Progress 01/01/11 to 12/31/11
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. Surveys of grapevine leafroll disease were performed for several California regions, including Napa, San Luis Obispo, Lodi and the Foothills. 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
Work by our group has had a wide range of impacts. Below are briefly discussed two examples that are noteworthy. First we showed that a species of grapevine leafroll virus is driving a disease epidemic in Napa Valley. This is important because different species are transmitted by different insect vectors and management is dependent on identification of the correct etiological agent. Second, we compared the rate of transmission of the grape pathogen Xylella fastidiosa, the etiological agent of Pierce's disease, by the invasive vector glassy-winged sharpshooter among various grape varieties of economic importance. Grapevine leafroll disease (GLD) is caused by a complex of several virus species (grapevine leafroll-associated viruses, GLRaV) in the family Closteroviridae. Because of its increasing importance, it is critical to determine which species of GLRaV is predominant in each region where this disease is occurring. A structured sampling design, utilizing a combination of RT-PCR based testing and sequencing methods, was used to survey GLRaVs in Napa Valley (California, USA) vineyards (n=36). 81% (n=109) were single infections with GLRaV-3, followed by GLRaV-2 (4%, n=5), while the remaining samples (15%, n=20) were mixed infections of GLRaV-3 with GLRaV-1, 2, 4, or 9. Phylogenetic analysis utilizing sequence data from the single infection GLRaV-3 samples produced seven well-supported GLRaV-3 variants, of which three represented 71% of all GLRaV-3 positive samples in Napa Valley. Furthermore, two novel variants, which grouped with a divergent isolate from New Zealand (NZ-1), were identified, and these variants comprised 6% of all positive GLRaV-3 samples. Overall, 86% of all blocks (n=31) were positive for GLRaVs and 90% of positive blocks (n=28) had two or more GLRaV-3 variants, suggesting complex disease dynamics that might include multiple insect-mediated introduction events. The pathogenic bacterium Xylella fastidiosa, the etiological agent of Pierce's disease in grapevines, is transmitted by the invasive vector glassy-winged sharpshooter. Pathogen infection level and transmission efficiency among several widely cultivated red and white wine, table and raisin grape cultivars, were compared with the expectation that vector transmission rate would differ among cultivars, because of underlying differences in susceptibility to infection. The 14 grapevine genotypes evaluated showed significant differences among cultivars in the populations of X. fastidiosa that developed in petioles. Flame seedless hosted the highest bacterial populations, between 1.81 to 2.05 times higher than the least susceptible cultivars Merlot, Crimson seedless, Grenache Noir, and Rubired. Although the transmission rate of X. fastidiosa by H. vitripennis varied substantially (zero to 33%), it was not significantly different among cultivars. These results suggest that either the relationship between vine infection level and transmission is weaker than previously reported or innate differences in vector preference among cultivars confounded any effects of vine susceptibility to infection.
Publications
- 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.
- 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.
- 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.
- 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 101: 445-450.
- 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.
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Progress 10/01/06 to 09/30/11
Outputs
OUTPUTS: The last report submitted was the final report. 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
The last report submitted was the final report including the information for Publications.
