Abstract
Inheritance of resistance to Alternaria blotch caused by Alternaria mali Roberts in apple was studied. F1 seedlings were inoculated at their four to six-leaf stage with spore suspension of an Alternaria strain AKI-3, and according to the criteria for the reaction, they were classified into R (resistant) and S (susceptible) groups (Figs. 1 and 2). A total of 27 F1 cross combinations among eight varieties of known disease reaction were investigated in the first experiment. As the result, segregation ratios of 1R:3S and 1R:1S were found in the parental crosses of S×S and S×R or its reciprocals, respectively, while few susceptible plants were seen in the crosses between resistant varieties. This will be plausibly explained on the assumption that the resistance to Alternaria blotch is controlled by a single recessive gene, and the genic constitution of the susceptible varieties used in this experiment are all heterozygous for the gene pair. So, a gene symbol Alt alt is allotted for susceptible vs. resistant condition for this disease.
