Response to Water Stress of Eight Novel and Widely Spread Citrus Rootstocks

Drought is a problematic abiotic stress affecting citrus crops in the Mediterranean basin and the rootstock plays a fundamental role in adopting adaptive mechanisms in response to water deficit. The aim of this study is to evaluate the response of eight rootstocks under three treatments imposed: control (100% of reference evapotranspiration, Et₀), 66% Et₀ and 50% Et₀. The rootstock genotypes studied were C35 citrange, Bitters, Carpenter and Furr which have been recently spread and so far, little investigated, while others have been widely used especially in the Mediterranean citrus industry, i.e., <i>Citrus macrophylla</i>, <i>C. volkameriana</i>, Swingle citrumelo and Carrizo citrange. Morphological analyses, leaf chlorophyll content determination, physiological measurement, proline accumulation, malondialdehyde determination and antioxidant enzyme activities were measured. The results exhibited that Bitters and Furr showed an increment in leaf area to reduce the effects of drought conditions. A decrement in gas exchanges and xylem water potential was noticed in Carrizo and C35 citrange at both water shortage treatments. Carrizo exhibited a significant increase in malondialdehyde at both stresses (90.3 and 103.3%, for 66 and 50% Et₀). Bitters and Furr performed better than the other rootstocks with regard to enzymatic and hormonal assays. Specifically, Bitters showed a significant reduction in CAT (−68.6%), SOD (−82.5%) and APX (−36.7%). Furthermore, Bitters and Furr were closely related to morphological parameters, e.g., leaf area and root length, and physiological measurements. <i>C. volkameriana</i> showed a decrease in xylem water potential, while overall Carrizo and C35 citranges showed a susceptible response to water stress reducing morphological and physiological measurements.