Varietal Differences in Susceptibility to Bacterial Spot (Xanthomonas arboricola pv. pruni) among 69 Peach Cultivars and Selections as Evaluated by Artificial Inoculation to Shoots

Peach (Prunus persica) shoots were artificially inoculated with stone fruit bacterial spot bacteria (Xanthomonas arboricola pv. pruni) to evaluate varietal differences in peach genetic resources for their susceptibility to this disease. Current shoots of cultivars/selections were wounded, a bacterial suspension was injected by a syringe attached to multiple needles, and lesion length was measured a few months later. Inoculation was carried out in May, June and July with two concentrations of bacterial suspension: 106 cfu·mL−1 or 108 cfu·mL−1. Although the effect of inoculation time was not significant and the effect of inoculum concentration was significant, inoculation in June at a concentration of 108 cfu·mL−1 was the most suitable treatment. Among 69 cultivars/selections tested, there was no immune cultivar, however; there were varietal differences in susceptibility to bacterial spot. ‘Nishiki’ and ‘Mochizuki’, two cultivars for canning use, ‘Chimarrita’, a Brazilian cultivar, and ‘Tsukikagami’, a table peach cultivar, were relatively resistant and may be useful sources for breeding aimed at disease resistance.