Progress 10/01/11 to 09/30/12
Outputs
OUTPUTS: Evaluating sweetpotato genotypes for resistance to sweetpotato virus disease (SPVD) has been slow and inefficient. Ipomoea setosa plants, normally used as the source of scions for graft infecting sweetpotatoes with viral diseases, are often severely stunted and their mortality is 10- 30% when infected with SPVD, making them unsuitable as scions. Tanzania, a landrace of I. batatas widely grown in East Africa, was found to be a superior host for 23 maintaining and increasing SPVD inoculum (scions) for mass grafting. Modifications to a cleft-grafting technique also increased survival of grafted SPVD-affected scions from 5 to 100%. These modifications, coupled with an efficient SPVD scoring technique, allowed rapid screening of large sweetpotato populations for SPVD resistance. Plant recovery from SPVD is reported here as a component of SPVD resistance. Differences in recovery from SPVD were detected amongst progenies, indicating its genetic basis. Plant tip dieback, a hypersensitivity response, was observed only in families with cv Wagabolige as a parent. These findings may open up new opportunities for improved understanding and control of this devastating disease. PARTICIPANTS: The results reported here were generated from a long term international collaboration involving scientistsw from N. C. State University, United Kingdom and Uganda. TARGET AUDIENCES: Report is relevant to scientists involved in sweetpotato cultivar development. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The findings reported in the First Look page of Plant disease have practical significance in aiding the assessment of quantitatively inherited virus resistance in sweetpotato. thus, will greatly aid plant breeding efforts.
Publications
- Mwanga, R.O.M, Yencho, C. G., Gibson, R. W., Moyer, J. W. 2012 Methodology for inoculating sweetpotato virus disease: discovery of tip dieback, and plant recovery and reversion in different clones. Plant Disease http://dx.doi.org/10.1094/PDIS-12-11-1072-RE
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Progress 10/01/07 to 09/30/08
Outputs
OUTPUTS: In the prior reporting period, we reported on the application of new analytical tools to our INSV data in order to better understand the mechanisms of change in this virus. We presented our findings in a poster at the 2008 American Phytopathological Society meeting, where it was well received. We are currently conducting a final analysis of the data and preparing the manuscript for publication. Because of the recent divergence time and sharing of ancestral polymorphisms that we previously reported for the North Carolina and California isolates, we performed additional analysis to better investigate their relationship. This analysis suggested that the NC and CA populations may not be fully differentiated yet. Together with the test statistic that we previously reported, KST, these tests suggest that INSV may be relatively young in it evolutionary history compared to TSWV, and may be just beginning to become geographically differentiated. Furthermore, since CA and NC are not fully differentiated, we combined them together with the other US isolates as a single population and are completing analyses of migration, compatibility, and anticipate including coalescent analysis in the manuscript that may better delineate the evolutionary history of this virus. In addition, we are currently resurrecting in our greenhouse two of the original INSV isolates to add to the analysis to aid in determining the origin of this virus in the US and provide us with ancestral sequences on which to root our analysis. Recent published reports on INSV have been solely accounts of infection on new host species; this publication will be the first published report on the molecular analysis of INSV since its characterization in the early 1990s. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: The information will be further refined and then made available to diagnosticians and offered to growers for their use. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The technology developed will improve the abiity to monitor changes in virus populations. By having this tool we can not only follow changes in Impatiens Necrotic Spot virus but it extends a previously identified methodology for Tomato Spotted Wilt Virus used to identify the geographic origin of the virus. the impact of this is that it allows diagnosticians the capability of advising growers as to the probability of the virus in an epidemic being local or introduced.
Publications
- Tsompana M and Moyer J W. Tospovirus. 2008 Encyclopedia of Virology, 5 vols. (B.W.J. Mahy and M.H.V. Van Regenmortel, Editors), pp. 157-163 Oxford: Elsevier.
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Progress 10/01/06 to 09/30/07
Outputs
OUTPUTS: We have begun to implement a diagnostic protocol based on the phylo-geographic results of our genetic studies of Tomato Spotted Wilt Virus and Impatiens Necrotic Spot Virus. We have been able to provide reliable estimates of the natural origin of individual isolates of these viruses. An example of the utility of this strategy was that it has been used to determine if virus-infected plants became infected on the growers farm or were infected at the primary propagators location. The information was reported to the grower. The strategy has been communicated to the floral crop industry.
TARGET AUDIENCES: This research is designed to support the floral crop industry worldwide.
