Drought is one of the most important abiotic stress factors limiting maize production worldwide. The objective of this study was to investigate whether photoprotection of PSII was associated with the degree of drought tolerance and yield in three maize hybrids (30Y87, 31R88, P3939). To do this, three maize hybrids were subjected to three cycles of drought, and we measured the activities of photosystem II (PSII) and photosystem I (PSI). In a second field experiment, three maize hybrids were subjected to drought by withholding irrigation, and plant water status, yield and yield attributes were measured. Drought stress decreased leaf water potential (Ψ_L) in three maize hybrids, and this reduction was more pronounced in hybrid P3939 (−40%) compared to that of 30Y87 (−30%). Yield and yield attributes of three maize hybrids were adversely affected by drought. The number of kernels and 100-kernel weight was the highest in maize hybrid 30Y87 (−56%, −6%), whereas these were lowest in hybrid P3939 (−88%, −23%). Drought stress reduced the quantum yield of PSII [Y(II)], photochemical quenching (qP), electron transport rate through PSII [ETR(II)] and NPQ, except in P3939. Among the components of NPQ, drought increased the Y(NPQ) with concomitant decrease in Y(NO) only in P3939, whereas Y(NO) increased in drought-stressed plants of hybrid 30Y87 and 31R88. However, an increase in cyclic electron flow (CEF) around PSI and Y(NPQ) in P3939 might have protected the photosynthetic machinery but it did not translate in yield. However, drought-stressed plants of 30Y87 might have sufficiently downregulated PSII to match the energy consumption in downstream biochemical processes. Thus, changes in PSII and PSI activity and development of NPQ through CEF are physiological mechanisms to protect the photosynthetic apparatus, but an appropriate balance between these physiological processes is required, without which plant productivity may decline.

Zinc as a micronutrient is highly essential for animals and plants to attain optimum growth and development. Zinc-deficient soils result in stunted and abnormal growth of plants. Three wheat varieties, i.e., Zincol-2016 (biofortified), Galaxy-2013, and Punjab-2011 (both non-biofortified), were sown in pots containing fertile soil in a completely randomized design with four replicas. The seedlings were sprayed with four zinc solutions (Control, 0.03%, 0.06%, and 0.09% of Zn as ZnSO₄.7H₂O) 40 days after sowing. It was observed that the impact of 0.06% zinc spray was more pronounced on wheat plants as compared to that of 0.03% and 0.09%. More pronounced improvement in growth, chlorophyll content, total soluble proteins, and sugars was observed in cv. Zincol-2016 as compared to that in the other two varieties, Galaxy-2013 and Punjab-2011. Similarly, Zn foliar spray significantly enhanced root, straw, and grain K⁺, Cu²⁺, Zn²⁺, and Fe²⁺ contents in all three cultivars. In contrast, grain phytate contents were reduced with increased supplementation of Zn. Data revealed that grain yield was improved significantly by exogenous application of zinc, especially at 0.06% in all three wheat varieties, but being more promising in Zincol-2016. Furthermore, Zincol-2016 accumulated higher zinc contents in grains as compared to that in Galaxy-2013 and Punjab-2011. Foliar application of zinc resulted in higher uptake and accumulation of this element from soil to seeds, thereby resulting in improved vegetative growth.