Scab of wheat: Epidemiology, inheritance of resistance, and molecular markers linked to cultivar resistance
Abstract
Wheat scab, caused by Fusarium graminearum, is a destructive disease of wheat. Uncertainty about the inheritance of cultivar resistance and lack of reliable screening techniques have impeded progress in breeding resistant cultivars. In this study, components and inheritance of cultivar resistance were characterized, and factors influencing resistance expression were investigated. Wheat cultivars significantly differ in degree of resistance to scab spread within a spike when tested with different isolates of the fungus in different experiments. When single spikelets were inoculated, spread of scab within a spike was less frequent, later and slower in resistant cultivars than in susceptible cultivars. Measurement of scab spread within a spike is a stable characteristic by which resistance of a cultivar may be assessed. Inheritance of cultivar resistance to spread of scab within a spike was investigated in F$\sb1,$ F$\sb2,$ and backcross populations of 11 wheat crosses and in F$\rm\sb5,\ F\sb6\ and\ F\sb7$ progenies of Ning 7840/Clark. One to 3 major genes, depending on the cultivars, with possibly modifying genes conditioned resistance to scab. Additive effects accounted for most of the genetic variation although dominance and epistasis were detected. With bulked segregant analysis, 10 out of 1120 random decamer primers showed polymorphisms between bulked DNAs from the most resistant and the most susceptible F$\sb6$ families of Ning 7840/Clark. Five polymorphic bands indicated a significant association with 2 resistance genes, either in repulsion or coupling. Scab incidence increased and incubation period decreased as moist periods increased from 0 to 3 nights after inoculation. Scab severity was not affected by moist period during incubation, but affected by temperatures (14, 23, or 30 C) after incubation. Scab spread within a spike was greatest at 23 C. Moisture had no effect on scab spread. Resistant cultivars had consistently low severity under all conditions studied. In addition, both scab incidence and severity significantly increased as inoculum concentration increased. Scab incidence was more affected by moist period after inoculation, inoculum concentration, and inoculation method (injecting spores versus spraying spores) compared to severity. Flowering was the most susceptible stage for infection.
Degree
Ph.D.
Advisors
Shaner, Purdue University.
Subject Area
Plant pathology|Genetics|Molecular biology
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