EVALUATION OF MORPHOLOGICAL AND PHYSIOLOGICAL TRAITS DETERMINING SEED YIELD AND HYDROTHERMAL STRESS TOLERANCE AMONG MAIZE VARIETIES

Abstract

Experiments were conducted at the Teaching and Research Farm of the Federal University of Technology, Akure, a humid rainforest zone of southern Nigeria, to evaluate the morphological and physiological traits determining seed yield and hydrothermal stress tolerance among five maize varieties. The varieties are TZEE – YPOSR C6, IBIZB – EC6, TZE – WROP DT C4/(STR C5) and 2000SYMEE – WSTR,TZE – YDTSTR CE (drought tolerant varieties), and SUWAN, a widely grown and adaptable, open pollinated early maturing variety . Seeds were sown on the field as late and early rainy season crops in August to December, 2015 and March to July, 2016 respectively. Data were collected on agronomic characters of root and shoot biomass, plant height, number of leaves, days to first and 50% flowering and seed yield and yield components. Data collected on plant parameters were subjected to analysis of variance (ANOVA) test for randomized complete block experiment and treatment means were separated using Duncan’s Multiple Range Test (DMRT) at 5% level of probability. The sowing seasons (early and late rainy seasons) were characterized by varying cumulative seasonal rainfall amount, open water evaporation (Eo), temperatures, vapour pressure deficits ( vpd) and growing degree days (GDD: thermal time coefficient). These weather events which imposed different degrees of hydrothermal stress conditions on maize affected its growth duration, biomass production, assimilate reserves and seed yield characters. Season effects were significant (P˃0.05) on maize growth and seed yield characters. However within a growing season, the varieties differed in growth characters, seed yield and yield components. Variety TZEE-YPOSR C6 produced the tallest plants in both seasons while 2000 SYMEE-WSTR had higher number of leaves in the early rainy season, SUWAN had higher number of leaves in the late season. Flowering date was delayed for 2000 SYMEE-WSTR and TZE-YDTSTR CE by about 4 days compared with other varieties. Higher root dry weights were produced by TZE-YDTSTR CE in the rainy season with variety TZEE-YPOSR C6 producing higher root dry weight in the late season. In both seasons, SUWAN had higher shoot weight while variety 2000 SYMEE-WSTR and IBIZB-EC6 had higher seed yield in the late season planting, SUWAN and TZE-YDTSTR variety had the highest seed yield in the early rainy season planting. Late season maize out-yielded the rainy season crop in terms of weights of cobs and seeds produced per plant. Among the maize varieties, significant differences were found for leaf concentrations of chlorophyll and water soluble carbohydrates. Lower values of chlorophyll concentrations in leaf tissues were obtained for early season maize while late rainy season crop had higher values of leaf chlorophyll contents. Leaf concentrations of water soluble carbohydrates were lower in late season crop compared with the early rainy season maize. Functional relationships were established between some weather variables and growth and yield characters of late rainy season maize. These relationships gave regression coefficient (R2) which ranged between 0.30 and 0.81 showing that some measured growth and seed yield characters of maize were strongly affected by weather parameters such as cumulative seasonal rainfall, minimum temperatures, vapour pressure deficit (humidity) and growing degree days (GDD). It is concluded that the weather conditions of the early and late rainy seasons are critical factors and determinants of growth and yield characters of maize