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Ancient Maize Varieties Provide Modern Solution to Tar Spot Complex

By Jennifer Johnson, Terry Molnar and Martha Willcox

Felix Corzo Jimenez , a farmer in Chiapas, Mexico, examines one of his many maize plants infected with tar spot complex.

Felix Corzo Jimenez , a farmer in Chiapas, Mexico, examines one of his many maize plants infected with tar spot complex.

In southern Mexico and Central America a fungal maize disease known as tar spot complex (TSC) is decimating yields, threatening local food security and livelihoods. In El Portillo, Chiapas, Mexico, local farmer Felix Corzo Jimenez surveys his maize field sadly… “It’s been a terrible year. We’ll be lucky if we harvest even 50 percent of our usual yields.” He fingers a dried up maize leaf covered in tiny black dots, and pulls the husk off of an ear to show the shriveled kernels, poorly filled-in. “Tar spot is ruining our crops.”

Named for the telltale black spots that cover infected plants, TSC causes leaves to die prematurely, weakening the plant and preventing the ears from developing fully, cutting yields by up to 50 percent or more in extreme cases. Caused by a combination of 3 fungal infections, the disease occurs most often in cool and humid areas across southern Mexico, Central America and into South America. The disease is beginning to spread, possibly due to climate change, evolving pathogens and susceptible maize varieties, and was reported in important maize producing regions of central Mexico and the northern United States for the first time last fall. To develop the TSC resistant maize varieties that farmers need, the Seeds of Discovery (SeeD) initiative is working to “mine” the CIMMYT genebank for native maize varieties that may hold genes for resistance against the disease.