|Liu, Hsing Yeh|
Submitted to: Proceedings XI National Congress of the Spanish Phytopathological Society
Publication Type: Proceedings
Publication Acceptance Date: 10/14/2002
Publication Date: N/A
Technical Abstract: Whitefly-transmitted criniviruses are an expanding group of plant viruses. Crinivirus is a new genus belongs to Closteroviridae family. The criniviruses have been characterized by a number of features including particle morphology, cytopathology, mode of transmission, and bipartite single stranded RNA genome. In early 1980's, lettuce, cucurbits, and sugar beet crops in the southwestern U.S. were ubiquitously infected with Lettuce infectious yellows virus (LIYV), resulting in losses exceeding $20 million in one growing season. In 1990-1991 the incidence of LIYV in the desert areas were reduced from 70% to 1% in spite of the record high population of its insect vector, the sweetpotato whitefly (Bemisia tabaci). With a hypothesis of the vector population shifting to a new biotype we discovered a new biotype: "B". This biotype "B" is indistinguishable morphologically from biotype "A". We developed an isozyme pattern technique to differentiate biotype "B" from biotype "A". Since 1991, a mixture of viruses including LIYV and a new clostero-like virus termed Lettuce chlorosis virus (LCV) have been isolated from sugar beet and lettuce plants in the desert regions. B-biotype whitefly can transmit LCV efficiently. However, because the only known virus source in the field is from the weed hosts. Therefore, so far LCV has not caused severe losses to crops. Since 1993, we have discovered at least two distinct tomato-infecting criniviruses, Tomato infectious chlorosis virus (TICV) and Tomato chlorosis virus (ToCV). These viruses have wide host ranges and include ornamentals, weeds, and agronomic crops. TICV has been identified in limited locations while the distribution of ToCV appeared to be considerably broader. Although TICV is only transmitted by the greenhouse whitefly (Trialeuordes vaporariorum), four whitefly vectors transmit ToCV, including T. vaporariorum, B. tabaci A and B biotypes, and the banded wing whitefly (T. abutilone). Movement of these viruses in breeding material and increases in both international trade and greenhouse vegetable culture contributes to the expansion of the natural range of these viruses.