First report of corm rot disease caused bySclerotium rolfsiiin banana

Abstract

A corm rot disease was observed for the first time in banana. The disease was found to occur in the majority of commercial cultivars grown in different banana-growing states of India. The incidence of the disease was up to 50% and found to occur at an altitude up to 3000 m asl. The pathogen was identified as Sclerotium rolfsii based on morphological characters and rDNA internal transcribed spacer sequence data. Bananas (Musa spp.) are the world's fourth most important global food crop grown in more than 120 countries (Molina and Valmayor 1999) and are the staple food for more than 400 million people (Swennen et al. 1995). India is the world's largest banana producer and 26 million tonnes are produced annually from 709 000 ha. However, various pests and disease problems, particularly Fusarium wilt, cause significant losses (Ploetz 2005). During a disease survey in different banana-growing regions of India in March 2005, a new wilt-like disease was observed in cv. Rasthali (Silk-AAB) in the Tirukattupalli area of Thanjavur district in Tamil Nadu, India. The important symptoms observed were yellowing of leaves from base to apex, extensive pseudostem sheath rot with profuse mycelial growth on the pseudostem (Fig. 1A, B). The colour of the rotted portion was yellowish-red to reddish-brown (Fig. 1B, C), with numerous brown sclerotia present. Splitting of the basal portion or the pseudostem sheath was observed, and the bottom leaves had desiccated. The infected plant emanated a mushroom odour. The inner tissues of the corm were spongy and colonised extensively with white mycelium (Fig. 2A). At higher altitudes of 2000-3000 m asl, the cortical portion of the corm was completely converted into a mass of fibre (like coconut fibre) with profuse growth of fungal mycelium (Fig. 2B). In some plants, the infection extended up to half of the medulla region. The emerging peeper was necrotic and colonised extensively with white mycelium. In some cases the mycelial growth was seen on the growing tip of the young bud and resulted in reddish brown necrosis. The symptoms were observed in all stages of plant growth. Samples of the diseased plant parts were collected and brought to the laboratory and cultured on potato dextrose agar (PDA). White mycelial growth was observed within a week. Subsequently, small round dark-brown sclerotia developed in