Cold and Drought Stresses in Wheat: A Global Meta-analysis of 21st Century

Cold and drought stress events are detrimental to plant growth and development in wheat, leading to severe damage and yield losses. This meta-analysis explored and covered all the major comparisons of (1) cold, drought, and combined cold and drought stresses and (2) spring and winter wheat. The risks of cold and drought associations in spring and winter wheat were quantitatively evaluated from 4000 observations across 149 peer-reviewed publications (2000–2021). The results showed a considerable decline in the activities of antioxidant enzymes under individual stresses, while an increase in the reactive oxygen species was noted under combined stresses, revealing the lower tolerance of both wheat types under combined stresses. Photosynthetic and fluorescence activities declined under combined stresses; however, winter wheat behaved well to estimate chlorophyll and chlorophyll fluorescence relative to spring wheat under individual and combined stresses. The lethal temperature for 50% plant population (LT50) revealed the capability of winter wheat to be − 15 °C, whereas spring wheat cannot survive under − 10 °C. In addition, grain weight was significantly reduced under drought in spring wheat and cold in winter wheat. Interestingly, combined stresses affected grain weight in spring wheat, while winter wheat showed no significant effect under combined stresses. The structural equation model estimated direct and indirect effects of stresses on grain weight and final grain yield concerning chlorophyll and chlorophyll fluorescence, antioxidant enzymes, and hydrogen peroxide. The linear regression model showed a negative correlation of water potential with grain yield under individual stresses while a positive correlation amid combined stress. In addition, spring wheat was more prone to losses under combined stresses than winter wheat. Water potential, proline, and stomatal conductance were the most important variables in projection to estimate cold, drought, and combined stresses. Exogenous salicylic acid is recommended as a management strategy to regulate antioxidant enzymes, leaf chlorophyll contents, and water potential by improving photosynthesis under interactive stresses.