Resistance in Cucumis sativus L. to Tetranychus urticae Koch. 4. The genuineness of the resistance

Summary For several generations subpopulations of the twospotted spider mite were reared on cucumber varieties previously selected as partially resistant. Subsequently resistance tests were carried out in the laboratory and the glasshouse with mites from these subpopulations and concurrently with mites from a basic population reared on a susceptible cucumber line. In these tests neither acceptance nor net reproduction or damage index on the partially resistant varieties depended on the kind of mite populations used as inoculum. Therefore it is concluded that the resistance is genuine. The stability of the resistance is discussed.     

Resistance in Cucumis sativus L. to Tetranychus urticae Koch. 3. Search for sources of resistance

Summary After a first screening of 800 cucumber varieties, a laboratory test and a practical test, the following nine varieties have been selected for their distinguishable level of resistance to the twospotted spider mite: PI 220860, Hybrid Long Green Pickle, PI 178885, Ohio MR 200, Taipei no 1, Robin 50, Aodai, PI 163222 and PI 218036. Besides resistance tolerance for the twospotted spider mite also appears to occur. Related Cucumis species do not seem to possess higher levels of resistance than the most resistant C. sativus varieties. The resistance-parameters acceptance and reproduction appear to be positively correlated. On resistant varieties the metabolism of the spider mites is clearly disturbed, but this seems not to be caused mainly by bitter principles.     

Resistance in Cucumis sativus L. to Tetranychus urticae Koch. 5. raising the resistance level by the exploitation of transgression

summary After crossing partially resistant varieties some lines with a markedly higher resistance level were selected. This transgression for resistance indicates a polygenic inheritance of the resistance. On the most resistant F₅ lines selected, oviposition was reduced by 50 to 60% and the economic damage threshold was reached 5 to 8 weeks later than in the susceptible control. The level of acceptance was not influenced by the selection.The selection of individual F₂ plants was hampered by low heritabilities, whereas the heritabilities of F₃- and subsequent line means were generally high enough. Selection for higher resistance levels was attended by an unintended increase in cucurbitacin content. This is explained by linkage of genes for resistance and bitterness rather than by identity of these genes.     

Resistance of Cucumis sativus L. to Tetranychus urticae Koch. 6. Comparison of near isogenic bitter and non-bitter varieties for resistance

Summary The bitter cucumber variety Improved Long Green did not differ in resistance to the twospotted spider mite from its near isogenic non-bitter mutant, the source of all non-bitter varieties. Four pairs of near isogenic bitter and non-bitter varieties gave similar results. Therefore any causal relation between bitterness and resistance is denied.     

Resistance in Cucumis sativus L. to Tetranychus urticae Koch. 1. The role of plant breeding in integrated control

Summary The role of plant breeding and particularly of host plant resistance in integrated control is discussed. Host plant resistance to insects and mites, especially to Tetranychus urticae is reviewed. A standard terminology for disease and pest resistance is recommended.     

Resistance in Cucumis sativus L. to Tetranychus urticae Koch. 7. The inheritance of resistance and bitterness and the relation between these characters

Summary The inheritance of resistance to the twospotted spider mite and of bitterness in cucumber has been studied in three sets of P₁, P₂, F₁, F₂, B₁₁ and B₁₂ of crosses between three bitter, resistant lines and one non-bitter, susceptible line. Resistance to the twospotted spider mite as measured by acceptance and oviposition appeared to be determined by several to many genes, which are inherited mainly in an additive fashion. Bitterness is basically governed by the gene Bi, which, contrary to earlier reports, is inherited in an intermediary way, while the expression of Bi is influenced by additively inherited intensifier genes. Whereas Bi and the bitterness intensifier genes are not related to the resistance factors acceptance and oviposition, they are related to resistance or tolerance as measured by the damage index. This relation is explained by linkage rather than by identity of the genes concerned. Changes in the test methods and breeding consequences are discussed.     

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.     

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.     

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.     

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.     

Search for novel genes for resistance to powdery mildew (Sphaerotheca fuliginae) in cucumber (Cucumis sativus)

Summary The current powdery mildew (Sphaerotheca fuligninea) resistant cucumber varieties suffer from leaf chlorosis during autumn, winter and early spring cultivation in the Netherlands. Therefore screening was carried out for novel powdery mildew resistance genes. From 177 accessions, derived from different sources, 108 accessions proved to be partially resistant to S. fuliginea. Crosses were made with 53 resistant accessions to distinguish the presence of novel genes. It is likely that the accessions C. sativus 2145, C. sativus LV 41, PI 188807, Vladivostokij, White and Yellow 1 have one or more recessive powdery mildew resistance genes, different from powdery mildew resistance genes of the line NPI, which was used for variety breeding. Powdery mildew resistance tests with S. fuliginea give similar results in different regions of the world.Abbreviations pmr powdery mildew resistance     

Mite responses in relation to trichomes of Lycopersicon esculentum x L. hirsutum F2 hybrids

Summary Leaflets from 11 L. esculentum x L. hirsutum F₂ individuals were bioassayed with spider mites (Tetranychus urticae). Densities of Type I, Type III, Type IV, Type V, and Type VI trichomes and the intensity of red fluorescence of the Type VI trichome tip varied widely among the 11 F₂ hybrids. Mite responses were analyzed in relation to these trichome characters and leaflet surface. Variation in Type IV density accounted for most of the variation in mite responses. Densities of Type I, V and VI trichomes also contributed to mite responses but their effects were obscured by high Type IV densities. Type VI tip fluorescence was not associated with responses of mites in bioassays of these hybrids.The investigation reported in the paper (84-10-123) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director. This material is based upon work supported, in part, by the U.S. Department of Agriculture, Agreement No. 59-2213-1-1-717-0 (Competitive Research Grants Program)     