Impacts
The results of this years research primarily involved extending concepts developed from a detailed genetic analysis of TSWV to Impatiens Necrotic Spot virus. The significance of this is that while TSWV occurs in fields and greenhouses, INSV occurs (until very recently) almost exclusively in greenhouse crops, primarily floral crops. Isolates were obtained from directed collections as well as contributed isolates, Three genes from each isolate are sequenced to provide a comprehensive database of INSV sequence. A phylogenetic analysis is conducted on the database, new samples from diagnostics are compared to the known sequences and geographically positioned based on sequence comparisons. New sequences are continually added to the database to expand the applicability of the data.
Publications
- No publications reported this period
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Progress 10/01/04 to 09/30/05
Outputs
The goal of this research was to investigate the population diversity of tomato spotted wilt virus and apply this information to improve diagnostic tools and to enhance management strategies. We have completed the identification of optimal sequences reflective of specific genome segments that are representative of the entire sequence. We have used these sequences to design primers and conducted an analysis of natural populations in North Carolina and California. The existence of a single phylogenetically based group of isolates for the Southeastern US was confirmed, however, a more complex population structure was revealed in California where two major groups were defined. In addition, we identified three possible reassortants based on these data that had segments identified with more than one geographic phylogenetic group. We have also examined the population structure of 13 natural populations of TSWV. Each population consisted of one or two dominant haplotypes with
10 or more other haplotypes detected in each population. Evolutionary networks were also constructed from the 187 extant haplotypes from which mutational 'pathways' could be inferred.
Impacts
This research provides an entirely new dimension to the diagnostic capabilities for Plant viruses. Although attribution has been a part of some high profile human viruses, most notably influenza, it has not been applied to plant viruses. This capability is based on a thorough and statistically supported investigation of the relationships between TSWV populations from multiple geographic and plant host sources. In addition, this study has also revealed additional support for possible natural mechanisms of viral evolution and adaptation. The identification of three natural reassortants provides additional support for reassortment as a product of selective forces as well as the selection of mutant haplotypes. These new tools are currently being adapted to improve our ability to develop and manage the deployment of resistant cultivars.
Publications
- M. Tsompana, J. Abad, M. Purugganan and J. W. Moyer. 2005 The molecular population genetics of the Tomato spotted wilt virus (TSWV) genome. Molecular Ecology 14:53-66.
- Abad, J.A., J.W. Moyer, G.G. Kennedy and M.A. Cubeta. 2005. An epidemic of tomato spotted wilt virus on potato in eastern North Carolina. Amer. J. Potato Res. 82:255-261.
- Sin, Sang-Hoon, McNulty, B. C., Kennedy, G. G. and Moyer, J. W. 2005. Viral genetic determinants for thrips transmission of Tomato spotted wilt virus. Proc Nat Acad Sci: 102:5168-5173.
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Progress 10/01/03 to 09/30/04
Outputs
Our research has identified partial sequence regions that contain similar phylogenetic information and perform as well as the complete NSm and RdRp genes, for branching points statistically supported (bootstrap value>50%). In addition, we have designed and tested primers that specifically amplify the NSm and RdRp local regions. We propose a new advanced diagnostic system, which will use the NSm and RdRp local regions together with the N gene of TSWV to assign attribution to initial TSWV infections and prevent their spread to an epidemic form. Other studies focused on TSWV-thrips interactions revealed that a specific nonsynonymous mutation (C1375A) in the GN/GC ORF of the M RNA resulted in the loss of thrips transmissibility without inhibition of virion assembly. This was in contrast to other nontransmissible SLIs which had frameshift and/or nonsense mutations in the GN/GC ORF but were defective in virion assembly. The GC glycoprotein was detectable in the C1375A
mutants but not in the frameshift or nonsense mutants. This is the first report of a specific viral determinant associated with virus transmission by thrips. In addition, it was demonstrated that loss of transmissibility is associated with the accumulation of defective haplotypes in the population, which are not transmissible by thrips, rather than with the presence of a dominant haplotype that is inefficiently transmitted by thrips. These results also indicate that the glycoproteins may be dispensable for TSWV infection of plant hosts, but not for transmissibility by thrips.
Impacts
This research will provide a new dimension to our ability to diagnose viral diseases by adding attribution to identity as the information provided. In addition, we have elucidated a significantly better understanding of the molecular determinants of the interaction that must occur between TSWV and its thrips vector, including the identification of one viral gene that is specifically required for virus transmission by thrips but not for multiplication in plants.
Publications
- Parks, E.J. and Moyer, J.W. 2004. Evaluation of AFLP in Poinsettia: Polymorphism selection, analysis, and cultivar identification. J. Amer. Soc. Hort. Sci. 129:863-869
- Sang-Hoon Sin. 2004 Molecular genetic determinants for thrips transmission of tomato spotted wilt virus. Ph D thesis. NCSU
- Maria Tsompana. 2004 Molecular evolution and population structure of tomato spotted wilt virus. PhD thesis. NCSU
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