Inheritance of susceptibility to bacterial spot (Xanthomonas arboricola pv. pruni) in peach offspring populations derived from Brazilian and Japanese cultivars/selections

Bacterial spot (caused by Xanthomonas arboricola pv. pruni) is a serious disease and difficult to control in peach cultivation, and inheritance manner of susceptibility is unclear. Five hundred and fourteen offspring and their parents from 27 peach full-sib families were evaluated for susceptibility to bacterial spot by evaluating lesion length value (LLV) after artificial inoculation to shoots from trees growing in the field. Brazilian cultivars including ‘Chimarrita’ and selections derived from them had notably lower LLVs ranging from 0.302 to 0.490 than those from Japanese cultivars/selections ranging from 0.514 to 1.295. Family means in offspring crossed between Brazilian cultivars/selections (low LLVs) and other cultivars/selections (high LLVs) showed rather low LLVs, whose values were close to Brazilian cultivar/selection parents. These results suggested that the susceptibility was controlled by single major gene and that the Brazilian and Japanese cultivar/selection parents showed dominant and recessive homozygotes, respectively. In contrast, the LLVs of family means were very high ranging from 0.719 to 1.194 in offspring population derived from crosses among Japanese cultivars. Repeated backcrosses of Brazilian cultivars/selections with Japanese cultivars/selections having high fruit quality are proposed as an effective method for developing new cultivars combining bacterial spot resistance and fruit quality in Japan.