Opportunities of marker-assisted selection for Plum pox virus resistance in apricot breeding programs

Evaluation of Plum pox virus (PPV) resistance is a laborious and expensive task, and the development of new accurate methods, including the use of molecular markers, would be very useful for breeding programs for resistance. In this work, the Plum pox virus resistance of 80 apricot genotypes of different genetic origins was evaluated in controlled greenhouse and natural field conditions. The genotypes for five simple sequence repeat (SSR) markers described as linked to PPV resistance were also determined. Depending on their behavior, cultivars were classified as resistant, susceptible, and uncertain, and the genotype was identified for each SSR linked to different phenotypes. Twenty genotypes were resistant and 37 susceptible in the greenhouse and in the field. However, 23 genotypes did not show clear behavior, probably due to the complex plant-virus interaction, so they were classified as uncertain. In general, results showed a narrow relationship between the SSRs PGS1.21 and PGS1.24, and resistance to PPV, although some genotypes did not show this relationship. Most of the susceptible genotypes did not show the alleles of resistance. Therefore, in most cases, marker-assisted selection (MAS) could be used as a means of screening new seedlings for early selection, making it possible to remove those that are susceptible. However, in certain cases, MAS using these markers has not proven to be completely effective. The origin of such discrepancies could be the presence of a second locus involved in PPV resistance. In addition, other factors affecting efficiency of MAS discussed in the work are the presence of null alleles and recombinant events. Resistant seedlings would have to be evaluated in greenhouse and natural conditions to confirm their actual behavior against PPV. From the breeding point of view, the use of homozygous resistant parents for the SSR resistance alleles, with good agronomic characteristics, would increase the efficiency of breeding programs, since all seedlings would be resistant regardless of the other parent. Finally, new molecular markers should be developed to accurately select resistant seedlings regardless of the resistant progenitors involved.