Occurrence and Yield Effects of Wheat Infected with Triticum mosaic virus in Kansas.

Triticum mosaic virus (TriMV) infects wheat (Triticum aestivum) in the Great Plains region of the United States. This study determined the occurrence of TriMV at three locations over 3 years and yield effects of wheat mechanically infected with TriMV. Wheat infection with TriMV, Wheat streak mosaic virus (WSMV), and the High Plains virus (HPV) was verified using enzyme-linked immunosorbent assay. Both wheat singly infected with TriMV and doubly infected with TriMV and WSMV occurred at three, two, and one locations in 2007, 2008, and 2009, respectively. Wheat singly infected with HPV occurred at one and two locations in 2008 and 2009, respectively. Wheat doubly infected with WSMV and HPV occurred at one location in 2008 and 2009. Infection with TriMV declined at two locations each year and, at the third location, it increased the second year and was not detected the third year. WSMV infection increased, except for a decline the third year at one location. In contrast to 3.0% infection of wheat with TriMV and WSMV at one location, 85% of the wheat 1.6 km from that site was infected with TriMV and WSMV in 2009. Infection of wheat with TriMV caused significant yield and volume weight reductions in Danby, RonL, and Jagalene but not KS96HW10-3 wheat.

The complete genome sequence of Triticum mosaic virus, a new wheat-infecting virus of the High Plains.

The genome of Triticum mosaic virus (TriMV), a recently discovered mite-transmitted wheat potyvirus, was sequenced, characterized, and compared to other members of the family Potyviridae. TriMV has a single mRNA strand of 10,266 nucleotides with a predicted polyprotein consisting of 3,112 peptides. Protein alignments of the coat protein demonstrate that TriMV has 45.9% identity to Sugarcane streak mosaic virus strain AP (SCSMV-AP), but shares only 23.2% identity to Wheat streak mosaic virus. Although TriMV is mite-transmitted and could be placed in the genus Tritimovirus, it is significantly divergent and should be placed in the newly proposed genus Susmovirus.

Identification of Variants of the High Plains virus Infecting Wheat in Kansas.

The properties of two virus isolates (U04-82 and U04-83) obtained from two wheat (Triticum aestivum) plants expressing mosaic symptoms were investigated using enzyme-linked immunosorbent assay (ELISA), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), time-of-flight mass spectrometry (TOFMS), and infection of wheat with resistance to Wheat streak mosaic virus (WSMV). The coat protein mass was estimated by SDS-PAGE as approximately 32 kDa for U04-82 and 30 kDa for U04-83. The amino acid sequence of the coat protein of U04-82 was 99.6 and 85.5% identical to two isolates, ABC58222 and TX96, respectively, of High Plains virus (HPV) described from Texas. U04-82 was transmitted by wheat curl mites and caused significant yield reductions in wheat resistant to WSMV. U04-83 was actually two distinct virus isolates whose capsid protein amino acid sequences were only 57 and 50% similar to that of TX96. Antiserum prepared to a synthetic peptide from the sequence of the U04-83 isolate recognized the two U04-83 isolates, but not the U04-82 isolate.

Isolation, transmission and purification of the High Plains virus.

The wheat curl mite (Aceria tosichella Keifer) often simultaneously transmits the High Plains virus and Wheat streak mosaic virus under field conditions, resulting in doubly infected plants. In this study, a pure culture of the High Plains virus (isolate HPV95ID), which was infected with both High Plains virus and Wheat streak mosaic virus, was mechanically transmitted from barley (Hordeum vulgáre L.) to maize (Zea mays L.) by vascular puncture inoculation. Different water temperatures and durations for soaking kernels at pre-inoculation and different incubation temperatures and durations at post-inoculation on transmission of High Plains virus were studied. Transmissions of the High Plains virus were significantly different for post-inoculation incubations at 11, 21, or 30 degrees C after a 2 h pre-inoculation soaking at 30 degrees C and post-inoculation incubations of kernels for 1 day versus 2 days. Use of Cs2SO4 in a partial purification protocol resulted in infectious final fractions. Bioassays, serological assays, analyses by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and examinations by electron microscopy confirmed isolation of a pure culture of High Plains virus from infectious final partially purified fractions. We demonstrate infectivity of the final fractions and associate it with the High Plains disease symptoms, the 32 kDa protein and double membrane bodies and discuss this evidence to support the viral nature of High Plains virus.

