Evaluation of physiological and agronomic responses as screening techniques for yield and water stress tolerance in wheat Cultivars In Tigray, Ethiopia

Water stress is one of the major environmental factors that inhibits metabolic processes and constrains plant growth and crop productivity in the majority of agricultural fields. Wheat is generally grown on arid-agricultural fields and water stress often causes serious challenges in wheat production areas. Field and green house experiments were conducted at Mekelle University to evaluate physiological and agronomic traits as screening techniques for yield and drought tolerance in wheat cultivars. The experiment comprised of six wheat genotypes and three water stress regimes. Water stress was maintained by withholding water for 10 days at tillering and at booting stages. The experiment was laid out in Randomized Complete Block Design in factorial combination of the six wheat genotypes and three water regimes with three replications in both experiments. Analysis of variance for parameters associated with physiological, agronomic and drought tolerance as well as yield componentsrevealed a significant difference among the genotypes . Water stress caused reduction in relative water content, initial water content, rate of water loss, yield and yield components and increment in excised leaf water retention of the six studied wheat genotypes. Pearson’s correlation coefficient at 5% probability level indicated that yield and drought tolerance index were positively and significantly correlated with relative water content, excised leaf water retention, initial water content, spike length, number of seed per spike, yield stability index, mean productivity and seed weight where as stress susceptibility index and rate of water loss were negatively associated with yield and drought tolerance index. Regression analysis also showed that rate of water loss, initial water content, relative water content at both stem elongation and grain filling stage explain more of the variation in grain yield under normal condition where as traits such as relative water contents at stem elongation, excised leaf water retention, initial water content at grain filling stage and plant height when water stress was imposed at tillering stage and traits like days to heading, initial water content at stem elongation and grain filling stage , relative water content ate grain filling stage and rate of water loss explained more of the variation in grain yield and drought tolerance index under water stress at booting stage. More over principal component analysis extracted three components which explained 91.47 percent of the total variation, were the first component explained 58.65 percent with, initial water content at grain filling stage, stress tolerance index, excised leaf water retention, spike length, mean productivity, initial water content at stem elongation, relative water content at stem elongation Seed per spike, yield stability index, seed weight and grain yield per plant. Genotypes Dandea, Mekelle 3 and Mekelle 4 had higher relative water content, excised leaf water retention, initial water content, mean productivity, yield stability index and stress tolerance index than the other three genotypes (Hawii, Shina and Medawalabu) whereas stress susceptibility index and rate of water loss was observed at its lowest. Traits like relative water content, excised leaf water retention, initial water content, days to flowering, are recognized as beneficial water stress tolerance indicators for selecting a stress tolerant variety. Similarly, total grain yield per plant, spike length, seed per spike and 1000 seed weight was also higher in the same wheat varieties, which put it as a good candidate for selection in wheat breeding program for drought resistance. Hence plant breeders should incorporate these physiological traits as a selection criterion in their breeding program for screening water stress tolerance wheat cultivars.