Assessment of agro-morphological traits diversity in cowpea landraces originated from arid and warm regions of Iran

Cowpea (Vigna unguiculata) is a neglected crop with a wide diversity of its landraces in Iran, which acclimated to different climates. Cowpea is considered as one of the most tolerant food legumes under heat and drought stress. Although cowpea is distributed in a wide range of arid and warm climate of Iran, no extensive study has been done to determine the diversity of the landrace originated from these regions. Increasing yield, early maturity for grain production, long vegetative period for fodder yield, nutrient in leaf and grains, cooking quality, and germination rate are some crucial traits in cowpea breeding programs. Agro-morphological characterization of the existence germplasm would help to identification of the valuable genetic resources which could be entered into cowpea breeding programs to overcome challenges facing this crop production. 

Fifty landraces of cowpea originated from the arid and warm climate of IRAN along with Sistan local cowpea landrace (Mak) were evaluated for the diversity of 39 quantitative and qualitative agro-morphological traits. IBPGR descriptor was used to the characterization of traits; including terminal leaflet shape, leaf area, plant height, number of main branches, hypocotyl length, growth habit, number of nodes on the main stem, internode length, plant vigor, number of fixation nodules in root, fresh weight, dry weight, days to flower initiation, days to flowering (50%), days to flower termination, days to first mature pods, days to maturity, days to harvest, flower color, raceme position, pod color, seed crowding, pod wall thickness, plant hairiness, attachment of testa, pod length, number of locules per pod, 100-seed weight, number of pods per peduncle, number of pods per plant, yield, seed length, seed width, pod curvature, eye pattern, testa texture, canopy temperature, leaf chlorophyll concentration, and heat stress effects %. This experiment was done at the Zahak agricultural station of Sistan Agricultural and Natural Resources Research and Education Center. The experiments were performed observationally using furrow planting. Each landrace was sown in a five-meter row. 100 and 10 cm were considered for between and within row spaces of plants, respectively. Irrigation was carried out based on the needs of the plant and considering the conventional method of cowpea irrigating in the Sistan region, almost every two weeks. Statistical methods, including correlation, factor analysis, canonical correlation, path analysis, and cluster analysis, were used to identify the diversity and relationship among traits. 

Yield components included 100-seed weight and number of pods per plant were the most diverse traits in the current study. Based on the results, studied landraces could be potentially categorized in two grain and forage types. N7222 (Sarmoshk local landrace) and Mak (Zabol local landrace) showed the highest grain yield among evaluated landraces. TN7241 (another Zabol local landrace) and TN7274 (Kahnouj local landrace) were detected as landrace with the highest potential for forage production. It was also identified that two other Kahnouj local landraces, including TN7292 and TN7291, are the earliest maturity landraces among evaluated landraces. Correlation analysis showed a significant positive relationship between yield and number of N2 fixation nodules in the root. A significant positive correlation was also identified between pod length with a dry weight of the plant, the number of locules per pod, and 100-seed weight. Furthermore, it was revealed that yield was directly affected by pod length using path analysis. Path analysis distinct phenological traits from quantitative traits related to yield. Canonical correlation showed a negative correlation between days to flowering with grain yield, and it was shown that dwarf bushes with high yield component and 100-seed weight matured lately. 

Notable diversity for cowpea landraces was observed in the current study. The results of this research divided the accession to two grain and forage types. It was identified that high biomass yielded plants were not comfortable for grain production while they product suitable forage production. According to the results, two landraces were the best ones in grain production that were confirmed by cluster analysis. Pod length and the number of locules per pod were detected as the main two traits related to yield. The observed diversity in yield components could be applied further in the cowpea breeding programs.