S-RNase genotyping of autochthonous apple cultivars grown in the region of central and southwestern Serbia

Abstract

Apple (Malus × domestica Borkh.) is one of the most important and widely cultivated deciduous fruit crop around the world, with an annual production of more than 93 million tonnes in 2021. This pome species, with average production of 468,258 tonnes (2017-2021) and together with plum, is crucial in the total fruit production of the Republic of Serbia. Although there are at least ten thousand reported apple cultivars in the world, as well as that new ones are realised every year within breeding programs, the number of cultivars is likely underestimated since many local landraces have not been documented. Identification of S-genotypes in autochthonous cultivars is an important step in their molecular characterization and also of enormous significance for breeders and growers, since apple exhibits a gametophytic self-incompatibility, controlled by the multi-allelic S-locus which prevents self-fertilisation. The aim of this work was to identify the S-genotypes in the following ten autochthonous apple cultivars grown in individual growers' orchards in the regions of central and southwestern Serbia: ‘Budimka’, ‘Džumurka’, ‘Ilinjača’ (Jezdina), ‘Ilinjača’ (Trnava), ‘Kolačara’, ‘Kraljica’, ‘Lepocvetka’, ‘Senabija’, ‘Šumatovka’ and ‘Vidovača’. The use of the polymerase chain reaction (PCR) method with consensus primers, that correspond to the previously identified C2 and C5 conserved regions, and allele-specific primers revealed eleven alleles: S1 to S5, S7, S20, S24, S26, S28, and S44. Among the assessed cultivars, the following ploidy levels at the S-locus were identified: four cultivars were diploids, three triploids and one was tetraploid; additionally, the S1Sx genotype was revealed in two cultivars. This study provides new information about cross-compatibility of cultivars and pollenizers, and might be used in parental choice within breeding programs, as well as in the choice of cultivars/pollenizers for the commercial orchards.