What is Charcoal Rot?
Charcoal rot is an economical disease of soybean that causes problem on soybean worldwide. The disease can cause a low or high yield loss or lower seed quality, depending on its severity. It is the second most damaging disease on soybean in the United States, and number one cause of yield loss in the Southern U.S States. The annual yield loss reported between 1996 and 2007 for charcoal rot on soybean in the United states was up to 27 million tons .
Which organism causes Charcoal Rot?
The fungus causing charcoal rot is known as Macrophomina phaseolina (Tassi) Goid. This fungus is pathogenic to over 500 species of plants and causes disease in many other economical crops, including corn (Zea mays L.), sorghum (Sorghum Moench), cotton (Gossypium L.), and tobacco (Nicotiana).
How and when does this fungus causes the disease?
The fungus is present in all agricultural soils, and can survive in plant residues in the form of sclerotia during harsh environmental conditions. But when conditions become favorable for the fungus (high soil moisture), the sclerotia germinate and infect soybean plants. But infections often remain dormant until during low moisture and high temperature conditions when the disease become severe.
What part of soybean is vulnerable to charcoal rot?
Soybean seeds, seedlings, and mature soybean plants are all vulnerable to charcoal rot. In seed infections, plants may not emerge. Seedling infection can be early as few days after seedling emergence, and seedlings may become discolored and die. In mature soybeans, the fungus will grow and colonizes within the infected plant tissues and clogs the vascular tissue, thus interferes with water movement within the xylem. This may result in a reduced plant vigor, leaf yellowing, and wilting – untimely dying – of plants, with the leaves still attached to the petioles.
What are the signs of the pathogen?
Most common signs associated with the disease include gray streaks on lower stem and taproots, small black specks (microsclerotia) in the epidermis and lower stems and taproots of infected plants, giving them a charcoal (blackish) appearance. And often, a reddish-brown discoloration may occur in the pith and vascular tissues of lower stem and root.
What strategies can used to manage charcoal rot?
There are strategies to manage charcoal rot disease. These strategies mainly include the use of resistant cultivars, seed treatments, and cultural practices such as tillage; rotation; irrigation; and seeding rate management. Basically, the strategies help to reduce charcoal rot pressure in soybean fields, since charcoal rot pathogen may not be completely eliminated once in a field. Also, there is no complete resistance to charcoal rot pathogen, and the disease is favored by varying environmental factors. So most management efforts are focused on practices that lower inoculum propagules in field soils.
Sources:
Hershman, D. E. (1993). Kentucky plant disease management guide for soybeans.
Kaur, S., Dhillon, G. S., Brar, S. K., Vallad, G. E., Chand, R., & Chauhan, V. B. (2012). Emerging phytopathogen Macrophomina phaseolina: biology, economic importance and current diagnostic trends. Critical Reviews in Microbiology, 38(2), 136-151.
Mengistu, A., Arelli, P. A., Bond, J. P., Shannon, G. J., Wrather, A. J., Rupe, J. B., … & Pantalone, V. R. (2011). Evaluation of soybean genotypes for resistance to charcoal rot. Plant health progress, 12(1), 6.
Smith, D., Chilvers, M., Dorrance, A., Hughes, T., Mueller, D., Niblack, T., & Wise, K. (2014). Charcoal rot management in the north central region. University of Wisconsin Extension Bulletin A, 4037.
Wrather, A., & Koenning, S. (2009). Effects of diseases on soybean yields in the United States 1996 to 2007. Plant Health Progress, 10(1), 24.
Great insight here into how this fungus incites Charcoal rot disease in Soybean.
I do feel that with further study into the activities of this fungus, we can search out the overall beneficial and harmful effects it pose on production (especially Maize and Soybean on US soil).
However, it wouldn’t be out of place to search out conditions that aren’t favourable for the development of this fungus and the factors responsible for it. Usually, taking a cue from the disease triangle, disease can’t occur unless we have a Virulent pathogen, Susceptible host and Favourable environment thus the degree of exposure (crops) or prevalence of infection (fungus) is largely dependent on the environmental condition (edaphic, atmospheric, etc) playing out in synchronized manner.
This unfavorable condition (root exudase, fungicidal properties of leaves, seeds, etc) can be incorporated to the rhizosphere soil and harnessed to break the cycle and reduce their population.
Thank you Mr Oluwatosin. Your comment is very is appreciated. Yes, more research is needed to understand more about this pathogen on many different crops including corn (maize). It is known that the pathogen can attack up to 500 species of plant including many important food crops. This make it particularly economic important pathogen.