Screening of Pyrus pyrifolia genotypes for resistance to Alternaria alternata

Black spot disease (BSD) caused by the fungus Alternaria alternate is one of the most devastating diseases in pear. Most cultivated sand pear (Pyrus pyrifolia Nakai) and its hybrids are susceptible to this disease, and the main measures for the disease control are bagging and spraying of fungicides. Here, we evaluated the resistance of various P. pyrifolia genotypes to the disease by both natural infection and artificial inoculation during the years of 2013-2015. Among the 331 genotypes, 9 were highly resistant (HR) to A. alternata. Multiple linear stepwise (MLS) regression analysis indicated that the susceptibility of P. pyrifolia to A. alternate was correlated with stalk length, branching ability, duration of fruit development, fruit weight and soluble solid content. Totally 11 simple sequence repeat (SSR) markers, which selected from previous RNA-Seq data, were used to check their contributions to the disease resistance and for analysis of genetic diversity. The mean polymorphism information content was 0.66, indicating a high level of SSR polymorphism. The proportions of SSR loci 6167B and 15091C were higher in disease-resistant varieties, while those of SSR loci 6484A, 6643A and 12717A were higher in disease-susceptible varieties. This study provides the genetic variations of pear genotypes resistant to A. alternate, which could contribute to future breeding of BSD resistant varieties.