MOLECULAR ANALYSIS OF THE SUPPRESSION OF COLLETROTRICHUM FALCATUM BY TRICHODERMA HARZIANUM IN SUGARCANE

Detailed tritrophic interaction studies were conducted under in vitro and in vivo conditions among sugarcane, Colletotrichum falcatum, the red rot pathogen of sugarcane and its antagonist Trichoderma harzianum. Two way interaction under in vitro conditions clearly indicated that T. harzianum was able to inhibit the growth of C. falcatum which was evidenced by degradation of C. falcatum proteins and expression of new proteins by Trichoderma both at intra- and extra-cellular level. Similar suppression of the pathogen by the antagonist was also observed during three way interaction with sugarcane tissue in vitro and reduction of symptom production in stalk tissue in vivo. At the molecular level, SDS-PAGE analysis of proteins extracted from different samples of three way interaction in vitro revealed that there were differentially expressed proteins (ca. 100-150kDa) when C. falcatum was inoculated in sugarcane tissue followed by Trichoderma at different intervals, particularly 72h after pathogen inoculation. Under field conditions, C. falcatum symptoms in the stalk tissue were inhibited by simultaneous inoculation of Trichoderma and C. falcatum. Protein profiles of these samples in SDS-PAGE indicated that the sugarcane proteins (ca. 80-100kDa) were degraded during the host-pathogen interaction and the same proteins were retained during three way interaction of pathogen along with the antagonist on sugarcane. Furthermore, the growth and proliferation of T. harzianum over C. falcatum inside the stalk tissue was shown by duplex PCR, tissue bioassay, and microscopic observations. All these results confirm that T. harzianum was able to suppress C. falcatum in sugarcane by antagonistic mechanism and expression of newer proteins that could be related to defence/antifungal nature.