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Pathologist Identifies Race 73 Anthracnose Variety in Region
January 15, 2003

A plant pathologist with the North Dakota State University has discovered the race 73 variety of anthracnose in the state of North Dakota and warns this strain can infect the most commonly planted cultivars in North Dakota and Minnesota.

"Our main goal is to provide producers with information as to what pathogens are affecting their crops and what can be done to stop or control them," says Luis del Rio, NDSU plant pathologist. "With this information, producers are prepared to make choices based on possible profit and cost."

In 2001, anthracnose was discovered in several areas of eastern North Dakota. Anthracnose can cause lesions on dry bean plants, can kill seedlings and results in significant losses in yield. It is a serious problem in many parts of the world. Anthracnose is seed borne, so anthracnose-free seed has lessened its impact in the U.S.

"The first thing that we needed to know about this anthracnose problem was which race or variety of the pathogen this was," del Rio says. "Once we know that, we are able to determine, by experimentation, what cultivars are resistant to this race of anthracnose."

"To identify the race present in our fields we inoculated a set of special cultivars with different isolates of the pathogen that we retrieved from infected plants from fields in North Dakota. We used isolates of races 7, 73 and 89 as control groups" del Rio says. "When compared to our control group, the resistance and susceptibility of the different cultivars showed that we were looking at race 73."

"In order to estimate the potential impact of this new pathogen on our bean industry, we inoculated three groups of ten seedlings of each of thirty cultivars that are the most common in our area," del Rio says. "We used samples of race 7, 73 and 89 of the pathogen. The results of this test pointed out the resistance or susceptibility of our cultivars to the pathogen. This is the type of information producers need."

The news resulting from this experiment is mixed for local producers. "On the one hand, local cultivars that are overwhelming favorites in the area such as Maverick (pinto bean) and Norstar (navy bean) are highly susceptible to race 73 anthracnose," del Rio says. "Topaz is the only pinto bean resistant to this strain of the pathogen. On the navy bean side, there are more options for producers. There are five varieties that proved to be resistant. The good news is that all varieties of kidney beans proved resistant."

The other problem is control or eradication of the pathogen. "The amount of damage done to a crop depends largely on when during the growing cycle the conditions are ripe for the fungus to spread," del Rio says. "Cool (65-80 degrees), wet weather is favorable for disease development. The problem is that the fungus can lie dormant in warmer temperatures and then continue to grow when more favorable conditions return."

Bringing in a crop that looks good does not necessarily mean that you are home free. "In late infections during pod-fill, you may not be able to see outward symptoms of anthracnose," del Rio says. "Infected, otherwise normal-looking seed can carry the fungus under the seed coat, and seedlings from this seed can become new sources of infection. When the fungus is deep inside the seed, its chances of surviving the chemical seed treatment are greater."

The best way to control anthracnose is by prevention. "Since infected seeds are the most important sources of infection, using certified anthracnose-free seeds is probably the most important decision to make. If you know that you had anthracnose in your fields in the previous season, do not use bin-run seed because in many instances the pathogen may be present in seeds without showing any signs of infection," del Rio says. "The pathogen also survives in infected plant residues and could be moved from field to field in machinery used to cultivate or to harvest. So working fields that may be infected with anthracnose last is one way to prevent spreading the pathogen."

"Chemical treatments are not as effective as we would like them to be. This creates a risky situation for producers because many may think that treating the seeds means the pathogen has been killed. This is not always true," del Rio says. "Until cultivars resistant to race 73 are available, prevention is the best option for producers."


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