Identi®cation of seven S-alleles from the European pear (<i>Pyrus communis</i>) and the determination of compatibility among cultivars

Abstract

SummaryThe European pear (Pyrus communis) belongs to the Rosaceae, which carries the gametophytic self-incompatibility fertilization system (GSI). GSI is haplotype speci®c and controlled by the S-locus. The S-locus carries a multi-allelic gene that encodes for RNase (S-RNase), which is involved in executing pollen rejection in a speci®c manner. The different S-alleles also serve for molecular identi®cation of the S-haplotypes. Orchards of trees carrying GSI contain at least two cultivars, which are fertilization-compatible with each other. However, compatibility may be full when the cultivars differ in both their S-loci or partial when they share one of the two S-loci. Semi-compatibility between cultivars can lead to yield reduction, since half of the pollinator's pollen is rejected. Identi®cation of semi-compatibility according to yield levels is not always trivial, since many factors are involved in yield production. On the contrary, the application of molecular analysis, for the identi®cation of S-RNase alleles can clearly determine the genetic compatibility between cultivars. Many S-alleles of Rosaceae fruit trees have been identi®ed, but only a few of them are from European pear cultivars. In Israel the yield of the European pear is relatively low. To elucidate if semi-S-allele compatibility could provide the explanation, the S-allele content of the four cultivars grown in the Israel was determined. It was found that `Spadona', the main cultivar carries the alleles Sj and Sk, and its pollinators, `Coscia', `Gentile' and `Spadochina' carry Sb-Sk, Si-Sj and Sk-Sl, respectively. Thus, each of the pollinators shares one of the `Spadona' S-alleles and therefore is semi-compatible with it. All of the alleles are new, apart from Sb, which has been identi®ed previously by Zuccherelli et al. (2002). To identify potential fully compatible pollinators for `Spadona', ®ve additional cultivars that are being considered for introduction into the Israel pear orchard were analysed. It was discovered that `Bon Rouge', `Doctor Jill Guyot', `Forelle' and `Red Clapp' are semi-compatible and that `Lawson' is fully compatible with `Spadona'. In this latter analysis, three additional European pear S-alleles, Sm, Sn and So were identi®ed.