Journal of Crop Production and Processing

Drought is one of the most important abiotic stresses that limits the growth and production of agricultural plants and affects many morphological, physiological, biochemical and metabolic aspects of plants (Blum, 2011). Changing the cultivation pattern and identifying heat and drought tolerant plant species and cultivars with high adaptability and low water requirements are among the main objectives of plant breeding in arid and semi-arid regions of the world. Cotton, as an oilseed crop and the world’s most important natural fiber source, holds exceptional agricultural, commercial, and economic significance. Its global value is so substantial that it is often referred to as “white gold” (Raphael et al., 2019; Singh et al., 2019). Although cotton is a glycophyte, it demonstrates relatively high tolerance to abiotic stresses compared with many other major crops. Nevertheless, severe environmental constraints- particularly drought can markedly impair cotton growth, reduce yield, and diminish fiber quality. Therefore, this study was conducted to evaluate the effect of drought stress on landraces of cotton, and to identify and select the drought-tolerant cultivars of cottons using 19 diploid genotypes.

Materials and Methods: For this purpose, an experiment was performed at the Kashmar Agricultural and Natural Resources Research Station, Kashmar, Northeast Iran based on a split-plot experiment within a randomized complete block design, with three replications, under normal and moisture stress conditions. Moisture stress was imposed by doubling the irrigation interval; specifically, while the non-stressed treatment involved a 10-day irrigation cycle, the stress treatment utilized a 20-day cycle-effectively doubling the interval. Then, some morphological traits (plant height, number of sympodial branches, number of monopodial branches, number of opened bolls, number of closed bolls, and crown diameter) along with yield of studied landraces were assessed under two irrigation regimes (normal and water stress conditions). To evaluate the drought tolerance of the mentioned genotypes, drought tolerance and susceptibility indices were calculated based on the seed yield under stress (Ys) and non-stress (Yp) conditions. Correlation analysis, principal component analysis based on the correlation matrix, and biplot analysis were performed using SPSS ver. 16, Statgraphics, and STATISTICA ver. 8 software.

Results and Discussion: High genetic variation was observed among landraces for most of the studied traits and indices. This indicates high genetic diversity among the selected landraces regarding the traits under study and can be effective in improving selection within breeding programs. Moisture stress had negative effects on the majority of the studied traits and altered inter trait relationships, thereby increasing genetic variability and enhancing selection efficiency for stress adaptive characteristics. On average, moisture stress reduced the seed yield and plant height by 74% and 51%, respectively. The low heritability of seed cotton yield (46%) indicates that direct selection based on yield is not effective for the improvement of this trait and indirect selection based on yield components which have moderate to high heritability and high correlation with yield (i.e. plant height, number of monopodial and sympodial branches, number of open and closed bolls), would be more effective. These traits, therefore, represent valuable targets for indirect selection aimed at improving yield and drought tolerance. Based on the results of correlation analysis and PCA method, five indices of MP, GMP, STI, YI and ATI showed significant and positive correlation with the seed cotton yield under both stress and non-stress conditions and therefore can separate the superior landraces. Therefore, these indices were identified as the best indices for distinguishing between moisture-stress-tolerant and moisture-stress-sensitive cotton landraces. Results showed that the native landraces of Shahreza, Sorkhe Semnan, and Kashmar red boll were drought tolerant whereas the native landraces of colored fibers and red boll green leaf of Qom were identified as sensitive ones. 

Conclusions: Overall, drought tolerance and susceptibility indices facilitated the identification of stress resilient landraces which may be suitable for cultivation in arid and semi arid environments. The tolerant landraces identified in this study can be used as suitable parents for genetic analysis and breeding for moisture stress tolerance in the future studies. Furthermore, crossing stress-tolerant and stress-sensitive landraces can be utilized to generate genetic maps in the breeding studies. Further research should refine selection models and validate these landraces across broader agro ecological contexts.