Molecular detection and pathological investigations on southern blight disease caused by Sclerotium rolfsii on cabbage (Brassica oleracea var. capitata): A new record in India

A severe outbreak of foot rot and head rot disease of cabbage was observed during September 2017 to November 2019 in major cabbage growing regions of southern Karnataka state of India. The disease incidence ranged between 3% and 28%. The initial symptoms were observed as tan, water-soaked lesions at the point of infection and development of mycelia, followed by quick wilting of the whole plant. Subsequently, numerous sclerotia were produced. The pathogen isolated on PDA medium produced white fluffy aerial mycelia and numerous reddish-brown sclerotia after 7-10 days. A total of 18 fungal isolates were used for mycelial compatibility analysis. Isolate SrBoC28 was used to test for pathogenicity on cabbage, marigold, chilli and brinjal plants. Typical disease symptoms on leaves, stem and roots were evident 5, 8 and 10 days' post-inoculation respectively. The isolate was pathogenic on all tested hosts, and the identity was confirmed by re-isolation and morpho-cultural and molecular studies. The latter were based on amplification of ITS-rDNA and phylogenetic analysis which showed 100% sequence similarity with reference sequences. The identity was confirmed as S. rolfsii. This is a well-known pathogen and causes disease on various economically important crop plants. To date, there are no reports on the association between S. rolfsii and foot and head rot disease of cabbage in India and elsewhere. Thus, to the best of our knowledge, this is the first report of foot rot and head rot of cabbage caused by S. rolfsii in India.