Heritability and correlation of agronomically important traits are useful information for plant breeders to formulate effective breeding strategies. The objective of this study was to estimate broad-sense heritability, phenotypic and genotypic correlation for nitrogen fixation and agronomic traits in 6 crosses of the F4 generation of peanut. The experiment was conducted at Khon Kaen University’s agronomy farm during rainy season of 2002. Six crosses with 20 families each, their five parents and a non-nodulating line were assigned in a randomized complete block design with 4 replications. Heritability estimates varied depending on crosses and traits. The crosses KKU 1 x PI 269109 and KKU 1 x KKU 72-1 had high heritability estimates for shoot dry weight, total dry weight, fixed nitrogen and total nitrogen, indicating that superior genotypes for these traits can be easily identified in this population. For the crosses having low heritability estimates for nitrogen fixation parameters, selection should be emphasized on agronomic traits. High heritability estimates were found for pod number/plant, pod weight/plant, seed weight/plant, 100-seed weight, shelling percentage and harvest index in most crosses. Means of crosses were also close to means of mid-parent for most traits, indicating that gene action controlling the inheritance of most traits were additive. Phenotypic and genotypic correlations among nitrogen fixation traits were positively correlated with each other. The traits were also positively correlated with pod weight/plant, seed weight/plant and 100-seed weight, but were not correlated with pod number/plant, seed number/plant and seed number/ pod. Nitrogen fixation parameters were negatively correlated with shelling percentage and harvest index.
