Aj. Monforte et al., Salt tolerance in Lycopersicon spp. VII. Pleiotropic action of genes controlling earliness on fruit yield, THEOR A GEN, 98(3-4), 1999, pp. 593-601
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.