Functional Synteny of Susceptibility Genes for Fungal Diseases Caused by Alternaria alternata in Apple and Japanese Pear

Alternaria alternata produces host-specific toxins (HSTs), which cause serious disease in several fruit trees and vegetables, and the relationships between HSTs of A. alternata pathotypes and their host plant species have been studied. A. alternata apple pathotype produces AM toxin responsible for Alternaria blotch of apple, and A. alternata Japanese pear pathotype produces AK toxin responsible for black spot of Japanese pear. The susceptibility gene Alt for Alternaria blotch of apple was mapped at the top of linkage group 11, using 114 F1 individuals from a cross between susceptible 'Starking Delicious' and resistant 'Jonathan'. In Japanese pear, Aki gene for black spot susceptibility was positioned at the top of linkage group 11, using 860 F1 individuals from susceptible 'Kinchaku' × resistant 'Hosui'. Forty-five simple sequence repeat (SSR) markers were designed based on genome sequence of 'Golden Delicious' (apple genome v1.0) with the positions of 1 to 8 Mb of chromosome 11. Of 45 SSRs, nine SSRs showed co-segregation to Alt, resulting that the Alt gene exists in 1.0 Mb regions. The genome region of Aki gene could be identified between Mdo.chr11.28 (2,915 kb of apple genome v1.0) and Mdo.chr11.34 (3,166kb). We concluded that susceptibility genes Alt of apple and Aki of Japanese pear could be refined within very close genome regions at the top of chromosome 11 and that functional synteny of susceptibility to A. alternata could be identified. (Genomics-based Technology for Agricultural Improvement, HOR2001)