Application of S-RNase allele molecular analysis as a means for elucidating low yields in the pear orchard

The European pear carries the gametophytic self-incompatibility fertilization system (GSI). Therefore pear orchards need to contain at least two cultivars which are fertilization-compatible. However, compatibility between cultivars in the orchard may be full, when the cultivars differ in both of their S-loci, or partial, when they share one of the two S-loci. Semi-compatibility between cultivars can lead to a reduced yield, since half of the pollinator's pollen grains are rejected. Identification of semi-compatibility according to yield levels is not easy, since many factors are involved in determining yield. Yet, the application of molecular analysis for the identification of S-RNase alleles can clearly determine the genetic compatibility between cultivars. In Israel the yield of the European pear is relatively low. The main cultivar is 'Spadona' and its pollinators are 'Coscia', 'Gentile' and 'Spadochina'. In order to elucidate whether semi-S-RNase allele compatibility can provide an explanation for the low yields, the S-RNase allele content of the four cultivars was determined. It was found that 'Spadona' shares one of its S-RNase alleles with each of its pollinators, and therefore is semi-compatible with them. In this analysis four S-RNase alleles were cloned, of which three were new. In order to identify fully-compatible potential pollinators for 'Spadona', five additional cultivars that are currently being considered for introduction in Israel were analyzed. In this latter analysis, 'Lawson' was found to be fully compatible with 'Spadona' and six new S-RNase alleles were identified.