Splash dispersal of Coniothyrium minitans in the glasshouse

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.