Photosynthetic efficiency and root plasticity promote drought tolerance in coffee genotypes

The plant breeding programs (PBP) of coffee plants ( Coffea arabica L.) are always looking for new genotypes that perform better under water deficit. The ability of coffee trees responding to water stress is important for drought tolerance. In the search for drought tolerance strategies of promising genotypes in the PBP of the Empresa de Pesquisa Agropecuária de Minas Gerais (EPAMIG), young plants of two genotypes [07 and 19] were compared with two commercial cultivars [Catiguá MG3 and Catuaí Vermelho IAC 144] challenged to drought, followed by rehydration. By integrating results of xylem water potential and response curves of photosynthesis to CO 2 and light with root anatomy, it was possible to identify the drought tolerance strategy of the new genotypes. Under water deficit conditions, the genotype 07 showed an increase in the number of root hairs and reductions in the root cross-section area, cortex thickness and tracheary element diameter, whereas genotype 19 showed an increase in the vascular cylinder area, in number of metaxylem poles and in number of tracheary elements. Despite the reduction of photosynthetic parameters under water deficit, the genotypes 07 and 19 showed higher values of maximum CO 2 assimilation after the rehydration period. The drought tolerance in genotypes 07 and 19 was induced by a greater root plasticity, which increased hydraulic conductivity under water deficit, contributing to the restoration of photosynthetic efficiency after the return of water availability.