Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2004
Publication Date: 6/1/2004
Citation: Baliji, S., Black, M.C., French, R.C., Stenger, D.C., Sunter, G. 2004. Spinach curly top virus:a newly described curtovirus species from southwest texas with incongruent gene phylogenies. Phytopathology 94:772-779. Interpretive Summary: A curly top disease epidemic in spinach that occurred in southwest Texas during Fall 1996 was caused by a previously undescribed curtovirus species. The virus, designated 'Spinach curly top virus' (SCTV) rendered infected plants unsuitable for fresh market. Molecular characterization of the viral DNA revealed that SCTV was distinct from all other previously characterized curtoviruses capable of causing curly top disease in spinach. Greenhouse inoculations with cloned DNA indicated that SCTV has a broad host range and was demonstrated to cause curly top disease symptoms in spinach in the absence of other pathogens. Evolutionary relationships of SCTV genes were incongruent, indicating that SCTV represents a recombinant viral genome in which portions of the viral DNA were derived from different curtovirus ancestors.
Technical Abstract: A curtovirus associated with a disease of spinach was isolated in southwest Texas during 1996. Disease symptoms included severe stunting and chlorosis, with younger leaves curled, distorted, and dwarfed. Viral DNA was purified and an infectious clone obtained. Agroinoculation using a construct bearing full-length tandem repeats of the cloned viral genome resulted in systemic infection of species in six of seven plant families tested, indicating that the virus has a wide host range. Symptoms produced in spinach agroinoculated with cloned viral DNA were similar to those observed in the field. Viral single-stranded and double-stranded DNA forms typical of curtovirus infection were detected in host plants by Southern blot hybridization. The complete nucleotide sequence of the infectious clone comprised 2925 nucleotides, with seven open reading frames encoding proteins homologous to those of other curtoviruses. Complete genome comparisons revealed that the spinach curtovirus shared 64.2 -83.9% nucleotide sequence identity relative to four previously characterized curtovirus species: Beet curly top virus, Beet severe curly top virus, Beet mild curly top virus, and Horseradish curly top virus. Phylogenetic analysis of individual open reading frames indicated that the evolutionary history of the three virion sense genes was different from that of the four complementary sense genes, suggesting that recombination among curtoviruses may have occurred. Collectively, these results indicate that the spinach curtovirus characterized here represents a new species of the genus Curtovirus, for which we propose the name Spinach curly top virus.