Bholanath Mondal, Vivek Kumar Khare, Najmun Naher and Ranjan Nath
Abstract
White rot of Parthenium hysterophorus L. caused by Sclerotinia sclerotiorum (Lib.) de Bary was recorded during the winter months of December, 2022âFebruary, 2023 in mustard fields at Supur of the Ajay River basin under the Lateritic-Red Agroclimatic Zone of West Bengal, India. Initially, water-soaked lesions developed on lower leaves near the soil line, followed by yellowing, marginal necrosis, profuse white mycelial growth, stem rot, and eventual death of plants. Disease incidence was more severe in young plants growing under dense and humid conditions inside mustard fields and near bunds. Black irregular shaped sclerotia developed on infected plant parts and on the soil surface. Higher disease incidence was recorded (100%) during the last week of February and significantly correlated with relative humidity and temperature. The pathogen was isolated on PDA medium and produced white, septate, branched mycelia with large irregular black sclerotia. Apothecia arising from sclerotia were also observed under cool and moist field conditions. Based on cultural and morphological characteristics, the pathogen was identified as Sclerotinia sclerotiorum. Pathogenicity was confirmed through artificial inoculation, and symptoms appeared within 5â7 days after inoculation. Host range studies revealed that isolates from parthenium (Parthenium hysterophorus L.), mustard (Brassica juncea (L.) Czern.), marigold (Tagetes erecta L.), and bean (Phaseolus vulgaris L.) infected several plant species including bean, mustard, marigold, holy basil (Ocimum sanctum L.), kulekhara (Hygrophila auriculata (Schum.) Heine), thankuni (Centella asiatica (L.) Urb.), and parthenium, indicating absence of host specificity. Although S. sclerotiorum has previously been reported on several medicinal and vegetable crops in West Bengal, the present study appears to be an important report of P. hysterophorus as a host of S. sclerotiorum in the Lateritic-Red Agroclimatic Zone of West Bengal, India.