Descritores fisioquímicos para a seleção de variedades promissoras de cana-de-açúcar quanto a tolerância ao déficit hídrico

Abstract

The aim of this work was to select promising varieties to water stress based on physiological parameters, biochemical and productivity. To this end, two experiments were conducted, one in greenhouse condition and another in field conditions. The experiment, the greenhouse experiment was completely randomized in a factorial 6 x 2 corresponding to six varieties of sugarcane (RB98710, RB962962, RB92579, C90-176, C90-178 and RB72454) and two treatments , daily irrigation (control) and suspension of irrigation (no irrigation). As for the field experiment, the experimental design was a randomized block consisting of eight installments, corresponding to the eight varieties (RB92579, RB867515, RB863129, RB962962, RB972631, RB002504, RB992506 and C90-176), grown in conditions irrigation rescue and dry. the physiological variables of gas exchange were evaluated, photosynthetic pigments and water relations, biochemical analysis to determine the carbohydrate content, proline and total amino acids for the greenhouse experiment, besides the growth analysis, total soluble protein and productivity for the field experiment. The collections for the analyzes were carried out after 24 h and 72 h after stopping irrigation for home experiment of vegetation and after 3, 6 and 10 months of cultivation in the field experiment, in addition to productivity after 11 months. The physiological variables were overall quite heavily in varieties of sugarcane at home conditions of vegetation, and in the field. However, the C90-176 variety stood out among those studied in a greenhouse, not to present changes in its gas exchange, water relations and efficiency of water use, and present significant accumulations of carbohydrate concentration in leaves and proline, roots after 24 h of stress, indicating greater tolerance to water deficit of short duration. And RB962962 variety was considered the most sensitive to water deficit by reducing gas exchange early in the stress, and presents reduction in leaf water potential and efficiency of water use after 72 h. In addition, this strain showed significant reductions of the proline content in leaves and roots after 24 h of water removal, which can lead to an oxidative damage plants in greater exposure to stress. As for the experiment conducted under rainfed conditions in the field, it observed a possible osmotic adjustment of RB92579 varieties RB867515, RB962962 and RB972631, with the accumulation of amino acids and proline, which linked to the partial closing of the stomata indicated RB92579 variety as more tolerant to drought, since even with all varieties representing a reduction in their productivity, this variety showed lower reduction (20%) compared to RB972631 not presented stomatal closure and reduced their productivity by 38%, and is considered, therefore, the most sensitive. The contrast of the responses to dryland farming through irrigation suspension, short or long term, presented in varieties indicated as tolerant and sensitive to drought is promising to assist in breeding programs. Therefore it presents the way of more efficient responses in order to provide greater tolerance of sugarcane drought and contributes to expanding the potential of already cultivated varieties or the development of new varieties recommended for regional crops.