Inheritance of Resistance to Loquat Canker (Pseudomonas syringae pv. eriobotryae, Group A) in Loquat (Eriobotrya japonica)

To investigate the inheritance of resistance to loquat canker caused by Pseudomonas syringae pv. eriobotryae, Group A, 1307 and 1189 loquat (Eriobotrya japonica) progenies from 31 (Exp.1) and 15 (Exp.2) crosses, respectively, were studied. F1 seedlings were inoculated with the bacterial suspension and classified as either resistant (R) or susceptible (S) based on the appearance of black-brown canker 1-2 months after inoculation. Crosses between resistant cultivars resulted in two types of segregation : one cross combination produced only resistant seedlings, whereas another combination yielded progenies with the segregation ratio of 3R : 1S. Progenies derived from crosses between resistant and susceptible cultivars segregated into 1R : 1S, except for five crosses derived from 'Champagne' or 'Fukujuin', in which all seedlings were resistant. All seedlings in the crosses between susceptible cultivars were rated susceptible, except for selfed 'Hondawase', which produced some resistant plants. These results indicate that the resistance to loquat canker is controlled by a single dominant gene. Except for 'Champagne' and 'Fukujuin' which are dominant homozygous plants, the genotype of resistant cultivars in this experiment is heterozygous, whereas that of susceptible cultivars is recessive-homozygous.