotetraploid form of the parthenocarpic variety Butchers Disease Resisting was produced by colchicine treatment. Immersing the seeds in water before treatment in 0.2% colchicine for 24 hours gave the highest percentage of vigorous tetraploids. The yield of fruit from tetraploids was better than the diploids at first but it declined later in the cropping period owing to slow sideshoot production.Self-fertility of autotetraploids was lower than diploids. When crossed with diploids, triploid plants were obtained. These were self-sterile but they could be crossed with diploids to give trisomic plants. Aneuploids with one additional chromosome were found amongst tetraploids and triploids.     

Inheritance of resistance to cucumber green mottle mosaic virus in muskmelon (Cucumis melo L.)

Summary Studies on inheritance of resistance to CGMMV showed that resistance was governed by polygenes with recessive nature. Out of 15 crosses studied, 10 were found to be interacting. All the interacting crosses (except one Phoot x Harela) showed duplicate type of epistasis. Kachri x Phoot (R × R type) cross exhibited heterosis in F₁ and transgressive segregation in F₂ for resistance. Studies pointed out the need to exploit this F₁ further to develop a new breeding line with higher level of resistance than both the parents.     

Search for resistance to gummy stem blight (Didymella bryoniae) in cucumber (Cucumis sativus L.)

Summary Resistance to gummy stem blight (Didymella bryoniae) was not detected among 1208 cucumber lines of diverse origin when cotyledons of four-day-old seedlings were inoculated with an aqueous suspension of 5000 spores of D. bryoniae delivered to freshly crushed tissue, followed by 48 h incubation at 20°C and 100% RH in the dark. Among 49 lots evaluated for gummy stem blight in the field, cv. Homegreen #2 and Pl 200818 from Burma were resistant. Earliness in fruit maturity was positively correlated with susceptibility to gummy stem blight (r=0.424). Cucumber accessions differed in the incidence of stem and hypocotyl cankers. In greenhouse grown plants at the 2nd–3rd leaf stage, differentiation of resistant lines was obtained by spraying plants with an aqueous suspension of 10⁶/ml D. bryoniae spores followed by 48 h incubation at 20°C and 100% RH in the dark. One cycle of mass selection in Homegreen #2 resulted in improved gummy stem blight resistance.     

Identification of quantitative trait loci for downy mildew resistance in cucumber (Cucumis sativus L.)

Downy mildew, caused by Pseudoperonospora cubensis (Berk. & Curt.) Rostov, is one of the most economically important foliar diseases in cucumber (Cucumis sativus L.). Cucumber line CS-PMR1, derived from self-pollination of USDA Plant Introduction 197088, has a high level of resistance to downy mildew and is considered to be promising breeding material. In this study, we performed quantitative trait locus (QTL) analysis for downy mildew resistance using 111 recombinant inbred lines (RILs) derived from a cross between CS-PMR1 and the old Japanese cultivar Santou, which exhibits moderate resistance. The resistance of the RILs and their parents was evaluated by diverse methods using different plant organs (cotyledons, true leaves), stages (seedlings and adult plants), and evaluation criteria (lesion expansion and extent of sporulation). The high resistance of CS-PMR1 was associated with many QTLs with relatively small effects, whereas the moderate resistance of Santou was associated with one major QTL and possibly two others with relatively small effects. In all assays, the major QTL at which the Santou allele was associated with increased resistance had the largest effect. This QTL allele from Santou and several of the most effective QTL alleles identified in CS-PMR1 should be highest priority for selection to efficiently breed new cultivars that carry adequate levels of downy mildew resistance.     

Linkage of random amplified polymorphic DNA markers to downy mildew resistance in cucumber (Cucumis sativus L.)

