Pollination requirements of new apricot (Prunus armeniaca L.) cultivars

Apricot (Prunus armeniaca L.) exhibits a gametophytic self-incompatibility system (GSI), the pollen-pistil recognition system present in the Rosaceae that prevents the self-fertilization. This mechanism is genetically controlled by a multiallelic locus (S), containing at least two linked genes that determine the pistil and pollen S-genotypes. Most of the traditional European apricot cultivars are self-compatible. However, the number of new commercial cultivars from different genetic backgrounds has increased in the last years. Most of these cultivars have been selected in several breeding programs for their tolerance to Sharka disease, caused by Plum Pox Virus, using self-incompatible cultivars selected in North America as parents. The pollination requirements of many of these new cultivars are unknown, and this can limit yield in the new orchards depending on the cultivars planted. In this work, the pollination requirements of 50 accessions have been determined, including 4 landraces, 36 commercial cultivars and 10 recent unregistered releases from different breeding programs. Self-(in)compatibility was analyzed by self-pollination experiments, followed by the observation of the pollen tube behavior through the pistil using fluorescence microscopy. The S-genotype was determined by PCR amplification of regions of the S-RNase and SFB genes and the self-incompatible cultivars were allocated to their corresponding incompatibility groups. The knowledge of pollination requirements is useful for apricot growers to select adequate pollinizers in commercial orchards, and for breeders to choose parental genotypes in breeding programs.