Progress 10/01/06 to 09/30/11
Outputs
OUTPUTS: Activities part of this report include experimental work, disease surveys, teaching and mentoring of students as researchers. Research was conducted on the ecology of grapevine leafroll disease and Pierce's disease of grapevines. Studies included vector transmission of pathogen, disease ecology and pathogen molecular ecology. Teaching and mentoring of several undergraduate and graduate students was performed, in addition, postdoctoral researchers were trained and visiting scientists visited our group for short and long term visits. Our work was disseminated through various events, such conferences (e.g. Entomological Society of America), symposia (Pierce's Disease and Glassy-winged sharpshooter symposium) and other venues. All data and information generated through our work is made available in publicly available databases (e.g. GenBank) and publications. Publications are listed and made available at: http://nature.berkeley.edu/~rodrigo/Lab%20page/publications.html PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Main output of this project was the identification of novel variants of Grapevine leafroll-associated virus 3, an emerging pathogen of grapevines in winegrape growing regions of California. Work performed not only showed that this species is driving an emerging epidemic in the state, but also that the species is very diverse and divided in multiple well established clades. In fact, newly identified clades will allow for better diagnostics of this important disease, especially with the use of molecular tools.
Publications
- Daugherty, M.P., Gruber, B.R., Almeida, R.P.P., Anderson, M.M., Cooper, M.L., Rasmussen, Y. and Weber, E. 2012. Testing the efficacy of barrier plantings for limiting sharpshooter spread. American Journal of Enology and Viticulture 63: 139-143.
- Daane, K.M., Middleton, M.C., Sforza, R., Cooper, M.L., Walton, V.M., Walsh, D.B., Zaviezo, T. and Almeida, R.P.P. 2011. Development of a multiplex PCR for identification of vineyard mealybugs. Environmental Entomology 40: 1595-1603.
- Tsai, C.W., Bosco, D., Daane, K.M. and Almeida, R.P.P. 2011. Effect of host plant tissue on the vector transmission of Grapevine leafroll-associated virus 3. Journal of Economic Entomology 104: 1480-1485.
- Rashed, A., Daugherty, M.P. and Almeida, R.P.P. 2011. Grapevine genotype susceptibility to Xylella fastidiosa does not predict vector transmission success. Environmental Entomology 40: 1192-1199.
- Sharma, A.M., Wang, J., Duffy, S., Zhang, S., Wong, M.K., Rashed, A., Cooper, M.L., Daane, K.M. and Almeida, R.P.P. 2011. Occurrence of grapevine leafroll-associated virus complex in Napa Valley. PLoS ONE 6: e26227.
- Killiny, N. and Almeida, R.P.P. 2011. Gene regulation mediates host specificity of a bacterial pathogen. Environmental Microbiology Reports 3: 791-797.
- Daugherty, M.P., Rashed, A., Almeida, R.P.P. and Perring, T.M. 2011. Vector preference for hosts differing in infection status: sharpshooter movement and Xylella fastidiosa transmission. Ecological Entomology 36: 654-662.
- Plucinski, M.M., Starfield, R. and Almeida, R.P.P. 2011. Inferring social network structure from bacterial sequence data. PLoS ONE 6: e22685.
- Gutierrez, A.P., Ponti, L., Hoddle, M., Almeida, R.P.P. and Irvin, N.A. 2011. Geographic distribution and relative abundance of the invasive glassy-winged sharpshooter: effects of temperature and egg parasitoids. Environmental Entomology 40: 755-769.
- Kung, S.H. and Almeida, R.P.P. 2011. Natural competence and recombination in the plant pathogen Xylella fastidiosa. Applied and Environmental Microbiology 77: 5278-5284.
- Coletta-Filho, H.D., Bittleston, L.S. and Almeida, R.P.P. 2011. Spatial genetic structure of a vector-borne generalist pathogen. Applied and Environmental Microbiology 77: 2596-2601.
- Degnan, P.H., Bittleston, L.S., Hansen, A.K., Sabree, Z.L., Moran, N.A. and Almeida, R.P.P. 2011. Origin and examination of a leafhopper facultative endosymbiont. Current Microbiology 62: 1565-1572.
- Rashed, A., Killiny, N., Kwan, J. and Almeida, R.P.P. 2011. Background matching behaviour and pathogen acquisition: Plant site preference does not predict bacterial acquisition efficiency by vectors. Arthropod-Plant Interactions 5: 97-106.
