Quantitative trait loci analysis of <Emphasis Type="Italic">Plum pox virus</Emphasis> resistance in <Emphasis Type="Italic">Prunus davidiana</Emphasis> P1908: new insights on the organization of genomic resistance regions

No valuable source of resistance to Plum pox virus (PPV), the causative agent of sharka disease, has been found in peach (Prunus persica), but polygenic resistance to PPV was described in Prunus davidiana clone P1908. Two previous studies using F₁ and F₂ populations derived from the nectarine cv. Summergrand and P. davidiana P1908 identified a total of six P. davidiana quantitative trait loci (QTLs) involved in PPV resistance (Marcus strain). In an effort to verify the QTL stability in a large progeny and to search for possible interactions of the genetic backgrounds, the current study evaluated the incidence of PPV infection in an F₁ population derived from the susceptible peach cv. Rubira and P. davidiana P1908 over three growth periods using an improved method of PPV phenotyping referred to as “heavy test.” The phenotypic dataset was analyzed using similar methods as the previous studies and a newly developed simple-sequence-repeat-based P. davidiana map. Nine regions involved in differential symptom expression were identified among which six were common between studies. However, the level of resistance observed in the population was very low compared to the other studies, and the main QTL previously identified in linkage group 6 was not conserved, suggesting strong interaction of the genetic background of the susceptible parent with that of P. davidiana 1908. Consequently, this could be a limiting factor for developing resistant cultivars derived from P. davidiana P1908.