Transgressive segregation for resistance in barley to net blotch
Bordelon, Bruce Patrick
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Research was initiated to demonstrate transgressive segregation in barley for resistance to net blotch, caused by Pyrenophora teres Drechsl. F2 plants from crosses between susceptible cultivars were selected under disease conditions in the field. Their F3 progenies were screened and selected for seedling resistance to a single isolate of P. teres. The selected plants were grown to maturity in the greenhouse and the F4 progenies were screened for seedling resistance to the same isolate. Additional F2 progenies were screened for resistance in both the field and growth chamber. The results showed that very little seedling resistance was expressed in the F3 progenies. However, many of the F progenies expressed high levels of resistance. A method to quantify levels of resistance was established and comparisons were made between the F4 lines and their parents. A total of 109 F4. lines from nine crosses were tested; 84 had means significantly less than the mid-parent mean, and 69 had means significantly less than the mid-parent and low-parent means. This proved the occurrence of transgressive segregation for net blotch resistance in barley. The increased resistance was apparently due to the additive effects of minor genes. Some of the best F4 lines were tested to a combination of isolates representing a wide range of virulence types. The reaction of the lines to the combination of isolates was similar to their reactions to a single isolate, indicating that the resistance was nonspecific in action. Screening for resistance in the field and growth chamber revealed that transgressive segregation was easiest to detect under seedling conditions in the growth chamber. The possibility of utilizing this type of resistance in commercial cultivars is discussed.