Marker assisted selection (MAS) may improve the efficiency of breeding downy mildew resistant cucumber cultivars. A study was conducted to identify random amplified polymorphic DNA (RAPD) markers linked to the downy mildew resistance gene (dm) which would be suitable for MAS. A total of 145 F₃ families from two populations (55 from the WI 1983G × Straight 8 population and 90 from the Zudm1 × Straight 8 population) were evaluated over five locations in North America and Europe. Resistant and susceptible F₃ families were identified and mean family resistance ratings were used to type individual F₂ plants. No evidence for race differences in the pathogen (Psuedoperonospora cubensis (Berk. & Curt.) Rostow) between North America and Europe was found. Phenotypic correlations between locations ranged from 0.3 to 0.7. Of the 135 polymorphic RAPD markers identified from 960 primers, five were linked to dm - G14₈₀₀, X15₁₁₀₀, AS5₈₀₀, BC519₁₁₀₀, and BC526₁₀₀₀. In the WI 1983G × Straight 8 population, G14₈₀₀ was linked to dm at 16.5 cm, AS5₈₀₀ at 32.8 cm, BC519₁₁₀₀ at 9.9 cm, and BC526₁₀₀₀ at 19.2 cm. In the Zudm1 ×Straight 8 population, G14₈₀₀ was linked at 20.9 cm, X15₁₁₀₀at 14.8 cm, AS5₈₀₀ at 24.8 cm, and BC526_{_1000} at 32.9 cm. MarkersG14₈₀₀ and BC519₁₁₀₀ were linked in repulsion to the dm allele, and X15₁₁₀₀, AS5₈₀₀, and BC526₁₀₀₀ were linked in coupling phase. These genetic markers may be exploited to develop an efficient MAS strategy for breeding resistant cucumber cultivars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gynoecious sex expression and stability in cucumber (Cucumis sativus L.)

Summary Results indicated that gynoecious stability in the F₁ is governed by partial dominance. The degree of gynoecious stability is dependent upon genotypes, stages of plant for AgNO₃ application and number of sprays. Depending upon the genotypes, the one-true-leaf stage and one spray of 250 ppm AgNO₃ showed more gynoecious stability in the F₁. Twice application of AgNO₃ at the two-true-leaf stage produced the maximum number of male flowers. Plants exposed to light for longer time (10.00 h) after AgNO₃ application produced less flowers than when exposed for shorter time (15.00 and 20.00 h).Present address: Division of Vegetable Crops, Indian Agricultural Research Institute, New Delhi-110012, India.     

New C-banding pattern for chromosome identification in cucumber (Cucumis sativus L.)

A chromosome study of cucumber, C. sativus L., was performed using orcein and C-banding techniques. The diploid and tetraploid plants investigated here showed the somatic chromosome numbers 2n=14 and 28, respectively. The haploid chromosome complement was composed of five metacentric and two submetacentric chromosomes. All C. sativus chromosomes had clearly visible C-bands, and each chromosome could be identified unequivocally after C-banding staining, with 13 C-bands appearing in the haploid complement. The haploid complement had a 44.9% ratio of total C-band length to total chromosome length. Chromosomes 1, 2, 4, 5 and 7 had stable C-bands. Three large, dark C-bands appeared at the proximal regions of chromosomes 1 and 2. Chromosome I had quite a large C-band and with a 68.4% ratio of C-band length to short arm length. Chromosome 2 also had quite a large C-band in the pericentromeric region with a 57.6% ratio of C-band length to the full length of this chromosome and possessed an elongated primary constriction in early metaphase. In prometaphase, chromosome 2 showed that the long arm was completely separated from the short arm. The number of secondary constrictions could not be clearly observed because these chromosomes are small and they could not be counted in every metaphase cell. However, six chromosomes seemed to have secondary constrictions in the diploid plants. Two silver-stained bands were observed at primary constrictions of two of the large chromosomes.     

Gummy stem blight resistance of cucumbers (Cucumis sativus L.)

Summary A start was made with breeding for resistance to gummy stem blight in cucumber. A method has been development for screening plants in a young stage. Using this method a distinct level of resistance was found in plants of Leningradsky, Wjarnikovsky,a P.I. entry from Birma, Rheinische Vorgebirge and a P.I.entry from Turkey. Lines developed from this material show a higher level of resistance than Dutch slicing and pickling cucumber varieties.     

