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William L. Summers

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William L. Summers

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William L. Summers

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William G. Gonzalez and William L. Summers

233 tomato accessions of the Central American tomato collection maintained at CATIE and 7 commercial cultivars were evaluated for resistance to 4 virulent strains of Pseudomonas solanacearum representing race 1 biovars 1 and 3. In general biovar 3 strains wilted seedlings faster than biovar 1 strains but by 20 days post inoculation no significant differences were noted in susceptible check ratings. Highly significant differences for disease index were noted but no line with complete resistance was found. Two CATIE accessions, 17334 and 17340, were found to be as resistant as Hawaii 7998 to all 4 strains. Accessions 17345 and MIP-CH1 were resistant to 3 strains.

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William G. Gonzalez and William L. Summers

Seven tomato lines and their 21 hybrid populations were evaluated for their ability to resist infection by 7 virulent strains of Pseudomonas solanacearum representing race 1 biovars 1 and 3. In all cases the Gardner and Eberhart model III analysis found GCA values to be significant. In 5 of 7 cases SCA was significant. In 4 cases the parent vs. cross contrast was significant. We conclude that resistance to Pseudomonas solanacearum is predominantly controlled by additive gene action and to a lesser degree by dominant gene effects. Hawaii 7998 was found to be resistant to all 7 strains, while Rotam 4 and Rodade were resistant to biovar 3 and one race of biovar 1 (UW 275). Venus and Saturn were resistant to 3 other biovar 1 strains. Hawaii 7998 transmitted disease resistance better than the other resistant parents but its small fruit size and indeterminate growth habit make it a poor choice for a hybrid parent.

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William G. González and William L. Summers

Seven tomato Lycopersicon esculentum lines, `Venus', `Saturn', `Rodade', `Rotam 4', `Hawaii 7998', `UC-82B', and `Stevens', and their 21 crosses were evaluated for their ability to resist infection by seven virulent strains of Pseudomonas solanacearum E.F. Sm. representing race 1 biovars 1 and 3. The Gardner and Eberhart model III analysis was used to evaluate the response of lines in crosses to P. solunaceurum infection. General combining ability mean squares were significant for all strains and in 5 of 7 instances specific combining ability mean squares were significant. In four instances the parent vs. cross contrast was significant. `Hawaii 7998' was resistant to all seven strains of P. solanacearum, whereas `Rotam 4' and `Rodade' were resistant to biovar 3 and two races of biovar 1. `Venus' and `Saturn' were resistant to two other biovar 1 strains. `Hawaii 7998' transmitted greater resistance than the other resistant parents, but its small fruit size and indeterminate growth habit make it a poor choice for a hybrid parent.

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William L. Summers, Juan Jaramillo, and Theodore Bailey

Anthers of L-680A', `Licato', and `Ailsa Craig' tomato (Lycopersicon esculentum Mill.) were plated on Doy's basal medium 1 to determine whether microspore developmental stage and anther length influence anther callus production. Although calli were induced at all stages of anther development, anthers containing prophase I-stage microspores produced the highest frequency of calli. Fewer calli were produced as microspores approached the uninucleate and binucleate pollen stage. Callus diameter also decreased as anther development progressed. Significantly larger calli were produced from prophase I than later-stage anthers. Time of anther harvest (morning vs. afternoon) did not significantly affect callus number or diameter. Anther and flower bud length both were significantly correlated with anther developmental stage, the number of anthers producing calli, and mean calli diameter. In each case, anther length exhibited a significantly better correlation than bud length.

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William L. Holdsworth, Carly F. Summers, Michael Glos, Christine D. Smart, and Michael Mazourek

Cucurbit downy mildew, a disease caused by the oomycete pathogen Pseudoperonospora cubensis (Berk. & Curt.) Rostov., is a serious threat to cucumber (Cucumis sativus L.) production worldwide and can result in 100% yield losses in affected environments. In the last decade, strains of the pathogen have overcome the resistance of commercial cultivars in the United States, and currently no cultivar has robust resistance to the disease. This lack of resistance has been especially problematic for cucumber growers seeking to capture the late-season market, when downy mildew is ubiquitous throughout Eastern and Great Lakes production environments. Our objectives were to identify sources of resistance genes and to introgress these genes into high-quality, high-yielding breeding material. Using the moderately resistant cucumber cultivars Marketmore 97 and Ivory Queen as well as the Cornell-developed cultivars Platinum and Salt & Pepper, we have developed lines with excellent disease resistance. In a trial of 27 lines that included Cornell breeding material and the most resistant cultivars and U.S. Department of Agriculture (USDA) accessions identified in previous studies, the Cornell breeding line DMR-NY264 had the highest level of downy mildew resistance and the highest yields under disease pressure. In New York, plants of DMR-NY 264 produced fruit until frost without fungicide application.