Journal of Agricultural Science and Practice Volume 5(4), pages 160-167, August 2020 Article Number: 08AFF2C41 ISSN: 2536-7072 https://doi.org/10.31248/JASP2020.187 https://integrityresjournals.org/journal/JASP Full Length Research A regression model to depict the influence of physiological and agronomic traits on yield of wheat cultivars under water stress in Tigray, Ethiopia Mohammed Mebrahtu Mossa Department of dryland crop and Horticultural science, Faculty of dryland agriculture and natural resources, Mekelle University, P. O. Box 231, Ethiopia. Email: mohammed4mam@yahoo.com; Tel: +251962 695475. Copyright © 2020 Mossa. This article remains permanently open access under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Received 30th January, 2020; Accepted 6th July, 2020 ABSTRACT: Although developing drought tolerance is the major objective of plant breeders, it is hampered by the lack of effective selection criteria. Most plant breeders use the single trait approach in identifying the crop response to drought condition, and little priority is given to the physiological traits. Thus, all the possible traits have not been critically evaluated, and correlation among the different traits and their relation to drought has not yet been critically examined. With those facts field and greenhouse, experiments were conducted at Mekelle University to determine the relationship among the different physiological, agronomic, yield and yield component of wheat genotype under water stress. The experiment was laid out in Randomized Complete Block Design using six wheat genotypes and three water regimes with three replications. Pearson’s correlation coefficient at 5% indicated that yield was positively and significantly correlated with relative water content, excised leaf water retention, spike length, number of seed per spike, and seed weight in contrast stress susceptibility index and rate of water loss were negatively associated with yield. Regression analysis also showed the rate of water loss, excised leaf water retention, and relative water content explain more of the variation (90%) in grain yield under different water stress regimes. Hence plant breeders should incorporate these physiological traits as a selection criterion in their breeding program for screening water stress on wheat cultivars. Keywords: Drought tolerance index, genotypes, moisture stress, physiological trait. INTRODUCTION Shortage of water is the most important component of life which limits plant growth and crop productivity, particularly in arid regions more than any other single environmental factor (Boyer 1982). Since wheat is grown mostly under rain-fed conditions, where water availability is a limiting factor, it inevitably suffers from drought stress. Balla et al. (2008) reported that drought had a negative effect on physiological processes and agronomic traits of wheat. Studies on plants identification and selection of physiological traits associated with plant water use efficiency (WUE) and drought tolerance under water- limited conditions are important for well-understanding plant physiological characters and taking physiological water-saving measures (Dulai et al., 2006). At the International Maize and Wheat Improvement Center (CIMMYT), researchers have demonstrated associations of some physiological traits, including leaf conductance and photosynthetic rate, the performance of a historic series of cultivars in a high-yielding environment (Nelson et al., 2007). In addition, historical traits associated with drought tolerance have been applied into a number of Australian wheats breeding programmers, including higher transpiration efficiency, greater early vigor and reduced tillering (Reynolds et al., 2009). Although developing drought tolerance is the major objective of plant breeders, it is hampered by the lack of effective selection criteria (yield other than all available potential markers). Most plant breeders use the single trait approach in identifying the crop response to drought condition, and little priority is given to the physiological