Genetic analysis of flowering time in lettuce

In order to investigate the genetic parameters and heritability of flowering time and FT gene expression in lettuce, experiments was carried out in both greenhouse and open field conditions. The gene “FT” is known as very important factor affecting flowering in many of plant including lettuce. At first, four Lettuce lines (including two late flowering and two early flowering lines) which were derived from Iranian lettuce landraces, crossed by late flowering line with early flowering line. Six generations were derived from mentioned crosses, including parents (P1, P2), F1, F2, BC1-P1 and BC1-P2, then planted in two seasons (spring and autumn) in order to find the genetic parameters and heritability of flowering time by using a GMA model. The expression of FT gene was studied by RT-PCR method in parents and F1 in two different temperature conditions including 15°C /25°C (night/day) and 25°C /35°C (night/day). Result show that Days to open the first flower in spring (99.88 days) was less than in autumn (145.4 days). The head weight in late flowering plant (724.6 g) was more than early flowering plant (462.2 g). Although head weight of late flowering plant in spring (876.37 g) was more than in fall (572.87 g). In F1 plants (96.1 days), days to open the first flower was significantly prior to early flowering parental line (110.3 days). These results stands for overdominace gene effect in flowering time in F1. The adequacy of five parametric model was confirmed for traits in spring and autumn trials. Additive and dominance effects were significant on Head weight, number of leaves and days to opening of the first flower; although dominant effect was higher than additive effect. Additive×additive and dominance× dominance epistatic effects were significant in all traits as well. In both spring and autumn seasons, the maximum dominance variance was estimated in days to opening of the first flower. Results of FT relative expression showed that the FT affected lettuce flowering time. Heat caused to enhanced FT relative expression in lettuce although the effect of heat on enhanced FT relative expression was different in late flowering lines, early flowering lines and F1. Highest and lowest effect of heat (25°C /35°C relative to 15°C /25°C) in FT relative expression was estimated in F1 and late flowering parent respectively.Key words: bolting, late flowering, lettuce, heat, generation mean analysis, FT gene expression