Inheritance and interactions of incompatibility alleles in the tetraploid sour cherry.

Three progenies of sour cherry (Prunus cerasus) were analysed to correlate self-(in)compatibility status with S-RNase phenotype in this allotetraploid hybrid of sweet and ground cherry. Self-(in)compatibility was assessed in the field and by monitoring pollen tube growth after selfing. The S-RNase phenotypes were determined by isoelectric focusing of stylar proteins and staining for RNase activity and, for the parents, confirmed by PCR. Seedling phenotypes were generally consistent with disomic segregation of S-RNase alleles. The genetic arrangements of the parents were deduced to be 'Köröser' (self-incompatible) S1S4.S(B) S(D), 'Schattenmorelle' (self-compatible) S6S13.S(B)S(B), and clone 43.87 (self-compatible) S4S13.S(B)S(B), where "." separates the two homologous genomes. The presence of S4 and S6 alleles at the same locus led to self-incompatibility, whereas S13 and S(B) at homologous loci led to self-compatibility. The failure of certain heteroallelic genotypes in the three crosses or in the self-incompatible seedlings indicates that S4 and S6 are dominant to S(B). However, the success of S13S(B) pollen on styles expressing corresponding S-RNases indicates competitive interaction or lack of pollen-S components. In general, the universal compatibility of S13S(B) pollen may explain the frequent occurrence of S13 and S(B) together in sour cherry cultivars. Alleles S(B) and S(D), that are presumed to derive from ground cherry, and S13, presumably from sweet cherry, were sequenced. Our findings contribute to an understanding of inheritance of self-(in)compatibility, facilitate screening of progenies for self-compatibility and provide a basis for studying molecular interactions in heteroallelic pollen.

Determining self-incompatibility genotypes in Belgian wild cherries.

ABSTRACT The self-incompatibility (S) genotypes of a collection of 65 Belgian accessions of wild cherry, selected within two populations and planted in a seed orchard, were determined using polymerase chain reaction (PCR) methods. Initially, DNA extracts were amplified with consensus primers that amplify across the second intron of the S-ribonuclease gene which shows considerable length polymorphism. The provisional genotypes deduced were checked with the appropriate allele-specific primers for the known alleles S(1) to S(16). Putative new alleles were subjected to PCR with consensus primers amplifying across the first intron. Six new alleles, S(17) to S(22), were thus indicated on the basis of the estimated lengths of the first and second intron PCR products. Examples of these alleles were partially sequenced and were indeed mutually distinct and different from the known alleles. The incompatibility genotypes of all 65 accessions were determined and one triploid individual was found. Seventeen alleles were detected in all. Allele frequencies differed between samples and the expected total number of alleles in the underlying populations was estimated. The wild cherry populations differed significantly with respect to allelic frequencies from sweet cherry cultivars; alleles S(4) and S(5), which are moderately frequent in sweet cherry, were absent from the wild cherry accessions. The knowledge of the S genotypes will be useful for studying the gene flow within the seed orchard and these approaches should also be informative in wild populations.

Identification of incompatibility alleles in the tetraploid species sour cherry.

The incompatibility genetics of sour cherry ( Prunus cerasus), an allotetraploid species thought to be derived from sweet cherry (diploid) and ground cherry (tetraploid), were investigated by test crossing and by analysis of stylar ribonucleases which are known to be the products of incompatibility alleles in sweet cherry. Stylar extracts of 36 accessions of sour cherry were separated electrophoretically and stained for ribonuclease activity. The zymograms of most accessions showed three bands, some two or four. Of the ten bands seen, six co-migrated with bands that in sweet cherry are attributed to the incompatibility alleles S(1), S(3), S(4), S(6, ) S(9) and S(13). 'Cacanski Rubin', 'Erdi Botermo B', 'Koros' and 'Ujfehertoi Furtos', which showed bands apparently corresponding to S(1) and S(4), were test pollinated with the sweet cherry 'Merton Late' ( S(1) S(4)). Monitoring pollen tube growth, and, in one case, fruit set, showed that these crosses were incompatible and that the four sour cherries indeed have the alleles S(1) and S(4). Likewise, test pollination of 'Marasca Piemonte', 'Marasca Savena' and 'Morello, Dutch' with 'Noble' ( S(6) S(13)) showed that these three sour cherries have the alleles S(6) and S(13). S(13) was very frequent in sour cherry cultivars, but is rare in sweet cherry cultivars, whereas with S(3) the situation is reversed. It was suggested that the other four bands are derived from ground cherry and one of these, provisionally attributed to S(B), occurred frequently in a small set of ground cherry accessions surveyed. Analysing some progenies from sour by sweet crosses by S allele-specific PCR and monitoring the success of some sweet by sour crosses were informative. They indicated mostly disomic inheritance, with sweet cherry S alleles belonging to one locus and, presumably, the ground cherry alleles to the other, and helped clarify the genomic arrangement of the alleles and the interactions in heteroallelic pollen.

Allele-specific PCR detection of sweet cherry self-incompatibility (S) alleles S1 to S16 using consensus and allele-specific primers.

PCR-based identification of all 13 known self-incompatibility (S) alleles of sweet cherry is reported. Two pairs of consensus primers were designed from our previously published cDNA sequences of S(1) to S(6) S-RNases, the stylar components of self-incompatibility, to reveal length variation of the first and the second introns. With the exception of the first intron of S(13), these also amplified S(7) to S(14) and an allele previously referred to as S(x), which we now label S(16). The genomic PCR products were cloned and sequenced. The partial sequence of S(11) matched that of S(7) and the alleles were shown to have the same functional specificity. Allele-specific primers were designed for S(7) to S(16), so that allele-specific primers are now available for all 13 S alleles of cherry (S(8), S(11) and S(15) are duplicates). These can be used to distinguish between S alleles with introns of similar size and to confirm genotypes determined with consensus primers. The reliability of the PCR with allele-specific primers was improved by the inclusion of an internal control. The use of the consensus and allele-specific primers was demonstrated by resolving conflicting genotypes that have been published recently and by determining genotypes of 18 new cherry cultivars. Two new groups are proposed, Group XXIII (S(3) S(16)), comprising 'Rodmersham Seedling' and 'Strawberry Heart', and Group XXIV (S(6) S(12)), comprising 'Aida' and 'Flamentiner'. Four new self-compatibility genotypes, S(3) S(3)', S(4)' S(6), S(4)' S(9) and S(4)' S(13), were found. The potential use of the consensus primers to reveal incompatibility alleles in other cherry species is also demonstrated.