Variants of Triticum mosaic virus Isolated From Wheat in Colorado ShowDivergent Biological Behavior

Seifers, D. L., Tatineni, S., and French, R. 2013. Variants of Triticum mosaic virus isolated from wheat in Colorado show divergent biological behavior. Plant Dis. 97:903-911. Triticum mosaic virus (TriMV) is a recently discovered virus infecting wheat. We compared Colorado isolates C10-492 and C11-775 with the 06-123 isolate. Comparisons were made using enzyme-linked immunosorbent assay (ELISA), infectivity assay, host range, dry weight (DW), inoculation of ‘Mace’ wheat with temperature-sensitive resistance to Wheat streak mosaic virus, and the deduced amino acid sequence of the coat proteins (CP) and P1 proteins. Both C10-492 and C11-775 infected ‘Gallatin’ barley and, when compared with 06-123, had significantly reduced ELISA values and virus titers in wheat. Both Colorado isolates caused symptomless infections in Mace, whereas 06123 caused mosaic symptoms. The amino acid sequences of the CP differed by two and one amino acids for C10-492 and C11-775, respectively, compared with 06-123. The sequence of C10-492 differed from C11-775 by one amino acid. The P1 amino acid sequence of C10-492 and C11-775 differed from 06-123 by three and one amino acids, respectively. The C10-492 and C11-775 isolates reduced DW significantly in ‘Karl 92’ but significantly less than 06-123. In ‘2317’ wheat, the Colorado isolates did not consistently cause significant reduction in DW, while 06-123 did. The data collectively indicate that C10-492 and C11-775 are isolates of TriMV showing biological behavior diverse from that of 06-123. Triticum mosaic virus (TriMV) was first identified infecting wheat (Triticum aestivum L.) in Kansas in 2006 (17). TriMV has since been identified from infected wheat in the Great Plains in Colorado, Nebraska, Oklahoma, South Dakota, Texas, and Wyoming (1). Field surveys were conducted in Colorado, Kansas, Nebraska, and South Dakota in spring and fall 2010 and 2011 to determine TriMV incidence and the frequency of its co-infection with Wheat streak mosaic virus (WSMV) or High Plains virus (HPV) in winter wheat (2). That study showed that TriMV was detected in all four states and that WSMV was the most prevalent virus, followed by TriMV and HPV. Furthermore, 91% of TriMV-positive samples were co-infected with WSMV, whereas WSMV and HPV were mainly detected as single infections. The virus is mechanically transmissible, and has a coat protein (CP) of approximately 35 kDa. Antiserum raised to the CP of TriMV reacted only with this virus in enzyme-linked immunosorbent assay (ELISA) and Western blot assay (17). Symptomatic plants were shown to be associated with flexuous rods when analyzed by electron microscopy (17). The sequence of the CP of the 06-123 isolate of TriMV determined by time-of-flight mass spectroscopy and reverse-transcription polymerase chain reaction (RT-PCR) showed that TriMV was distantly related to Sugarcane streak mosaic virus (17). The complete nucleotide sequences of the Kansas 06-123 (5) and a Nebraska isolate (21) and partial sequences of other Kansas, Oklahoma, and Texas isolates of TriMV have been determined (6). Wheat curl mites (WCMs; Aceria tosichella Keifer) have been demonstrated to transmit TriMV both singly and in combination with WSMV (16). Thus, in addition to TriMV, the WCM also transmits WSMV (19) and the HPV (11). Previously, only naturally infected wheat and barley have been confirmed as hosts of TriMV (17). The reaction of row crop species to infection by TriMV and WSMV and the identification of differential hosts for these viruses have been conducted (13,14,20). Infection of wheat by TriMV was demonstrated to cause significant yield losses in replicated field trials at Hays, Kansas in ‘Danby’, ‘RonL’, and ‘Jagalene’ wheat but not the wheat line KS96HW10-3 (15). In a greenhouse study, yield determinants such as tillers per plant and shoot and root weight were reduced in ‘Millennium’ but not ‘Mace’ wheat when singly infected with TriMV or doubly infected with TriMV and WSMV (3). Wheat samples C10-492 (collected in Colorado in 2010) and C11-775 (collected in Colorado in 2011) with virus-like symptoms reacted weakly (low ELISA values for TriMV) with antibodies against TriMV and against WSMV but not with those against HPV. We report characteristics of these isolates when compared with the original 06-123 isolate of TriMV isolated in Kansas in 2006 (17) and show that field-collected Colorado viruses are isolates of TriMV showing divergent biological characteristics. Materials and Methods Infectivity assays. ‘Tomahawk’ wheat, ‘Arcia’ triticale, ‘Gallatin’ barley, and ‘N28Ht’ maize were used as the assay plants and inoculated mechanically (finger rub) at the single-leaf stage for wheat, barley, and triticale and at the two-leaf stage for maize, with 1:10 (wt/vol) extracts prepared from appropriate infected wheat sources (as described above). Following inoculation, the plants were held in a growth chamber at 22°C (as described above) for 14 or 21 days post inoculation (DPI) and numbers of symptomatic plants were recorded. Virus source and maintenance. The 06-123 isolate of TriMV was isolated from KS06HW79 wheat in 2006 at the Kansas AgriCorresponding author: D. L. Seifers, E-mail: [email protected] Contribution number 13-094-J from the Kansas Agricultural Experiment Station. The C10-492 and C11-775 CP sequences have been assigned the GenBank accession numbers JX843399 and JX843400, respectively, and the P1 sequences KC262645 and KC262644, respectively. The findings and conclusions in this article do not necessarily reflect the view of United States Department of Agriculture. Accepted for publication 17 January 2013. http://dx.doi.org/10.1094 / PDIS-10-12-0925-RE © 2013 The American Phytopathological Society