- Killiny, N., Rashed, A. and Almeida, R.P.P. 2012. Disrupting the transmission of a vector-borne plant pathogen. Applied and Environmental Microbiology 78: 638-643.
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: To understand ecological factors mediating the spread of insect-borne plant pathogens, vector species for these pathogens need to be identified. Grapevine leafroll disease is caused by a complex of phylogenetically related closteroviruses, some of which are transmitted by insect vectors; however, the specificities of these complex virus-vector interactions are so far poorly understood. Through biological assays and phylogenetic analyses we studied the role of vector-pathogen specificity in the transmission of several grapevine leafroll-associated closteroviruses (GLRaVs) by their mealybug vectors. Using plants with multiple virus infections several virus species were screened for vector transmission by the mealybug species Planococcus ficus and Pseudococcus longispinus. In addition, we studied the diversity of Grapevine leafroll-associated virus 3 (GLRaV-3, Ampelovirus, Closteroviridae), associated with grapevine leafroll disease. It is an important pathogen found across all major grape-growing regions of the world. The genetic diversity of GLRaV-3 in Napa Valley, California, was studied by sequencing 4.7 kb in the 3'terminal region of 50 isolates obtained from Vitis vinifera cv. Merlot. Results are being made available to the community through peer-reviewed publications, presentations at scientific meetings and in talks to growers and stakeholders in the agricultural community. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Project focus on emerging grapevine viral diseases of importance to California, the West Coast and other grape growing regions in the country. One of our goals is to deliver science-based knowledge to farmers and those directly impacted by these diseases. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
We found that two GLRaV species (-4 and -9), for which no vector transmission evidence was available, are mealybug-borne. The analyses performed indicated no evidence of mealybug-GLRaV specificity; for example, different vector species transmitted GLRaV-3, and one vector species, Pl. ficus, transmitted five GLRaVs. Based on available data, there is no compelling evidence of vector-virus specificity in the mealybug transmission of GLRaVs. However, more studies aimed at increasing the number of mealybug species tested as vectors of different GLRaVs are necessary. This is especially important given the increasing importance of grapevine leafroll disease spread by mealybugs in vineyards worldwide. In our diversity study, we found that GLRaV-3 isolates were subdivided into four distinct phylogenetic clades. No evidence of positive selection was observed in the data set, although neutral selection (ratio of non-synonymous to synonymous substitution rates = 1.1) was observed in one open reading frame (ORF 11, p4). Additionally, the four clades had variable degrees of overall nucleotide diversity. Moreover, no geographical structure among isolates was observed, and isolates belonging to different phylogenetic clades were found in distinct vineyards, with one exception. Considered with the evidence of purifying selection, i.e. against deleterious mutations, these data indicate that the population of GLRaV-3 in Napa Valley is not expanding and its effective population size is not increasing. Furthermore, research on the biological characterization of GLRaV-3 strains might provide valuable insights on the biology of this species that may have epidemiological relevance. Lastly, this work will improve diagnostic tools used to detected this important pathogen
Publications
- Tsai, C.W., Rowhani, A., Golino, D.A., Daane, K.M. and Almeida, R.P.P. 2010. Mealybug transmission of grapevine leafroll viruses: an analysis of virus-vector specificity. Phytopathology 100: 830-834.
- Wang, J., Sharma, A.M., Duffy, S. and Almeida, R.P.P. 2011. Genetic diversity in the 3' terminal 4.7-kb region of Grapevine leafroll-associated virus 3. Phytopathology, in press.
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: Outputs are being made available to community through peer-reviewed publications, presentations at scientific meetings and to the agricultural community. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
This project now focuses on identifying the etiological agent of the emerging grapevine leafroll disease in the North Coast of California. Leafroll disease is caused by a complex of 10+ viruses. We developed a protocol based on multiplex-PCR using fluorescent-tagged primers to detected leafroll viruses in grapevines. Our preliminary data suggest that the species leafroll-3 is the predominant one in vineyards surveyed. During last year we discovered that leafroll-3 is in fact subdivided in 4 genetic groups. Another similar protocol was developed and we are now processing hundreds of samples of epidemiological importance to determine if (or which) a leafroll-3 strain is driving this epidemic.
