GENETICS AND INHERITANCE PATTERN OF TIME OF FLOWERING AND QUANTITATIVE TRAITS IN COWPEA (Vigna unguiculata (L.) Walp).
Field experiments were carried out in 2006 and 2007 cropping seasons at the Teaching and Research Farm of the Department of Crop Science, University of Nigeria, Nsukka, to study the inheritance pattern of days to flowering and quantitative traits in cowpea. The experimental materials comprised 10 cowpea accessions sourced from Plateau and Enugu States of Nigeria. Reciprocal crosses were generated and the parents, F1, F2 and BC populations were evaluated for days to flowering under long day length (averaged 13.4 hd-1) and short day length (10hd-1)
conditions. Characters assessed included days to 50% emergence, number of leaves plant-1, number of primary branches plant-1, vine length, number of peduncles plant-1, number of flowers plant-1, number of pods plant-1 and grain yield. The study established the accessions from Plateau state as short day (SD) plants and those from Enugu state as day neutral (DN) plants. The parental lines differed significantly (P<0.05) in days to flowering, pod and grain yields. The mean number of days to first and 50% flowering for SD accessions were delayed significantly (P<0.05) when compared to DN accessions. The result of the principal component (PC) analysis revealed that the most effective characters for distinguishing the parents and progenies included days to first and 50% flowering, number of peduncles plant-1, number of flowers plant-1, number of pods plant-1 and grain yield. The scatter plot and cluster means of the first two principal axes grouped the cowpea accessions into two main clusters, based on their response to day-length. Cluster I comprised day neutral (DN) cowpea accessions (Akidi-ani, Akidienu1, Akidi-enu2 and Akidi-enu3) that flowered early (<45 days) with poor yield components and cluster II comprised the short day (SD) accessions (Bwa-Tal, Bwa-Chip, Gag, Gazum and Du’ut) that flowered late (>45 days), and were prolific in the yield traits assessed. However, the accession, Jalbang alienated itself from the clusters and was genetically independent. The F1 and F2 populations also differed significantly in days to first and 50% flowering, pod and grain yields. The distribution of the progenies with respect to days to flowering showed combined effects of both maternal and nuclear influence on the inheritance of flowering time in cowpea. Photoperiod sensitive short day accessions used as maternal parents produced F1 progenies that were short day, while day neutral mothers produced F1 hybrids that flowered irrespective of day length. Pearson correlation coefficients revealed significant positive relationship between grain yield and number of peduncles plant-1(0.796**), number of flowers plant-1(0.774**), number of pods plant-1 (0.758**) and pod length (0.728**). However, inverse relationships were obtained when days to flowering were associated with grain yield. Grain yield of the SD accessions were significantly higher (>1000 Kgha-1) than those of the DN accessions (<1000 Kgha-1). The accession, Gag was distinct in grain yield as it produced over 1600Kg ha-1.