High variability in spore infectivity and factors influencing native arbuscular mycorrhizal fungi diversity in Côte d’Ivoire cacao rhizospheres

Arbuscular mycorrhizal fungi (AMF) play a central role in enhancing nutrient uptake by plants, increasing resilience to biotic and abiotic stresses, and supporting proper functioning of tropical agroecosystems, such as cacao plantations. However, little is known about diversity and capacity of native strains in rhizospheres, as well as soil factors shaping AMF communities. This study aimed to assess (i) AMF diversity and abundance in cocoa rhizospheres and the relationship with soil chemical properties and climatic variables at seven distinct areas in Côte d’Ivoire, i.e., Adzope, Agnibilekrou, Azaguie, Biankouma, Ble, Bonon and Soubre; (ii) in-situ capacity of strains from these rhizospheres. Soil samples were collected in 66 cocoa plots and AMF spores were extracted and identified based on morphometric criteria. Part of soils was used for trap cultures, while another part was used for determination of chemical properties. Our findings indicate that fungal communities associated with cacao are dominated by families Glomeraceae and Acaulosporaceae. Before establishment of trap cultures, cacao rhizospheres showed highest spore abundance at Ble (103 ± 47 spores/100 g soil) and lowest abundance at Biankouma (47.3 ± 21.6 spores/100 g soil). AMF strains from Agnibilekrou and Biankouma soils showed highest quantitative sporulation capacity, whereas strains from Soubré soils exhibited strongest infective capacity. 18.49% of variance in AMF community is explained by soil chemical variables, whereas 5.32% is explained by climatic variables, with Mn, Zn, Cr, and precipitation as main drivers. This study highlighted that a clear understanding of AMF communities in cocoa rhizospheres is essential to facilitate the design of efficient soil and plant conservation strategies, thus ensuring the sustainability and long-term productivity of cocoa agroecosystems in Côte d’Ivoire.

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