Abstract

An increase in chlorophyll content is an adaptive response to low-light stress and can be used to evaluate low-light tolerance. The effects of low-light stress (100 µmol·m^-2.s^-1) on the chlorophyll content of cucumber (Cucumis sativus L.) were investigated in a set of 123 F_2:3 lines in the seedling stage in the autumn of 2008 and spring of 2009. Quantitative trait loci (QTL) analysis was undertaken on the basis of a genetic linkage map of the corresponding F₂ population that was constructed using composite interval mapping. F_2:3-based QTL analysis of the chlorophyll-a (chl.a), chlorophyll-b (chl.b) and chlorophyll-a+b (chl.a+b) content in the 2 environments revealed 21 QTLs located on the linkage groups 1, 2, 3, 4, 6 and 7, which accounted for 4.8 - 17.3% of the phenotypic variation. In the spring of 2009, the total phenotypic variation among the F_2:3 lines accounted for by the QTLs for chl.a, chl.b and chl.a+b were 44.5, 29.4 and 39.0%, respectively. In the autumn of 2008, 11 QTLs were identified, which accounted for 4.8 - 14.9% of the observed phenotypic variation and an additive effect of -8.10 to 20.85. Four major-effect QTLs (chla2.1, chlb2.2, chlb3.1 and chla+b2.2) were detected under both conditions. The QTL information presented in this research, together with the data from our previous study on heredity of low-light tolerant traits, will facilitate the breeding of low-light-stress-resistant cucumbers.

Key words: Cucumber (Cucumis sativus L.), seedling, quantitative trait loci analysis, low-light stress, chlorophyll content.

Abbreviation

QTL, Quantitative trait loci; chl.a, chlorophyll-a; chl.b, chlorophyll-bchl.a+b, chlorophyll-a+b; MAS, marker-assisted selection; RAPD, random amplified polymorphic DNA; RIL, recombinant inbred lines; SSR, simple sequence repeat; SRAP, sequence-related amplified polymorphism; SSD, single-seed descent; CTAB, cetyl trimethylammonium bromide; PCR, polymerase chain reaction; LOD, log-likelihood; CIM, composite interval mapping.