ENVIRONMENTAL EFFECTS ON THE HERITABILITY OF QUANTITATIVE TRAITS OF HYBRIDS WHITE GUINEA YAM (Dioscorea Rotundata) IN THE RAINFOREST AGRO-ECOLOGICAL ZONE OF SOUTHEAST NIGERIA

The study was conducted at the western experimental field of National Root Crops Research Institute (NRCRI) Umudike Umuahia Abia State-Nigeria from 2017 to 2018, to determine the environmental effect on the heritability of quantitative characters of the intra-specific hybrids of White yam (Discorea rotundata) in the rainforest agro-zones of Southeastern Nigeria. A total of 13 white yam genotypes were used in the study. The trial was laid out in a two factor factorial in a Randomized Complete Block Design (RCBD). Each plot measured 4.5m2, while each block contained 13 plots replicated six times. Data collected were on three competitive plants on the following plant characters: number of upright shoots, number of leaves, number of lateral branches, leaf area, leaf area index, Stand count at harvest, fresh tuber weight, dry matter of the tuber, tuber shape index, crop growth rate at 4 months after planting and days to physiological maturity. Data collected were subjected to analysis of variance, simple linear correlation, genetic correlation, estimation of the variations of genotypic and phenotypic coefficients in both environments plus Broad sense heritability estimates in both seasons. The result indicated that the physiological maturity of the yam genotypes evaluated had very low coefficient of variability of 0.61% in 2017 and 2018 respectively. This indicated limited scope for further improvement by direct selection of this character. The low heritability estimates of days to physiological maturity (5.07% in 2017 and 0.07% in 2018) and crop growth rate at 4 months after planting (0.02% in 2017 and 0.01% in 2018) indicated that environmental factors played a predominant role in the determination of the expression of these plant characters. If selected, these characters may not be repeated as indicated by its genetic correlation. As a result the yield of tuber dry matter and yield may not be predicted.