Mechanisms involved in spatial and temporal mobility of disease patches caused by Rhizoctonia solani in sugar beet field : Induction of antagonists within disease patch

Rhizoctonia solani AG 2-2 causes damping-off and root rot on sugar beet in patches that are highly mobile both on spatial and temporal scales. They never occur in the same place where they were in the previous season. The aim of the present study was to uncover the mechanisms underlying the dynamics of disease patches. It was observed that soil inoculum potential was higher within diseased patch than in healthy area. However, the dormant pathogen in healthy area was stimulated by addition of buckwheat meal more than that in diseased patch. In addition soil from diseased area was more suppressive towards the disease. We did not observe significant differences in bacterial genetic structure with the origin of the soil. However, diseased area could be easily distinguished from healthy area by their bacterial physiological fingerprints.It was observed that Trichoderma isolates from diseased patch were more antagonistic than the ones from outside the patch both in vitro and in vivo. These results suggest that R. solani when active may stimulate the development of antagonistic organisms. Their presence may inhibit the formation of patches in the subsequent season in that part of the field