Inheritance and Combining Ability of Leafhopper Defense Mechanisms in Common Bean1

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Abstract
The leafhopper (Empoasca kraemeri Ross and Moore) is a serious pest of common bean (Phaseolus vulgaris L.) in Latin America. Previous studies showed that different leafhopper defense mechanisms were present in bean lines, although all lines suffered considerable damage when leafhopper populations were high. Studies were undertaken to determine the inheritance and combining ability of leafhopper defense mechanisms in beans under field conditions. Bean lines EMP 81 and EMP 82, tolerant to leafhopper feeding damage, and lines EMP 89, EMP 94, and EMP 97, containing antixenosis resistance (a defense mechanism that makes these lines less preferred for leafhopper oviposition) were selected to study. A generation means analysis using EMP 81, EMP 89, and EMP 94, in crosses with a susceptible line, BAT 41, showed that the additive‐dominance genetic model was sufficient to explain the inheritance of tolerance and antixenosis defense mechanisms in these lines. Additive and dominance gene effects were significant for yield of plants under leafhopper attack and feeding damage, although dominance gene effects appeared to be more important in the inheritance of yield. Only additive gene effects were significant for nymphal counts. Similar results were found in the estimation of general and specific combining ability effects in a diallel study of F1 and F2 progeny of crosses among the five resistant bean lines. Certain crosses combining antixenosis and tolerance defense mechanisms resulted in higher F2 yields than would be expected on the bases of the mean performance of their parental lines. The results suggest that transgressive segregation for higher resistance levels may result from crosses among bean lines containing different defense mechanisms.

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