The present study aims to establish pathogenic variability among Colletotrichum truncatum, an incitant of anthracnose disease across different chilli growing regions of Karnataka. Thirty suspected C. truncatum isolates were identified based on their morphological and conidial characteristics and further confirmed by Internal Transcribed Spacer DNA sequence analysis. Pathogenicity test was carried out by in vitro detached leaf and fruit assay, and also under greenhouse conditions using 20 different chilli cultivars grown across Karnataka. Colletotrichum truncatum isolates recorded the varied degree of pathogenicity index (PI) on different chilli cultivars. Isolate UOM-02 was found highly virulent (PI > 80 against 12 tested cultivars) and cultivar cv. 4 was found highly resistant to C. truncatum infection (Average PI, 48.21). Further, the involvement of enzymes such as cellulase, pectin methylesterase and ascorbate peroxidase in determining the virulence of the pathogen was established. The highest activity of catalase (UOM-24; 7.38 units), ascorbate peroxidase (UOM-02; 2.9 units), cellulase (UOM-02; 0.58 units), and pectin methylesterase (UOM-02; 6.7 units), was recorded by different C. truncatum isolates. Cellulase and pectin methylesterase activities were positively correlated with their pathogenicity, while catalase activity was found least correlated. Results of RAPD and ISSR analysis recorded higher polymorphism among the isolates. Interestingly these isolates were not clustered based on their geographical origin, Pathogenicity index and biochemical characters. From this study, the existence of highly virulent C. truncatum isolate (UOM-02), which can cause severe loss under favourable conditions, was revealed. Further, possible use of specific enzymes as an indicator of virulence of the pathogen is discussed.
Keywords: Anthracnose; Colletotrichum truncatum; Detached fruit assay; Pathogenicity index.
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