Rice seedlings showed a higher heat tolerance through the foliar application of biostimulants

Abstract

The use of biostimulants is an agronomic tool to improve plant tolerance to abiotic stress in plants. This study explored the effect of foliar biostimulants sprays such as brassinosteroids (BR), amino acids (AA), nitrophenolates (NP) or a biostimulant based on botanical extracts (BE) on leaf gas exchange parameters [photosynthesis (PN), stomatal conductance (gs) and transpiration (E)], leaf photosynthetic pigments, lipid peroxidation of membranes and proline content of two commercial rice genotypes [‘Fedearroz 67’ and ‘Fedearroz 60’] under heat stress conditions. The established treatments were: i) plants without heat stress and foliar applications of biostimulants (C), ii) plants under heat stress and without foliar applications of biostimulants (HT), and iii) plants with heat stress and three foliar applications with BR (1 mL·L-1), AA (30 mL·L-1), NP (15 mL·L-1) or BE (15 mL·L-1). The results showed that the application of BR, AA, NP or BE increased the values ​​of PN (~14.5 µmol CO2·m-2·s-1), gs (~0.46 mmol·m-2·s-1) and E (~43.9 H20 day-1·plant-1) compared to plants (both genotypes) not treated with biostimulants under heat stress (9.9 µmol CO2·m-2·s-1 for PN, 0.31 mmol·m-2·s-1 for gs, and 27.3 H20 day-1·plant-1 for E). Foliar biostimulant sprays also caused a lower malondialdehyde and proline production in rice genotypes under heat stress. In conclusion, the biostimulants BR, AA, NP, or BE can be considered an agronomic strategy to help mitigate the adverse effects of heat stress in rice areas where periods of high temperatures are expected during the day in Colombia.