Mycorrhizae as a biological method for improving soil fertility and controlling Rhizobium-inoculated soybean collar rot disease in Benin

Abstract

The current study aims to improve soybean productivity without mineral fertilizer inputs by testing the effect of indigenous species of arbuscular mycorrhizal fungi (AMF) in double inoculation with Bradyrhizobium on soybean collar rot (SCR). The trial was conducted in North Benin and included 11 treatments, namely eight AMF species in double inoculation with Bradyrhizobium and three controls, namely Bradyrhizobium + 100 kg.ha-1 of P2O5 (RP100), Bradyrhizobium without mycorrhiza (RM0) and the untreated control without either Bradyrhizobium or mycorrhiza (R0M0). The results showed R0M0 to have the highest incidence of collar rot disease. The causal agent of the disease was identified in the current study as Sclerotium rolfsii. When not treated, the disease incidence in the current study was more than 70%, while, when treated with AMF as Racocetra crispa, Gigaspora margarita, Scutellospora savannicola, Paraglomus occultum, Rhizophagus partial (Unc) and Diversispora sp., this disease incidence was significantly (p < 0.05) as low as 6% and was not more than 27%. The treatment RP100 as positive control also resulted in a disease incidence lower than 27%. The AMF species Racocetra crispa gave the highest plant height while R. crispa, P. occultum, S. savannicola and R. partial (Unc) gave the highest grain yields, best symbiotic parameters and high soil phosphorus and nitrogen levels at harvest. This is the first report of S. rolfsii-caused collar rot disease in soybean in Benin and also of the effect of indigenous arbuscular mycorrhizal fungi on the disease incidence.