| The interaction between Theobroma cacao and Crinipellis perniciosa results in witches' broom disease. My research showed that the biotrophic phase of the pathogen infects meristematic tissues by forming club shaped hyphal tips and, depending on the developmental of stage of the host and acquired nutritients, the pathogen undergoes phase transition and becomes saprophytic. The saprophytic fungus produces hydrolytic enzymes that are capable of reducing cellulose, xylan and pectin into simple sugars. The presence of host tissue reduced the activity of pectin-related hydrolases, suggesting that the plant has a mechanism to defend pathogen attack. Host-pathogen interaction also caused expression of several genes in the host and the pathogen. We isolated, cloned, and sequenced 20 potential transcripts from 3d infected tissues, of which five transcripts were studied further to understand their role during disease progression. Temporal profile of fungal transcripts related to hormones is supported by the quantitative profile for IAA and SA in the infected tissues. My studies provide first evidence for presence of hormones in Crinipellis. Endogenous changes in hormones and the effects of hormones on fungal growth suggest that the phase transition in the fungus and disease symptoms are auxin-mediated and SA accumulation may lead to SAR responses. These studies suggest that physiological and molecular signals are exchanged during the interaction of Crinipellis and Theobroma. |