Publications
- No publications reported this period
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: Outputs are being made available to community through peer-reviewed publications, presentations at scientific meetings and to the agricultural community. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
In this report we will focus on research conducted to fill a knowledge gap in our understanding of how mealybugs transmit grapevine leafroll-associated virus 3. Grapevine leafroll disease is caused by grapevine leafroll-associated viruses (GLRaVs). Within this virus complex, GLRaV-3 is the predominant species in the world. Several GLRaVs have been shown to be transmitted from vine to vine by mealybugs although a detailed characterization of transmission biology is lacking. The introduction of the vine mealybug (Planococcus ficus) in California and other regions of the world may result in increasing disease incidence of established GLRaVs. We studied the characteristics of GLRaV-3 transmission by the vine mealybug. Our results indicate that the vine mealybug transmits GLRaV-3 in a semipersistent manner. First instars were more efficient vectors than adult mealybugs. GLRaV-3 transmission lacked a latent period in the vector. Virus transmission occurred with a 1-h acquisition access period (AAP) and peaked with a 24-h AAP. Mealybugs inoculated GLRaV-3 with a 1-h inoculation access period (IAP), and transmission efficiency increased with longer plant access period up to 24 h, after which transmission rate remained constant. After an AAP of 24 h, mealybugs lost GLRaV-3 and infectivity 4 days after virus acquisition. In addition, GLRaV-3 was not transovarially transmitted from infected females to their progeny as detected by reverse transcription polymerase chain reaction. In summary, we systematically analyzed transmission parameters of GLRaV-3 by the vine mealybug and showed that transmission of this virus occurs in a semipersistent manner. This research fills in important gaps in knowledge of leafroll virus transmission, which is critical for development of leafroll disease management practices. When mealybugs were first determined as potential vectors of grapevine viruses, transmission and epidemiology studies were hindered by limited tools to (i) identify the viruses they transmit and (ii) detect low virus titers in plants and mealybugs. The recent improvements in molecular detection (e.g. RT-PCR and real-time quantification) provide better tools to study the transmission biology of GLRaVs. This study provides a framework for future studies on GLRaVs transmission by different mealybug and coccid vectors, and the garnered information will be used to develop better management practices for grapevine leafroll disease.
Publications
- Daugherty, M.P. and Almeida, R.P.P. 2009. Estimating Xylella fastidiosa transmission parameters: decoupling sharpshooter number and feeding period. Entomologia Experimentalis et Applicata accepted pending revision.
- Prado, S.S. and Almeida, R.P.P. 2009. Role of symbiotic gut bacteria in the development of Acrosternum hilare and Murgantia histrionica (Hemiptera, Pentatomidae). Entomologia Experimentalis et Applicata accepted.
- Hooks, C.R.R., Fukuda, S., Perez, E.A., Manandhar, R., Wang, K.H., Wright, M.G. and Almeida, R.P.P. 2009. Aphid transmission of Banana bunchy top virus to bananas after treatment with a bananacide. Journal of Economic Entomology accepted.
- Prado, S.S., Golden, M., Follett, P.A., Daugherty, M.P. and Almeida, R.P.P. 2009. Demography of gut symbiotic and aposymbiotic Nezara viridula (L.) (Hemiptera, Pentatomidae). Environmental Entomology in press.
- Almeida, R.P.P., Bennett, G.M., Anhalt, M.D., Tsai, C.W. and O'Grady, P. 2009. Spread of an introduced vector-borne banana virus in Hawaii. Molecular Ecology 18: 136-146.
- Prado, S.S. and Almeida, R.P.P. 2009. Phylogenetic placement of pentatomid stink bug gut symbionts. Current Microbiology 58: 64-69. 2008
- Tsai, C.W., Chau, J., Fernandez, L., Bosco, D., Daane, K.M., and Almeida, R.P.P. 2008. Transmission of Grapevine leafroll-associated virus 3 by the vine mealybug (Planococcus ficus). Phytopathology 98: 1093-1098.
- Lopes, J.R.S., Daugherty, M.P. and Almeida, R.P.P. 2009. Context-dependent transmission of a generalist plant pathogen: host species and pathogen strain mediate insect vector competence. Entomologia Experimentalis et Applicata accepted.
- Kiliny, N. and Almeida, R.P.P. 2009. Xylella fastidiosa afimbrial adhesins mediate cell transmission to plants by leafhopper vectors. Applied and Environmental Microbiology 75: 521-528.
