Water-assisted dissemination of conidia of the mycoparasite Coniothyrium minitans in soil

A study was conducted to determine water-assisted dissemination of conidia of Coniothyrium minitans (Cm), a mycoparasite of Sclerotinia sclerotiorum (Ss), in four soils (yellow–brown soil, red-clay soil, fluvo-aquic soil and black soil) and one sand. Conidial suspensions (1×10⁷ conidia mL^?1) of Cm were applied to sieved (2 mm screen) soil or sand in glass tubes to test vertical dissemination (VD) and in aluminum boxes to test horizontal dissemination (HD) of conidia. Results showed that conidia of Cm could be disseminated with water and spread in soil or sand for 16–20 cm vertically and for 5–10 cm horizontally. The conidial concentration of Cm was logarithmically reduced with the increase in depth of VD or the distance of HD. Dissemination of Cm conidia in sand was better than that in four soils. Potting experiments were done to further understand the potential of water-assisted dissemination of Cm conidia in suppression of Ss carpogenic germination. Results showed that more apothecia were produced by Ss sclerotia located at the soil surface than those at 5 and 10 cm in depth. The minimum Cm concentration for suppression of Ss carpogenic germination was 1000 conidia g^?1 soil. Two-season field trials indicated that water-assisted application of Cm was an effective strategy used at the time for transplanting oilseed rape seedlings to suppress Ss carpogenic germination, thereby reducing the primary infection source for sclerotinia diseases of oilseed rape.