Combining ability between lines of Cucumis sativus L. and Cucumis sativus var. hardwickii (R.) Alef

Summary Three Cucumis sativus L. (CS) lines adapted to USA growing conditions were used as female parents in crosses to one line each of seven Cucumis sativus var. hardwickii (R.) Alef. (CH) accessions used as male parents to determine the relative combining ability of the CH accessions for six horticultural characters. The 21 F₁ progenies were grown in a randomized complete block design in two locations and evaluated for fruit number, lateral branch number, fruit length, fruit length/diameter ratio, number of female flowering nodes, and days to anthesis. General combining ability (GCA) was significant for all characters in each location. Specific combining ability (SCA) was significant for all characters except days to anthesis in one location and lateral branch number in both locations. Significant location × combining ability interactions were also evident for several characters. Results suggest that CH may be useful for improving fruit yield in commercial cucumber, but that limitations may lie in the attainment of acceptable fruit.Research supported by the College of Agric. and Life Sci., Univ. of Wisconsin, Madison; USDA, ARS, and by funds from Pickle Packers Intl., Inc. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee of warranty of the product by the USDA and does not imply its improval to the exclusion of the other products or vendors that may also be suitable.     

Inheritance of parthenocarpy in pickling cucumbers (Cucumis sativus L.) and linkage with other characters

Summary The inheritance of parthenocarpy in the pickling cucumber has been studied with progenies of an incomplete diallel cross between lines with different degrees of parthenocarpy and with two sets of F₁, F₂ and B₁ of crosses between parthenocarpic and non-parthenocarpic lines. The inheritance of parthenocarpy could be explained by three independent, isomeric major genes with additive action, together with a non-allelic interaction of the homozygote-heterozygote type. Indications have been found for linkages between genes that govern parthenocarpy, femaleness and the spined/hairy fruit character. Consequences for breeding parthenocarpic varieties are discussed.     

Identification of quantitative trait loci for powdery mildew resistance in highly resistant cucumber (Cucumis sativus L.) using ddRAD-seq analysis

Powdery mildew, caused by Podosphaera xanthii (syn. Sphaerotheca fuliginea ex Fr. Poll.), is one of the most economically important foliar diseases in cucumber (Cucumis sativus L.). Cucumber parental line ‘Kyuri Chukanbohon Nou 5 Go’, developed from weedy cucumber line CS-PMR1, is highly resistant to powdery mildew and is promising breeding material. We performed quantitative trait locus (QTL) analysis using double-digest restriction-site-associated DNA sequencing (ddRAD-Seq) in a population from a cross between ‘Kyuri Chukanbohon Nou 5 Go’ and the Japanese native cultivar ‘Kaga-aonaga-fushinari’, which is susceptible to powdery mildew. The resistance of the population and its parents was evaluated using leaf disc assays and image analysis. We detected one major QTL on Chr. 5 that was effective at both 20°C and 25°C and one minor QTL on Chr. 1 effective at 20°C. We detected two additional QTLs in subpopulation: one on Chr. 3 effective at 20°C and one on Chr. 5 effective at both 20°C and 25°C in a position different from the major QTL. The resistance alleles at all four QTLs were contributed by ‘Kyuri Chukanbohon Nou 5 Go’. The results of this study can be used to develop practical DNA markers tightly linked to genes for powdery mildew resistance.     

Variance component analysis of parthenocarpy in elite U.S. processing type cucumber (Cucumis sativus L.) lines

Summary Parthenocarpic (seedless) U.S. processing type cucumber (Cucumis sativus L.) germplasm can bear more high quality fruit when compared to their seeded counterparts. Knowledge of genetic components of variation for parthenocarpy would assist cucumber breeders to incorporate this economically important trait into commercial varieties. The inheritance of parthenocarpy in elite U.S. processing type cucumber was, therefore, investigated by examining the single-harvest yield of F₃ progeny derived from a mating between line 2A (P₁, parthenocarpic) and line Gy8 (P₂, non-parthenocarpic) grown in two fields (E-block and G-block at Hancock, Wisc.) in the summer of 2000. Environmental variance accounted for about 90% of total phenotypic variance in both locations. The degree of dominance genetic variance was 0.3 and 2.2 at G-block and E-block, respectively, and the minimum number of effective factors controlling parthenocarpy was estimated as 5 (G-block) to 13 (E-block). Estimates of heritability were significantly lower when based on individual plants within an F₃ family and on F₃ family mean performances. While narrow-sense and broad-sense heritability of individual plants within F₃ family was always < 0.1, narrow-sense heritability for F₃ family mean performance ranged between 0.33 (E-block) and 0.62 (G-block), and broad-sense heritability ranged between 0.53 (E-block) and 0.67 (G-block). Thus, in this population, advanced generation selection for parthenocarpy based on F₃ family mean performance will be more effective than selection of individual plants within F₃ family.