Association of a Virus with Wheat Displaying Yellow Head Disease Symptoms in the Great Plains.

Wheat with yellow head disease (YHD) (yellow heads and mosaic leaf symptoms) has been observed in Kansas since 1997. A pathogen was transmitted from the infected wheat to maize by vascular puncture inoculation and to Nicotiana benthamiana by rub inoculation. The original infected wheat and infected maize and N. benthamiana test plants all produced a unique 32- to 34-kDa protein when analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Time-of-flight mass spectrometry analysis of the unique 32- to 34-kDa protein showed that the amino acid sequence was most closely related to the nucleoprotein of Rice hoja blanca virus, indicating that the virus causing YHD symptoms in wheat is a tenuivirus. Antiserum made to this protein failed to react with extracts made from healthy wheat or wheat infected with Wheat streak mosaic virus or the High Plains virus. The antiserum did react to extracts made from symptomatic wheat, maize, and N. benthamiana, shown by SDS-PAGE to contain the unique protein, and to extracts of wheat with YHD symptoms from Kansas, North Dakota, South Dakota, and Oklahoma. The name Wheat yellow head virus is proposed for this virus.

Biological and Molecular Variability Among High Plains virus Isolates.

The High Plains virus (HPV), vectored by the wheat curl mite (WCM) (Aceria tosichella), causes a severe disease of maize (Zea mays) in the U. S. High Plains. In the present study, five HPV isolates from five states were separated from co-infecting Wheat streak mosaic virus and their molecular and biological variability studied. Molecular studies involved time-of-flight mass spectrometry (TOFMS) to determine amino acid sequence variability of the 32-kDa nucleoprotein (32 np) of the isolates. Biological studies involved testing the ability of the five HPV isolates to infect a maize line previously shown to have resistance. Inoculations of the HPV isolates were conducted using vascular puncture inoculation (VPI) and viruliferous WCM. TOFMS analyses demonstrated an 18-amino acid sequence in the isolates at the N-terminus of the 32 np, the presence of amino acid sequence differences among the isolates, and variability among amino acid sequences of the 32 np of some isolates. Three of the five HPV isolates infected the resistant maize inbred, B73, using VPI, and two of the same three HPV isolates infected this line using WCM inoculation, albeit low numbers of plants were infected by each technique.

Differential Transmission of Isolates of the High Plains virus by Different Sources of Wheat Curl Mites.

High Plains virus (HPV) isolates from Colorado, Idaho, Kansas, Texas, and Utah were serologically related, had similar relative molecular masses (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) for the 32-kDa diagnostic HPV protein, and were transmissible and maintained free of Wheat streak mosaic virus (WSMV) by vascular puncture inoculation. Collections of wheat curl mites (Aceria tosichella Keifer; WCM) from Kansas, Montana, Nebraska, South Dakota, and Texas differentially transmitted these isolates. For collections from South Dakota and Texas, little or no HPV transmission occurred, whereas WCM from Nebraska and Montana transmitted all five isolates. The collection from Kansas mostly transmitted only one HPV isolate. Aviruliferous or viruliferous WSMV Nebraska WCM transmitted HPV at similar rates and aviruliferous Montana WCM transmitted HPV at lower levels than viruliferous Montana WCM.

A Partial Host Range of the High Plains Virus of Corn and Wheat.

Barley (Hordeum vulgare), cheat (Bromus secalinus), corn (Zea mays), oat (Avena sativa), rye (Secale cereale), and wheat (Triticum aestivum) were infected by a Kansas isolate of the High Plains virus (HPV) in greenhouse experiments, but several other grass species were not. Infection of a host was dependent upon wheat curl mite numbers. Although both green foxtail (Setaria viridis) and yellow foxtail (S. glauca) are found naturally infected by HPV, only yellow foxtail could be infected in greenhouse experiments. Field sampling (1994 to 1996) of symptomatic yellow foxtail showed that it is a good indicator of the presence of HPV, with 252 of 278 symptomatic plants testing positive in enzyme-linked immunosorbent assay (ELISA) for HPV, 2 of 278 for American wheat striate mosaic virus, and 1 of 278 for johnson grass mosaic virus, whereas 23 of 278 symptomatic plants were negative for all viruses tested by ELISA and were not infectious in back-assays.