Interaction of reserves and osmoprotection in dwarf cashew clones under water stress1

ABSTRACT Adverse conditions such as low rainfall have led to a reduction in cashew productive areas in the Brazilian Northeast region. The use of rootstocks and scions with characteristic metabolites associated with drought tolerance influences the plant responses. This study aimed to evaluate the interaction between energetic reserves and osmoprotection in grafted dwarf cashew clones under water restriction. The experiment followed a randomized block design, in a 4 × 4 factorial scheme, consisting of four irrigation levels (25, 50, 75 and 100 % of the crop evapotranspiration - ETc) and four scion/rootstock combinations: CCP76/CCP76 (self-graft of CCP76), CCP76/BRS226 (CCP76 grafted onto BRS226), BRS226/BRS226 (self-graft of BRS226) and BRS226/CCP76 (BRS226 grafted onto CCP76), with three replications. Measurements included scion and rootstock stem diameter, relative water content, leaf moisture percentage, membrane damage, carbohydrates, total free amino acids, total soluble proteins, glycine betaine, proline and ionic content. The CCP76/BRS226 combination was efficient under water-restricted conditions (25 and 50 % of the ETc), as evidenced by a significant reduction in the oxidative damages to leaf membranes and a concomitant increase in osmoprotectants such as total free amino acids and proline. Proline emerges as a potential molecular marker for drought tolerance in early dwarf cashew trees. The self-grafted BRS226 and the BRS226/CCP76 combination under the irrigation with 25 % of the ETc were the most affected, exhibiting greater membrane damage, lower foliar potassium accumulation, moisture content and relative water content, and are therefore not recommended under water-restricted conditions.