Identification of soils suppressive against Helminthosporium solani, the causal agent of potato silver scurf

Silver scurf, caused by the fungus Helminthosporium solani, is an important disease affecting potato tubers. Control of the disease has been hampered by the development of H. solani strains resistant to thiabendazole. Currently, there is no alternative to thiabendazole for the efficient control of the disease. In this study, 45 selected soils from the province of Québec were tested in greenhouse assays for their effect on silver scurf development. The results showed that soil influenced significantly silver scurf development and that specific soils displayed an interesting level of suppressiveness against potato silver scurf. Investigations into the cause(s) of soil suppressiveness revealed on the one hand, significant negative correlations between silver scurf severity and soil N-NO3 and available Fe contents, and on the other hand, absence of significant correlations between silver scurf severity and the different soil microbial populations. Investigations also revealed the presence of microorganisms antagonistic to the pathogen in the most suppressive soils. The antagonist microorganisms isolated in those soils were Bacillus cereus, Cellulomonas fimi, Kocuria varians, Pseudomonas putida, Rhodococcus erythropolis and Rhodococcus globerulus. Considering that few microorganisms were previously reported to display antagonism against H. solani, these results open the way to new avenues of investigation towards achieving biocontrol of silver scurf.