A new collar rot disease of cowpea (Vigna unguiculata) caused by Aplosporella hesperidica in India

Cowpea is an important pulse crop cultivated in arid and semi-arid regions of the world. During field survey, a characteristic wilt was observed in around 45 ha of cowpea fields with incidence 17-25%. Infection was seen in pre-flowering stage and infected plants showed quick wilt symptoms with tan lesions near the stem-soil interface. Fungal pathogens associated were isolated on PDA, which produced dark to grey olivaceous colonies in the centre, and aerial mycelia were appressed with floccose and white to smoke-grey. Conidia are aseptate, initially hyaline, smooth-walled, broadly ellipsoidal with rounded ends becoming dark brown. Based on these morphological features, the fungal pathogen was identified as Aplosporella sp. The ITS-rDNA region was amplified using ITS1/ITS4 primers and sequenced. The nBLAST and phylogenetic analysis confirmed the pathogen as Aplosporella hesperidica. The Koch's postulates were performed on 45-days-old cowpea plants with mycelial disc of A. hesperidica. Development of typical necrotic lesions was observed after 28 days of post-inoculation and the pathogen's identity was confirmed based on re-isolation. Efficacy of fungicides evaluated in vitro showed that the pathogen is highly sensitive to systemic fungicides rather than the contact fungicides. The cowpea production was severely affected owing to the causative agent A. hesperidica. The collar rot disease of cowpea by A. hesperidica is the first report in India