Salt tolerance in Lycopersicon spp. VII. Pleiotropic action of genes controlling earliness on fruit yield

The change from vegetative to reproductive development (earliness) in Lycop ersicon chesmannii line L2 was delayed for 20 weeks when compared to other Lycopersicon species under greenhouse conditions. The interspecific hybrid of L. chesmannii L2 and L. esculentum E9, a cherry tomato cultivar, also sh owed this delay in reproductive development. The distribution of this chara cter in the F-2-derived population showed a bimodal shape, plants could be scored easily as "early" or "late" in two nutrient conditions (optimum and high salinity). A QTL with major effects on earliness was detected in salin ity, which explained 35.6% of the phenotypic variation. The effect of this QTL greatly diminished under control conditions, indicating differences in the genetic control of earliness between treatments. ACC synthase or phytoc hrome B2 are the products of candidate genes for such a major QTL. Other QT Ls with minor effects, and epistatic interactions, are also involved in ear liness under both conditions. A "late" F-2 subpopulation yielded twice as m uch as an "early" F-2; conversely, "early" plants were taller than "late" p lants, regardless of the treatment. QTL analysis, carried out in both subpo pulations, showed that yield differences may be explained by chesmannii all eles showing negative additive effects at some QTLs only in the "early" sub population. The effect of population subdivision on QTL analysis was invest igated by computer simulations to show sample-size or random effects; thus, important pleiotropic or regulatory effects of genes controlling earliness on yield that affect QTL analysis, have been revelled. Therefore alleles c ontrolling earliness in L. chesmannii have to be taken into account for a m ore efficient utilization of the genetic resources of this species.