Evaluation of Tomato Hybrids for Resistance against Tomato Mosaic Virus (ToMV)

Tomato mosaic virus (ToMV) drastically affects the tomato production worldwide. To deal with this problem, breeding of ToMV-resistant hybrids/varieties is the ultimate need and most successful approach. In wild tomato species, three dominant ToMV-resistant genes (Tm-1, Tm-2 and Tm-22 ) were identified and the World Vegetable Center developed few fresh market tomato lines resistant to ToMV by the introgression of these genes. Recently at Nuclear Institute for Agriculture and Biology, Faisalabad, Pakistan a breeding programme was initiated to develop high yielding and ToMV tolerant hybrids using these lines. Current study was performed to screen elite F1 hybrids carrying Tm gene along with their parents against ToMV using mechanical inoculation, confirmation of the virus using DAS-ELISA and marker assisted selection of hybrids. Out of 28 hybrids and 17 parent accessions/genotypes, eight hybrids and five accessions were found to be highly resistant and the virus was not detected in DAS-ELISA. Five hybrids were resistant, nine hybrids and four genotypes were tolerant, while the remaining six hybrids and eight genotypes were susceptible. For the confirmation of Tm-22 gene, the tomato hybrids and their parents were subjected to molecular analysis using cleaved amplified polymorphic sequence (CAPS) primers. The result of CAPS markers for the confirmation of Tm-22 gene was found consistent with phenotypic data of the inoculated tomato genotypes/ hybrids. Higher phenolic content, total soluble proteins, better CAT and SOD activities were positively correlated with resistance. Screening results based on phenotype, biochemical and molecular marker data indicate that hybrids carrying Tm-22 gene are good sources of resistance against ToMV

DETECTION OF EPISTASIS AND ESTIMATION OF ADDITIVE AND DOMINANCE COMPONENTS OF GENETIC VARIATION USING TRIPLE TEST CROSS ANALYSIS IN RICE (ORYZA SATIVA L.)

Genetic analyses were performed to uncover the supremacy of additive, dominance and epistasis genetic variances following triple test cross analysis involving three testers (P1, P2 and F1) and four lines of rice. Epistasis was found to be an integral part of genetic variation for days to flowering, plant height, number of tillers per plant and yield per plant. The partitioning of total epistasis revealed that i type (additive x additive) were highly significant for days to flowering whilst j and l type (additive x dominance and dominance x dominance) were important for plant height with predominant effect of i type interaction. j and l type epistasis also played significant role in the inheritance of number of tiller per plant and yield per plant respectively. The additive and dominance effects were highly significant for number of grains per panicle and grain weight per panicle with the exception of 1000-grain weight where dominance effects were non-significant coupled with highly significant additive effects. The degree of dominance was less than unity, indicating partial dominance for number of grains per panicle, grain weight per panicle and 1000-grain weight. The direction of dominance was observed towards less grain weight per panicle. Non-allelic interactions registered for days to flowering, plant height, number of tillers and yield per plant can be manipulated through recurrent selection technique for the improvement of these traits. The predominance of additive gene action for number of grains per panicle, grain weight per panicle and 1000 grain weight suggest that the selection may be delayed to later segregating populations for the improvements of yield through yield components in rice