The relationship between powdery mildew (Sphaerotheca fuliginea) resistance and leaf chlorosis sensitivity in cucumber (Cucumis sativus) studied in single seed descent lines

Summary The genetic relation between powdery mildew resistance and sensitivity for leaf chlorosis of glasshouse cucumber was investigated. The powdery mildew resistant, leaf chlorosis sensitive hybrid variety Profito was crossed with the powdery mildew susceptible, non chlorosis sensitive hybrid variety Corona. Forty four F₆ inbred lines of this cross, produced by single seed descent, were tested for powdery mildew resistance (PMR) and leaf chlorosis sensitivity (LCS). PMR and LCS were positively correlated (r=0.59). One or more of the PMR genes probably causes LCS as a pleiotropic effect or is closely linked to LCS, but also other factors, not genetically linked to PMR can cause LCS. Five F₆ lines combined a significantly higher level of PMR than Corona with a significantly lower LCS than Profito. Three of these lines could hardly be distinguished from Corona for the level of LCS.Abbreviations LCS leaf chlorosis sensitivity - PMR powdery mildew resistance - SSD Single Seed Descent     

Occurrence and chromosome number of Cucumis sativus var. hardwickii (Royle) Alef. in South India and its bearing on the origin of cultivated cucumber

Summary Cucumis sativus var. hardwickii (Royle) Alef., the wild progenitor of cultivated C. sativus is reported for the first time from peninsular India. The South Indian specimens showed n=7 bivalents in PMCs. The discontinous occurrence of the wild taxon in the Himalayan regions and peninsular hills and the existence of cultivars of C. sativus adapted to the tropical and temperate climates suggest polytopic domestication of the cultivated forms. The possibility of utilizing this wild germplasm for crop improvement is indicated.     

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 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.     

Evaluation of the U.S. cucumber germplasm collection for root size using a subjective rating technique

Summary Root size in cucumber (Cucumis sativus L.) has received little research attention until recently. However, a large root system could improve nutrient and water uptake, and ultimately yield. Knowledge of root size could help cucumber breeders develop cultivars with improved performance. A study was conducted in the greenhouse to evaluate 857 cultigens (827 plant introduction accessions, 22 breeding lines, and 8 cultivars) of cucumber for root length. Complete data were obtained for 794 cultigens. Plants were grown from seeds in 2 replications in the greenhouse. Plants were rated for root length using a 1 to 9 scale (1–3 = small, 4–6 = medium 7–9 = large). Also, root length was measured from soil surface to the tip of the longest main root. In addition, all cultigens were evaluated for root length and dry weight to provide meaning to the subjective rating. Root rating was highly correlated with both root length (r=0.92) and dry weight (r=0.64) of roots. Root length averaged 74 mm and most cultigens (579, or 68%) had roots 40 to 110 mm long. The cultigen with the longest roots was PI 183056 (193 mm), and the shortest was PI 176954 (2 mm). The subjective rating technique provided a simple, accurate and rapid method to estimate root growth in the greenhouse.     

Breeding for resistance to Fusarium oxysporum f. sp. Tulipae in tulip (Tulipa L.). I. Development of a screening test for selection

Summary Fusarium oxysporum causes the most serious fungus disease in tulip. Breeding for resistant cultivars may considerably contribute to a solution of the problem.Bulbs of various cultivars planted in contaminated soil showed important and significant differences in resistance. Inoculation trials in the field and in the glasshouse have led to recommendations for the screening of juvenile and adult bulbs.     

Validity of a leaf inoculation test to assess the resistance to Phytophthora megakarya in a cocoa (Theobroma cacao L.) diallel mating design

Cocoa pod rot, caused by different Phytophthora species, is rife in all production zones. Phytophthora spp. control is therefore a major challenge for world cocoa cultivation, and selection of resistant material is a priority research theme for many producing countries. Various genetic trials have been set up over many years in zones affected by the disease. In Cameroon, a 6x6 diallel mating design was set up to study heritability of the resistance trait. Field observations led to the classification of parents according to their ability to transmit resistance to their progenies. These field measurements were long and laborious, so a resistance test based on artificial leaf inoculations was developed. This article studies the correspondence between results obtained with the test and observations of rot rates in the field. There was a significant genetic correlation between pod rot rate in the field and leaf test data, so using this resistance test could shorten cocoa tree selection cycles. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic control of resistance to soft rot caused by Erwinia carotovora subsp. carotovora in Zantedeschia spp. (Araceae), section Aestivae

The pattern of heredity of resistance to Erwinia carotovora subsp. carotovora in Zantedeschia spp. is investigated. Four species with different resistance levels (Z. albomaculata, Z. elliotiana, Z. pentlandii, Z. rehmannii) were compared to their reciprocal offspring. The occurrence of plastome-genome incompatibility (PGI) affected plant resistance in all families. Therefore, plants that suffered from PGI were omitted from genetic analyses. Resistance was quantitative and the correlation between resistance levels of parents and offspring (h ²= 0.33;r ²= 0.66) indicated a genetic basis of resistance. Z. rehmannii and Z. albomaculata contributed more resistance genes than Z. elliotiana or Z. pentlandii. Transgression among some of the offspring of Z. rehmannii and Z. albomaculata indicated the presence of complementary resistance genes in these two species and good potential for resistance breeding.