Quantitative trait loci analysis of the time of floral initiation in tomato

- Days to floral initiation (DFI) and flowering (DTF) were studied in tomato.
- Four and two additive QTLs for DFI and DTF were identified, respectively.
- Three and one epistatic QTL pairs for DFI and DTF were identified, respectively.
- Three additive QTLs for DFI were co-located with additive or epistatic QTLs for DTF.
- This study suggests that DFI QTLs play an important role in determining DTF.

The potential of a single-truss tomato production system is dependent on earliness, but few genetic studies have investigated QTLs for earliness component traits in tomatoes. Thus, QTL analyses were performed using a backcross inbred line (BIL) population after dissecting days to the ripening of the first fruit into two stages, i.e., days from sowing to anthesis and days from anthesis to first fruit ripening, in one experiment. In other experiments, the days to flowering (DTF) were further dissected into several stages, i.e., days from sowing to germination or cotyledon expansion and days from cotyledon expansion to floral initiation. A BIL family comprising 111 lines of the BC1F8 generation was derived from a cross between Solanum lycopersicum and Solanum pimpinellifolium. Two DTF, three FMP (fruit maturation period), two LN (number of leaves preceding inflorescence) and four DFI (days to floral initiation) QTLs with additive effects were identified in the present study. One pair of DTF QTLs exhibited epistatic effects. Additive QTLs for DTF, LN and DFI were co-located on chromosome 7, whereas LN and DFI QTLs were co-located on chromosome 3. An additive QTL for DFI located on chromosome 3 was co-located with an epistatic QTL for DTF. In the regions on chromosome 4 where an additive QTL for DFI was located, a DTF QTL was not detected, but additive QTLs for germination-related traits, such as the mean germination time (MGT), time to 90% of the final germination percentage (GT90) and hypocotyl length (HYL), were clustered. In conclusion, it is likely that DFI QTLs are one of the important components of DTF QTLs, but other QTLs controlling early seedling development, such as the MGT and days to cotyledon expansion (COT), may also become important components of DTF QTLs. Furthermore, DFI QTLs could be classified into two types: the first type of QTLs hasten the developmental stage up to floral initiation, whereas those classified as belonging to the second type shorten the plastochron without any effect on the developmental stage.