Pod quality, yields responses and water productivity of okra (Abelmoschus esculentus L.) as affected by plant growth regulators and deficit irrigation

Water scarcity severely impacts agricultural productivity and quality in arid and semi-arid regions. Specific elicitors like plant growth regulators (PGRs) and bio-stimulants as well as deficit irrigation (DI) practices have been put forward to alleviate the effect of resultant water stress and enhance crop productivity. Hence, a field experiment was conducted for two years (2020-2022) to elucidate the effects of PGRs and bio-stimulants of organic and chemical origins under variable deficit irrigation levels on okra (Abelmoschus esculentus L.), a major crop grown in the semi-arid region of peninsular India. Treatments included combinations of the foliar sprays with PGRs i.e. irradiated chitosan (IC, 5 ml L-1), sea weed extracts (SWE, 5 ml L-1), thio-urea (TU, 600 ppm), salicylic acid (SA, 20 mu M), bacterial biopolymer (BP, 5 ml L-1) along with control (no PGR) and DI levels i.e. equalling 100 %, 75 %, 50 % and 25 % of the crop evapotranspiration (ETc). Irrigation levels were maintained using line source sprinkler (LSS) system. Reductions in pod yield (PY) and above ground biomass (AGB) ranged between 12 and 83 and 20-79 % with DI of 0.75-0.25 ETc. Exogenous foliar application of PGRs improved plant growth, physiological traits and thereby increased PY by 6.1-19.2 %. Beneficial role of PGRs for mitigating water stress was associated with cooler canopy temperatures, maintenance of higher leaf relative water content by modulating stomatal conductance, enhanced plant vigour and photosynthetically active surface. The lower values of yield response factors viz., KSWE <= 1 with SWE further indicated increased tolerance of okra to water stress. The maximum crop water productivity (CWP) was 3.43-3.79 kg m-3 with PGRs as compared with 3.32 kg m-3 without PGR. Especially PGRs of organic origin (SWE and IC) were more effective under medium to severe water stress conditions. The response to BP, bio-stimulant of bacterial origin was almost at par with SA. DI reduced physical quality attributes such as mean pod weight and pod length but firmness and seed/peel ratio got improved; the maximum being with 75 % ETc. Improved rehydration quality and higher accumulation of total soluble solids, dry matter, protein, total phenolics, and flavonoids that potentially affect enzymatic activity were monitored with PGRs. It is concluded that the exogenous foliar application of PGRs from organic origins such as SWE and IC in combination with low to moderate DI (50-75 % ETc) is optimal for improving production and post-harvest quality of okra grown in water-scarce areas of peninsular India.