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  • Author or Editor: Phillip N. Miklas x
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Foliar diseases are a major constraint to cultivated tepary bean (Phaseolus acutifolius A. Gray var. latifolius Freeman) production in some environments. The reactions of 12 cultivated teparies to eight individual races (41, 47, 49, 51, 53, 58, 67, and 73) of the bean rust fungus Uromyces appendiculatus (Pers.) Unger var. appendiculatus maintained at Beltsville, Md., were examined under greenhouse conditions. These diverse races, used together, overcome all of the major rust-resistance genes present within the 19 host differential cultivars of common bean (Phaseolus vulgaris L.). Seven lines (GN-605-s, GN-610-s, PI 321638-s, PI 502217-s, Neb-T-6-s, Neb-T-8a-s, and Neb-T-15-s) exhibited similarly high levels of resistance (immunity or necrotic spots without sporulation) to all eight races. Inheritance of resistance was examined across five susceptible × resistant (S × R) and three resistant × resistant (R × R) populations. The rust reactions in the F1, F2, and F3 generations derived from S × R crosses revealed that the immune or necrotic resistance response was conditioned by a single locus exhibiting incomplete dominance. The rust resistance of four lines tested for allelism in R × R crosses was found to be derived from the same gene. This apparent lack of variability for rust resistance suggests that a single introgression event may realize the full potential for cultivated tepary bean to contribute rust resistance to common bean through interspecific hybridization. In addition, the limited variability for resistance to the highly variable rust pathogen in cultivated tepary bean supports the occurrence of a “bottleneck effect” during domestication of this species, as observed in germplasm diversity studies.

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Cultivated tepary bean (Phaseolus acutifolius A. Gray var. latifolius Freeman) has potential for production during the hot, dry seasons in the tropics. Bean golden mosaic virus (BGMV), however, seriously limits production of Phaseolus spp. in such environments. Twelve select tepary beans were evaluated for reaction to BGMV across four field nurseries near Isabela, Puerto Rico. Disease reaction was principally determined by measurement of seed yield (kg·ha–1) and weight (g 100/seeds). All tepary beans possessed some tolerance to BGMV, as they produced comparatively moderate seed yield despite expression of severe foliar yellow mosaic symptoms. On average, tepary bean yielded 133% of the BGMV-resistant dry bean (Phaseolus vulgaris L.) control `Dorado'. Four teparies, Neb-T-6-s, GN-610-s, Neb-T-8a-s, and PI 321637-s, expressed superior tolerance to BGMV as they yielded above the trial mean in at least three of four trials. Harvested seed quality was uniformly poor across all lines, averaging 18% less weight than in the non-BGMV trials. The combination of the observed tolerance with escape mechanisms and cultural disease control practices may enable production of tepary bean in regions and seasons that experience moderate to severe BGMV epidemics.

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We investigated the partial physiological resistance (PPR) of common beans (Phaseolus vulgaris L.) to white mold disease caused by Sclerotinia sclerotiorum (Lib.) deBary. The activity of phenylalanine ammonia-lyase (PAL) was measured in detached stems inoculated with a growing mycelium of the pathogen. Noninoculated detached stems and whole plants were included as controls. Five bean cultivars-Upland, Bunsi, Sierra, UI-114, and Montcalm-and one breeding line-NY 5394-were tested; all varied in PPR to white mold disease. Greater PAL activity in the resistant NY 5394 than in the susceptible `Upland' suggests that PAL activity may be involved in the PPR of common beans to S. sclerotiorum.

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A genetic linkage map of 170 RAPD markers mapped across 79 recombinant inbred lines (Dorado and XAN-176) reveal genomic regions that condition multiple disease resistance to fungal (Ashy Stem Blight—Macrophomina phaseolina), viral (bean golden mosaic virus—BGMV), and bacterial (common bacterial blight—Xanthomonas campestris pv. phaseoli) pathogens of common bean (Phaseolus vulgaris). A genomic site on linkage group US-1 had a major effect, explaining 18%, 34%, and 40% of the variation in phenotypic reaction to ashy stem blight, BGMV, and common bacterial blight disease, respectively. Adjacent to this region was a QTL conditioning 23% of the variation in reaction to another fungal pathogen, web blight (Thanatephorus cucumeris). A second genomic site on linkage group US-1 had minor affect on multiple resistance expression to the same fungal (15%), viral (15%), and bacterial (10%) pathogens. It is unknown whether these specific genomic regions represent a series of linked QTL affecting resistance to each disease separately or an individual locus with pleiotropic effect against all three pathogens.

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