Thiourea application improves heat tolerance in camelina (Camelina sativa L. Crantz) by modulating gas exchange, antioxidant defense and osmoprotection

Heat stress can have devastating effects on agricultural production and crop productivity. This study was conducted to evaluate the effect of exogenously applied thiourea on heat stress tolerance through osmotic adjustment in camelina (Camelina sativa L.). The study comprised of three factors: i) Heat stress; HS₀ = 25 °C (control) and HS₁ = 35 °C (stress), ii) camelina genotypes; G₁ = 611 and G₂ = 618, and iii) thiourea; TU₀=control-no thiourea supplementation, TU₁=thiourea supplementation (1000 mg/L) at vegetative stage (BBCH (Biologische Bundesanstalt Bundessortenamt and Chemical Industry) two codes scale-31), and TU₂=reproductive stage (BBCH two codes scale-59). Heat stress caused a reduction in the growth, carbon assimilation, and chlorophyll contents with more so where no thiourea was applied. Heat stress also caused a significant increase in lipid peroxidation (measured by leaf malondialdehyde contents), hydrogen peroxide, and electrolyte leakage in plants not receiving thiourea application. In addition, dry matter per plant, photosynthetic rate, and seed yield was reduced by 32.7, 40.8, and 60.9 %, respectively under elevated temperature as compared with control-no stress. However, the foliage applied thiourea alleviated the adverse effects of heat stress in camelina applied either at vegetative or reproductive growth stage by protecting the photosynthetic pigments (chlorophyll a, b) which helped to maintain photosynthetic efficiency by (14 %) than no thiourea applications). Foliar-applied thiourea also reduced oxidative damage by upregulating the antioxidants such as catalase, protease, and ascorbate peroxidase, and by improving osmolytes i.e., total soluble sugars, total soluble proteins, proline, and glycine betaine. Seed yield was improved by 57.8 % due to thiourea supplementation under heat stress compared with no thiourea application. Among the stages, thiourea application at the reproductive stage was more effective than the vegetative. Genotype 618 has produced highest dry weight per plant, photosynthetic efficiency, antioxidant activity under heat stress relative to genotype 611. In conclusion, thiourea application (1000 mg/L) improved heat tolerance in camelina by modulating gas exchange, antioxidant defense, and osmoprotectant. Thiourea application at the reproductive stage was more effective than the vegetative stage and 618 was heat stress tolerant genotype compared with genotype 611 which was relatively sensitive to heat stress.