Graduate Thesis Or Dissertation
 

Inheritance of resistance to Septoria leaf blotch in selected spring bread wheat genotypes (Triticum aestivum L.)

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/k930c1335

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  • Septoria leaf blotch of wheat is a major biotic factor limiting the grain yield. To determine the nature of inheritance involving selected genotypes, three resistant semidwarf spring wheat lines exhibiting durable global resistance and one susceptible cultivar were crossed in all possible combinations, excluding reciprocals. Parents, Fl, F2, and F3 generations were inoculated with one pathogenic strain of Septoria tritici and evaluated under field conditions. Data were collected on an individual plant basis. F2 and F3 frequency distributions were computed to determine the nature of inheritance. Combining ability analysis of the 4x4 diallel cross and narrow-sense heritability were employed to estimate the nature of gene action. Phenotypic correlations were obtained to examined the possible association between disease severity traits and their relationship with heading date and plant height. The continuous distribution of the F2 and F3 populations among crosses made it impossible to classify plants into discrete classes in crosses between resistant x susceptible genotypes. Mean values of the disease traits Septoria progress coefficient, Relative coefficient of infection, and Septoria severity of flag leaf among the segregating populations were similar to the midparent values. Transgressive segregation was also observed in the F2 and F3 suggesting that parents had different resistance genes. Additive gene effects were found to be the major component of variation although nonadditive gene action played an important role in the expression of all three disease traits. The resistant parents Bobwhite"S" and Kavkaz /K4500 L.A.4 were found to have the largest negative general combining ability effects for the disease traits suggesting that these parents would be the best source for resistance to Septoria leaf blotch. High general combining ability and high narrow sense heritability estimates in the F3 population, indicated that substantial progress for resistance to Septoria tritici would be effective selecting in this generation. Of the three disease measures it would appear that selection for the lowest percentage of Septoria infection on the flag leaf would provide the most progress in developing resistant cultivars. Moderate and low negative phenotypic correlations were found among generations for the disease traits with heading date and plant height. From the results of this study the selection of early maturing short stature progeny would be possible within the genetic materials employed in this study.
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