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An new virus was discovered in wheat in Comanche County, Kansas in the fall of 1992. The virus was eventually identified as American wheat striate mosaic virus (AWStMV) which was first reported in 1953 in the northern Great Plains. Since 1992, AWStMV had been found all over the state of Kansas, but always at a low percentage of infected plants. Therefore, losses have been very low. Certain varieties are highly susceptible while others are highly resistant. However, it is probably not an important enough disease to affect variety selection. The main significance of the disease is that it can easily be confused with other problems such as black chaff, glume blotch, melanism, Cephalosporium stripe, genetic mutants, nutrient deficiency, or possibly wheat streak mosaic virus. SYMPTOMSSymptoms of AWStMV depend strongly on variety. Some resistant varieties like Ike or Karl can be infected but show either a very mild mosaic or no symptoms at all. The initial symptoms on susceptible varieties are very thin white to yellow striations or lines on the undersurface of the lower leaves. These distinctive symptoms look more like insect feeding injury than a normal viral mosaic. As leaves age, they may get necrotic brown streaks and start to die. Symptoms on upper leaves usually consist of extremely long, extremely thin green, white, and brown striations that may extend for the entire length of the leaf. These symptoms are strange and almost look like genetic variegations on the leaves. The streaking extends from the leaves down into the leaf sheaths. When heads emerge, glumes have very striking brown stripes that resemble black chaff symptoms. Unlike black chaff, the glume stripes tend to be very uniform from spikelet to spikelet. The neck region of the stem below the head usually is brown. There may be brown streaks on the lower culms. Heads do not fill well and often ripen prematurely. Tillers are usually stunted. All the tillers on a plant will be affected, but adjacent plants are often completely free of symptoms. Plants seem to occur randomly in the field with no apparent pattern. Identification can be confirmed with an ELISA test. LIFE CYCLEAWStMV is carried by the painted leafhopper. Wheat, corn, barley, oats, some bromegrasses, and some Panicums are known hosts. We have no information on the source of the virus for Kansas wheat fields. It could be coming via migratory leafhoppers from far away or it could be local. In Kansas, most infections appear to occur in the fall, but symptoms are hard to detect until mid- spring. Early planting probably favors fall infections. We have not observed plant to plant spread of the virus. CONTROLThe two ways to control AWStMV would be with resistant varieties and by avoiding early planting. However, AWStMV is probably not an important enough disease to warrant special control measures. For completeness, and to aid diagnosis, a list of variety reactions is included here. Susceptible varieties include Hickok, Laredo, Mesa, Ogallala, Ponderosa, Rio Blanco, Thunderbird, Tomahawk, Victory, and Vista. Longhorn, TAM 200, and T13 are intermediate in reaction. As far as we know, all other common varieties show very high resistance. |
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Web updated 9/01/06 |
