Cochliobolus miyabeanus

Cochliobolus miyabeanus (formerly known as Helminthosporium oryzae) is a fungus that causes brown spot disease in rice. This disease was the causal agent of the Bengal famine of 1943.

Cochliobolus miyabeanus
Symptoms of Cochliobolus miyabeanus on rice
Scientific classification
Kingdom:	Fungi
Division:	Ascomycota
Class:	Dothideomycetes
Order:	Pleosporales
Family:	Pleosporaceae
Genus:	Cochliobolus
Species:	C. miyabeanus
Binomial name
Cochliobolus miyabeanus

It was considered for use by the USA as a biological weapon against Japan during World War II.[1]

Hosts and symptoms

Brown spot of rice is a plant fungal disease that usually occurs on the host leaves and glume, as well as seedlings, sheaths, stems and grains of adult host plants. Hosts include Oryza (Asian rice), Leersia (Cutgrass), Zizania (Wild rice), and other species as well such as Echinochloa colona (junglerice) and Zea mays (maize).[2][3]

Cochliobolus miyabeanus may cause a wide range of symptoms. General symptoms occurring on the hosts can be observed on many parts of the plant, including leaves, seeds, stems and inflorescences, along with the presence of brown spot. Discoloration of stems is another symptom develops from brown spot of rice disease. Oval-shaped brown spots are the fungal growth sign, which have grey colored center developed on host leaves.

Dark coffee-coloured spots appear in the panicle and severe attacks cause spots in the grain and loss of yield and milling quality.[4]

Also, lesions on glumes and seeds occur if the pathogen associates with other fungi and insects. Such lesions may develop when favorable condition for sporulation is present.

Importance

Cochliobolus miyabeanus is an important plant pathogen because it causes a common and widespread rice disease that causes high level of crop yield losses. It was a major cause of the Bengal famine of 1943, where the crop yield was dropped by 40% to 90% and the death of 2 million people was recorded.[3] It is a possible agroterrorism weapon.[5] Other known severe crop loss cases caused by Cochliobolus miyabeanus are globally distributed.[3] In the Philippines, rice seedling mortality rate has been recorded up to 60%. In India and Nigeria, it can reduce total crop yield by up to 40%. Similar losses are observed in Suriname and Sumatra.

Environment

There are several factors influencing the disease cycle and epidemics of brown spot of rice disease.[6]

1. Rainfall and drought [6] - The first factor affecting Cochliobolus miyabeanus life cycle is rainfall and drought. It tends to proliferate when there is reduced rainfall and in dewy conditions. In addition to a low level of precipitation, severe epidemics of rice brown spot occur during drought season. Compared to well flooded or irrigated areas, disease occurrence is favored in drier environments where a reduced amount of water is present.

2. Temperature and humidity - Another factor affecting disease development for Cochliobolus miyabeanus is temperature and humidity. Infection efficiency is influenced by the humidity level of the leaves, and lowered minimum temperature for crop cultivation favors epidemics of this disease. Cochliobolus miyabeanus grows well at lower temperatures during its developmental stages compared to the developed stage,[7] so if high temperatures are maintained in the area it is likely that farmers can restrict the growth of this pathogen. The optimal temperature for the pathogen is 28 °C (82 °F).[8]

3. Nutrition level[6] - Nutrition of the host plant may also influence the level of disease development. For example, low soil nutrient content is associated with epidemics of rice brown spot. If soil minerals such as nitrogen, potassium, phosphorus, silicon and manganese are deficient, this will likely favor disease development. In specific, in areas where silicon is present in a high amount in the soil, the host becomes less susceptible to this disease because silicon not only alleviates physiological stresses of the host, but also promotes disease resistance ability in the host. Furthermore, soil moisture level contributes to disease occurrence. Brown spot of rice is favored in areas where water content is low in soil.

Management

Prevention

The spread of the fungus can be prevented by using certified disease-free seed and using available resistant varieties such as MAC 18.[4][9][10]

Avoiding dense sowing will can also help prevent the spread of the fungus as it reduces humidity [11]

Maintaining control of weeds and removal of volunteer crops in the field can also prevent fungal spread,[4][12][13] as well as burning the stubble of infected plants.[9][10][11]

Seed treatments can also be used as a preventative measure. Seeds can be treated with fungicides [4][12][13] or alternatively soaking seeds in cold water for 8 hours before treating with hot water (53-54°C) for 10-12 minutes prior to planting.[4][11][13]

Soil treatments can also be used to prevent the spread of C. miyabeanus. The addition of potassium and calcium if the soil is deficient can help boost disease resistance.[13][14] However, excessive application of nitrogen fertilisers should be avoided.[9][12]

Control

Once symptoms are observed the disease may be controlled by burning removal and burning of any plants and maintaining water levels up to 3 inches at grain formation. below grain formation.[9][10][11][13][14]

Sources

 This article incorporates text from a free content work. Licensed under CC-BY-SA License statement/permission on Wikimedia Commons. Text taken from Plantwise Factsheet for Farmers: Helminthosporiosis in rice, Dalcy Montenegro Coca, Raquel Pardo, Fabiola Mareño, Dionicio Sosa, CABI.

