Genetic variability, association and diversity studies in wheat (Triticum aestivum L.) germplasm

Seventy local and exotic wheat genotypes grown in Faisalabad, Pakistan during the Rabi season of 2005/2006 were evaluated for variability parameters, correlations and path coefficients for eight metric traits i.e., plant height, number of productive tillers per plant, number of spikelets per spike, spike length, number of grains per spike, fertility %, 1000 grain weight and yield per plant. Significant genotypic differences were observed for all the traits studied indicating considerable amount of variation among genotypes for each character. The estimates of genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) were high for yield per plant, number of productive tillers per plant and number of grains per spike. The remaining traits recorded moderate to low PCV and GCV estimates. Moderate heritability was observed for number of productive tillers per plant and fertility %. High heritability estimates were recorded for plant height, number of spikelets per spike, spike length, number of grains per spike, 1000 grain weight and yield per plant. These traits also indicated high genetic advance (except fertility %). Grain yield per plant showed highly significant positive correlation with number of productive tillers per plant, number of spikelets per spike and number of grains per spike and significant positive correlation with spike length. Path coefficient analysis revealed that number of productive tillers per plant and number of grains per spike had the highest direct effect on grain yield per plant and each must be given preference in selection along with optimum plant height to select superior wheat genotypes. The cluster analysis grouped 70 wheat genotypes into 4 different clusters. Five genotypes of China were grouped in cluster-I that showed the maximum diversity. Genetic diversity was partially related to the geographic origin. From the cluster mean values, Chinese genotypes deserve consideration for their direct release as a variety(s) or as parents in hybridization programmes to develop high-yielding wheat varieties. The genotypes in cluster II may be used for the improvement of plant height and 1000 grain weight in wheat.