C. glycines produces monophialidic, ampulliform, conidiogenous cells formed from the inner cells of the pycnidial wall (Hartman and Sinclair, 1988). Pycnidiospores are ellipsoidal, one-celled, and 4-8 µm long by 1-3 µm wide. Sclerotia range in size from 96 to 357 µm in diameter, and are mostly spherical, dark brown to black, and covered with setae, 5 to 36 µm long. It is interesting to note that when the name changed from Dactuliochaeta glycines to Phoma glycinicola (de Gruyter and Boerema, 2002) and then to C. glycines (de Gruyter et al., 2013), there was no mention of the importance of the sclerotia produced by the fungus. It appears that species of Phoma and Coniothyrium do not produce similar sclerotia to C. glycines, which makes this fungus unique in its biology. The uniqueness of the sclerotia may provide a characteristic that can be used for field diagnosis as they can be seen clearly with the aid of a hand lens.
There are limited or no exports of soyabean from countries in sub-Saharan Africa to countries outside of Africa, and there have been no documented cases of movement of the pathogen from countries with this disease. Any shipment of soyabean seeds from infected countries would need to enter the USA through a seed permit process managed by USDA APHIS. Similar permitting processes are presumably in place in other countries, which would be the first step in excluding the pathogen from establishment in countries without the disease.
Related invasive species
- Coniothyrium glycines
Related Farm Practice
- Host plants
- Development
- Diagnosis
- Biology
Red leaf blotch affects soyabean in central and southern Africa. The disease and the causal fungus (Coniothyrium glycines) were first reported in Ethiopia in 1957. C. glycines is native to Africa, living on the native legume, Neonotonia wightii, and perhaps other native or non-native legumes. The jump of the pathogen to soyabean occurred as early as 1957 and reports of the occurrence of red leaf blotch have increased along with soyabean production in Africa. The disease is currently a serious threat to soyabean production in sub-Saharan African countries with losses of up to 70% reported. C. glycines is considered a threat to soyabean-producing countries such as Brazil and the USA. The pathogen is not known to be disseminated by seed or wind. Infection is thought to occur via rainsplash of soilborne inoculum onto the leaves of soyabean plants. Symptoms include characteristic dark red spots on the upper leaf surface and reddish-brown lesions with dark borders on the lower surface. Premature leaf drop may occur in heavy disease conditions, releasing sclerotia back into the soil. The disease is favoured by wet, humid conditions.
C. glycines produces similar symptoms on soyabean and Neonotonia wightii. Initial symptoms can occur at the seedlings stage on unifoliolate leaves. Early lesion development is often associated with primary veins (see Pictures). Under conditions conducive for disease development, symptoms appear over time from the lower to the upper trifoliolate leaves as dark red blotches on the upper surfaces and similar reddish-brown blotches with dark borders on the lower surface s. The fungus also causes lesions on petioles, stems and pods (see Pictures).
Soyabean is the only known crop host under field conditions. The only other host found to be naturally infected is Neonotonia wightii. The experimental host range through inoculation includes the crops cowpea, lima bean, pigeon pea and winter vetch, and non-crops Glycine argyrea, G. canescens, G. clandestina, G. cyrtoloba, G. falcata, G. latrobeana, G. soja [ G. max subsp. soja ], G. tabacina, G. tomentella, N. wightii and Pueraria lobata [ Pueraria montana var. lobata ] (Hartman and Sinclair, 1992).