Caracterização fenotípica em híbridos de milho sob déficit hídrico

Abstract

The water deficit in mesophyte plants, like maize, can compromise the development of the plant depending on the intensity, duration of the restriction period and also the genotype considered. However, observed differences between maize cultivars growing under restrictive water conditions in several regions of the world suggest that this feature can be improved. In the studies that involve maize phenotyping under drought conditions, physiological and morphological indicators have been evaluated in aerial organs, as well as yield in biomass and grains. Despite the recognized importance of roots in the exploration and acquisition of soil resources by the plant, few studies have been conducted with the objective of measuring the relationship between root system characters and water exploitation by maize roots. The present work, in two parts, explores this field of research from the cultivation of hybrids BRS1010, BR1055 and DKB390 growing in pots under two distinct water regimes: water restriction from the fourth day of sowing and water comfort from the sowing until the harvest of the plants. When the maize reached the V5 stage, the plants were harvested, registering shoot indicators, followed by the removal of the substrate adhered to the roots, and later scanning and characterization of the roots by the WinRHIZO system. In the first chapter, the objective was to evaluate aerial part and root system indicators with contrasting response to restricted and comfort cultivars in the evaluated hybrids, using the univariate analysis. Multivariate analysis was also performed with application of main components to group variables that best express the difference between the treatment factors: hybrids and water regime. SPAD index, leaf temperature, stem length, aerial dry biomass, D95, root surface area and root volume showed contrasting responses between water regimes. The analysis by canonical variables revealed that SPAD index, phenology, leaf temperature and mean root diameter explain, jointly, differences between the hybrids in the water regimes studied. The chapter two characterizes the root system of the plant at different depths, aiming to know if the architecture and development of roots at 10 cm depth express differences in response to the water regime in the studied hybrids; another objective was to evaluate the root length density in the root system profile, as well as to identify the group of variables that analyzed together, explain the differences obtained between the water regimes in the evaluated hybrids. For this, when they reached the V5 stage, the root system of the plants was sectioned in consecutive fractions of 10 cm in height. From each fraction an aliquot with 100 cm3 volume composed of soil and roots was extracted, from which the wet and dry mass was extracted. The roots from each fraction were then washed, scanned and characterized in the WinRHIZO system for root length density (DCR - cm cm- 3), root surface area (ASR - cm2) and mean root diameter (DMR - mm) and root volume (VR - cm2). The dry biomass (BS) was then dried and greenhouse determined. The number of root nodules (NRS), nodal roots insertion angle in the first (RNAV1) and second (RNAV2) verticils, and the number of nodal roots in the first one were evaluated in the fraction that housed the mesocotyl, after careful root washing. (RNV1) and second (RNV2) whorls, and the number of verticils in mesocotyl (NVM). Only the nodal roots expressed developmental variation in response to the water regime employed. Depending on the hybrid, differences in the architecture (ARNV1, ARNV2, NVM) and root development (BS, DM, DCR, ASR) were observed according to the water regime employed. DKB390 conducted under water restriction showed higher RNAV1 and lower RNV2. DKB390 expressed the lowest DCR at the different depths among the evaluated hybrids, regardless of the water regime. In the joint analysis, ARNV1, ARNV2 and NVM were the characteristics that best explained the variation obtained in the corn root system under water deficit in comparison to comfort.