A comprehensive analysis of the physiological and biochemical responses of raspberry cultivars to water stress

Drought tolerance mechanisms are crucial for global crop production under increasing water scarcity. It is important to understand these mechanisms in raspberry (Rubus idaeus L.) cultivars to support their water-limited stress tolerance. This study assessed the physiological, biochemical, and leaf morphological responses of two commercial cultivars, 'Diamond Jubilee' and 'Jade', across two seasons (2022 and 2024) under controlled irrigation: full irrigation (100%), moderate drought (50%), and PEG-induced osmotic stress in 2022 and two treatments (100% and PEG) in 2024. The responses were significantly influenced by both genotype and treatment. Under PEG stress conditions, 'Jade' maintained superior water status with RWC of 48.1% in 2022 and 66.7% in 2024 compared to 'Diamond Jubilee' (56.0% in 2022 and 32.4% in 2024), representing 37.4% reduction vs 63.8% reduction relative to their respective controls, indicating greater physiological stability. In contrast, 'Diamond Jubilee' showed stronger biochemical responses, with proline increasing from 0.037 to 0.114 μmol/g (1,171% increase) and peroxidase activity rising from 24.4 to 93.9 U/g/min (284.8% increase) in 2022, suggesting enhanced antioxidant defense through multiple enzymatic and non-enzymatic components. Both cultivars accumulated soluble sugars under drought stress, with glucose content increasing from 2.56 to 4.25% (66.0% increase) in 2022 and from 2.59 to 3.09% (19.5% increase) in 2024, indicating osmotic adjustment mechanisms. Total phenolic content increased from 432 to 620 mg GAE/100 g (43.6% increase) in 2024 under PEG treatment. Organic acid analysis in 2024 revealed cultivar-specific responses: citric acid increased from 4.41 to 7.10 mg/g DW (61.0% increase) in 'Diamond Jubilee' and from 2.83 to 3.77 mg/g DW (33.2% increase) in 'Jade', while ascorbic acid was completely depleted from 0.31 and 0.21 mg/g DW to 0.00 mg/g DW in both cultivars. Oxalic acid showed contrasting responses, increasing from 2.54 to 3.33 mg/g DW in 'Diamond Jubilee' but decreasing from 4.12 to 3.60 mg/g DW in 'Jade'. Principal Component Analysis captured 77.1% of variance in 2022 and 90.2% in 2024, clearly separating cultivars and treatments. Based on superior water retention capacity and maintenance of photosynthetic efficiency across both years, 'Jade' demonstrated greater physiological resilience, while 'Diamond Jubilee' showed enhanced metabolic plasticity through active osmotic and biochemical stress responses. These findings highlight key traits-relative water content, proline accumulation, phenolic compounds, peroxidase activity, and cultivar-specific organic acid profiles-that can support drought-tolerant raspberry cultivar selection in breeding programs.