Features Agronomy Diseases
Anthracnose in corn: the eastern Canadian snapshot

Tracking the incidence of anthracnose in corn in Ontario and Quebec shows a marked increase in less than 10 years. Graph and photo courtesy of Albert Tenuta, OMAFRA.

While incidence continues to increase, new resistant hybrids are being developed.

Incidence of anthracnose in corn in Ontario and Quebec is growing, and that growth is expected to expand during the foreseeable future.

Albert Tenuta, extension plant pathologist for field crops with Ontario Ministry of Agriculture, Food and Rural Affairs, says the disease is a significant concern in the province, noticeably impacting on overall corn yield. However, anthracnose incidence is variable, and depends on location, rotational schedule, weather and hybrid choice. “We’ve seen an increase in anthracnose leaf blight and dieback over time,” says Tenuta, “surprising not just in Southwestern Ontario but Eastern Ontario as well.

Dr. Steven King, senior research manager with Pioneer Hi-Bred in Tavistock, Ontario, says the increased incidence in Eastern Ontario is largely a result of farming practice choices. “There are more corn-corn rotations seen in Eastern Ontario and Quebec, and that’s mostly due to economics,” he says. “The incidence in those areas was very high in 2007, with large differences in disease severity seen in hybrids that are more susceptible.”

“Any agricultural practice that leaves residue on the soil surface increases your risk of these types of diseases,” adds Tenuta. “The worst thing farmers can do is leave residue on the land and grow the same crop year after year.” The anthracnose fungus primarily survives from year to year (overwinters) in corn residue, and does very well in warm, wet weather.

During the last six years, a team that includes Tenuta and Ottawa-based Agriculture and Agri-Food Canada scientists Dr. Xiaoyang Zhu, Dr. Lana Reid and Tsegaye Woldemariam, has conducted surveys of anthracnose leaf blight in corn fields in both Ontario and Quebec. Among examined fields in Ontario in 2002, virtually no disease was observed. In 2003, that rose to 25 percent, followed by 55 percent in 2004, 68 percent in 2005 and 80 percent in 2006.

In surveyed Quebec fields, incidence rose from very little in 2003 to about 79 percent in 2004, dipping to roughly 24 percent in 2005, and then reaching 86 per cent in 2006.
 

Anthracnose incidence is variable, and depends on location, rotation schedule, weather and hybrid selection.

Resistant hybrids
Pioneer Hi-Bred scientists have been working for several years to boost the anthracnose resistance of several North American-adapted hybrids in their lineup. This has been accomplished through incorporation of genes from South American varieties.

King says “You always have to look at sources for new genes. At Pioneer, as with other large companies, you have operations around the world where you have access to local gene pools.” Resistance to anthracnose was observed in some South American plants and through the use of genetic markers, these genes are bred into hybrids adapted to Ontario and Quebec climate and growing conditions. “By using molecular markers, we are able to determine if the resistance genes of interest have been successfully transferred to new hybrids. This allows us to much more efficiently track these genes in the breeding population, rather than relying on growing the phenotype and observing its degree of resistance. The markers tell us if the gene is there or it’s not.”

King adds, “We then ‘characterize’ the resistance of our experimental hybrids by introducing the disease and assessing their reaction to disease. This particular set of genes from South America has increased the resistance score of hybrids in question by two points, which is very significant.” These new
hybrids will be introduced in the US in 2009 and in Canada most likely in 2010.