Plant Growth Promoters Boost the Photosynthesis Related Mechanisms and Secondary Metabolism of Late-Sown Wheat under Contrasting Saline Regimes

There is an imminent risk of higher crop failures owing to weather vagaries for agriculture-based livelihood systems, which are already fragile due to several challenges. The most important challenge is the encounter of crops against multiple environmental stresses under natural field conditions, the combination of these stresses poses complex effects on plant physiological and metabolic activities. To date, the combined effects of salt stress (SS) and late-sown (LS) on physiological and biochemical attributes have not been studied on wheat. A two-year field study was designed to evaluate the effect of plant growth promoters (PGRPs) to alleviate the individual SS, LS and combinations on wheat. The experiment was conducted for three factors, a) late sown and timely sown, b) saline and non-saline conditions and c) PGRPs treatments (thiourea (TU @ 1000 mg L−1), salicylic acid (SA @ 100 mg L−1), hydrogen peroxide (H2O2 @ 100 µM), water spray (H2O) and control). Data revealed that under stress conditions, especially under SS+LS stress plants increased the synthesis of secondary metabolites, enhanced heat dissipation, and showed strict control over the stomatal regulation and gas exchange attributes, all these mechanisms were tweaked to deal with all the stresses. In addition, SS+LS stress followed by SS and LS stress severely reduced the flag leaf area (FLA), chlorophyll pigment contents and chlorophyll fluorescence and carboxylation capacity. However, foliar treatments of PGRPs TU, followed by SA, H2O2, H2O and control improved the chlorophyll fluorescence, pigments contents, gas exchange indicators, and relative water content (RWC). Moreover, PGRPs application improved the FLA, pigment biosynthesis and carboxylation capacity that improved the synthesis of metabolites such as anthocyanin, niacin, flavonoids, phenolics, alkaloids, saponin and riboflavin, which acted as defensive compounds to preserve the photosynthetic capacity irrespective of stress treatments.