GENETIC-RESISTANCE TO SCAB DISEASE IN PECAN

Thirty-six cultivars and 948 seedlings from 15 controlled crosses in t he U.S. Dept. of Agriculture-Agricultural Research Service pecan [Cary a illinoinensis (Wangenh.) K. Koch] breeding program at Brownwood, Tex as, were rated for susceptibility to nut scab [Cladosporium caryigenum (Ell. et Lang.) Gottwald] to determine heritability of this trait. Di fferences between parents and progenies, and within progenies, were hi ghly significant. Within most families, a complete range of resistance reactions were evident, from fully susceptible to fully resistant. He ritability of resistance was determined by regressing individual proge ny values on female, male, and midparent values, with the midparent he ritability estimate being the highest (0.54). This moderate level of a dditive gene action and the identification of superior parents in this study will contribute to the efficiency of breeding resistant cultiva rs.