Restrição hídrica induz crescimento de sistema radicular em mudas de Coffea arabica L. tolerantes à seca

Abstract

Drought stress damages coffee plants in all growth stages, especially just after transplantation to field. Identify strategies of drought stress tolerance in genotypes of Coffea arabica, may supply useful information for plant breeding selection programs, aiming to improve productivity even under repeated drought events. Considering this, the present study aimed to test two different materials from Plant Breeding Program of EPAMIG. These genotypes, G07 and G19, which had showed drought tolerance under field conditions, were tested. As a reference, we compared to other genotypes highly exploited in Brazil, namely Catiguá and Catuaí. All young plants of the four different materials were planted in rizotron, with capacity of 22L, aiming to evaluate and characterize the root morphology and growth during periods of drought and rehydration. The experimental design was randomized blocks [4x3; four genotypes and three water conditions, considering n = 4] regarding two samplings, resulting in 96 plants. The plants were kept under three water conditions: reference (no water restriction); subjected to a single water restriction cycle and subsequent rehydration; and two water restriction cycles followed by rehydration. For each treatment, two destructive sampling were performed: one under the stress phase and one after rehydration. During the experiment the following parameters were evaluated: water potential, relative water content, gas exchange, biometric parameters, soluble and insoluble carbohydrates in the leaves and roots, and growth and morphology of the root system. For the last parameter, images taken from rhizotron were analyzed with ArcGIS® software. Drought stress induced a reduction in water potential and relative water content for all four genotypes, as well as a reduction in photosynthesis, transpiration and stomatal conductance. Biometric parameters were similar between Catiguá, G07 and G19, however, Catuaí presented changes in the formation of new shoots at the base of the plant, comparing the treatments with water restriction to the reference treatment. Genotypes G07 and G19 showed better performance than the reference genotypes in response to the water restriction cycles, demonstrating greater root system development and dry matter maintenance. This suggests that early tolerance characteristics expression, mainly in the first year after transplantation, may be used in plant breeding selection, once a greater root development is a highly desirable trait in improvement of Coffea arabica.