Charcoal rot is a fungus that is extensively distributed in soils worldwide. It is usually one of the top 10 soybean diseases annually, but not every state will be affected every year. The pathogen has been found throughout the U.S. north central soybean-growing region.
Hot and dry conditions during flowering and pod set often result in soybean yield losses due to charcoal rot. Generally, seedlings are most susceptible to attack by charcoal rot when weather is cool and moist from two to four weeks after planting,. The pathogen can attack the roots throughout the season, but it is assumed that early infection is what leads to the greatest yield losses. Studies show that charcoal rot infection can reduce plant height, root volume and root weight by more than 50 percent.
Small gains have been made by researchers in the control of charcoal rot. Many in the research group studying the root disease believe that diagnostic tools will soon be developed.
Jason Bond, an agronomist at Southern Illinois University is project manager for the frogeye leaf spot frogeye leaf spot and charcoal rot research funded by the North Central Soybean Research Program. believes his team is close to “turning the corner” in developing the charcoal rot-resistant check varieties needed to screen germplasm.
However, the researchers face several challenges. To develop a charcoal rot-resistant check variety, greenhouse assays must agree with what is found in field trials, which hasn’t been the case with charcoal rot. Also, the hot, dry conditions that charcoal rot thrives in may not occur every year.
“The second major hurdle is that we do not have varieties resistant to charcoal rot. It is very easy to develop screening protocols if you have a resistant “check” variety,” says Bond. This is true for diseases like SCN, sudden death syndrome and frogeye leaf spot. If you don’t have the resistant check varieties, you are in effect trying to identify them at the same time you are developing the protocol, which is very difficult and time-consuming.”
Elite germplasm lines from the USDA and public institutions in the NCSRP project are being evaluated in the field and the greenhouse. Several of these lines seem to hinder colonization by the charcoal rot pathogen. Researchers are trying to determine if this ability to hinder colonization is consistent across time and locations. The next step currently underway is to try to take some of the potentially resistant lines and cross them to known charcoal rot susceptible lines. This will allow the agronomists to determine if this is a trait that can be inherited.
