Variation among populations of Puccinia recondita on partial resistant winter wheat cultivars
Abstract
The durability of resistance in slow-rusting wheat cultivars (i.e., partially resistant cultivars) depends on the amount of genetic variation in parasitic fitness within populations of the wheat leaf rust pathogen, Puccinia recondita f. sp. tritici. To assess the durability of partial resistance, variation in latent period, a major component of parasitic fitness, was assessed for P. recondita isolates on susceptible and partially resistant cultivars. On partially resistant cultivars, significant differences existed among isolates with phenotypically short and long latent periods; latent periods for short latent period isolates were 18-27% shorter than those for long latent period isolates. In simulated epidemics, isolates with short latent periods had 2-2.5 times more disease and overcame 13-35% of the resistance of four partially resistant cultivars. However, simulated disease levels for any isolate on a partially resistant cultivar were substantially less than susceptible levels. Variation in latent period of wild-type fungal populations was also explored in selection experiments. Three P. recondita populations were selected for shortened latent period on partially resistant cultivars CI 13227 and Sw 72469-6. On these, as well as other partially resistant cultivars, selected populations had characteristics, not limited to latent period, that could provide greater fitness in nature. Often, these characteristics were no different than those of susceptible host-pathogen combinations. Therefore, P. recondita seems capable of making the corresponding genetic changes required to overcome the oligogenic or polygenic nature of partial resistance. In the field, selected populations caused more disease in 1 m rows and 1 x 3 m plots than wild-type populations. In addition, differences in virulence diversity support the hypothesis that the selection for shortened latent period altered the composition of wild-type populations. The heritability of latent period was estimated from variation among single-uredinial isolates and from the response to selection for shortened latent period. Because estimates were moderately high (0.28-0.76), natural selection should operate in favor of increased parasitic fitness for latent period. Based on the realized heritabilities for latent period and the relative specificity in quantitative resistance, partially resistant cultivar CI 13227, the most resistant cultivar, was hypothesized to be the least durable.
Degree
Ph.D.
Advisors
Shaner, Purdue University.
Subject Area
Plant pathology
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