Outbreak of Red Leaf Blotch, Caused by Dactuliochaeta glycines, on Soybeans in Nigeria. C. N. Akem, Grain Legume Improvement Program, International Institute of Tropical Agriculture, PMB 5320, Ibadan, Nigeria. C. O. Akueshi, O. A. Uwala, and K. E. Dashiell. University of Jos, Jos, Nigeria; National Cereals Research Institute, Mokwa, Nigeria; and Grain Legume Improvement Program, International Institute of Tropical Agriculture, PMB 5320, Ibadan, Nigeria. Plant Dis. 76:323. Accepted for publication 12 September 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0323C.
Red leaf blotch, caused by Dactuliochaeta glycines (R.B. Stewart)
Hartman & Sinclair (2) (= Pyrenochaeta glycines R.B. Stewart), was
observed on soybeans (Glycine max (L.) Merr.) at Bukuru, near Jos
in the state of Plateau, Nigeria, in 1990. Over 80% of the plants in
the 4-ha nonirrigated, sandy loam field nursery showed symptoms.
Dark red to brown lesions on primary leaf veins eventually enlarged
and coalesced to form irregular blotches 5-10 mm in diameter. Most
blotches had ash-gray centers with dark margins and some were
surrounded by chlorotic halos. Pycnidia with setae clustered around the ostiole were observed within older blotches on the upper leaf
surface. Premature senescence was common on severely infected plants.
The pathogen was isolated on acidified potato-dextrose agar and lima
bean agar; brown to black pycnidia, 156-248 µm long X 87-215 µm
wide, formed only on lima bean agar. Plants of the cultivars TGx
1440-2D and TGx 1636-8F were inoculated in the greenhouse with
an isolate of D. glycines. Symptoms were reproduced and the pathogen
was reisolated. D. glycines has been a problem on soybeans mainly
in Zambia and Zimbabwe, with yield losses of up to 50% (1). This
is the first report of this important disease of soybeans under field
conditions in Nigeria.