ABSTRACT

Heat stress causes significant fruit yield loss in tomato (Lycopersicon lycopersicum

Mill.). Breeding of tomato hybrids tolerant to high temperature will reduce fruit yield

losses caused by heat stress in Nigeria. The genetics of heat tolerance in tomato was

studied using half diallel mating design of six parents comprising two heat tolerant and

four heat susceptible varieties. The resultant 15 hybrids, with the 6 parents and 4 checks

were evaluated at two locations: Bagauda and Samaru under heat stress condition

between July-October, 2014 rainy season. Data collected on agronomic, heat tolerance

and physiological characters were used to determine heterosis, combining ability,

heritability and correlations under field conditions. Analysis of variance indicated

highly significant (P < 0.01) differences among the genotypes for most traits.

Significant level of heterosis were observed in crosses Icrixina × Rio Grande, Icrixina

× Roma Savana, Icrixina × Tima, Icrixina × Petomech and Petomech × Roma Savana

which ranged from -551.00 to 80.82% and from -31.81 to 120.80% for fruit yield and

percentage fruit set, respectively. Combining ability analysis revealed that both additive

and non-additive gene action were important for the inheritance of the number of

clusters per plant, number of flowers per plant, number of fruits per plant, fruit length,

fruit yield per plant and percentage fruit set. However, the variance components due to

SCA were higher in magnitude than the GCA variance components for all traits except

number of fruits per cluster and fruit length, indicating preponderance of non-additive

gene action in the inheritance of the traits. Estimates of gca effects revealed that the

parent Icrixina was a good general combiner for all traits except plant height, average

fruit weight, fruit diameter and leaf chlorophyll content. The estimates of sca effects of

vi