Characterisation of partial self-compatibility in the European pear cultivar, ‘Grand Champion’

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SummaryMost cultivars of European pear (Pyrus communis L.) exhibit S-RNase-based gametophytic self-incompatibility (SI), but the cultivar, ‘Grand Champion’, is partially self-compatible (SC). We used pollination and molecular genetic approaches to study the cause of the partial SC, and its effects on fruit set and quality. ‘Grand Champion’ was genotyped to SbSe by an S-RNase-based cleaved amplified polymorphic sequence marker system. Crossing ‘Grand Champion’ with pollen from an SI cultivar, ‘California’ (SbSe), showed that partial SC was caused by the disruption of pistil function. Of the Sb- and Se-RNase alleles cloned from ‘Grand Champion’, the Sb-RNase allele had two nonsynonymous nucleotide substitutions compared with the Sb-RNase allele previously cloned from ‘Doyenné du Comice’, but it retained the typical primary structure of S-RNases of the Maloideae. The sequence of the Sb-RNase allele from ‘Grand Champion’ was also obtained from two SI cultivars: ‘Joséphine de Malines’ and ‘Urbaniste’. Similar levels of Sb- and Se-RNase allele transcripts were found in the pistils of the partially SC and SI cultivars. Sb- and Se-haplotypes in the selfed progeny of ‘Grand Champion’ segregated in a 1:1 ratio. ‘Grand Champion’ fruits formed by self-pollination were the same size and quality as those formed by cross-pollination. Our results suggest that partial SC was not caused by a mutation in the S-RNase allele. The partial SC in ‘Grand Champion’ results in efficient fruit set and fruit of economic size and quality.