Apple (Malus domestica) has a gametophytic self-incompatibility (GSI) system. Consequently, fertilization is achieved by cross-pollination with a compatible pollinator. Compatibility is governed by a multiallelic S locus. Cultivars are fully compatible when both of their S-loci differ and are semi compatible when one locus is identical and the other differs. In a previous study we found that the fruit set and yield of the apple cultivar `Topred' was reduced when it was pollinated by a semi compatible cultivar. To examine if this occurrence is a general feature in apples grown under suboptimal conditions, three additional cultivars, `Golden Delicious', `Granny Smith' and `Royal Gala', were studied as pollen recipients of semi and fully compatible pollinators. Based on PCR analysis of the S-RNase allele, it was determined that the pollination rate of the semi compatible was significantly lower than that of the fully compatible pollinator in all cases. This was reflected by the lower fruit set and seed set of `Golden Delicious' and `Royal Gala', but not of `Granny Smith'. In hand pollination experiments, where pollen was in excess, no difference was found between the semi and fully compatible pollinators in all three cases. These results indicate that the low yield, conferred by semi compatible pollinators, is due to insufficient cross-pollination (and not to cultivar characteristics). Thus, low yields due to semi compatibility may be avoided by appropriate honeybee management that will increase pollination. Still, under suboptimal conditions, for growth and pollination, full compatibility is preferable.
Doron Schneider, Raphael A. Stern, and Martin Goldway
Reut Niska, Martin Goldway, and Doron Schneider
Loquat (Eriobotrya japonica Lindl.), a member of the Rosaceae, carries the RNase-dependent gametophytic self-incompatibility fertilization system. Analysis of S-RNase-allele content in the commercial loquat cultivars Avri, Yehuda, and Akko 1 revealed that each of them contains one different S-RNase allele—S2, S3, and S4, respectively, and one that they all share, S6. Although all four S-alleles were isolated in this work, only S6 was found to be novel. Amino acid similarity between the partial sequence of S6-RNase and other known loquat RNases (S1 to S4) ranged between 62% and 65% with highest similarity (83%) to the S110-allele of European pear (Pyrus communis). Determination of S-RNase-allele content in progeny of ‘Avri’, ‘Yehuda’, and ‘Akko 1’, obtained in an open-pollinated, mixed-cultivar orchard, revealed that all of the progeny derived from self-fertilization contained the S6 haplotype, indicating that a mutation in the S6 locus is responsible for the self-fertilization. However, sequencing of most of the S6-RNase gene (from C1 to C5) did not reveal any mutation and the alignment of the deduced amino acid sequence showed that it has the expected S-RNase primary and tertiary structural organization. Nonetheless, because it is apparent that the S6-RNase allele is linked to the self-compatibility trait, it could serve as a marker for early selection of self-compatible loquat cultivars.
Gal Sapir, Raphael A. Stern, Martin Goldway, and Sharoni Shafir
Japanese plum (Prunus salicina Lindl.), a species of the Rosaceae family, carries the S-RNase-mediated gametophytic self-incompatibility system. Self-incompatibility is manifested if the S-haplotype of the pollen is carried also by the pollinated flower. Thus, for fertilization to occur, the cultivars have to be genetically compatible. The haplotype is conferred by an S-locus, which contains the style-specific expressed S-RNase and the pollen-specific expressed F-box genes (SFB). Since both the S-RNase and the SFB genes are multiallelic and are characteristic of each of the S-haplotypes, they are ideal markers for molecular S-typing. In this work, seven SFBs, from eight japanese plum cultivars, were cloned and sequenced. Five of the alleles were published recently and two SFBg and SFBk are new. The physical linkage of SFBb and SFBc to their adjacent S-RNase was determined; it is 544 base pairs (bp) and 404 bp for the Sb and Sc loci, respectively.