Web Blotch Disease of Groundnut (Arachis hypogaea) in Nsukka

Abstract

Web blotch diseases of groundnut were observed in groundnut farms in Nsukka on the Spanish groundnut cultivars. The disease was characterized by tan-coloured web like blotches on infected leaves. Blotches have grayish irregular margins and lower leaves were affected while new leaves were rarely attacked. The fungus in culture showed a creamy white mycelial growth that became black or dark brown within two weeks when it produced abundant chlamydospores in chains. Pycnidia of the fungus were observed on leave tissues when the leaves were maintained in moist environment within four weeks. The organism is called Phoma sorghina and confirmed by International Mycological Society in Kew, England (IMI number 368112). The best type of inoculum of the organism was a two weeks old culture since it produces the best lesion than other sources of inoculum (9.5 ± 0.94). It also induces the highest leaf abscission (5.1 ± 1.9).The more the inoculum the higher the disease incidence (9.6 ± 0.94) at 105 spores. Two weeks old inoculum was also the best at inducing lesions (11.30 ± .80) as well as inducing defoliation (5.5 ± 0.92).