Molecular S-genotyping and determination of S-RNase-based incompatibility groups in loquat [Eriobotrya japonica (Thunb.) Lindl.]

Loquat (Eriobotrya japonica Lindl.; Pyrinae, Rosaceae) is an evergreen fruit tree which is acquiring increasing importance as an alternative crop in warm-temperate and subtropical regions. Recent pollination studies suggest that crop intensification has resulted in a reduction of fruit productivity in different locations. Loquat exhibits gametophytic self-incompatibility (GSI) and, consequently, fruit set strongly depends on cross-pollination between intercompatible cultivars. S-genotyping and incompatibility group assignment is therefore essential for adequate loquat orchard design. This study reports the molecular characterization of the S-RNase allele composition of 31 loquat cultivars grown in Spain. PCR with primers developed from loquat S-RNase sequences was used in combination with high-performance capillary polyacrilamide electrophoresis for the fine-evaluation of length polymorphisms at the S-RNase gene. This approach allowed to uncover a new S-RNase allele (S (5)), whose sequence is reported and to characterize the first six S-RNase-based incompatibility groups (I-VI) in loquat, resulting from the combination of five S-alleles (S (1)-S (5)). The large number of cultivars that could be assigned to only six groups suggests a narrow genetic base for this crop in Spain and stresses the need for careful determination of the S-genotype of cultivars in an attempt to overcome production problems associated with inadequate pollination.