Selection of peach cells for insensitivity to culture filtrates of Xanthomonas campestris pv. pruni and regeneration of resistant plants.

Individual callus cultures were initiated from 400 immature embryos of bacterial leaf spot-susceptible 'Sunhigh' peach. Each was subjected to several selection cycles of a toxic culture filtrate produced by Xanthomonas campestris pv. pruni, the causal agent of leaf spot of peach. Progressively higher concentrations of the filtrate were used in each cycle. Two calli survived, and two plants were regenerated from each of the surviving calli. Each of the four clones was propagated in vitro and tested for whole plant resistance to X. c. pv. pruni. Results from bioassays on greenhouse-grown plants indicated that two out of the four selected clones were significantly more resistant to X. c. pv. pruni than the parental cv 'Sunhigh'. In addition, one clone was significantly more resistant than the moderately resistant cv 'Redhaven'.