Naphthalene Acetic Acid Mediated Morphological and Biochemical Changes in Squash [Lagenaria siceraria (Molina) Standl.] Under Alkaline Stress

Alkaline stress promotes ionic toxicity and ultimately reduce plant growth and yield. Cucurbita pepo is an annual plant of the family cucurbiteacea and moderately sensitive to alkalinity but limited literature is available on the use of plant growth regulators to alleviate alkali stress in C. pepo. In this study, a pot experiment was carried out to study the effect of foliar application of NAA (0, 50, 75, 100 ppm) on C. pepo growth, yield and biochemical parameters under control and alkaline stress conditions (0,40 mM), respectively. The results showed that, alkali stress prominently reduced the plant growth, biomass, leaves and fruit count but NAA application enhanced all growth and yield attributes both under stress and non-stress conditions. Further, alkaline stress significantly reduced the photosynthetic pigments but 75% NAA application increased Chl a by 43%, Chl b by 53% and carotenoids by 66% compared to only salt treated plants. In addition, a significant improvement in plant primary and secondary metabolites such as total soluble proteins by (27%), total free amino acids by (38%), total phenolics and flavonoid contents by 28% and 27%, respectively as compared to only stress treated plants. To further investigate the effects of NAA on antioxidant enzymes, catalase (CAT) and peroxidase enzyme activities (POD) were calculated and results showed that alkali stress increased the enzyme activities while under the foliar applied NAA in stress conditions further enhanced these enzyme activities compared to only stress treated plants. These findings suggests the positive role of NAA exogenous application under alkali stress conditions to mitigate harmful effects of stress on C.pepo.