Respostas biométricas,ecofisiológicas e nutricionais em genótipos diplóides de bananeira (Musa spp) submetidos à salinidade

Abstract

The banana plant is cultivated in tropical and sub-tropical regions, encompassing over 100 countries throughout the world. In Brazil, banana cultivation constitutes the second largest volume of fruit produced and consumed in the country, ranking third in terms of area harvested. The Northeast region is responsible for 34% of the national banana production. Salinity in the region is one of the most serious factors limiting growth and productivity of this crop, especially in irrigated areas. Ten diploid genotypes of banana plants (Musa spp) from plant tissue cultures were cultivated in a nutrient solution with and without the addition of NaCl (0 and 100 mol.m-3). The experiment was carried out in the greenhouse of the Chemistry Department of the UFRPE, with an entirely randomized design, 3 replications and a 10 x 2 factorial arrangement. The aim of the study was to assess the effect of NaCl on biometric, eco-physical and nutritional variables. Throughout the experimental period, air temperature ranged from 27.7 to 30.4 oC, relative humidity ranged from 46.2 to 64.8 % and photosynthetically active radiation ranged from 24.54 to 109.57μmol.m-2.s-1. Samples were collected 21 days after initiating the treatments. Biometric variables (number of leaves, pseudostem diameter, plant height and leaf area) were measured weekly. Eco-physical variables (transpiration, diffusive resistance and leaf temperature) were determined at 20 days of the treatment differentiation. Upon collection, shoot fresh matter (leaf stalk and pseudostem) and roots + rhizome were determined. The fractioned parts (shoot and roots + rhizome) were conditioned separately in paper bags, duly identified and placed in a greenhouse for drying with forced aeration at 65oC until reaching a constant weight, in order to obtain the dry matter (shoot and roots + rhizome). Next, the allocation of biomass and succulence of the different organs, leaf area ratio, sclerophyll index, liquid assimilation rate, shoot/roots ratio and both relative and absolute growth rate were determined. After the drying of the plant material, the analyses of sodium, potassium, chloride, calcium and magnesium were carried out on the different parts of the plants. For most of the genotypes studied, salinity caused significant reductions in nearly all the biometricvariables analyzed, especially leaf area, dry matter (stalk, pseudostem and roots + rhizome), allocation of biomass in the different organs (stalk, pseudostem and roots + rhizome) and both absolute and relative growth rates. Salinity also caused areduction in transpiration and a tendency toward an increase in diffusive resistance and leaf temperature in all the genotypes subjected to salt stress. There was an increase in the Na+ and Cl- content in the different plant organs, triggering a reduction in the Ca2 content, especially in the roots + rhizome, and a consequent alteration in total dry matter, leaf area, absolute growth rate and relative growth rate. There was also an increase in the Mg2+ content only in the pseudostem and roots + rhizome, as well as an increase in the K+ content in the latter organ alone. The Tungia genotype presented the greatest sensitivity to stress in 48% of the biometric variables evaluated. The Lidi genotype presented tolerance in 60% of these variables. The remaining genotypes presented intermediate degrees of tolerance. Based on transpiration (E) and diffusive resistance (Rs) values of the contrasting genotypes, it can be inferred that the Tungia genotype presented lower transpiration and greater stomatic resistance, characterizing greater sensitivity to salt stress when compared to the Lidi genotype. The present study highlights the sensitivity of the Tungia genotype,especially in consequence of the high Na+ content in the leaf stem, though it is likely that there was compartmentalization of part of this cation in the vacuole, evidencing the magnitude of its content in the leaf stem. At any rate, the Na+ that was not compartmentalized possibly affected, through toxicity, metabolic processes such as assimilation of CO2, photosynthesis, protein synthesis and respiration due to enzymatic inactivation, reflecting this effect in the form of necrotic spots, chlorosis and burned edges of the leaf stem. The effect of salt stress on banana plant diploids can be better understood through the assessment of these variables, allowing the identification of promising genotypes with genes of interest that can be integrated to genetic improvement programs.