Growth and physiological responses of melon plants inoculated with mycorrhizal fungi under salt stress

Abstract

The accumulation of salts in the soil is a common problem of arid and semi-arid regions, that cause reduction in plant growth and yield. In this context, the arbuscular mycorrhizal fungi (AMF) have been studied in recent years, with results indicating that their associations with the plant roots minimize some effects of salt stress. The objective of this work was to evaluate the influence of increasing levels of salinity of the irrigation water in the melon plants mycorrhized with AMF. The experiment design was completely randomized in factorial 2 x 4 corresponding to two mycorrhiza treatments (inoculated and not inoculated plants) x 4 levels of salinity (ECw = 0.5, 1.5, 3.0 and 4.5 dS m-1), with 4 replicates.The mycorhizal colonization, plant growth, leaf gas exchange and the concentrations and contents of ions (N, P, K+, Na+ e Cl-) were measured. The mycorrhized plants showed higher production of shoot dry matter and leaf area, in relation to non-inoculated plants, mainly in the 0.5 dS m-1 treatment. However, this beneficial effect decreased with salinity levels increasing. Stomatal conductance, transpiration rate and photosynthetic rate were positively influenced by AMF, the values being higher in mycorrhized plants. The results showed a peak of colonization in treatment with EC of 1.36 dS m-1 with a tendency to decrease in higher salt concentrations. The symbiotic association between AMF and melon roots increased the contents of N, P and K, at low and medium salinity, and reduced the absorption of potentially toxic ions (Na, Cl) from the salinity caused by irrigation water with 3.0 dS m – 1.