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Progress 01/01/07 to 12/31/07
Outputs
Here we summarize our recent activities on the transmission of grapevine leafroll-associated virus 3 by the invasive vine mealybug. Grapevine leafroll disease is caused by grapevine leafroll-associated viruses (GLRaVs). Within this virus complex, GLRaV-3 is the predominant species in the world. Several GLRaVs have been shown to be transmitted from vine to vine by mealybugs although a detailed characterization of transmission biology is lacking. The introduction of the vine mealybug (Planococcus ficus) in California and other regions of the world may result in increasing disease incidence of established GLRaVs. We studied the characteristics of GLRaV-3 transmission by the vine mealybug. Our results indicate that the vine mealybug transmits GLRaV-3 in a semipersistent manner. First instars were more efficient vectors than adult mealybugs. GLRaV-3 transmission lacked a latent period in the vector. Virus transmission occurred with a 1-h acquisition access period (AAP) and
peaked with a 24-h AAP. Mealybugs inoculated GLRaV-3 with a 1-h inoculation access period (IAP), and transmission efficiency increased with longer plant access period up to 24 h, after which transmission rate remained constant. After an AAP of 24 h, mealybugs lost GLRaV-3 and infectivity 4 days after virus acquisition. In addition, GLRaV-3 was not transovarially transmitted from infected females to their progeny as detected by reverse transcription polymerase chain reaction. In summary, we systematically analyzed transmission parameters of GLRaV-3 by the vine mealybug and showed that transmission of this virus occurs in a semipersistent manner. This research fills in important gaps in knowledge of leafroll virus transmission, which is critical for development of leafroll disease management practices. Outputs are being made available to community through peer-reviewed publications, presentations at scientific meetings and to the agricultural community.
Impacts
The control of insect-borne plant diseases is often strongly based on a solid understanding of pathogen transmission biology. However, the virus-vector relationships and transmission biology of GLRaVs remain unclear. The objective of our research was to determine transmission parameters for GLRaV-3 by the vine mealybug (Pl. ficus), which has already been shown to transmit GLRaV-3 and Grapevine virus A. The vine mealybug is an invasive pest in most grape-growing regions worldwide, and GLRaV-3 is the most widespread grapevine virus worldwide. We suggest using this study as a framework to further examine the transmission biology of other GLRaVs by insect vectors. We systematically analyzed the transmission parameters of GLRaV-3 by the vine mealybug. Our results indicate that the vine mealybug transmits GLRaV-3 in a semipersistent manner. Virus transmission occurred with a 1-h AAP and a 1-h IAP, and transmission efficiency increased with longer plant access period up to 24
h. GLRaV-3 transmission lacked a latent period in the vector. Mealybugs lost GLRaV-3 and infectivity 4 days after virus acquisition. GLRaV-3 was not transovarially transmitted from infected females to their progeny. This information will be valuable for the development of leafroll disease management practices. Our data contribute to ongoing epidemiology studies of grapevine leafroll disease. First instars were more efficient vectors than adult mealybugs. First instars are the most mobile stage of mealybugs, and wind borne dispersal of first instars is much easier than that of last instars and adults. The vine mealybug seems to have higher transmission efficiency than other vectors of GLRaV-3. There are many diseases constantly threatening the grape industry worldwide. These diseases include new emerging diseases as well as the epidemic reemergence of previously established diseases that were rare or of little importance. An example is the reemergence of Pierce's disease as a major
production limiting factor in California after the introduction of the glassy-winged sharpshooter into the state. The vine mealybug was accidentally introduced into southern California in the early 1990s. The invasion of the vine mealybug in California and elsewhere may result in increased disease incidence of established GLRaV-3.
Publications
- Chatterjee, S., Almeida, R.P.P. and Lindow, S.E. Living in two worlds: the plant and insect lifestyles of Xylella fastidiosa. Annual Review of Phytopathology in press. Anhalt, M.D. and Almeida, R.P.P. 2008. Effect of temperature, vector life stage and plant access period on transmission of Banana bunchy top virus to banana. Phytopathology in press. Almeida, R.P.P., Nascimento, F.E., Chau, J., Prado, S.S., Tsai, C.W., Lopes, S.A. and Lopes, J.R.S. 2008. Genetic structure and biology of Xylella fastidiosa causing disease in citrus and coffee in Brazil. Applied and Environmental Microbiology in press. Prado S.S. and Almeida, R.P.P. 2008. Phylogenetic placement of pentatomid stink bug gut symbionts. Current Microbiology in press. Almeida, R.P.P. 2008. Ecology of emerging vector-borne plant diseases. p70-77. In: Institute of Medicine Forum on Vector-borne diseases: Understanding the environmental, human health, and ecological connections. The National Academies Press,
Washington, D.C. 350p. Hooks, C.R.R
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