Drought induced alterations in the physiological traits of novel citrus hybrids

This study focused on the response of citrus rootstocks under 28 days long induced drought stress followed by rewatering for 14 days. In the present investigation, nine rootstocks including four own developed rootstocks (CRH 21-9, CRH 21-13, SCSH 9-19 and SCSH 17-12), Kinkoji, Cleopatra mandarin, Shun Chu Sha, US-812 and X639 were studied. Visual screening of genotypes exhibited significant variations in respect of drought injury and wilting scores, being most sense in SCSH 17-12 and Cleopatra mandarin, while X639, CRH 21-13 and US-812 remained largely unaffected. Leaf traits exhibited substantial variability among genotypes, with X639 showing higher leaf counts and lower expressions of yellow, rolled, and scorched leaves. Drought stress adversely affected growth traits, inhibiting shoot length increment, and causing reductions in stem diameter and leaf area, and particularly impacted most the SCSH 17-12, SCSH 9-19, and Cleopatra mandarin. Physiological assessments revealed pronounced reductions in relative water content, membrane stability index and highest canopy temperature under drought stress in SCSH 17-12. Moreover, chlorophyll fractions, carotenoid content and leaf gas exchange parameters tended to decrease in susceptible genotypes (SCSH 17-12, SCSH 9-19, and Cleopatra mandarin) than tolerant genotypes (X639 and CRH 21-13). Also, most of the stomatal parameters decreased in SCSH 17-12 showing significant reductions in density, conductance index, and stomata area, while Cleopatra exhibited pronounced decrease in pore area and increased number of closed stomata, however, limited reduction was noticed in tolerant genotypes like X639 and CRH 21-13. Subsequently, rewatering efforts demonstrated a positive trend towards recovery across all genotypes. Overall, the study sought to the significance of drought-resilient genotypes to secure food production in the context of water scarcity.