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.

Identification of the Wheat Curl Mite as the Vector of Triticum mosaic virus.

Triticum mosaic virus (TriMV) is a newly discovered virus found infecting wheat (Triticum aestivum) in Kansas. This study was conducted to determine if the wheat curl mite (WCM, Aceria tosichella) and the bird cherry oat aphid (Rhopalosiphum padi) could transmit TriMV. Using different sources of WCM and two different isolates of TriMV, we were able to show the WCM is the vector of TriMV. Field analysis by enzyme-linked immunosorbent assay (ELISA) demonstrated natural infection patterns of wheat infected with TriMV, Wheat streak mosaic virus (WSMV), or both TriMV and WSMV, putatively infected by viruliferous WCM from a volunteer source growing adjacent to the wheat. Moreover, by single WCM transfers using WCM obtained from different wheat plants naturally infected with TriMV and WSMV and naturally infested with WCM, we showed that these WCM also transmitted TriMV only to wheat or transmitted both TriMV and WSMV to wheat. The infection rates of wheat with TriMV only using WCM transmission was low in both laboratory and field analyses. However, field analyses by ELISA showed that levels of infection of wheat by both TriMV and WSMV were high. No transmission of TriMV to wheat by R. padi occurred in our studies.

Triticum mosaic virus: A New Virus Isolated from Wheat in Kansas.

In 2006, a mechanically-transmissible and previously uncharacterized virus was isolated in Kansas from wheat plants with mosaic symptoms. The physiochemical properties of the virus were examined by purification on cesium chloride density gradients, electron microscopy, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), sequencing of the nucleotides and amino acids of the coat protein, and immunological reactivity. Purified preparations contained flexuous, rod-shaped particles that resembled potyviruses. The coat protein was estimated from SDS-PAGE to have a mass of approximately 35 kDa. Its amino acid sequence, as deduced from DNA sequencing of cloned, reverse-transcribed viral RNA and separately determined by time-of-flight mass spectrometry, was most closely related (49% similarity) to Sugarcane streak mosaic virus, a member of the Tritimovirus genus of the family Potyviridae. The virus gave strong positive reactions during enzyme-linked immunosorbent assays using polyclonal antibodies raised against purified preparations of the cognate virus but gave consistent negative reactions against antibodies to Wheat streak mosaic virus (WSMV), other wheat potyviruses, and the High Plains virus. When the virus was inoculated on the WSMV-resistant wheat cv. RonL, systemic symptoms appeared and plant growth was diminished significantly in contrast with WSMV-inoculated RonL. Taken together, the data support consideration of this virus as a new potyvirus, and the name Triticum mosaic virus (TriMV) is proposed.

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.

Assessment of Aegilops tauschii for resistance to biotypes of wheat curl mite (Acari: Eriophyidae).

Aegilops tauschii, the wild diploid D-genome progenitor of wheat, Triticum aestivum L., is an important source of resistance to several arthropod pests and pathogens. A total of 108 Ae. tauschii accessions from different geographic regions were evaluated for resistance to biotypes of the wheat curl mite, Aceria tosichella Keifer, from Kansas, Nebraska, and Montana. The wheat curl mite is the only vector known to transmit wheat streak mosaic virus. Wheat curl mite resistance was detected in germplasm from all the geographic locations represented. The highest percentage of resistant accessions originated from Turkey, followed by Afghanistan and the Caspian Sea region of Iran. Sixty-seven percent of the accessions exhibited resistance to at least one wheat curl mite biotype and 19% were resistant to all the three biotyopes. Resistance to the accessions tested occurred more frequently in the Nebraska and Kansas biotypes (69% and 64%, respectively) than did resistance to the Montana biotype (42%), although the frequency of resistance was not significant. The differential reactions of accessions to the different wheat curl mite biotypes suggests that Ae. tauschii has at least five different genes for resistance to mite colonization. Ae. tauschii continues to be a very useful source for wheat curl mite resistance genes for bread wheat improvement.

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.

Natural Infection of Sorghum by Foxtail Mosaic Virus in Kansas.

Sorghum (Sorghum bicolor) was infected by a mechanically transmissible, flexuous, rod-shaped virus. Antiserum made against the purified virus reacted specifically in enzyme-linked immunosorbent assay to the virus and to the potexvirus foxtail mosaic virus (FoMV), indicating that the sorghum virus was an isolate of FoMV. Comparison of the sorghum isolate (H93) to FoMV PV 139 showed that H93 differed biologically by causing severe symptoms in sorghum, not readily infecting certain barley lines, and causing only faint symptoms in barley. At the molecular level, the capsid of H93 had a mass of 23.9 kDa and 217 amino acid residues compared with 23.7 kDa and 215 residues previously reported for the nucleic acid sequence of FoMV. The amino acid sequences of the two viruses were greater than 96% identical. They varied by having four substitutions, one deletion, and three insertions between residues 66 and 67. This is the first report of natural infection of sorghum by FoMV, thus extending its host range among cereal crops.

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.