Molecular marker-assisted discovery of novel QTLs in a Lycopersicon esculentum x L. pimpinellifolium cross and characterization of fs8.1, a major QTL influencing fruit shape in tomato

A BC{dollar}sb1{dollar} population of 257 plants, derived from a cross between Lycopersicon esculentum (cv M82-1-7) and L. pimpinellifolium (LA1589), was used to develop a genetic linkage map comprising 115 restriction fragment length polymorphism (RFLP), 3 random amplified polymorphic DNA (RAPD) and 2 morphological markers and spanning 1279 cM of the tomato genome with an average distance between markers of 10.7 cM. Length and marker order are comparable to those of the high density RFLP map derived from a L. esculentum x L. pennellii F{dollar}sb2{dollar} population, however there are considerable differences in the distribution of recombination along the chromosomes. The segregation of 6 GATA-containing loci and 47 RAPD markers was also analyzed in subsets of the population. All microsatellite loci and 35 (75%) of the RAPDs mapped to clusters associated with centromeric regions.; All BC{dollar}sb1{dollar} plants and 100 controls were scored for 19 quantitative traits of agronomic and biological interest. A minimum of 54 putatively significant quantitative trait loci (QTLs) (P {dollar}<{dollar} 0.001; LOD {dollar}>{dollar} 2.4) were found for all characters with a range of 1-7 QTLs detected per character. Of the total 54 QTLs 11% had alleles with effects opposite to that predicted by the parental phenotypes. The percentage of phenotypic variation associated with single QTLs ranged from 4% to 47%. No significant evidence was found for digenic epistasis. The difference in fruit weight and shape were controlled largely by single major QTLs: fw2.2 and fs8.1 respectively.; Near Isogenic Lines (NILs) were developed to better characterize fs8.1. Substitution mapping shows that fs8.1 is tightly linked to the marker CD40, on chromosome 8. The main effect of fs8.1, is exerted on fruit length, while fruit diameter is not significantly affected. The wild allele at fs8.1 reduces fruit length, giving round-shaped fruit and the gene was found to be partially dominant. A highly significant correlation (r = 0.89; P {dollar}<{dollar} 0.01) was found between fruit and ovary shape indicating that the fs8.1 genic product acts before anthesis. The feasibility of map-based cloning of fs8.1 is discussed.