Diversity of Arbuscular Mycorrhizal Fungi Associated with Cocoa (Theobroma cacao L.) Agroforestry Systems in Togo

Abstract

This study aims to assess the diversity and prevalence of arbuscular mycorrhizal fungi (AMF) associated with cocoa trees in different agroforests of the agroecological zones of cocoa production in Togo. The substrates, consisting of soil samples, were collected from twenty-four (24) cocoa orchards belonging to four types of agroforests (< 10 years, 10 to 20 years, 21 to 30 years, and > 30 years) in the three agroecological subzones of cocoa production (Agou peneplain, piedmonts, and plains and plateaus and mountains) of Togo. These samples were used to trap in pots the AMF spores associated with cocoa trees using sorghum (Sorghum bicolor) as a reference trap plant. The culture was maintained for 12 months in a greenhouse after which the densities and diversity of the spores were evaluated. The AMF spores extracted were identified based on morphological criteria. The results showed a great diversity of spores identified in the different agroforests. A total of thirty species of AMF belonging to sixteen genera and nine families (Acaulosporaceae, Ambisporaceae, Archaeosporaceae, Gigasporaceae, Claroideoglomeraceae, Dentiscutataceae, Diversiporaceae, Glomeraceae and Paraglomeraceae) were identified. Furthermore, the study revealed the predominance of the genera Rhizophagus, Acaulospora, and Gigaspora. However, the less frequent genera are represented by Entrophospora, Ambispora, Archaeospora, Cetraspora, Racocetra, Dentiscutata, Diversipora, and Paraglomus. The most frequent species were Claroideoglomus etunicatum, Acaulospora scorbiculata and Acaulospora sp. Results showed that AMF spore density varied from 16 spores/gram of soil in young plantations entering production and old plantations to 37 spores/gram of soil in mature plantations in production on the Agou peneplain. Finally, the highest AMF densities were recorded in agroforests less than 30 years old. This study has identified a great diversity of AMF associated with cocoa orchards in the different agroforests and some strains could be used as biofertilizers for sustainable cocoa production in Togo.