STUDIES ON THE GENETIC PATHWAY AND SELECTION RESPONSE FOR INCREASED FRUIT SIZE AND YIELD IN TOMATO
ABSTRACT
Modified three-way crosses involving advanced interspecific tomato hybrids (W x R), (R x
W) and (W x T) at F12 generation and commercially cultivated tomato varieties namely
Supersteak (S), Beef (Florida) (BF) and Plumb (Rio grande) (PR) were made to generate F1
hybrids. The F1 hybrids were crossed to both the pollen and seed parents to produce the
backcrosses and were also allowed to random mate to produce the F2 and F3 populations. The
parents, F1s, F2s, F3s, and backcrosses were evaluated under rainfed conditions. Floral trait
and genomic analyses using Single Nucleotide Polymorphisms (SNPs) markers of the
quantitative trait loci (QTL) underlying fruit size in tomato were also performed. The
Analysis of Variance (ANOVA) on agronomic, yield, floral and fruit traits showed significant
differences (P < 0.05) among the tomato genotypes. The cross, S x (W x R), was the most
promising three-way hybrid that can be exploited for increased tomato fruit size and yield in
the humid tropics. Mean fruit weight had significant and positive correlation with all the
floral traits with the exception of flower and style lengths. The number of locules per fruit
had the highest correlation value (r = 0.984**) with fruit size. Path coefficient analysis
revealed that the number of locules per fruit had the highest positive direct effect (p = 0.8086)
on fruit size. This was closely followed by ovary diameter (p = 0.7942) and stigma diameter
(p = 0.7685). On the other hand, style length had the highest negative direct effect (p = -
0.9147) on fruit size.
The fruit shape index showed significant positive correlation with the
ovary shape index (r = 0.835**) and seed shape index (r = 0.718**). However, fruit shape
index was negatively and significantly correlated with ovary diameter (r = -0.601*), fruit
diameter (r = -0.576*) and seed diameter (r = -0.519*). The population structure analysis
revealed that the tomato genotypes studied had three sub-populations. The association
mapping using 25 SNPs markers detected nine markers with significant association with
mean fruit weight, fruit length, fruit diameter, number of locules per fruit and fruit shape
index. The SNP marker, Solyc11-17, exhibited significant association with both fruit
diameter, number of locules per fruit and fruit shape index. The variation in fruit diameter
explained by the marker, Solyc11-17, was higher than the variations in number of locules per
fruit and fruit shape index (141.5%, 23% and 18.3%, respectively). All the nine markers
detected are recommended for fruit size improvement breeding programe in tomato.
Modified three-way crosses involving advanced interspecific tomato hybrids (W x R), (R x
W) and (W x T) at F12 generation and commercially cultivated tomato varieties namely
Supersteak (S), Beef (Florida) (BF) and Plumb (Rio grande) (PR) were made to generate F1
hybrids. The F1 hybrids were crossed to both the pollen and seed parents to produce the
backcrosses and were also allowed to random mate to produce the F2 and F3 populations. The
parents, F1s, F2s, F3s, and backcrosses were evaluated under rainfed conditions. Floral trait
and genomic analyses using Single Nucleotide Polymorphisms (SNPs) markers of the
quantitative trait loci (QTL) underlying fruit size in tomato were also performed. The
Analysis of Variance (ANOVA) on agronomic, yield, floral and fruit traits showed significant
differences (P < 0.05) among the tomato genotypes. The cross, S x (W x R), was the most
promising three-way hybrid that can be exploited for increased tomato fruit size and yield in
the humid tropics. Mean fruit weight had significant and positive correlation with all the
floral traits with the exception of flower and style lengths. The number of locules per fruit
had the highest correlation value (r = 0.984**) with fruit size. Path coefficient analysis
revealed that the number of locules per fruit had the highest positive direct effect (p = 0.8086)
on fruit size. This was closely followed by ovary diameter (p = 0.7942) and stigma diameter
(p = 0.7685). On the other hand, style length had the highest negative direct effect (p = -
0.9147) on fruit size.
The fruit shape index showed significant positive correlation with the
ovary shape index (r = 0.835**) and seed shape index (r = 0.718**). However, fruit shape
index was negatively and significantly correlated with ovary diameter (r = -0.601*), fruit
diameter (r = -0.576*) and seed diameter (r = -0.519*). The population structure analysis
revealed that the tomato genotypes studied had three sub-populations. The association
mapping using 25 SNPs markers detected nine markers with significant association with
mean fruit weight, fruit length, fruit diameter, number of locules per fruit and fruit shape
index. The SNP marker, Solyc11-17, exhibited significant association with both fruit
diameter, number of locules per fruit and fruit shape index. The variation in fruit diameter
explained by the marker, Solyc11-17, was higher than the variations in number of locules per
fruit and fruit shape index (141.5%, 23% and 18.3%, respectively). All the nine markers
detected are recommended for fruit size improvement breeding programe in tomato.
