Indicadores de toxicidade e respostas bioquímicas e nutricionais em combinações de dez porta-enxertos de citros com a limeira ácida 'tahiti' sob estresse salino

Abstract

Citriculture in the Northeast has great socioeconomic importance for job creation. However, the problems of water availability and salinity of irrigation water are factors that limit citrus productivity. So, searching for salt tolerant genotypes is a basic strategy to reduce the impacts of salinity on agriculture sustainability in this region. For species propagated by grafting, as citrus, evaluating scion/rootstock combinations seems to be the best strategy for obtaining salt tolerant genotypes, due to the mutual influences that occur. In this study we evaluated indicators of ionic toxicity (Cl-, Na+, and Na+/K+ ratio), biochemical responses (activities of APx and SOD and contents of organic solutes), mineral nutrition (N, P, K, Ca, Mg, P, Zn, Cu, Mn and Fe), and leaf gas exchange in leaves of ten rootstocks of citrus when grafted with Tahiti lime under irrigation with saline water, aiming to identify salt tolerant genotypes. The experiment was conducted in a randomized block design, with three repetitions, following a factorial arrangement (2 x 10 x 2): Two levels of electrical conductivity of irrigation water (0.3 and 3.0 dS m-1); Ten scion/rootstock combinations, with Tahiti lime as the scion variety; Two evaluation times (November 2016 and November 2017). The experiment was carried out in the field, under semi-arid conditions, and the plants were grown in lysimeters. Salinity affected leaf gas exchange, but no correlation was observed between leaf photosynthetic rate and the levels of mineral nutrients evaluated. The data on mineral nutrition and leaf gas exchange did not allow the identification of genotypic dissimilarities in terms of salt tolerance of citrus. On the other hand, strong correlations between ionic toxicity indicators and biochemical responses were more associated to evaluation period than with differences between genotypes. The ionic toxicity indicators, especially Cl- content, enabled better genotypic difference for the selection of salt-tolerant citrus rootstocks, compared to biochemical responses. Among the crosses studied, TSKC x (LCR x TR) was the most promising for obtaining salt-tolerant citrus rootstock, considering the criterion of lower increase in leaf chloride contents in the grafted plant.