Quantitative trait loci analysis of flowering-time-related traits in tomato

The regulation of flowering time has been studied mainly in photoperiod-sensitive model plants. Little is known about the environmental and genetic regulation of flowering time in photoperiod-insensitive plants. Here, we studied the genetic control of flowering time in day-neutral tomato using quantitative trait locus (QTL) analysis. We used a BC1F6 population developed from Solanum lycopersicum ‘M570018’ and its wild relative Solanum pimpinellifolium (PI124039) to measure days to flowering (DTF) and number of leaves preceding the first inflorescence (LN), as well as their underlying developmental processes, which include the number of leaves initiated (LI), percentage of flower-induced plants (reproductive index, RI), days to macroscopic flower bud appearance (DMB) and flower development duration (FDD: DTF−DMB). A composite interval mapping detected 12 QTLs for the six traits, which included two QTLs for DTF on chromosomes 1 and 6. The DTF QTLs explained 43% of the phenotypic variation of this trait. The presence of S. pimpinellifolium alleles in the detected QTLs increased the rate of leaf initiation, reduced LN and hastened flower induction, floral development and anthesis. Most QTLs for LN, LI, RI, DMB and FDD clustered with the DTF QTLs; dmb1, fdd1, li_14d1, li_19d1 and ri_19d1 clustered with dtf1 on chromosome 1, and ln6 and fdd6 clustered with dtf6 on chromosome 6. These results suggest that the QTLs on chromosomes 1 and 6 may form a functional “gene cluster” that drives tomato flowering in synergy. Alternatively, the two DTF QTLs may act as “master genes” that control flowering time through pleiotropic effects on multiple developmental processes.