Exogenous application of calcium chloride, 6-Benzyladenine and salicylic acid modulates morpho-physiological and tuber yield responses of sweet potato exposed to heat stress

Abstract

It is most elusive and challenging to sustain the productivity of sweet potato under extreme climatic scenarios. Heat stress is major abiotic stress affecting sweet potato productivity. One of the approaches to manage heat stress is to develop suitable and feasible agronomic strategies. With this objective, current experiment was planned to ameliorate heat stress tolerance in sweet potato with exogenous application of 6-Benzyladenine (0.1%; BA), calcium chloride (0.2%; CaCl2), salicylic acid (0.2%; SA) to compare the differences against water spray (control). Planting sweet potato under three different seasons (I, II and III) and three different growing conditions (OPEN, HUM+ and HUM-) significantly impacted morpho-physiological, biochemical and yield parameters. The highest mean tuber yield was recorded under season III followed by season II and I. Growing condition 2 (G2) i.e. polychamber structure with humidifier operated throughout the cropping period (HUM+) was the most suitable growing condition with the realization of the highest photosynthetic efficiency and tuber yield in comparison to open field (OPEN) and HUM- condition. Heat stress was induced in HUM- condition (polychamber structure with humidifier stopped during 2–3 months after planting). All the parameters declined significantly (P<0.0001) upon exposing plants to ∼32 to 37.5°C of heat stress (+2–6°C of stress as compared to OPEN and HUM+) under HUM- condition. The mean tuber yield reduced up to 18–44, 35–41 and 5–6%, under season I, II and III in comparison to OPEN and HUM+ conditions, respectively. Application of 0.2% CaCl2 had an improved effect on above-ground biomass, photosynthetic efficiency, biochemical parameters under heat stress resulting into 22–35 (season I), 20–28 (season II) and 13–22% (season III) of increment in mean tuber yield across different growing conditions in comparison to control. Further, a positive and significant relation was observed between leaf area index (r2=0.402), photosynthesis (r2=0.399), relative water content (r2=0.336) and harvest index (r2=0.398) with tuber yield. Evident from this study, application of CaCl2, 6-Benzyladenine and salicylic acid significantly ameliorated the negative effects of heat stress. Integration of this agronomic strategy into the future cropping system may enhance the resilience of sweet potato. Furthermore, there is a requisite to assess the efficacy of these chemicals across various ecosystems to develop location specific heat stress management strategy for sweet potato.