Variability of Sclerotium rolfsii Causing Collar Rot of Yams in Kerala, India

Abstract

The present study investigated on the diversity, pathogenicity, and cultural characteristics of Sclerotium rolfsii associated with collar rot in tuber crops across six Agro-Ecological Units (AEUs) of Kerala, India. Thirty-two samples were collected from infected elephant foot yam (Amorphophallus paeoniifolius), Taro (Colocasia esculenta), and Dioscorea (Dioscorea alata) plants in five districts during 2023-2024, exhibiting typical symptoms such as leaf yellowing, collar rot, and sclerotia formation. The pathogen was isolated using standard isolation techniques on Potato Dextrose Agar (PDA), and pathogenicity is proved by Koch’s postulates by mass multiplying tha pathogen in sand oat meal and inoculating in soil. Virulence assays revealed IA17 (from Orkatteri) was identified as the most aggressive isolate in elephant foot yam, while IC4 (from Chonadam) and ID3 (from Cherthala) were most virulent on Colocasia and Dioscorea, respectively. Cultural characterization demonstrated significant variability in mycelial growth, time for sclerotial initiation, number of sclerotia, and their distribution patterns. Notably, IA10 produced the highest number of sclerotia (211 per plate), whereas IC1 had the lowest (25). The findings underscore the morphological and pathogenic diversity of S. rolfsii in Kerala, with implications for resistance breeding strategies against the diseases in yams.