1.11.8
ABUTILON YELLOWS VIRUS - A NEW CLOSTEROVIRUS TRANSMITTED BY BANDED-WING WHITEFLY (TRIALEURODES ABUTILONEA)

HY LIU, GC WISLER and JE DUFFUS

USDA-ARS, 1636 East Alisal Street, Salinas, CA 93905, USA

Background and objectives
Whitefly-transmitted clostero or clostero-like viruses are emerging as one of the most numerous subgroups of plant viruses [1]. The closteroviruses have been characterized by a number of features including particle morphology, cytopathology, mode of transmission and, more recently, genome organization. Abutilon yellows virus (AYV) was first found on velvetleaf (Abutilon theophrasti) in Illinois, and has been maintained in greenhouse culture by whitefly transmission since 1977. However, this virus has never been characterized. The purpose of the research on the AYV agent was to verify evidence of its viral nature, to measure some of its properties, and to investigate its relationship with its whitefly vector and the relationship with other whitefly-borne closteroviruses.

Results and conclusions
Recent studies on the virus have shown that leaf dips and purified preparations contained long, flexuous, filamentous particles approximately 800-850x12 nm. The virus was transmitted by the banded-wing whitefly (Trialeurodes abutilonea) in a semi-persistent manner and retained by the vector for 4 days. The virus has an apparently narrow host range and could not be mechanically transmitted. Inclusion bodies, characteristic of closteroviruses, were associated with the phloem of AYV-infected Nicotiana clevelandii. Ultrastructural studies of infected tissue revealed the consistent presence of cytoplasmic vesicles in phloem parenchyma cells characteristic of closterovirus infections [2]. AYV was cloned using dsRNA isolated from AYV-infected N. clevelandii as a template. These clones specifically reacted with dsRNA, as well as with total nucleic acids extracted from AYV-infected plants, in dot blot analyses. No reactions were observed in dot blot hybridizations against uninfected host plants and other known whitefly-transmitted closteroviruses. Based on particle morphology, whitefly transmission, cytopathology, and phloem-limitation, AYV appears to be another member of the subgroup of whitefly-transmitted closteroviruses. Currently, only two other closteroviruses have been reported to be transmitted by the banded-wing whitefly: (i) diodia vein chlorosis virus which differs significantly from AYV in dsRNA profiles and host ranges, and (ii) tomato chlorosis virus which differs from AYV in insect transmission biology, host ranges and nucleic acid hybridizations.

References
1. Wisler GC, Duffus JE, Liu HY, Li RL, 1998. Plant Disease 82, 270-280.
2. Pinto RL, Hoefert LL, Fail GL, 1988. Journal of Ultrastructure and Molecular Structure Research 100, 245-254.