Variations in chemical constituents of the rhizosphere of bread wheat genotypes and their significance for using as markers for heat and drought tolerance

In rhizosphere, root exudates act as food and chemo-attractants for the microbes, whereas microbes help in plant growth. The present study investigated the chemical changes in the rhizosphere of 10 contrasting wheat genotypes each for heat and drought stress at two stages of plant growth under stress conditions, and their root exudates profiles under semi-hydroponic conditions. The heat-tolerant genotypes exhibited significantly higher content of P by 1.59 fold, while drought-tolerant genotypes exhibited Mg and P by 1.22 and 1.24 fold, respectively compared to sensitive genotypes. Further, the heat stress tolerant genotypes exhibited significantly higher contents of Fe, Cu and Zn at anthesis by 1.53, 1.31 and 1.44 fold, respectively than at the booting stage, while the drought stress tolerant genotypes exhibited higher contents of Na, K, Mg and P at booting by 1.27, 3.05, 1.32 and 2.45 fold, respectively than at anthesis stage. Both heat and drought-tolerant genotypes exuded higher concentrations of most of the studied root exudates, and it ranged between 1.34 fold higher for succinic acid to 12.96 fold for sucrose in drought-tolerant genotypes. Similarly, in heat-tolerant genotypes, it varied from 1.01 fold for D-galactose to 10.39 fold for malic acid. Overall, the study revealed that the tolerant genotypes modulated their rhizosphere composition with respect to higher contents of Na, K, Mg, Fe, Cu, Zn and P, and exuding higher quantities of sugars and organic acids than the sensitive genotypes, which could contribute to their survival under abiotic stress conditions.