Morpho-physiological evaluation of susceptible and drought tolerant genotypes of winter bread wheat

Wheat, as one of the most important crops, occupies about 20% of the world's cultivated area. In the FAO report, more than 90% of Iran is classified as arid and semi-arid. The impact of drought stress on crops is devastating every year, resulting in yield losses of 17%. It is therefore of high importance to research to improve crop resilience to drought stress and minimize water losses in agriculture. Accordingly, four advanced tolerant and sensitive bread wheat genotypes against drought stress were studied regarding yield and other physiological, morphological, and phenological traits under normal and water deficit conditions during the flowering stage. The objective was to discover the main causes of stress tolerance or sensitivity from different aspects of the studied genotypes. To explore the effect of moisture stress at flowering stage, four genotypes were investigated as the main factor (A) by factorial experiment based on the randomized complete block design (RCBD) with three replications under the normal and moisture stress conditions at flowering stage as the sub-factor (B) in the research field. The results of analysis of variance showed a significant difference at least at 5% probability level between genotypes and drought stress levels according to most studied traits. Based on the results from the comparison of means of traits, the high tolerance of Eroum cultivar to drought stress was due to the higher increase in MDA and H2O2 and lower decrease in traits of chlorophyll a, total chlorophyll content, carotenoid content, 1000-seed weight and plant height. Also, the Mihan cultivar was more tolerant to drought stress because of the higher increase of proline, carotenoid, POX, CAT, peduncle length and number of days to 50% flowering and the lower decrease in the number of grains per spike due to drought stress. The results of biplot analysis based on the principal component analysis (PCA) showed that the flag leaf area, vegetative growth rate, number of fertilizer tillers, grain yield, number of grains per spike, 1000-seed weight, CAT, proline, POX, MDA and carotenoid play a decisive role in genotype discrimination under the normal and stress conditions. The results of path analysis showed that the vegetative growth rate, total chlorophyll content, chlorophyll a content and plant height, due to significant direct effects, and also the MDA, proline content and peduncle length, chlorophyll a concentration, chlorophyll b concentration, carotenoid content, total chlorophyll concentration, length of grain filling period and vegetative growth rate, due to the greater correlation with grain yield, can be used as suitable indicators for the selection of tolerance genotypes. According to the mean comparison, causality, and biplot analyses, the high yield of the Arum genotype under normal and water stress conditions can be explained by total protein, vegetative growth rate, grain filling rate, 1000- grain weight, grain filling period, grains number in spike, fertile tillers number, plant height, and malondialdehyde. Whereas, the high yield of the Mihan genotype under both normal and moisture deficit conditions can be attributed to vegetative growth rate, 1000 grain weight, flag leaf area, grain filling period, grains number in spike, fertile tillers number, plant height, total chlorophyll concentration, chlorophyll a and b concentration, peduncle length, carotenoid content, and proline content.