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 Agropecuaria de Minas Gerais (EPAMIG), young plants of two genotypes [07 and 19] were compared with two commercial cultivars [Catigua MG3 and Catuai Vermelho IAC 144] challenged to drought, followed by rehydration. By integrating results of xylem water potential and response curves of photosynthesis to CO2 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 CO2 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.

Automated summary

The study compared the responses of two potential genotypes and two commercial cultivars to drought and water recovery, and determined the drought tolerance strategies of the new genotypes by measuring root anatomy and photosynthetic parameters. The results showed that the new genotypes enhanced drought tolerance by increasing root hair number and adjusting root structure. Despite the reduction of photosynthetic parameters under drought conditions, the genotypes showed higher photosynthetic efficiency after water recovery.