COMBINING ABILITY AND HETEROSIS FOR FRUIT YIELD AND HEAT TOLERANCE IN TOMATO (LYCOPERSICON LYCOPERSICUM Mill.) UNDER FIELD CONDITIONS
COMBINING ABILITY AND HETEROSIS FOR FRUIT YIELD AND HEAT TOLERANCE IN TOMATO (LYCOPERSICON LYCOPERSICUM Mill.) UNDER FIELD CONDITIONS
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Date
2016-08
Authors
HAMISU, Habu Saleh
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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
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crosses indicated that Icrixina × Rio Grande, Icrixina × Tima, and Petomech × Roma
Savana were the most desirable cross combinations for fruit yield per plant and
percentage fruit set indicating that they are more heat tolerant. Cell membrane
thermostability and heat injury at 30oC, 40oC and 50oC exhibited significant variations
among the genotypes for electrolyte leakage at flowering stage, suggesting that cell
membrane thermostability was good index for screening and evaluating tomato
genotypes for heat tolerance. The genotypes Icrixina, Icrixina × Tropimech, Rio Grande
× Tropimech, Rio Grande × Roma Savana and Rio Grande × Petomech were heat
tolerant. Broad sense heritability was high for all traits, while narrow sense heritability
was low to moderate for most of the traits. Correlation results suggests that selection
for number of flowers per plant, number of fruits per plant, leaf chlorophyll content and
cell membrane thermostability would increase fruit yield per plant and percentage fruit
set under high temperature, but with a reduction in days to flowering, average fruit
weight and fruit size.Icrixina × Rio Grande and Icrixina × Tima gave higher yields per
plant compared with the hybrids checks. Therefore, considering the predominance of
non-additive gene action and large negative genetic association between percentage
fruit set and fruit size, heterosis breeding could be exploited in developing heat tolerant
tomato with acceptable fruit size.
Description
A DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE
STUDIES AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD
OF A
DEGREE MASTER OF SCIENCE IN PLANT BREEDING
DEPARTMENT OF PLANT SCIENCE
FACULTY OF AGRICULTURE,
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA
Keywords
COMBINING ABILITY,, HETEROSIS,, FRUIT YIELD,, HEAT TOLERANCE IN TOMATO,, LYCOPERSICON LYCOPERSICUM Mill,, FIELD CONDITIONS