Seleção de porta-enxertos de videiras e amenizantes como estratégias para reduzir a fitotoxidez por cobre

Abstract

Frequent applications of chemical products, such as phytosanitary treatment to prevent and control leaf fungal diseases in vineyards, can be responsible for soil contamination with high copper (Cu) contents. Excess Cu in the soil can cause crop toxicity and, consequently, productivity losses. Thus, it is necessary to develop remediation strategies for contaminated soils in order to minimize the harmful effects caused by excess Cu and maintain the viability and productivity of the cultivation areas. Among these management strategies is the cultivation of grape genotypes that present mechanisms of tolerance to toxicity and the application of amendments to reduce Cu availability. The objective of this study was to verify plant responses to high Cu concentrations, to identify grape rootstock genotypes tolerant to high Cu contents in solution, and to evaluate the potential use of softeners as a strategy to reduce Cu bioavailability and toxicity in young vines. Five studies were conducted. They were conducted under controlled conditions, in a growing room (Studies I and II) and a greenhouse (Studies III, IV and V). The soil used in the study V was collected in the Campanha Gaúcha, in Santana do Livramento (RS), while the other studies were conducted in nutritive solution. In study I, three concentrations of Cu (0.2, 5 and 50 μM) and three pH conditions (4.5, 6.0 and 7.5) were used in two plants (Cucumis sativus L. and Avena sativa cv. Fronteira). In study II, two grapevine rootstocks (Vitis rotundifolia cv. Magnolia and Vitis vinifera cv. Paulsen 1103) were cultivated in nutritive solution containing increasing concentrations of Cu (0.2; 20; 40 and 80 μM). In study III, different grapevine rootstocks (Paulsen 1103, IAC 572, SO4 and Isabel) were grown in standard nutritive solution and with Cu excess (80 μM). In study IV, the same grapevine rootstocks used in study III were cultivated in nutritive solution with the addition of amendments (phosphorus and calcium). In study V, a grapevine rootstock (Paulsen 1103) was cultivated in soil contaminated with Cu, with the application of amendments treatments (limestone and vermicompost). In all studies, parameters related to plant growth and nutritional parameters were determined. It has also been determined photosynthesis activity (Studies III, IV, V), chlorophyll a fluorescence (Studies II, III and V), concentration of photosynthetic pigments (Studies I, IV and V), biochemical analyses (Studies II and III), morphology of the root system (Studies I and V), and root exudates (Study I). All plants presented reduced growth parameters and nutritional changes, with increased Cu concentration in the root system, when cultivated under high Cu concentration conditions. Plants (Study I) grown in solution with 50 μM Cu and pH 4.5 suffered greater toxicity effect from Cu excess. However, there has been greater exudation of organic compounds, flavonoids and phenolic compounds, in these plants, which can act as a strategy to decrease the bioavailability and absorption of Cu by plants. Grapevine rootstocks showed changes in the structure and functioning of the photosynthetic apparatus and efficiency of photosynthetic activity, increased oxidative stress and synthesis of antioxidant enzymes, and changes in the morphology of the root system when cultivated under conditions of high Cu concentration. Paulsen 1103 and SO4 plants have tended to perform better with excess Cu in solution, which can be an alternative to growing in vineyard sites contaminated with Cu excess. The addition of Ca and P as amendments treatments in nutritive solution had a positive effect on the photosynthetic activity of all rootstocks in solution with high Cu concentration, however, it was not enough to promote changes in plant growth parameters. The application of limestone was efficient as a soil amendment for Cu phytotoxicity. On the other hand, the application of vermicompost as an amendment treatment was not an effective alternative, causing the death of the grapevines, which may be related to the phytotoxic effect by the excess of Cu and Mn available in solution. In this way, the use of integrated management strategies can favour the cultivation and maintenance of productivity in areas of vineyards contaminated by Cu excess.