Publications
- No publications reported this period
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: Research activities performed include: experimental design, conduction of assays, data analyses and preparation and submission of research manuscripts. In addition, mentoring of a graduate student was a component of our research activities. Finally, the work performed here included the collaborative efforts of other members of our research group and from other groups and institutions, encouraging the exchange of ideas and methodological advances. The results of our research were presented in several national and international scientific conferences and symposia. In addition, we participated in day-long seminars that specifically targeted farmers and pest control advisors, which focused on one of our objectives - to study the ecology of grapevine leafroll viruses. Product outputs have been limited to the development of new methods and technical approaches to address specific research questions. For example, we have developed new methods for the quick and reliable detection of new emerging pathogens affecting California's agriculture, focusing on grapevine leafroll disease. In addition, we are testing compounds that may block pathogen transmission by insect vectors. Outreach and dissemination of our results have focused on i) scientists and ii) farmers and other stakeholders affected by the disease systems we work with. The scientific community has been aware of our work through formal and informal meetings, such as conferences or invited talks at university departments, in addition of peer-reviewed publications. Talks to growers and commodity groups have allowed the direct transfer of knowledge to stakeholders. PARTICIPANTS: 1. Principal Investigator - Rodrigo Almeida. Experimental design, data analyses, preparation of reports and manuscripts. 2. Stephanie Kung - Graduate student performing research on the ecology of Xylella fastidiosa, an emerging insect-borne plant pathogen. Project has provided opportunity to train a graduate student directly and other students and post-doctoral researchers through collaborative research. In addition, results have been made available to farmers, pest control advisors and others involved in the agricultural disease systems we work on through various talks. TARGET AUDIENCES: Projects focus on emerging crop diseases of economic importance to California. One of our objectives is to generate and deliver science-based knowledge to farmers and those directly involved in agricultural activities to improve disease management strategies and sustainability of food production. PROJECT MODIFICATIONS: Not relevant to this project. 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
We are studying the ecology of an emerging grapevine diseases, Grapevine leafroll-associated viruses (GLRaV). Despite the emerging nature of this problem in California, primarily in the North Coast, and the potential economic impact of this disease, the etiological agent driving this epidemic is yet to be identified. We developed a series of detection methods to address this question in a hierarchical fashion. These methods are based on multiplex-PCR using fluorescently-tagged primers. Our data show that one GLRaV species, GLRaV-3, is the dominant one in the Napa Valley. A sequencing project performed in our laboratory showed that GLRaV-3 is in fact divided into 7 genetically distinct groups. Therefore, we developed another multiplex-based system to identify all GLRaV-3 groups and potentially new GLRaV-3 yet to be identified. Altogether, we hope that this approach will allow us to identify the etiological agent of this emerging disease. Another goal is to generate information on how the plant pathogenic bacterium Xylella fastidiosa interacts with sharpshooter vectors at the molecular level. We identified generalist molecules (carbohydrates and lectins) that competed with X. fastidiosa for binding sites in its insect vectors and blocked the adhesion of this pathogen, effectively blocking transmission. We conducted experiments with these molecules and showed that both carbohydrates and lectins can block X. fastidiosa transmission to plants, probably by competing with cells for binding sites in the foregut of vectors. This approach would represent a novel mechanism to limit the impact of an economically important plant pathogen. Furthermore, it could serve as a model for other vector-borne diseases. Outputs are being made available to community through peer-reviewed publications, presentations at scientific meetings and to the agricultural community.
Publications
- Chatterjee, S., Killiny, N., Almeida, R.P.P. and Lindow, S.E. 2010. Role of cyclic di-GMP in Xylella fastidiosa biofilm formation, plant virulence and insect transmission. Molecular Plant-Microbe Interactions 23: 1356-1363.
- Killiny, N., Prado, S.S. and Almeida, R.P.P. 2010. Chitin utilization by the insect-transmitted bacterium Xylella fastidiosa. Applied and Environmental Microbiology 76: 6134-6140.
- Lopes, J.R.S., Daugherty, M.P. and Almeida, R.P.P. 2010. Strain origin drives virulence and persistence of Xylella fastidiosa in alfalfa. Plant Pathology 59: 963-971.
- 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.
- Daugherty, M.P., Lopes, J.R.S. and Almeida, R.P.P. 2010. Strain-specific alfalfa water stress induced by Xylella fastidiosa. European Journal of Plant Pathology 127: 333-340.
- Daugherty, M.P., Lopes, J.R.S. and Almeida, R.P.P. 2010. Vector within-host feeding preference mediates transmission of a heterogeneously distributed pathogen. Ecological Entomology 35: 360-366.
- Prado, S.S., Hung, K.Y., Daugherty, M.P. and Almeida, R.P.P. 2010. Indirect effects of temperature on stink bug fitness via maintenance of gut-associated symbionts. Applied and Environmental Microbiology 76: 1261-1266.
