RFLP mapping, QTL identification, and cytogenetic analysis in sour cherry

Three separate but related projects were carried out to establish a foundation for the utilization of molecular markers and cytogenetic tools in the genetic study and breeding of tetraploid sour cherry (Prunus cerasus L., 2n = 4x = 32).; In the first project, restriction fragment length polymorphism (RFLP) linkage maps of two tetraploid sour cherry cultivars, Rheinische Schattenmorelle (RS) and Erdi Botermo (EB), were constructed from 86 progeny from the cross RS x EB. The RS linkage map consists of 126 single dose restriction fragment (SDRF, Wu et al. 1992) markers assigned to 19 linkage groups covering 461.6 cM. The EB linkage map has 95 SDRF markers assigned to 16 linkage groups covering 279.2 cM. Fifty-three markers mapped in both parents were used as bridges between both maps and 13 sets of homologous linkage groups were identified. Fifty-nine of the markers on the linkage maps were detected with probes used in other Prunus genetic linkage maps. Six of the sour cherry linkage groups may be homologous with six of the eight genetic linkage groups identified in peach and almond.; In the second project, the map locations and effects of quantitative trait loci (QTLs) for eight flower and fruit traits in sour cherry were estimated using the RFLP genetic linkage maps constructed in the first project. Eleven putatively significant QTLs (LOD > 2.4) were detected for six characters (bloom time, ripening time, % pistil death, % pollen germination, fruit weight and soluble solids concentration). The percentage of phenotypic variation explained by a single QTL ranged from 12.9% to 25.9%. Fifty percent of the QTLs identified for the traits in which the two parents differed significantly had allelic effects opposite to those predicted from the parental phenotype. Three QTLs affecting flower traits (bloom time, % pistil death, and % pollen germination) mapped to a single linkage group, EBI. The RFLP closest to the bloom time QTL on EB1 was detected by a sweet cherry (P. avium L.) cDNA clone pS141 whose partial amino acid sequence was 81% identical to that of a Japanese pear (Pyrus pyrifolia Nakai stylar RNase.; In the final project, genomic in situ hybridization (GISH) was used to examine meiotic pairing behavior and parental genomic contributions in the allotetraploid sour cherry. Three sour cherry cultivars were studied: Montmorency, Rheinische Schattenmorelle (RS), and Erdi Botermo (EB). GISH analysis suggested that EB may have a higher genomic contribution from P. avium than P. fruticosa (the two putative progenitor species). In contrast, GISH analysis only identified a relatively few number of species-specific chromosomes and chromosome segments in RS, suggesting that significant intergenomic recombination had occurred. In the meiotic analyses, in addition to the normal bivalent pairing configuration, univalents, trivalents, and quadrivalents were frequently observed in the pollen mother cells of the three cultivars. RS had the most bivalents and the least number of quadrivalents. Montmorency and EB had approximately the same numbers of bivalents and quadrivalents. RS had a bivalents to non-bivalents ratio of 4.4:1 while EB and Montmorency had a ratio of 3.5:1. The ratio of bivalents, to non-bivalents may be an important factor in determining the proportion of balanced and unbalanced meiotic products.