Comparing Fusarium inoculation protocols for soybean root rot infection

Most soybeans' (Glycine max L.) yield losses around the world are attributable to soil-borne diseases caused by pathogenic fungal species such as those from the genus Fusarium. When studying infection processes of soil-borne plant pathogens, maintaining consistency and effectiveness of disease assessment based on the visual estimation of host resistance is often challenging. To standardize the inoculation protocol, we studied Fusarium root rot (FRR) infection on soybean plants using three Fusarium species (F. graminearum, F. avenaceum and F. poae) and four different inoculation methods (i) root dipping, (ii) soil-conidia, (iii) cornmeal-soil, and (iv) mycelial plugs. The most efficient method to infect soybean plant roots with the tested Fusarium species and to observe the infection process was by using the cornmeal-soil method. After inoculation, seedlings were assessed at the V3 stage for root rot symptoms as well as for the effects of infection on root length, root weight, and shoot height. In parallel, Fusarium colonization was monitored using polymerase chain reaction (PCR). A significant difference in final disease ratings was observed when comparing the tested methods. The cornmeal-soil-conidia method was the most efficient in inducing soybean root rot disease in response to inoculation with the three tested Fusarium species. This optimized inoculation protocol will allow more consistency for soybean-pathogen interaction studies, such as early plant responses to soil-borne fungi, which will also contribute to more standardized methods aimed at developing new management strategies for soil-borne diseases of soybean.