Landuse affects the likelihood of soil colonization by a key plant pathogen

Fencing and other biosecurity measures can help to reduce the spread of soil-borne pathogens, but are often compromised by weather, animals and insects. Once contaminated soil spreads beyond a farm, neighbouring land can either help or hinder pathogen dispersal based on its susceptibility to colonization. Fusarium wilt of banana, caused by the soil-borne pathogen Fusarium oxysporum f. sp. cubense (Foc), poses a serious threat to global banana production. In the Wet Tropics Region of Queensland, where most of Australia’s bananas are grown, we found that banana production land is mostly bordered by rainforest, grassland, and sugarcane production areas. In soil inoculation experiments using quantitative PCR, we found that Foc was highly likely to colonize banana soils, moderately likely to colonize sugarcane soils, and unlikely to colonize rainforest or grassland soils, suggesting that rainforest and grassland may act as natural barriers against Foc spread. When sterilized soils were inoculated, Foc proliferated to high levels regardless of landuse, indicating that biotic factors underpin the differential response of landuses to Foc colonization. Differences in the extent and likelihood of Foc soil colonization between soils were associated most strongly with the soil fungal and bacterial community composition and fungal:bacterial biomass ratio. Based on our findings, we propose that future work should explore the use of ground covers, soil amendments and other strategies to improve soil suppressiveness to Foc. Together, our findings offer valuable insights for land managers and demonstrate the importance of rainforest and grassland soils in limiting Foc spread across the landscape.