QTL analysis for fruit quality traits and resistance to Colletotrichum acutatum and Phytophthora cactorum in octoploid strawberry (Fragaria x ananassa)

Mapping of quantitative trait loci (QTL) controlling components of strawberry (Fragaria x ananassa Duch., 2n=8x=56) fruit quality and resistance to Colletotrichum acutatum and Phytophthora cactorum can be used to provide a better understanding of the genetic control of the traits, and to develop marker assisted selection for breeders. A segregating population of 213 individuals of a cross between 'Capitola' and 'CF1116', two genotypes with many contrasting fruit quality traits, was used for genetic mapping. 'Capitola' was resistant to the C. acutatum pathogenicity group 1 (pg1) and to P. cactorum while 'CF1116' was susceptible to C. acutatum and moderately susceptible to P. cactorum. Fruit quality was evaluated on a total of 34 traits, including developmental and fruit aspect related traits, texture related traits, fruit acidity, sugars, ascorbate and amino acid concentrations. Most of the traits except the amino acid concentrations were evaluated during two successive years. Disease responses to C. acutatum (pg2) and P. cactorum were evaluated using a scale from 0 (no observed symptom) to 5 (dead plant) in two successive independent experiments. Data were analysed for putative QTLs using MapQTL. For the fruit quality traits, a total of 22 significant QTLs were detected by simple interval mapping (LOD>3.0) in the first year of analyses and 17 were detected in the second year. Only two QTLs could be detected in both years. The percentages of phenotypic variance explained by each QTL ranged from 6.5% to 16.0%. For resistances, a total of nine QTLs was detected (LOD>2.0), 4 for resistance to C acutatum and 5 for resistance to P. cactorum with the percentage of variation explained by a QTL ranging from 6.5 to 12.2%. No QTL for the P. cactorum resistance overlapped the QTLs for the C acutatum resistance.