Study of genetic variability, character association, path analysis and selection parameters for heterotic recombinant inbred lines of garden peas (Pisum sativum var. Hortense L.) under mid-hill conditions of Himachal Pradesh, India

The present investigations involving forty five diverse pea recombinant inbreds and three standard checks were carried out for two successive years during 2011-2012 and 2012-13. The objective of the study was to ascertain genetic variability, heritability, genetic advance, correlation and path coefficient among yield and other horticultural and quality traits and identification of superior recombinants for their utilization in crop improvement programme. Wide range of variability was observed for most of the characters under study. The magnitude of phenotypic coefficient of variation (PCV) was higher than the genotypic coefficient of variability (GCV) for all the traits. High phenotypic and genotypic coefficient of variations were recorded for protein content, ascorbic acid, plant height and pod yield per plant for both the years. Pod yield per plant and plant height exhibited high heritability associated with high genetic advance in the respective years indicating the additive gene action for their expression and are likely to respond better to selection. Pod yield showed a positive and significant correlation with number of pods per plant, pod length and number of seeds per pod both the years. Path analysis revealed that number of pods per plant and pod length have highest positive direct effect both the years and thus it may be treated as selection criteria for isolating higher yielding genotypes in garden peas. In heterosis study, some of the recombinant inbreds were found superior over standard checks which include L-14 and L-13 for pod yield/plant, number of pod/plant and earliness. These findings can be further utilized to develop and enhance the yield potential of garden pea.

The recovery of recombinant inbreds outyielding the hybrid in tomato

Publications commenting on the possibility of fixing heterosis and the possibility to transgress heterosis through partition of crop yield into genetic components have prompted us to reconsider our views on the relative importance of hybrid versus inbred vigour. The three genetic components of crop yield, all assessed in the absence of competition, are: (1) yield per plant assessed by the progeny mean, (2) tolerance to stresses assessed by the progeny standardized mean, and (3) responsiveness to inputs assessed by the progeny standardized selection differential. Although fixation of heterosis using the top commercial tomato hybrids was based only on the first genetic component of crop yield and quality, inbreds outyielding the original hybrid were obtained relatively easily. The results indicated that selection for homozygote superiority on the basis of the three genetic components of crop yield and quality, would lead to the development of tomato inbreds outperforming the hybrids.

Approximate thresholds of interval mapping tests for QTL detection.

A general method is proposed for calculating approximate thresholds of interval mapping tests for quantitative trait loci (QTL) detection. Simulation results show that this method, when applied to backcross and F2 populations, gives good approximations and is useful for any situation. Programs which calculate these thresholds for backcross, recombinant inbreds and F2 for any given level and any chromosome with any given distribution of codominant markers were written in Fortran 77 and are available under request. The approach presented here could be used to obtain, after suitable calculations, thresholds for most segregating populations used in QTL mapping experiments.