Identification of S-Alleles in the Pear cv. Rocha and Other European Pear Cultivars

The European pear carries the gametophytic self-incompatibility system (GSI). Therefore, pear orchards should include cultivars that are fertilisation-compatible. Field results do not clearly indicate significant differences in yield between semi- and totally compatible cultivars. Thus, in the selection of pollinators among compatible cultivars the fruit grower has to consider mainly the blooming season(s) and the economical value(s) of the fruits of the pollinator(s). Portuguese pear production relies on one main cultivar 'Rocha', which contributes to more than 90% of total pear production. The present study was undertaken to identify the S-RNase alleles responsible for GSI of 'Rocha' pear and those of other European pear cultivars that might be used as its pollinators, namely 'Tosca', 'Beurre Precoce Morettini', 'Beurre d'Avril' and local cultivars such as 'Carapinheira', 'Amendoa' and 'Perola'. Partial sequences of S-RNase alleles were amplified by PCR, cloned and sequenced. The S-genotype of 'Rocha' was fully determined (SaSe). The cultivar 'Tosca' (SbSl) shared no S-alleles with 'Rocha' and is totally compatible with this cultivar, whereas 'Beurre Precoce Morettini' (SeSk) shared the Se allele with 'Rocha', and therefore, is only semi-compatible. For cultivars 'Beurre d'Avril', 'Carapinheira', 'Amendoa' and 'Perola' only one S-RNase allele could be assigned. The S-RNase allele identified in 'Beurre d'Avril' showed strongest similarity to the S-RNase allele of Pyrus pyrifolia SI and was not previously described in Pyrus communis. We designated this allele as St, and we suggest that 'Beurre d'Avril' is, therefore, likely to he at least semi-compatible with 'Rocha'. The same holds true for 'Carapinheira' (harbouring Sb) and 'Perola' (harbouring Sk), since they have one allele distinct than those of 'Rocha'. The S-RNase allele Se was found in the cultivar 'Amendoa'. However, as the amplification pattern of this cultivar was different from the one observed in 'Rocha', it should also be semi-compatible. The results show that all the cultivars analysed should be either fully or semi-compatible with 'Rocha'.