Metabolic responses to drought stress and rehydration in leaves and roots of three Citrus scion/rootstock combinations

Drought is one of the most destructive environmental challenges for agriculture, and citrus trees are cultivated in semiarid areas. The current study used physiological and untarget mass spectrometry analysis to assess the differential response to drought and rehydration in leaves and roots of three scion/rootstock combinations in which the same scion Valencia Orange was grafted onto three different rootstocks, namely, 'Rangpur Lime', 'Sunki Maravilha' and 'Sunki Tropical', known to have a different response to drought. The main question to be answer was whether the soil disease tolerant 'Sunki Tropical' could be used as alternative to the drought tolerant/disease susceptible rootstock 'Rangpur lime' to cultivate citrus in semiarid areas. Thirty-seven metabolites in leaves and forty-six in roots, mainly amino acids, as well as a few carbohydrates and organic acids were found differentially expressed after drought and/or rehydration in the three combinations. Overall, the results demonstrated that the three scion/rootstock combinations responded differently at metabolite levels to water changes. The few leaf metabolites found in the scion grafted on 'Rangpur Lime' and 'Sunki Maravilha' support the respective drought avoidance and tolerance strategy, already observed in those rootstocks.'Rangur Lime' and 'Sunki Tropical' shared at roots levels several common drought response mechanisms. Moreover, the high number of differential metabolites triggered in the scion by 'Sunki Tropical' seems to be useful for overcoming the drought effects without depleting the fruit quality. From our data, we argue that 'Sunki Tropical' is a drought tolerant genotypes that could be used as alternative to 'Ranpur Lime' to sustain citrus production in semiarid areas.