A native arbuscular mycorrhizal fungus inoculant outcompetes an exotic commercial species under two contrasting yam field conditions

This study aimed to assess the performance of an indigenous arbuscular mycorrhizal fungus (AMF) inoculant isolated from yam rhizosphere on yam (Dioscorea rotundata Poir.) growth and yield in field conditions. For this purpose, a factorial experiment was carried out in two contrasting agricultural soils located in Duokro and INP-HB in Yamoussoukro, Côte d'Ivoire. The Duokro soil was neutral sandy loam with high nutrient content and an established AMF community dominated by Glomeraceae whereas the INP-HB soil was acidic sand with low nutrient content and codominance of Glomeraceae and Paraglomeraceae. The inoculation treatments were two native AMF species, namely Rhizophagus irregularis (Blaszk., Wubet, Renker & Buscot) isolated from yam rhizosphere and Acaulospora colombiana (Spain & N.C. Schenck) isolated from cassava rhizosphere, applied singly or together, and Rhizophagus intraradices (N.C. Schenck & G.S. Sm.), an exotic commercial species. Mycorrhizal colonization frequencies of inoculated yam plants were substantially higher at Duokro than INP-HB. As consequence, all the growth and yield parameters measured were higher at Duokro than at INP-HB. Plants inoculated with the native inoculant R. irregularis had the highest mycorrhizal frequencies, the best growth and tuber production at both sites. Moreover, the exotic commercial inoculant was outcompeted by the native inoculants. R. irregularis appeared therefore to be a good candidate for commercialization as an inoculant for yam crops.