Effect of Inoculum Rates and Sources of Coniothyrium minitans on Control of Sclerotinia sclerotiorum Disease in Glasshouse Lettuce

Abstract

Coniothyrium minitans isolate Conio grew on both maizemeal-perlite and ground maizemeal-perlite, producing high numbers (1.6×107 conidiag−1 inoculum) of germinable conidia. Coniothyrium minitans isolate Conio applied as a preplanting soil incorporation of maizemeal-perlite inoculum at full application rate (0.6lm−2; 1011 colony forming units (cfu)m−2) significantly reduced Sclerotinia disease in a sequence of three lettuce crops grown in a glasshouse. No reduction in disease was achieved with any of the reduced rate treatments (108cfum−2) of a range of C. minitans isolates (Conio ground maizemeal-perlite at reduced rate, Conio and IVT1 spore suspensions derived from maizemeal-perlite, IVT1 spore suspension derived from oats and Contans® WG spore suspension). After harvest of the second and third crops, C. minitans maizemeal-perlite at full rate reduced the number and viability of sclerotia recovered on the soil surface and increased infection by C. minitans compared with spore suspension and reduced rate maizemeal-perlite inocula. Coniothyrium minitans was recovered from the soil throughout the trial, between 105 and 107cfucm−3 in maizemeal-perlite inoculum full rate treated plots and 101–104cfu cm−3 in all other inoculum treated plots.