Morphophysiological characteristics of sunflower genotypes under water deficit

Abstract

Sunflower (Helianthus annuus L., Asteraceae) is a plant classified as drought tolerant. However, its productivity is affected under water deficit conditions, depending on the reproductive stage and duration of water limitation. Therefore, it is essential to investigate characteristics that attribute sunflower tolerance or susceptibility to controlled water deficit, contributing to crop genetic improvement programs. This study evaluated morphological, anatomical, physiological, and biochemical characteristics in four sunflower genotypes under controlled water deficit. The experiment was developed in a 2×4 factorial scheme (two water conditions and four sunflower genotypes), distributed in six replicates, with one plant per rhizotron-type pot, totaling 48 plants. The water conditions were well-irrigated plants (field capacity) and water deficit (40% of field capacity). The sunflower genotypes tested were OLISUN03, AGUARÁ06, BRS323, and HÉLIO250. Water deficit reduced development and dry masses of the aerial part and roots of sunflower genotypes. Changes in stomatal morphology and density occurred in the water deficit condition, reflecting a reduction in stomatal conductance, transpiration, and intercellular CO2 concentration. Under these conditions, there was better water use and instant carboxylation efficiency and an increase in leaf proline content, intercellular spaces of the palisade parenchyma and substomatal chamber (AGUARÁ06 and BRS323), and collenchyma area (OLISUN03, BRS323 and, HELIO250) in the leaves. The OLISUN03 and BRS323 genotypes also have a narrow and deep root system architecture under water deficit. Furthermore, under water deficit, the OLISUN03 and AGUARÁ06 genotypes reduced the endodermis's thickness and the area of the vascular cylinder in the roots. The four sunflower genotypes have strategies for absorbing water available in the soil, evidenced in root morphoanatomical characteristics and leaf anatomical modifications, contributing to physiological efficiency. Therefore, a set of characteristics attribute tolerance to sunflowers' water deficit, contributing to the crops' genetic improvement programs.