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: Research activities performed include: experimental design, conduction of assays, data analyses and preparation and submission of research manuscripts. In addition, mentoring of a graduate student was a component of our research activities. Finally, the work performed here included the collaborative efforts of other members of our research group and from other groups and institutions, encouraging the exchange of ideas and methodological advances. The results of our research were presented in several scientific conferences and symposia. In addition, we participated in day-long seminars that specifically targeted farmers and pest control advisors, which focused on one of our objectives - to study the ecology of grapevine leafroll viruses. Product outputs have been limited to the development of new methods and technical approaches to address specific research questions. For example, we have developed new methods for the quick and reliable detection of new emerging pathogens affecting California's agriculture. In addition, we are testing compounds that may block pathogen transmission by insect vectors. Outreach and dissemination of our results have focused on i) scientists and ii) growers and farmer affected by the disease systems we work with. The scientific community has been aware of our work through formal and informal meetings, such as conferences or invited talks at university departments, in addition of peer-reviewed publications. Talks to growers and commodity groups have allowed the direct transfer of knowledge to stakeholders. PARTICIPANTS: 1. Principal Investigator - Rodrigo Almeida. Experimental design, data analyses, preparation of reports and manuscripts. 2. Stephanie Kung - Graduate student performing research on the ecology of Xylella fastidiosa, an emerging insect-borne plant pathogen. Project has provided opportunity to train a graduate student directly and other students and post-doctoral researchers through collaborative research. In addition, results have been made available to farmers, producers, pest control advisors and others involved in the agricultural disease systems we work on through various talks. TARGET AUDIENCES: Projects focus on emerging crop diseases of economic importance to California. One of our objectives is to generate and deliver science-based knowledge to farmers and those directly involved in agricultural activities to improve disease management strategies and sustainability of food production. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
One of our goals is to generate information on how the plant pathogenic bacterium Xylella fastidiosa interacts with sharpshooter vectors at the molecular level. We took advantage of an in vitro system developed in our laboratory to deliver transmissible cells to vectors to study how X. fastidiosa colonizes sharpshooters. Based on this work we identified generalist target molecules (carbohydrates and lectins) that could compete with X. fastidiosa for binding sites in its insect vectors and block the adhesion of this pathogen, effectively blocking transmission. We conducted experiments with these generalist molecules and showed that both carbohydrates and lectins can block X. fastidiosa transmission to plants, probably by competing with cells for binding sites in the foregut of vectors. This approach would represent a novel mechanism to limit the impact of an economically important plant pathogen. Furthermore, it could serve as a model for other vector-borne diseases. Another objective is to determine the relative importance of different parameters on X. fastidiosa transmission to plants by sharpshooters. We have shown that transmission of X. fastidiosa is context-dependent, and efficiency is dependent on the combination of pathogen strain, vector species, and host plant used for pathogen acquisition. This observation is of ecological importance, but did not allow us to determine the likely mechanisms behind these differences. We tested the hypothesis that vector preference for different plant tissues, coupled with a heterogeneous pathogen distribution within plants, could affect transmission efficiency. Our results showed that both vector and pathogen within-plant distribution affects transmission rates. We are now expanding these results to test the role of vector behavior on disease spread. Lastly, we are also studying the ecology of an emerging grapevine diseases and its invasive vector, namely Grapevine leafroll-associated viruses (GLRaV) and the vine mealybug. Despite the emerging nature of this problem in California, primarily in the North Coast, and the potential economic impact of this disease, the etiological agent driving this epidemic is yet to be identified. We developed a series of detection methods to address this question in a hierarchical fashion. These methods are based on multiplex-PCR using fluorescently-tagged primers. Although we are still processing hundreds of samples of epidemiological relevance, preliminary data suggest that one GLRaV species, GLRaV-3, is the dominant one in the Napa Valley. A sequencing project performed in our laboratory showed that GLRaV-3 is in fact divided into 4 genetically distinct groups. Therefore, we developed another multiplex-based system to identify all 4 GLRaV-3 groups and potentially new GLRaV-3 yet to be identified. Altogether, we hope that this approach will allow us to identify the etiological agent of this emerging disease. Outputs are being made available to community through peer-reviewed publications, presentations at scientific meetings and to the agricultural community.
Publications
- Kiliny, N. and Almeida, R.P.P. 2009. Host structural carbohydrate induces vector transmission of a bacterial plant pathogen. Proceedings of the National Academy of Sciences USA 106: 22416-22420.
- 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 banana after treatment with a bananacide. Journal of Economic Entomology 102: 493-499.
- Hooks, C.R.R., Manandhar, R., Perez, E.A., Wang, K.H. and Almeida, R.P.P. 2009. Comparative susceptibility of two banana cultivars to Banana bunchy top virus under laboratory and field environments. Journal of Economic Entomology 102: 897-904.
- Prado, S.S. and Almeida, R.P.P. 2009. Role of symbiotic gut bacteria in the development of Acrosternum hilare and Murgantia histrionica. Entomologia Experimentalis et Applicata 132: 21-29.
