Abstract
Inheritance of necrotic reaction from the Japanese pear cultivar 'Okusankichi', and Chinese pear cultivars 'Beijing-bai-li', 'Xiang-ya-li', 'Yuan-ba-li', and 'Zao-su' to pear scab caused by Venturia nashicola Tanaka et Yamamoto was examined, using hybrid seedlings of known parentage. The seedlings were inoculated with conidial suspension, and the resistance to scab was classified into three categories: highly resistant (HR), susceptible (S), or necrotic (N). All seedlings, derived from 'Hosui' (S)×'Beijing-bai-li' (N), were classified as S. N and S seedlings were obtained from 'Hosui'×'Xiang-ya-li' (N) and 'Hosui'×'Yuan-ba-li' (N), whereas HR, N, and S seedlings were derived from S×'Zao-su' (N). Most seedlings from S×'Okusankichi' (N) were classified as S. Progenies of N×N crosses were ranked as HR, N, and S. These results suggest that the necrotic reaction in 'Okusankichi', 'Beijing-bai-li', 'Xiang-ya-li', 'Yuan-ba-li', and 'Zao-su' to Venturia nashicola is controlled by polygenes, and that differences in the transmissibility of these genes, as parents, would significantly affect the segregation of the resistance.
