CHANGE IN VIRULENCE OF WHEAT CURL MITE DETECTED ON TAM-107 WHEAT

Wheat streak mosaic is the most important wheat (Triticum aestivum L.) disease in western Kansas. The wheat cultivar TAM 107 has been resist ant to the wheat curl mite (WCM, Aceria tosichella Keifer), which is t he vector of wheat streak mosaic virus (WSMV) and as the most popular wheat cultivar in western Kansas has effectively reduced the incidence of the disease. In 1991, several observations indicated that the inci dence of WSMV infection in TAM 107 was much heavier than usual. In 199 2, a survey of 10 field collections of WCM showed that one collection from TAM 107 was virulent to that cultivar. In 1995, WCM collections f rom TAM 107 and 'Karl' (susceptible to WCM) were made from 14 western Kansas counties and tested for virulence to TAM 107. All collections o f WCM obtained from TAM 107 were adapted to TAM 107, and nine of the 1 4 collections from Karl were adapted to TAM 107. The high incidence of a WCM strain virulent to TAM 107 may explain the increased losses to WSMV recently observed in that cultivar. TAM 107 probably cannot be re lied on in the future to provide protection against WSMV in western Ka nsas. Lines derived from sources of resistance that are effective agai nst WCM virulent to TAM 107 or that are resistant to WSMV are being ad vanced in wheat breeding programs and should be deployed in the field as soon as possible.