The Effect of Inoculum Substrate and Dew Period on the Pathogenicity of Sclerotinia Sclerotiorum When Applied as a Mycoherbicide to Californian Thistle (Cirsium Arvense).

Abstract

Sclerotinia sclerotiorum was grown on solid substrates based on kibbled (cracked) wheat and pine sawdust with various additives to examine its potential as a mycoherbicide against Californian thistle (Cirsium awense). Mycelial growth was vigorous on wheat but very weak on sawdust. Growth was only marginally slower on a substrate of equal weights of wheat and sawdust than on wheat. The addition of vegetable oil to the substrates did not enhance the basic growth rates. The subsequent growth out of the fungus-infested particles into pure culture was faster from wheat than from sawdust particles in the wheat plus sawdust mixture substrate. The rate of lesion development on excised leaves of Californian thistle inoculated with these substrates reflected these differences. Neither vegetable oil nor oxalic acid as additives, increased the speed of infection or rate of lesion development. When plants of C. awense were inoculated in the glasshouse, the mycelium-infested sawdust plus wheat substrate gave slower disease development than the wheat substrate. Increasing the length of the dew period caused faster disease development, especially in the sawdust plus wheat substrate. These results suggest S. sclerotiorum will require a suitable energy source and free moisture when used as a mycelium-based mycoherbicide.