Exploring the effects of drought and salt stress on physiology, leaf reflectance, and growth dynamics of Brassica carinata

Drought and salt stress are two major abiotic factors that limit crop productivity worldwide. However, our understanding of the physiological mechanisms and growth responses that enable plant tolerance to these stressors is limited, hindering improvements in carinata (Brassica carinata A. Braun) production. To enhance our understanding of the physiological mechanisms governing stress adaptation in carinata, we evaluated 14 genotypes under early-season drought and salt stress conditions. We analyzed physiological, biomass, and reflectance traits three weeks after the onset of these stress conditions. Drought and salt stress resulted in significant declines of 76 % and 35 % in stomatal conductance, which were correlated with elevated canopy temperatures. Biomass production was severely affected, with total biomass decreasing by 73 % under drought conditions and 38 % under salinity conditions. Spectral reflectance-derived vegetation indices revealed shifts in canopy greenness, with indices such as the Wide Dynamic Range Vegetation Index showing a 67 % decline under drought and a 49 % decline under salt stress, respectively. Principal component analysis showed that these spectral indicators clustered with physiological traits, highlighting their potential as non-destructive tools for monitoring stress responses. Genotypic responses varied; AX19028 conserved water by reducing growth, whereas AX19026 maintained growth through water-conserving strategies. Stress response indices revealed that traits relating to physiological responses were associated with drought tolerance (R² = 0.66) and salt tolerance (R² = 0.85) followed by biomass and growth-related traits. This research addresses knowledge gaps regarding carinata's physiological responses to drought and salt stress and provides a framework for selecting genotypes with optimized resource allocation strategies under stress.