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The main constraint on rice cultivation in the Mediterranean area is the limited irrigation and its large water consumption. In addition, rice is very sensitive to drought conditions because of drought stress on morpho-physiological traits and yield reduction. The application of salicylic acid (SA) has been noticed to be very effective in alleviating the adverse effects of drought stress on rice. The current investigation was conducted as a split-split arrangement under a randomized complete block design with two lowland rice cultivars (Giza177 and Giza179) and SA as a foliar application at four concentrations (0, 400, 700, and 1000 µM) under normal and drought conditions. The results showed that plant growth, leaf photosynthetic pigments, yields, and the most studied traits were significantly affected by irrigation (I), cultivar (C), and SA concentration (p ≤ 0.05 or 0.01). The interaction effect of I × C × SA was only significant on the carotenoids content (p ≤ 0.05). The reduction in grain yield and most studied traits was more pronounced under drought conditions. The Giza179 proved to be a drought-tolerant cultivar under all SA concentrations under drought conditions, while Giza177 was a drought-sensitive cultivar. The application of 700 µM SA gave the best grain yield in both rice cultivars under drought conditions compared to other SA concentrations. Grain yield for normal irrigation (Yp) and drought stress (Ys) conditions were highly positively correlated with indices of the mean productivity (MP), geometric mean productivity (GMP), stress tolerance index (STI), yield index (YI), yield stability index (YSI), drought resistance index (DI), harmonic mean (HM), and golden mean (GOL). While they are highly negatively correlated with the indices of the stress susceptibility index (SSI), tolerance index (TOL), yield reduction ratio (YR), stress susceptibility percentage index (SSPI), and abiotic tolerance index (ATI). It could be concluded that SA, as a growth regulator, could be used to alleviate the harmful effect of inadequate water availability in soil on rice cultivars as well as to improve the growth, water productivity, and grain yield.

In order to evaluate genetic parameters and drought tolerance indices using multivariate analysis, seventeen genotypes of rice were evaluated under normal and drought conditions. The combined analysis of variance indicated highly significant effects of genotype on all studied traits under normal and drought conditions. Most studied genotypes were better than the grand mean during normal and drought conditions. Drought stress reduced the studied traits while other was tolerant to drought, suggesting genetic variability in these genotypes for drought tolerance. The environmental and genetic variances and heritability showed highly significant for all studied traits under normal and drought conditions. The maximum values of genetic variance were found for all studied traits followed by the environmental and genotypes × season variances at normal and drought conditions. High heritability coupled with high genetic advance as percent of the mean was observed for most studied traits under normal and drought conditions. The differences between phenotypic coefficients of variation (PCV%) were higher than the values of genotypic coefficients of variation (GCV%) for all

Drought stress is a major factor limiting wheat crop production worldwide. The application of humic acid (HA) and the selection of the appropriate genotype in the suitable site is one of the most important methods of tolerance of wheat plants to drought-stress conditions. The aim of this study was achieved using a three-way ANOVA, the stress tolerance index (STI), the Pearson correlation coefficient (rp), and principal component analysis (PCA). Three field experiments in three sites (Al-Qasr, El-Neguilla, and Abo Kwela) during the 2019/21 and 2020/21 seasons were conducted, entailing one Egyptian bread wheat variety (Sakha 94) with three HA rates (0, 30, and 60 kg ha−1) under normal and drought-stress conditions (supplemental irrigation). According to the ANOVA, the sites, supplemental irrigation, HA rates, and their first- and second-order interactions the grain yield and most traits evaluated (p ≤ 0.05 or 0.01) were significantly influenced in both seasons. Drought stress drastically reduced all traits registered in all factors studied compared with normal conditions. The wheat plants at the Al-Qasr site in both seasons showed significantly increased grain yield and most traits compared with that of the other sites under normal and drought-stress conditions. HA significantly promoted all studied traits under drought stress, and was highest when applying 60 kg HA ha−1, regardless of the site. The greatest grain yield and most traits monitored were observed in wheat plants fertilized with 60 kg HA ha−1 at the Al-Qasr site in both seasons under both conditions. Grain yield significantly (p ≤ 0.05 or 0.01) correlated with water and precipitation use efficiency as well as the most studied traits under normal and drought-stress conditions. The results of STI, rp, and PCA from the current study could be useful and could be used as a suitable method for studying drought-tolerance mechanisms to improve wheat productivity. Based on the results of statistical methods used in this study, we recommend the application of 60 kg HA ha−1 to improve wheat productivity under drought conditions along the north-western coast of Egypt.