Pest/Pathogen of the Month: October
Scientific name: Cercospora zeina Crous & U.Braun
Common names: Gray leaf spot
In Africa, Cercospora zeina is the predominant causal pathogen of gray leaf spot disease of maize. This fungus is a threat to food security, since it can cause severe yield losses on both small-holder and large-scale farms. The foliar symptoms caused by this fungus are tan to gray rectangular lesions that are restricted within veins of maize leaves. After consuming its “maize meal” inside the leaf, the fungus bursts out of the leaf stomata with a fresh set of spores to infect the next leaf. Many things still puzzle scientists about this fungus, such as the questions “Where did it come from?” and “How has it moved around Africa?” Gray leaf spot disease was first reported in the 1980’s in KwaZulu-Natal, South Africa. Reports of the disease have since emerged from other maize producing countries in sub-Saharan Africa. Could this be due to international and local trade of maize material that may contain infected leaf sheaths and ear husks, or has it been hiding in a wild grass species? Molecular analysis has shown C. zeina to have high genetic diversity in Africa and that it undergoes cryptic sex. No one has yet observed its sexual stage, but we suspect that this contributes to its high diversity and aggressiveness. Clearly, there is need to design and employ integrated pathogen management strategies to limit its reproduction and dispersal to ensure optimal maize production and food security in Africa and globally.
