Inheritance of resistance to Plum pox virus in apricot (Prunus armeniaca L.)

The inheritance of resistance to Plum pox virus (PPV) has been studied in 1,178 apricot hybrids. Seven hundred and eighteen F1 hybrids, obtained from controlled crosses between the susceptible Greek cultivar “Bebecou” and the resistant PPV cultivars of American origin (“Stark Early Orange,” ‘NJA2,” ‘Veecot,” “Sunglo,” “Harlayne,” and “Orangered”) were evaluated for resistance to the PPV-M (Marcus) strain, 8 years after artificial inoculation. The inheritance of resistance to PPV has been additionally studied for the first time in a BC₁ population of 95 apricot hybrids for four vegetative periods. Reaction of each hybrid to PPV-M was scored through visual symptoms, indexing onto GF-305 and double-antibody sandwich enzyme-linked immunosorbent assay tests. Segregation within the hybrids, determined by Chi-squared analysis, fits a 1:1 ratio (P ≤ 0.05) of the resistant vs susceptible, indicating that resistance to PPV is controlled by a single dominant gene locus and that the above six resistant cultivars are heterozygous for the trait. Plants carrying this gene may initially develop disease symptoms on leaves but eventually recover and no virus can be detected in leaves. Susceptible plants show similar symptoms initially but remain symptomatic. Inheritance of resistance to PPV also has been studied in 365 F1 hybrids by crossing the resistant cultivar “Stella” with the susceptible “Bebecou” and the resistant cultivars “Sunglo” and “NJA2,” for 8 years after inoculation. The segregation ratio was 1:0 (resistant/susceptible) suggesting that “Stella” is homozygous for the resistance trait. The purpose of this work was the enhancement of the knowledge of inheritance of resistance to PPV for the selection of new cultivars.