Elucidation of stage specific physiological sensitivity of okra to drought stress through leaf gas exchange, spectral indices, growth and yield parameters

Abstract

Timely irrigation at specific phenophases of crop plays an important role in agricultural water management. Understanding stage specific crop response to drought becomes important in formulating strategies to mitigate stress. Experiment was conducted to assess the sensitivity of okra in terms of growth, biomass partitioning, leaf photosynthetic parameters and spectral reflectance at different growth stages to stress exposure with known extent and duration of drought. Results revealed that vegetative and flowering stages are more sensitive to drought compared to late pod-filling stage. Drought stress affected the growth, biomass partitioning and gas exchange characteristics of okra. Significant (P < 0.001) reduction in relative water content (RWC) and membrane stability index (MSI) along with reduced leaf photosynthetic rate explains the possible membrane damage in okra affecting photosynthetic efficiency under drought stress at vegetative and flowering stages compared to stress exposure at late-pod filling stage. Correlation analysis reveals that photosynthesis (A), stomatal conductance (gs), transpiration (E), photochemical reflectance index (PRI), water index (WI), normalized difference value index (NDVI) closely followed MSI and RWC. Significant correlation of PRI with RWC and A justifies the sensitivity of PRI to pigment concentrations and photosynthesis. Conversely, water index (WI) was notably correlated to leaf transpiration (E). Dry matter partitioning and yield parameters have reconfirmed the reduction in pod yield of okra attributed to poor assimilate transport, membrane damage and associated with biochemical alterations during vegetative/flowering stage. In summary, stress detection based on physiological traits in okra could be used for devising water management strategies under future drought-prone climate.