IDENTIFICATION OF PATHOGENICITY DETERMINANTS IN COLLETOTRICHUM FALCATUM CAUSING SUGARCANE RED ROT AND ITS SUPPRESSION BY ANTIFUNGAL MICROBES

摘要

As pathogen variability plays crucial role in the breakdown of red resistance, attempts were made at different angles to characterize factors responsible for the development of newer races. Since no tool could identify its virulence determinants, present study was undertaken on the production of metabolites viz, toxin, enzymes and melanin in relation to disease expression. The nine major pathotypes used in screening programme were found to vary significantly in the production of toxin, its effect on symptom production and loss of electrolytes and they increased with pathotype virulence. They varied in the production of pectinolytic and cellulolytic enzymes particularly exo-PG which corresponds with the virulence. They also varied in the production of melanin during host pathogen interaction in response to virulence and the pathogenic virulence has been proved by bioassay in stalks and leaves. Involvement of these factors has also been proved by utilizing wild and temperature adapted mutants which were characterized for cultural, morphological, pathogenicity, production of secondary metabolites and at molecular level. Simultaneously attempts have been made to identify the sources of anttfungal genes to suppress these factors during their interaction. The effective biocontrol agents identified against C. falcatum inhibited the production of secondary metabolites of the pathogen and also detoxified/ inactivated the toxin/enzymes, when the antagonists were grown along with pathogen or its metabolites in liquid cultures as well as at the point of entry, where it failed to elicit characteristic symptoms on the host. High molecular proteins specifically produces by the antagonists to inactivate the pathogenic metabolites were identified in SDS-PAGE. These results indicate that isolation of potential antgungal genes from antagonistic fungal/bacterial strains would lay foundation to improve defense mechanism in sugarcane clones by means of genetic transformation and other strategies.