|Liu, Hsing Yeh|
Submitted to: International Plant Virus Epidemiology Symposium
Publication Type: Proceedings
Publication Acceptance Date: 5/12/2002
Publication Date: N/A
Technical Abstract: In 1981, lettuce, cucurbits, and sugarbeet crops in the southwestern United States wee ubiquitously infested with Lettuce infectious yellows virus (LIYV), resulting in losses exceeding $20 million in one growing season. LIYV is a Crinivirus, which is classified as a new genus of Closteroviridae family. The cucurbits appear to play an important role in the epidemiology of LIYV. The cucurbits are a breeding host of the whitefly and also serve as a source of LIYV for newly emerging crops in September. 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 with no or low efficiency of virus transmission, we surveyed the desert areas for whitefly and found a new biotype: "B". This biotype "B" is different from the original biotype "A" in host preference, larval development, transmission efficiency of LIYV, and the induction of silverleaf symptom on squash, but 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 newly descried clostero-like virus termed Lettuce chlorosis virus (LCV) have been isolated from sugarbeet and lettuce plants in the desert regions. B-biotype whitefly can transmit LCV efficiently. However, because cucurbits are not LCV hosts, the only known virus source in the field is from the weed hosts. Therefore, so far LCV has not caused severe losses to crops.