Splash dispersal of Coniothyrium minitans in the glasshouse

Summary Coniothyrium minitans , a mycoparasite with biocontrol activity against Sclerotinia sclerotiorum , was found to disperse during glasshouse trials where overhead irrigation was used. Consequently, the role of water splash in dispersal of C. minitans was investigated using soil‐incorporated inoculum and a range of irrigation regimes found to occur in the glasshouse. The resulting inoculum deposition over horizontal distances up to 2 m was measured. Using drops < 6 mm diameter at 680 mm h ‐1 , C. minitans was splash‐dispersed at least 2.0 m, whereas with drops > 6 mm diameter at 30 mm h ‐1 it was dispersed to only 1.75 m. Irrigation with droplets < 1mm diameter at 49 mm h ‐1 failed to disperse inoculum beyond 0.5 m. The dispersal gradient produced by drops < 6 mm diameter at 680 mm h ‐1 was best described mathematically by the power function, whereas irrigation with drops > 6 mm diameter at 30 mm h ‐ resulted in a gradient described well by power or exponential functions. The latter regime produced a significantly steeper gradient than irrigation with drops < 6 mm diameter at 680 mm h ‐1 . C. minitans was isolated using an Andersen air sampler at concentrations of 2839 cfu m ‐3 or 22 cfu m ‐3 during irrigation with drops < 6 mm diameter at 680 mm h ‐1 or > 6 mm diameter at 30 mm h ‐1 , respectively. After irrigation, deposition of C. minitans‐canying aerosol particles declined exponentially and distance from source had no effect on the amount of inoculum isolated. Conidia of C. minitans , splash‐dispersed by irrigation with drops < 6 mm diameter at 680 mm h ‐1 were able to infect sclerotia of S. sclerotiorum such that almost all sclerotia at 0.5 m from the inoculum source, and c. 50% of those at 2.0 m, became infected with the mycoparasite.