Arbuscular mycorrhiza reduces the negative effects of M. phaseolina on soybean plants in arsenic-contaminated soils

Abstract

All crops are negatively affected by several abiotic and biotic stresses, alone or jointly; however, some microorganisms, such as arbuscular mycorrhizal fungi (AMF), are able to alleviate them. Here, we investigated the effects of the AMF Rhizophagus intraradices (N.C. Schenck & G.S. Smith) C. Walker & A. Schüßler on soybean plants (Glycine max L.) grown in arsenic-contaminated soils and infected by the fungus Macrophomina phaseolina (Tassi) Goid., (charcoal rot). Two pots experiments were carried out in a glasshouse, and three levels of As (0, 25, and 50 mg As kg−1) were evaluated. Plant and mycorrhizal parameters, disease severity, glomalin content, and arsenic content in roots and leaves were analyzed. Both arsenic and the pathogen negatively affected soybean biomass and morphological parameters. Moreover, both stresses adversely affected mycorrhizal symbiosis. Low levels of AMF colonization and vitality were observed in high As concentration and in pathogen presence; however AMF inoculation not only reduced the disease but also lowered arsenic accumulation rate in soybean biomass. On the other hands, disease severity was reduced by arsenic. Total glomalin content, produced by the AMF was increased in arsenic-enriched substrates, but was not modified in the presence of the pathogen. Increases in glomalin production could be one of the reasons by which soybean plants accumulate low arsenic amounts while the competition between AMF and the pathogen plays an important role in reducing the disease severity.