Ecofisiologia de milho tolerante a seca em competição com senna obtusifolia l. sob déficit hídrico

Abstract

Soil water scarcity is an increasingly common situation in rainfed crops in Brazil and can lead to reduced plant growth and production. This situation can be further aggravated by the emergence of weeds and the establishment of competition for growth resources, such as water. This study evaluated the influence of competition between the drought-tolerant UFT Robusto corn variety and the weed Senna obtusifolia, as well as the effects of water deficit on the physiological behavior of corn. The study was conducted in a nursery at the Federal University of Tocantins, using a randomized block experimental design with 4 replications. The treatments were arranged in a 3x4 factorial scheme. The first factor was water management: 80% (control), 60% and 40% of field capacity (f.c.). The second factor was the densities of weeds coexisting with corn (0, 2, 4 and 6 Senna obtusifolia plants). which varied according to water availability conditions and weed density. Water deficit was established at the V3 stage of corn and from the date of irrigation suspension, the plants were subjected to the following evaluations: stomatal conductance (gs; μmol H2O m-2 s -1), transpiration (E; mmol H20 m-2 s -1) and net photosynthetic rate (A; μmol CO2 m-2), performed daily until the CO2 assimilation rates of the plants subjected to water deficit were similar to those of the irrigated plants. Through the physiological data, the quantification of carboxylation efficiency (A/Ci) (μmol.m-2.s-1) and instantaneous water use efficiency (EUA) (A/E) [(μmol m-2 s-1) (mmol H2O m-2 s-1)-1] and intrinsic carboxylation efficiency (E/Ci) [(mmol H2O m-2 s-1)-1/(μmol.m-2.s-1)] were performed. At the end of the experiment, the following were evaluated: plant height, shoot dry biomass, root dry biomass, root volume, water potential and proline. The corn variety maintained high levels of CO2 assimilation, stomatal conductance and transpiration, even under adverse conditions. Although the increase in plant density caused a reduction in corn root biomass, shoot development was not significantly affected. Furthermore, the most severe water management, corresponding to 40% of field capacity, was proven to result in greater water use efficiency, demonstrating the adaptive capacity of the genotype to the limiting conditions of the cerrado. The increase in proline concentration in the leaves suggests an adaptive physiological response to water stress, reflected in the adjustment of leaf water potential. Thus, it is concluded that UFT Robusto corn exhibits tolerance to both water deficit and competition with Senna obtusifolia.