Differential response of quinoa genotypes to drought and foliage-applied H₂O₂ in relation to oxidative damage, osmotic adjustment and antioxidant capacity

Quinoa (Chenopodium quinoa Willd.), a highly nutritious grain crop, is resistant to abiotic stresses (drought, salinity, and cold) and offers an alternate crop to endure harsh environmental conditions under the face of climate change. Naturally, quinoa genome displays a wide degree of variabilities in drought tolerance strategies. Therefore, the present study was designed to investigate drought tolerance variations and stress tolerance enhancement in four quinoa genotypes (Pichaman, Colorado-407D, IESP and 2-Want) thorough foliage-applied H₂O₂ with the purpose of identifying suitable genotype for water limited environments. The plants were exposed to two watering regimes (75% and 30% pot WHC) and foliage-applied H₂O₂ treatments (15 mM). The drought stress significantly reduced plant growth, relative water contents, chlorophyll and carotenoids contents and increased ROS production (H₂O₂ and O₂ ^•−) resulting in higher oxidative damage in all quinoa genotypes. Besides, drought stress significantly enhanced the antioxidants (SOD, PPO, and PAL) activity, total soluble sugars, proline, AsA contents and increased the total accumulation of measured inorganic ions in all quinoa genotypes. The PCA analysis indicated that parameters related to osmotic adjustment and antioxidant capacity were more pronounced in 2-Want and IESP genotypes, while parameters depicting oxidative damage were higher in Colorado-407D and more specifically in Pichaman. However, foliage-applied H₂O₂ effectively improved the osmolytes accumulation, antioxidants activity and K⁺/Na⁺ ratio which increased water relations, reduced lipid peroxidation and ultimately resulted in higher plant growth. Overall, 2-Want and IESP genotypes were found relatively more drought resistant, while exogenous application of H₂O₂ can be opted for more improvement in osmotic adjustment and antioxidant system, which may further enhance drought tolerance, even in sensitive genotypes of quinoa, such as Pichaman.