Abstract
Sunflower is classified as a moderately drought tolerant crop. Genotypic variations and water availability are factors that influence the root development of the crop, which is important for water absorption in deep regions of the soil. Therefore, tests in controlled water deficit environments allow evaluating a set of morphoanatomical characteristics of the root system that attribute tolerance to water deficit, contributing to sunflower genetic improvement programs. The objective of this study was to identify a set of root morphoanatomical characteristics of four sunflower genotypes subjected to controlled water deficit. We tested four commercial sunflower genotypes (OLISUN03, AGUARÁ06, HELIO250 and BRS323) under well-irrigated (field capacity) and water restriction (40% of field capacity) conditions, completely randomized design with six replicates was applied, grown in rhizotron pot, allowing to evaluate root development through imaging and anatomical characteristics related to water absorption in different regions of the sunflower root system. Plants under water deficit showed changes that contributed to water absorption in different positions of root development. Under water deficit, the tissue differentiation occurred first near the root apex, while at field capacity differentiation occurred close to the root base. In the condition of water deficit, it was verified narrow root system architecture (RSA) for the genotype OLISUN03, deep RSA for BRS323, reduced endoderm thickness in OLISUN03 and vascular cylinder area in AGUARÁ06. In general, water deficit promoted changes in the morphological and anatomical characteristics of the root system. Morphological and anatomical modifications of the root system contribute to the anchoring and absorption of water and nutrients in places with little water availability in the soil.