Two-gene resistance to Plum pox virus in apricot

In this study, we determined the mode of inheritance for resistance to Plum pox virus (PPV) in apricot. The apricot cultivar Stark Early Orange (SEO) was used as the source of resistance to PPV. A reciprocal backcross was performed between the susceptible cultivar Vestar and a resistant selection LE-3241 ('SEO' x 'Vestar'). The BC1 seedlings were inoculated with the PPV-M strain by an infected bud. PPV infection was evaluated over 4 consecutive growth periods through visual symptoms and ELISA. Chi-square analysis of each BC1 progeny was performed to determine if the observed segregation ratio differed from the theoretic ratio. One quarter of the BC1 plants, regardless of the direction of the cross, was resistant. The absence of reciprocal differences in BC1 progenies demonstrates that genetic control of PPV resistance in apricot is nuclear and not cytoplasmic. The simplest explanation for these results is that two nuclear complementary loci confer resistance to PPV in this genetic background.