Collar rot caused by Calonectria hawksworthii, a new record for pomegranate (Punica granatum)

Pomegranate is an important horticultural crop grown in arid and semi-arid regions worldwide. Moreover, due to its widespread nutraceutical and pharmaceutical properties, expansion in its cultivated area has taken place extensively in India which has now become a global leader in its production and export. However, due to changing climatic conditions a plethora of diseases affect its quality and yield. Recently, we observed a typical collar rot occurring on pomegranate plants with 10-25% incidence. The current study was undertaken to identify the causative organism and prove its pathogenicity on pomegranate plants. Therefore, isolation of fungi was carried out using symptomatic tissues. Among the isolated fungi, one of the fungi was recovered up to 80% and, therefore, it was evaluated further. The colony morphology and other microscopic features suggested that it belonged to the genus Calonectria. Homology search using reliable barcode regions, both coding and non-coding, revealed close genetic similarities between the isolate and C. hawksworthii. Pathogenicity tests were performed on pomegranate seedlings, groundnut seedlings (a susceptible host to Calonectria sp.) and 6-month-old pomegranate plants. Artificially inoculated seedlings/plants developed typical symptoms while control plants did not, proving that the isolate was pathogenic. Hence, based on morphological and molecular data we identified the pomegranate collar-rot causal organism as C. hawksworthii, which is a novel record and highlights the expansion in geographical distribution and host range of the fungus.