Does Fusarium solani Form an Endophytic Association with Soybean Roots?

Abstract

Fusarium solani (F. solani) is a soil-borne filamentous fungus which causes seed and seedling rot in soybean (Glycine max). Infection during germination can cause severe stand reductions. However, if a soybean seedling is able to survive through the initial infection the plant tends to be larger in size and produces higher yield. The objective of this research is to determine if infection by F. solani persists in the soybean roots after initial infection. Seedlings were grown in soil inoculated with uninfested and infested red sorghum for 28 days. Three observation techniques, plating, staining, and quantitative PCR (qPCR) using primers specific for F. solani, were conducted on roots after the plants were harvested. When roots were plated on ampicillin rifampicin infused water agar (ARWA) media there was general contamination of the roots with what appears to be Pythium spp., a fungus-like genus which interferes with the growth of filamentous fungi. This contamination may also complicate microscopic assessment of fungal infection of stained roots due to our inability to distinguish hyphae of F. solani from those of Pythium spp. Use of specific primers allowed us to detect F. solani in the sampled roots; however, competition with Pythium spp. compromised our results. Use of selective culture media and sterilization of growth media may be necessary to prevent the growth of contaminating Pythium spp.