Pathogenic Specialization of Venturia nashicola, Causal Agent of Asian Pear Scab, and Resistance of Pear Cultivars Kinchaku and Xiangli.

Scab caused by Venturia nashicola is one of the most serious diseases of Asian pears, including Japanese pear (Pyrus pyrifolia var. culta) and Chinese pears (P. bretschneideri and P. ussuriensis). Breeding scab-resistant pear cultivars is essential to minimize fungicide use and development of fungicide resistance. A survey of pathogenic specialization in V. nashicola is needed to ensure durable scab resistance in cultivated pears. V. nashicola race 1, 2, and 3 isolates, each differing in pathogenicity to Japanese pear cultivar Kousui and Asian pear strain Mamenashi 12, have been reported in Japan. In this study, isolates collected from scabbed pears in China and Taiwan were classified as V. nashicola based on conidial size and mating ability. However, various isolates had pathogenicity distinct from races 1, 2, and 3 according to tests on seven differential host genotypes of pear cultivars from Japan (Kousui and strain Mamenashi 12), China (Jingbaili, Yali, Linyuli, and Nanguoli), and Taiwan (Hengshanli). These new races were designated as races 4 to 7. Progenies characteristic of race 3 isolates were produced using a cross between race 1 and race 2 isolates, suggesting the possible role of sexual recombination in the emergence of novel races. Japanese pear cultivar Kinchaku and Chinese P. sinkiangensis 'Xiangli' (a Korla fragrant pear grown in China) did not show visible symptoms after inoculation with any of the seven races. Broad scab resistance in Kinchaku and Xiangli makes them a promising genetic resource for resistance breeding programs.