Wheat Soilborne Mosaic

Wheat Soilborne Mosaic


Wheat soilborne mosaic (WSBM) was first discovered in Illinois in 1919. It is now considered one on the major wheat diseases of the central and eastern United States and can also be found in parts of eastern Canada, South America, Europe, Asia, and northern Africa. The disease was thought to be confined to areas east of the Rocky Mountains in the U.S. until it was discovered in Oregon in 1993. The causal organism of WSBM is the wheat soilborne mosaic virus. It was one of the first soilborne viruses to be identified on wheat. The pathogen is a member of the furovirus group. Virus particles consist of stiff rods in two lengths. WSBMV is divided into several strains. Winter wheat is the most important host and suffers the greatest amount of injury as a result of infection by the pathogen. Spring wheat, barley, rye, bromegrasses and certain weeds also serve as hosts. The fungus, Polymyxa graminis, vectors the virus. This organism is a primitive or plasmodiophoraceous f ungus which is an obligate parasite on the roots of higher plants. Polymyxa graminis is soilborne and is found in cool, wet soils. Under favorable conditions resting spores in the soil produce flagellated zoospores which swim to roots and enter the host through root hairs or epidermal cells. The fungus forms plasmodial bodies inside the roots which later split up into more zoospores or resting spores. Particles of WSBMV survive in or attached to the surface of zoospores and resting spores. The fungus survives for many years in the soil as resting spores. The virus can also survive for long periods in association with these spores. WSBMV is also capable of surviving for long periods (10 years or more) in dry plant tissue. Both the fungus and the pathogen are transported on infested soil. The soil may be wind or water disseminated as well as being spread on contaminated equipment. Plants most commonly become infected in the fall when temperatures range between 10-20oC. Disease development is arrested at temperatures above this range. The virus particles multiply during the fall and may predispose the plants to winter injury and infection by other organisms. However, symptoms are not usually expressed until the following spring.

Symptoms


Symptoms of wheat soilborne mosaic are most visible in early spring. Affected areas of the field appear as irregular yellow patches in low, poorly drained areas. Individual plants are dwarfed and a green and yellow mosaic pattern appears on the leaves. Stunting ranges from mild to severe. Mosaic pattern are also variable and may appear as mild green to yellow mottling or striping. A common pattern is composed of dark green islands on a yellow background. Some wheat cultivars may also be rosetted. Affected areas do not enlarge during the growing season and mosaic symptoms fade as temperatures rise. However plants may remain stunted until maturity. The longer the symptoms persist, the greater the amount of yield loss. Infected plants produce fewer and smaller heads resulting in reduced yield. In some cases this loss may be as high as 50%.

Plant Health Management

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Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was researched and drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

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This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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Copyright (C) 2003 J.E. Partridge, University of Nebraska-Lincoln. All Rights Reserved.