Physio-Biochemical and Growth Response of Contrasting Reciprocal Grafting in Citrus Under Water Deficit and Rehydration

The present study investigated how contrasting citrus rootstocks, drought susceptible, Citrus jambhiri Lush cv. Jatti Khatti (JK) and drought-tolerant, X639 (C. reshni Hort. ex Tan. × Poncirous trifoliata), responded to water deficit and re-watering through reciprocal grafting. Self-graft JK showed the most declines in scion growth traits, the highest wilting score and drought injury index and a higher increase in leaf proline content compared to self-graft X639. JK/X639 witnessed a lesser decline in growth, the lowest wilting score and drought injury index among reciprocal grafts after experiencing water deficit as of normal moisture conditions. The plant combinations where X639 was used as rootstocks displayed good recovery in scion growth after re-watering. The root growth traits significantly improved in self X639/X639. The total phenol increased more in self-graft X639 and hetero-graft X639/JK after experiencing water deficit over respective normal moisture conditions. The X639, as scion or rootstock, was able to moderate lipid peroxidation significantly as compared to self-graft JK. Auto-graft X639 and hetero-graft X639/JK exhibited a higher decline in thiobarbituric acid reactive substances (TBARS) content, catalase, and glutathione reductase activities after re-watering. X639 rootstock prioritised growth, displaying the development of a vigorous root system under water scarcity, attributed to elevated relative water content, membrane stability index, and a robust antioxidant system in both self and reciprocal grafting. Conversely, JK focused on survival indicated by leaf shedding and reduced leaf area. These findings offer insights into citrus rootstock responses to water stress, valuable for citrus cultivation in regions with varying water availability.