Effect of naphthyl acetic acid foliar spray on the physiological mechanism of drought stress tolerance in maize (Zea Mays L.)

Owing to climate change, there has been an alarming increase in drought conditions, which has led to an expected increase in the loss of water in soil and water bodies. Moreover, the concomitant climatic disasters are causing severe crop losses worldwide. The designed experiment is aimed to determine the potential effect of naphthyl acetic acid (NAA) foliar spray and how it neutralizes the adverse effects of different drought stress levels (5d, 7d, 10d, 12d and 15d drought) on two maize varieties namely Pakhari and Jalal. A pot experiment was conducted in the Department of Botany, Bacha Khan University Charsadda, during the maize growing season in 2014. Results indicated that the drought-sensitive variety Pakhari is markedly affected, as observed from their reduced level of antioxidant enzymes including peroxidase, superoxide dismutase and catalase along with osmoprotectants including proline and sugar content at the lowest drought stress level of 5 days compared with that observed in the drought-tolerant variety Jalal. Furthermore, a marked decrease in the leaf water status 0.05-0.415 g(-1), chlorophyll and carotenoid contents are associated with an increase in the accumulation of sugar, proline and antioxidant enzyme activities under drought stress. Analysis of variance between genotype, drought stress and NAA treatment was performed, and the results were considered significant at p<0.05, except for the germination rate index (GRI), total biomass (TB), carotenoid content (CC), seed vigor index (SVI-II), soluble protein content (SPT) and superoxide dismutase (SOD). Variance analysis was performed to examine the interactions between drought and NAA treatment,and the results were found to be significant at p < 0.05 for seed vigor index (SVI-I, SVI-II), root-shoot ratio (RSR), leaf area index (LAI), leaf area ratio (LAR), TB, chlorophyll 'a' (CA), chlorophyll 'b' (CB), CC, peroxidase (POD) and SOD content under high drought stress (15d) irrespective of SVI-I, CB, POD, SOD, RSR, CB, SSC and SPC under low drought (5d) conditions. It has been concluded from the obtained results that maize varieties exhibit tolerance when subjected to low levels of drought stress; however, high drought stress (15d) reduces crop yield via high osmotic potential, which poses an alarming threat to Pakistani agriculturists in the forthcoming climate change.