RESUMEN
Okra production in eastern India at present is severely threatened by whitefly-mediated okra enation leaf curl disease(OELCuD). Identification of resistant genotype and understanding the genetic control and biochemical relationship of OELCuD resistanceare prerequisite for developing an effective breeding strategy. This study was conducted employing six populations (P1, P2, F1, F2, BC1 andBC2) of two selected (resistant 9 susceptible (R9S)) crosses. Associationship between severity of OELCuD and biochemical parametersof parents and hybrids at preflowering and flowering stages was studied. Segregation pattern of the genotypes in F2 generation showingOELCuD reaction of two crosses suggested that two duplicate recessive genes was operative for resistance to OELCuD. Generation meananalysis revealed involvement of both additive and nonadditive effects in the inheritance of disease resistance. Hence, postponement ofselection in later generations or intermating among the selected segregates followed by one or two generations of selfing to break theundesirable linkage and allow the accumulation of favourable alleles could be suggested for the development of stable resistant genotypeagainst this disease. Higher peroxidase activity and total phenol content in leaf emerged as reliable biochemical markers for early selectionof genotype resistant to OELCuD.
RESUMEN
Development of mutants and their effective utilization to incorporate desirable traits in tomato would be a sound improvement strategy to develop so called ‘smart’ tomato variety of the coming century. Initially we developed three induced mutants from two varieties, ‘Patharkuchi’, a local adapted cultivar and an introduced variety ‘Berika’, and then three crosses (Berika 9 P Mut-5, Berika 9 P Mut-11, Patharkuchi 9 B Mut-1) were made to involve in these two varieties and their respective mutants. Six generations (P1, P2, F1, F2, BC1 and BC2) of three crosses were utilized to study the genetic control of yield and quality traits, and to study the genetic basis of formation of dark green fruit. The nature and magnitude of gene action controlling the inheritance of 27 quantitative traits differed from one cross to another and from one trait to another, mostly conditioned by nonadditive gene action and duplicate epistasis. The prevalence of duplicate epistasis in three crosses for most of the traits revealed that the pace of progress through conventional selection process would be hindered as this kind of epistasis might result in decreased variation in F2 and subsequent generations. Recurrent selection in biparental progenies would be helpful for exploiting this type of nonallelic interaction through generation of high frequency of desirable recombination and concentration of genes having cumulative effects in the population. We also observed complex genetic behaviour of some of the traits revealing significant epistatic components. Inheritance study of ‘dark green fruit’ (dg1) of Berika 9 P Mut-5 cross revealed a single recessive gene governing the trait and expressed when the mutant gene was in homozygous recessive condition (designated as dg-1/dg-1).