Plant Pathology Faculty and Staff Research
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Browsing Plant Pathology Faculty and Staff Research by Subject "disease resistance"
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Item Identification of markers associated with race-specific resistance to Aphanomyces root rot in alfalfa, Poster at the 2017 APS meeting(2017) Samac, Deborah; Bucciarelli, Bruna; Dornbusch, Melinda; Miller, Susan; Yu, Long-XiAphanomyces root rot, caused by Aphanomyces euteiches, is one of the most important diseases of alfalfa in the United States. Two races of the pathogen are recognized and although most cultivars are resistant to race 1, fewer have resistance to race 2, the predominant race in North America. Molecular markers are needed to facilitate breeding for resistance and to clarify race/resistance gene structure. Resistant and susceptible seedlings were identified from three resistant cultivars, WAPH1, WAPH5 and 53V52, and used as parents to produce F1 populations. Severity of symptoms corresponded with amount of pathogen DNA and oospore density in roots. Race-specific resistance involves a hypersensitive response of individual epidermal or cortical cells upon pathogen attack followed by suberization of cells surrounding the stele and strong autofluorescence in cortical cells, indicating the presence of phenolic compounds. Segregation ratios of F1 populations suggested that resistance to race 1 in WAPH1 is conditioned by a single gene but resistance to race 1 is multigenic in WAPH5 and 53V52, and resistance to race 2 is multigenic in all three cultivars. Segregation for resistance to seven strains of A. euteiches in 70 F1 full-sib plants derived from 53V52 suggested the presence of clustered resistance genes and multiple race types. Identification of resistance gene loci is in progress using genotyping by sequencing and genetic mapping of F1 populations.Item Lignin reduction in alfalfa (Medicago sativa) does not affect foliar disease resistance(2018) Samac, Deborah A; Ao, Samadangla; Dornbusch, Melinda R; Grev, Amanda M; Wells, M Scott; Martinson, Krishona; Sheaffer, Craig CDisruptions in the lignin biosynthetic pathway have been shown to reduce disease resistance in a number of crops. Recently, genetically modified alfalfa (Medicago sativa) varieties have been marketed with reduced lignin and improved forage quality traits, including increased digestibility by ruminants at later stages of plant maturity. The objective of this study was to compare foliar disease resistance in three reference alfalfa varieties, 54R02, DKA43-22RR, WL355.RR, and the reduced lignin variety, 54HVX41, to evaluate the effect of the reduced lignin trait on foliar disease resistance. Alfalfa plants in research plots at three locations in Minnesota were evaluated for percent defoliation caused by foliar pathogens at four maturity stages; early bud, bud, early flower, and flowering; with natural inoculum. Spring black stem and leaf spot, Leptosphaerulina leaf spot, and common leaf spot were observed from June through September in all locations on all varieties. Summer black stem and leaf spot was most prevalent in August on all varieties at one location. The amount of defoliation increased with maturity stage for all varieties. When harvest was delayed until the flowering stage, moderate to severe (32 to 64%) leaf loss occurred, depending on location. Alfalfa varieties did not differ in percent defoliation at any maturity stage indicating that the reduced lignin trait did not affect foliar disease resistance.