Indução de estresse salino e hídrico in vitro em bananeira: abordagem fitotécnica, fisiológica e biotecnológica

Abstract

Abiotic stresses are among the most limiting factors of plant growth and productivity, being salinity and water deficit the main factors responsible for this limitation. Banana plant is among the main crops produced in the world and is the main tropical fruit grown in the national territory. Understanding the physiology and biochemistry of this plant in relation to stress tolerance mechanisms, also identification of tolerant cultivars and the use of techniques such as tissue culture, it can brings great benefits and optimization on the growing of this plant. The aims with this work was to identify banana cultivars for tolerance or susceptibility to in vitro induced saline and water stress, based on phytotechnical, physiological and biotechnological tools. Two experiments were carried out. On the first one, salinity stress was induced in vitro by the addition of 0; 0.1; 0.2 and 0.4% (w / v) NaCl in the MS culture medium, in the Caipira, Princesa, Thap Maeo and Vitória cultivars. On the second experiment the induction of in vitro water stress in the cultivars Tropical, Grand Naine, Prata Anã and Pacovan Ken, was generated by the addition of 0; 2.5; 5 and 10% (w / v) PEG in the MS culture medium. After 36 days growth; physiological [relative water content (RWC); Electrolyte leakage (EL); chlorophyll and carotenoids content; CO2 / O2 and CO2 / MS] and biotechnological [expression of pyruvate decarboxylase (saline stress experiment only); Biological activity by biospeckle laser; DNA content by cytometry] traits were evaluated. With the induction of salt stress, the cultivar Princesa showed significant reduction in growth, drastic changes in physiological parameters, higher expression of pyruvate decarboxylase, lower biological activity and reduction in DNA content, in response to increased salinity. On the other hand, Vitória cultivar was more tolerant to stress, and the concentration of 0.1% NaCl was beneficial for some parameters. The cultivars Thap Maeo and Caipira presented variable responses, either demonstrating susceptibility or tolerance, the former being less sensitive to stress than the latter one. In addition, it was possible to select the root as being the best indicator of biological activity on the biospeckle technique. The induction of water stress led to reduced growth and negatively influenced the physiological parameters in all cultivars tested. In general, the cultivar Tropical presented the larger limitation on growth and physiological parameters. Grand Naine was less sensitive to the presence of PEG in relation to growth parameters, such as leaf height and leaf length, when compared to other cultivars. Physiological responses of the cultivars Prata Anã, Grand Naine and Pacovan Ken at concentrations of 2.5 and 5% of PEG were similar for most of the variables. Shoot growth was only observed in the cultivar Grand Naine at the highest concentration of PEG. Only the cultivar Prata Anã showed no reduction in the DNA content with the increase of PEG concentration. The biological activity measured at the root correlated with a greater number of variables than on the leaf. We can conclude that Vitória is the most tolerant cultivar and Princesa is the most sensitive cultivar to salt stress induced in vitro. Tropical is the most sensitive cultivar to water stress and Grand Naine is the most tolerant in these growing conditions.