COMBINING ABILITIES OF 5 JAPANESE PLUM CULTIVARS FOR RESISTANCE TO XANTHOMONAS STEM CANKER

Analysis of a five-parent diallel in a greenhouse estimated general an d specific combining ability (GCA and SCA) effects for resistance of J apanese plum (Prunus salicina Lindl. and hybrids) to Xanthomonas campe stris pv. pruni (Smith) Dye stem canker, as measured by length of inoc ulated cankers, canker appearance rating, and canker expansion rate. ' Friar' and 'Gulfruby' were the most susceptible parents. 'Burbank', 'W ilson', and 'Wade' had similar GCA values for length of inoculated can kers, but 'Wade' was the superior parent in transmitting canker resist ance, as measured by canker appearance rating. SCA was not important i n determining the performance of a cross. Canker appearance rating was the best measure of resistance in the greenhouse tests and provided a greater separation of GCA estimates and lower coefficient of variatio n.