Sensibilidade de cultivares de bananeira a níveis de salinidade na água de irrigação

Abstract

The banana is a crop of great social and economic importance, being grown in more than 100 countries. Brazil is the fifth largest banana producer, and the northeast is the main producing region of the country. However in this region, salinity is one factor which limits the growth and productivity, especially in places irrigated. The purpose of this study was to evaluate the effect of salinity on biometric, physiological and nutritional variables in banana cultivars. The experiment was carried out on the experimental fields of Embrapa Cassava & Tropical Fruits in Cruz das Almas – Bahia - Brazil. The experiment followed a completely randomized design in a split plot, with four levels of salinity in irrigation water (0.5, 2.0, 3.0 and 4.0 dS m-1), equivalent to four levels of salinity in the soil solution (0,86; 2,28; 3,25 e 4,58 dS m-1), four different banana cultivars (“Pacovan”, “Prata Anã”, “BRS Platina” and “Princesa” ) and three replications. Biometric variables (plant height, pseudostem diameter, number of leaves, leaf area and leaf area affected by salinity), physiological (stomatal conductance, osmotic potential in leaf, relative water content in the leaf, proline content in the leaf, turgor pressure on the leaf and relative transpiration) and nutritional variables in the leaf and root (N, P, K+ , Ca2+, Mg2+, Na+, and the Na+ /K+ ratio) were determined. The salinity caused significant reductions in all variables, reduced height of plants (23.3%), diameter of pseudostem (13.9%), the number of leaves (20.5%) and the plant leaf area (53.5%). The “Princesa” cultivar showed greater sensitivity to the plant height parameter with increased of salt stress, while “BRS Platina” was more tolerant to the same effect. Gas exchange in banana cultivars were significantly affected when applying increasing levels of salinity. The stomatal conductance was reduced by 49,86% at the level 4,0 dS m compared to control treatment. The relative transpiration of plants significantly reduced with increasing salinity. The cultivars had different behaviors as to the relative water content, especially the cultivars “Prata Anã” and “BRS Platina” who maintained constant the CRA levels and are considered more tolerant to salt effect. The osmotic potential of leaves of the banana cultivars was not affected by salinity. The proline content in the leaf was not affected by salt levels in the irrigation water, but were different between the banana cultivars, with emphasis on the highest levels presented by “Princesa” cultivars and “BRS Platina”. There were differences in the levels of nutrients in the roots, between the salinity levels to the levels of Ca2+, Na and Na+ /K+ ratio, and between cultivars for the levels of Ca2+, K+, Mg2+, Na+ and the Na+ /K+ ratio. The higher content of Na+ at the root and lower in leaf in the cv. “BRS Platina”, showed a lower salinity sensibility. The lower Na+ /K+ ratio in root and leaf Higher in the “Princesa” cultivar reflected a higher salinity sensitivity of this cultivar.