Contribution to the inheritance of resistance to Plum pox virus in apricots

The resistance/susceptibility of 935 individuals from 13 different crosses between apricot cultivars and selections was evaluated under controlled conditions in the screen-house for 3-5 consecutive growth periods. Susceptibility was defined by presence of visual symptoms on leaves and by positive ELISA and RT-PCR assays. The rootstocks and seedlings were inoculated with PPV by an infected bud. Chi-square analysis of each progeny was performed to determine if the observed segregation ratio differed from the expected ratio. The ratios of resistant to susceptible plants in progenies derived from crosses between resistant and susceptible parents ranged from 3:5 to 1:7. Segregation ratio 27:37 was obtained from crosses between resistant parents. The results are compatible with the hypothesis of three dominant genes being responsible for PPV resistance, with resistant parents being heterozygous for all three genes.