PEACH BREEDING PROGRAM IN SOUTHERN BRAZIL

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.

Brown Rot Strikes Prunus Fruit: An Ancient Fight Almost Always Lost

Brown rot (BR) caused by Monilinia spp., has been an economic problem for the stone fruit market due to dramatic losses, mainly during the postharvest period. There is much literature about basic aspects of Monilinia spp. infection, which indicates that environment significantly influences its occurrence in the orchard. However, progress is needed to sustainably limit this disease: the pathogen is able to develop resistance to pesticides, and most of BR resistance research programs in plant models perish. Solving this problem becomes important due to the need to decrease chemical treatments and reduce residues on fruit. Thus, research has recently increased, exploring a wide range of disease control strategies (e.g., genetic, chemical, physical). Summarizing this information is difficult, as studies evaluate different Monilinia and Prunus model species, with diverse strategies and protocols. Thus, the purpose of this review is to present the diversity and distribution of agents causing BR, focusing on the biochemical mechanisms of Monilinia spp. infection both of the fungi and of the fruit, and report on the resistance sources in Prunus germplasm. This review comprehensively compiles the information currently available to better understand mechanisms related to BR resistance.