Plant Growth Regulators Mediated Changes in the Growth, Photosynthesis, Nutrient Acquisition and Productivity of Mustard

Plant growth regulators (PGRs) are naturally occurring signaling molecules that modulate numerous phenological traits and physicochemical features of plants throughout their life cycles. Exogenous supplementation of PGRs is an effective strategy for improving the productivity of important agricultural crops. This research was planned to evaluate the effects of six PGRs, namely indole-3-acetic acid (IAA), 24-epibrassinolide (EBL), gibberellic acid (GA3), putrescine (put), salicylic acid (SA) and triacontanol (Tria), on morphology, photosynthesis, nutrient acquisition, and the yield and quality characteristics of three mustard cultivars, i.e., Chutki, Nath Sona, and Rohini. Two foliar sprays each of water, IAA (10−6 M), EBL (10−6 M), GA3 (10−5 M), put (10−3 M), 10−5 M SA, and Tria (10−6 M) were applied to plants at fifty and seventy days after sowing (DAS). The crops’ phenological, physicochemical and microscopic parameters were evaluated at ninety DAS, and yield characteristics were evaluated at harvest (120 DAS). The observations of this study indicated that foliar feeding with PGRs increased all studied parameters, relative to water-spray treatment. The Nath Sona cultivar displayed a stronger response than Rohini and Chutki. Among the leaf-applied PGRs, 24-EBL, followed by IAA and GA3, proved the most effective and improved all the studied parameters. Moreover, the exogenous application of PGRs, especially EBL, significantly enhanced stomatal dimensions and root cell longevity. Treatment with EBL enhanced plant dry weight by 34.7, 35.4, and 37.6%, the net photosynthetic rate by 65.3, 64.7, and 60.2%, seed yield per plant by 67.1, 65.2, and 67.3%, and oil yield per plant by 42.6, 48.2, and 41.1%, in the Chutki, Nath Sona, and Rohini cultivars, respectively, relative to the water-spray treatment. It may be concluded that of the tested PGRs, 24-EBL proved most effective at enhancing the morphological, physicochemical, and yield features of the mustard cultivars.