High cadmium concentration resulted in low arbuscular mycorrhizal fungi community diversity associated to cocoa (Theobroma cacao L.)

Arbuscular mycorrhizae fungi (AMF) are obligate symbionts present in rhizosphere of cocoa plants and their community diversity is modified depending on several factors, such as cadmium (Cd) presence in soil. AMF persistence on Cd natural enriched soils might be an indicator of their tolerance and their potential in biotechnological applications. In this research we characterized local AMF community structure present in cocoa rhizosphere soils with low (B-Cd: 0.1 mg kg(-1)) and high (A-Cd: 20.9 mg kg(-1)) natural Cd concentrations. AMF spore identification was carried out using taxonomic keys and their abundance, richness and diversity were determined in original samples and after multiplication process using onion trap cultures. AMF communities were compared using alpha and beta diversity indexes and principal component analysis (PCA). The results indicated that A-Cd presented significative lower values of abundance (21 %), richness (20 %) and diversity (11 %) of AMF morphospecies in comparison with B-Cd. Both AMF communities presented five of seven genera in common, but only four of 23 morphospecies described were found in two communities. Low similarity and turnover were found among AMF communities throughout beta diversity analysis and PCA. Dominance of Diversispora spurca, Rhizoglomus sp. and Claroideoglomus etunicatum in A-Cd suggests that these morphospecies are stresstolerant and they are potential candidates for the development of mitigation strategies in cocoa plants under Cd stress.