Comparison of QTLs for seed germination under non-stress, cold stress and salt stress in tomato

The purpose of this study was to examine whether rate of tomato seed germin ation under non-stress, cold-stress and salt-stress conditions was under si milar genetic control by identifying and comparing quantitative trait loci (QTLs) which affect germination rate under these conditions. A fast-germina ting accession (LA722) of the wild tomato species Lycopersicon pimpinellifo lium Jusl. and a slow-germinating cultivar (NC84173, maternal and recurrent parent) of tomato (Lycopersicon esculentum Mill.) were hybridized and BC1 and BC1S1 progeny produced. The BC, population was used to construct a link age map with 151 restriction fragment length polymorphism (RFLP) markers. T he BC1S1 population (consisting of 119 BC1S1 families) was evaluated for ge rmination under nun-stress (control), cold-stress and salt-stress condition s and the mean time to 50% germination (T50) in each treatment was determin ed. Germination analyses indicated the presence of significant (P < 0.01) p henotypic correlations between T50 under control and cold stress (r = 0.71) , control and salt stress (r = 0.58) and cold stress and salt stress (r = 0 .67). The QTL analysis indicated the presence of genetic relationships betw een germination under these three conditions: a few QTLs were identified wh ich commonly affected germination under both stress- (cold-, salt- or both) and non-stress conditions, and thus were called stress-nonspecific QTLs. A few QTLs were also identified which affected germination only under cold o r salt stress and thus were called stress-specific QTLs. However, the stres s-nonspecific QTLs generally exhibited larger individual effects and togeth er accounted for a greater portion of the total phenotypic variation under each condition than the stress-specific QTLs. Whether the effects of stress -nonspecific QTLs were due to pleiotropic effects of the same genes, physic al linkage of different genes, or a combination of both could not be determ ined in this study. The results, however, indicate that the rate of tomato seed germination under different stress and nonstress conditions is partly under the same genetic control.