Airborne versus soilborne inoculum: White mould, where do you come from?

Abstract

Identifying the sources of fungal inoculum that induces epidemics is instrumental to managing crop health in a more efficient way by implementing prophylactic methods and by using better targeted biocontrol and fungicide applications. For some phytopathogenic fungi, this identification is hampered by the multiplicity of inoculum types. This is the case for Sclerotinia sclerotiorum, the agent of white mould, which can produce ascospores disseminated via the atmosphere, sclerotia stored in the soil and mycelium in plant debris of a large variety of hosts. The present study aims to assess the relative importance of airborne and soilborne inocula in white mould disease development and its persistence across two crop seasons. S. sclerotiorum isolates were collected from air, soil and carrot plants during two crop seasons in south‐western France and genotyped with 16 microsatellite markers. Among the 490 isolates, 162 clonal lineages were identified. The genetic characteristics did not differ significantly among isolates collected from air, soil and carrots. The epidemics of white mould on carrots were initiated either by airborne inoculum or by soilborne inoculum. It also appears that some isolates from airborne inoculum persisted from year to year.