Disease Note

Basal Stem Rot and Wilt of Sunflower in Nigeria Caused by Sclerotium rolfsii. C. A. N. Okoli, Department of Biology, Imperial College, London. I. D. Erinle, S. M. Misari, M. A. T. Poswal, and A. M. Emechebe. Department of Crop Protection, Ahmadu Bello University, Zaria, Nigeria. Plant Dis. 75:750. Accepted for publication 17 November 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0750B.

Surveys of sunflower (Helianthus annuus L.) farms in the northern Guinea Savanna zone of Nigeria revealed a sporadic occurrence of wilted and dried-out plants with basal stem dry rot caused by Sclerotium rolfsii Sacco. Symptoms included an initial acropetal wilting of the entire plant. Affected plants gradually dried out but remained erect. Initially, leaves remained green and attached to the stem. Within 24 hr of wilt onset, a white mat of mycelia had formed around the discolored site on the stem base. Within 1-2 days, the mat had rounded off into small, white, sclerotia initials, which grew and changed into the characteristic brown of mature sclerotia within 24 hr. The symptoms of Sclerotium wilt are strikingly similar to those caused by Sclerotinia sclerotiorum (Lib.) de Baryon sunflower. The disease occurred sporadically and with a low incidence in the field. One of every 15-20 farms visited showed a 5-8% incidence of Sclerotium wilt. Because of rotation, successive crops include ground nuts, soybeans, and other legumes, as well as okra, tomatoes, potatoes, and other vegetables, most of which are susceptible to Sclerotium wilt. Inoculum density may therefore increase rapidly, leading to extensive epidemics of the disease in Nigeria. Although S. rolfsii is an ubiquitous pathogen that has been known to cause wilt of crops all over the world, including Nigeria, this is the first time its potential as a wilt-causing pathogen on sunflower in Nigeria is highlighted. If the potential of sunflower as an alternative oil crop to the dwindling ground nut and oil palm crops in Nigeria is to be realized, not only should the damage and subsequent loss caused by S. rolfsii be considered but steps should be taken to avoid the potential epidemic it will cause in large-scale production of sunflower.