Comparação de variedades de cana-de-açúcar durante a fase de estabelecimento em cultivo irrigado e sequeiro

Abstract

The objective of this research was to evaluate the response of four sugarcane varieties (Saccharum spp.) In the formative phase of the crop submitted to two irrigated and irrigated water regimes, while simultaneously identifying the parameters of adaptability and phenotypic stability. Varieties that have a better adaptation to the conditions can represent gains of up to 30% in the agribusiness productivity of the sugarcane plantations, so that for each type of cropping system there are more adapted genotypes, so the researches with the objective of identifying varieties more tolerant to stress Water. Environmental factors such as water scarcity is a problem that affects many of the world's cultivated areas, especially those located in semi-arid regions, reducing plant growth and production, causing socioeconomic losses. Water deficiency compromises the metabolism and, consequently, the growth, development and productivity of the crop. Evidence indicates that drought causes oxidative stress, as a result of the formation of reactive oxygen species (ROS), producing radicals such as superoxide (*O2-), hydroxyl radical (*OH-), hydrogen peroxide (H2O2), and Singlet oxygen (1O2). These ROS are byproducts of aerobic and photosynthetic metabolism where they are maintained at concentrations compatible with cellular homeostasis, however, the excess of these ROS cause oxidative damage in proteins, lipids and nucleic acids, which characterizes oxidative stress. In order to reduce the cytotoxic damages of ROS, the plants disentangle a complex antioxidative system where specific enzymes neutralize the action of these radicals, among them ascorbate peroxidase (APX, EC 1.11.1.11) and catalase (CAT EC 1.11.1.6). As is known, the great majority of genotypes present different behaviors in relation to the different cultivation environments. Because of this, it is essential to identify genotypes of predictable behavior and responsive to environmental changes for broad or crop specific conditions. It is very important to identify genotypes that show predictable behavior and respond to environmental changes for broad or crop specific conditions. Conventional breeding is still the main means of obtaining improved varieties. The search for varieties with broad adaptability and good stability involves the use of methods that can provide more accurate estimates of the parameters of adaptability and stability, so that the evaluation methodology is easy to interpret, using few statistics, but That is reliable and can be used for both small and large environments. The experiment was carried out by the sugarcane microregion of Miriri Alimentos and Bioenergia S / A, in Santa Rita (PB). The statistical design used was in a factorial involving 4 varieties and 2 water regimes, the research was conducted up to 150 days after planting (DAP), biometric data, leaf area index (FF), stem height (AC), number of stems per linear meter (NC) and stem diameter (DC) and for oxidative stress tolerance parameters, the activities of the antioxidative system, ascorbate peroxidase (APX), and catalase (CAT), The contents of the reactive oxygen species (ROS), hydrogen peroxide (H2O2) and malondialdehyde (MDA). For the evaluation of the adaptability and stability, the methodology was based on the analysis of joint variance of the experiments, considering all the environments and the posterior unfolding of the sum of squares of the effects of environments and interaction genotypes x environments, having the advantage of auxiliary In the recommendation of the varieties, observing the risk of performance below a given standard, such as the general average, where the higher the variety confidence index, the lower its likelihood of failure. For the biometric parameters, the RB867515 and RB92579 varieties presented higher averages during the research, where they also showed high efficiency in the antioxidative system, that is, for the CAT and APX enzymes, with a reduction in H2O2 and consequently MDA levels. These same varieties also presented higher stability indices, so it can also be verified that the irrigated regime as the water condition more favorable to the development of sugarcane. Both the RB867515 and RB92579 varieties, have proven their high performance in relation to development, proving the preference for the use of these varieties in the sugar cane market of the Northeast region.