Marasmiellus Leaf Disease on Maize in West Africa

A leaf disease of maize previously described as borde blanco (1) or horizontal banded blight (2) was recently observed for the first time in three West African countries. The symptom was white, dry lesions that grew phasically on the edge of the leaf, resulting in horizontal bands delineated by purple to brown margins. Minute basidiocarps (1 mm high) were seen in the white zone of the banded lesions, often arranged linearly. The appearance of the fungus was consistent with a report from Sierra Leone and Guinea Conakry of a basidiomycete on maize of the order Agaricales, Marasmiellus paspalli (Petch) Singer (2). Lamellae were lacking, replaced on mature basidiomes by up to four ridges, which concurred with the description of an unnamed West African variety (1). The pileus and stipe of the mushroom were consistently white when fresh, and light beige when mature. The fungus grew readily on potato dextrose agar, forming a cottony white colony with occasional dark stromatic tissue, and hyphae with abundant clamp connections. Out of over 100 fields visited in 1993 and 1994, the disease was seen in one site only in southern Cameroon in 1994. In 1997, it was found in all maize fields in four separate areas in the southern humid forest zone of that country. In Ghana in November 1996, it was prevalent in a survey of 60 fields, with leaf area losses from 30 to 40%. In August of 1997, the disease appeared in low incidence on maize in Nigeria. The appearance of the Marasmiellus disease in Cameroon, Nigeria, and Ghana in the last 3 years represents a geographic shift from where the pathogen has been previously reported (1,2). It is not known at this time if significant yield loss is being incurred. References: (1) F. M. Latterell and A. E. Rossi. Plant Dis. 68:728, 1984. (2) M. M. Payak and R. C. Sharma. Curr. Sci. 55:1135, 1986.