 This article incorporates text from a free content work. Licensed under CC-BY-SA License statement/permission on Wikimedia Commons. Text taken from PMDG: Brown spot in rice -Thailand, Bureau of Rice Research and Development , Rice Department, CABI.

 This article incorporates text from a free content work. Licensed under CC-BY-SA License statement/permission on Wikimedia Commons. Text taken from PMDG: Brown spot of rice - Pakistan, Yasar Saleem Khan and Amna Palwasha, CABI.

 This article incorporates text from a free content work. Licensed under CC-BY-SA License statement/permission on Wikimedia Commons. Text taken from PMDG: Brown leaf spot of rice - Ghana, E. Moses, S. Akrofi and P. Beseh, CABI.

 This article incorporates text from a free content work. Licensed under CC-BY-SA License statement/permission on Wikimedia Commons. Text taken from PMDG: Rice - Brown spot - Cambodia, GDA, Phnom Penh, Cambodia, CABI.

 This article incorporates text from a free content work. Licensed under CC-BY-SA License statement/permission on Wikimedia Commons. Text taken from PMDG Green List: Brown leaf spot on rice, Plantwise, CABI.

 This article incorporates text from a free content work. Licensed under CC-BY-SA License statement/permission on Wikimedia Commons. Text taken from PMDG: Brown spot on rice - Malawi, T. Maulana, D. Kachigamba, J. Chipole,H. Msatilomo and J. Nthenda, CABI.

See also

• list of rice diseases

References

1. Cochrane, Rexmond (1947). History of the Chemical Warfare Service in World War II (1 July 1940 - 15 August 1945): Biological Warfare Research in the United States (Report). Vol. II. pp. 387–394. Retrieved 19 December 2018.
2. "Cochliobolus miyabeanus (Japanese Fungi on Plants)".
3. "Brown leaf spot of rice (Cochliobolus miyabeanus)".
4. "Plantwise Knowledge Bank | Helminthosporiosis in rice". www.plantwise.org. Retrieved 2020-05-21.
5. Suffert, Frédéric; Latxague, Émilie; Sache, Ivan (2009-03-11). "Plant pathogens as agroterrorist weapons: assessment of the threat for European agriculture and forestry". Food Security. 1 (2): 221–232. doi:10.1007/s12571-009-0014-2. S2CID 23830595.
6. Barnwal, M. K.; Kotasthane, A.; Magculia, N.; Mukherjee, P. K.; Savary, S.; Sharma, A. K.; Singh, H. B.; Singh, U. S.; Sparks, A. H. (2013-03-10). "A review on crop losses, epidemiology and disease management of rice brown spot to identify research priorities and knowledge gaps". European Journal of Plant Pathology. 136 (3): 443–457. doi:10.1007/s10658-013-0195-6. ISSN 0929-1873.
7. Moore, David. Fungal Morphogenesis. p. 186.
8. Ou, Shu Huang. Rice Diseases. p. 207.
9. "Plantwise Knowledge Bank | Brown Leaf Spot of Rice - Pakistan". www.plantwise.org. Retrieved 2020-05-21.
10. "Plantwise Knowledge Bank | Brown leaf spot of rice - Ghana". www.plantwise.org. Retrieved 2020-05-21.
11. "Plantwise Knowledge Bank | Rice - Brown Spot - Cambodia". www.plantwise.org. Retrieved 2020-05-21.
12. "Plantwise Knowledge Bank | Brown Spot in rice - Thailand". www.plantwise.org. Retrieved 2020-05-21.
13. "Plantwise Knowledge Bank | Brown leaf spot on rice". www.plantwise.org. Retrieved 2020-05-21.
14. "Plantwise Knowledge Bank | Brown spot on rice - Malawi". www.plantwise.org. Retrieved 2020-05-21.

Sources

• World Food Crisis: Meeting the demands of a growing population by Jeff Batten, APS/CPS Annual Meeting, Monday, August 9, 1999