- Daugherty, M.P., Bosco, D. and Almeida, R.P.P. 2009. Temperature mediates vector transmission efficiency: inoculum supply and plant infection dynamics. Annals of Applied Biology 155: 361-369.
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: Research activities performed include: experimental design, conduction of assays, data analyses and preparation and submission of research manuscripts. In addition, mentoring of a graduate student was a component of our research activities. Finally, the work performed here included the collaborative efforts of other members of our research group and from other groups and institutions, encouraging the exchange of ideas and methodological advances. The results of our research were presented in several scientific conferences and symposia. In addition, we participated in day-long seminars that specifically targeted farmers and pest control advisors, which focused on one of our objectives - to study the ecology of grapevine leafroll viruses. Product outputs have been limited to the development of new methods and technical approaches to address specific research questions. For example, we have developed new methods for the study of pathogen ecology, focusing on increasing the resolution of molecular markers for typing purposes. In addition, a novel approach has been developed to deliver a bacterial pathogen to its insect vectors, which eliminates the requirement of plants and a pathogen reservoir for experimental research. This method will, for example, permit the testing of compounds that may block pathogen transmission. In addition, it will assist the research community in studying how this pathogen interacts with vector species. Outreach and dissemination of our results have focused on i) research collaborators and ii) growers and farmer affected by the disease systems we work with. Research collaborators have been aware of our work through formal and informal meetings, such as conferences or invited talks at university departments. Talks to growers and commodity groups have allowed the direct transfer of knowledge to stakeholders. PARTICIPANTS: 1. Principal Investigator - Rodrigo Almeida. Experimental design, data analyses, preparation of reports and manuscripts. 2. Stephanie Kung - Graduate student performing research on the ecology of Xylella fastidiosa, an emerging insect-borne plant pathogen. Project has provided opportunity to train a graduate student directly and other students and post-doctoral researchers through collaborative research. In addition, results have been made available to farmers, producers, pest control advisors and others involved in the agricultural disease systems we work on through various talks. TARGET AUDIENCES: Projects focus on emerging crop diseases of economic importance to California. One of our objectives is to generate and deliver science-based knowledge to farmers and those directly involved in agricultural activities to improve disease management strategies and sustainability of food production. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
We have summarized our outputs in three sections, based on the objectives of our project. One of our goals is to generate information on how the plant pathogenic bacterium Xylella fastidiosa interacts with sharpshooter vectors at the molecular level. Although this has been assumed to be a complex association, so far it remains poorly understood. Based on our studies, we have created a model for the X. fastidiosa-vector interactions that can be explored for the development of strategies to disrupt these interactions. For example, our experiments demonstrated that X. fastidiosa cells have surface proteins that bind to the polysaccharide molecules on the mouthparts of insect vectors. This information allowed us to screen for a protocol to deliver cells in vitro to insects, which has been developed and will allow the testing of compounds to block transmission without the need for long, expensive and laborious greenhouse-based experiments. The determination of how X. fastidiosa interacts with vectors will open new venues to control disease spread, as understanding how pathogen and vector interact may lead to strategies to block the transmission of X. fastidiosa to plants. Another objective is to determine the relative importance of different parameters on X. fastidiosa transmission to plants by sharpshooters. This process is fundamental to any scientific understanding of the epidemiology of X. fastidiosa diseases in California and elsewhere. Our work is expanding the basic knowledge on this system. Among many things, we are researching the factors responsible for context-dependent transmission rates when different pathogen strain, host plant, or insect vector species are used in variable ecological contexts. This is relevant to these systems because California's agricultural landscape is variable, and so are the vector and host plant species present in different regions. Our goal is to identify factors driving transmission efficiency, which may allow us to forecast disease spread rates for different crops and locations. We are also studying the ecology of an emerging grapevine diseases and its invasive vector, namely Grapevine leafroll-associated viruses (GLRaV) and the vine mealybug. We are focusing on the identification of vectors of different grape viruses, characterizing transmission biology, and using molecular tools to study pathogen epidemiology. We have found, so far, that mealybug transmission of ampeloviruses seems to be non-specific and that first instars are efficient vectors of the pathogen. In addition, our preliminary work has indicated that a new strain of leafroll type 3 may be responsible for the current epidemic of leafroll disease in Coastal California; we are now working on a large number of samples to determine if that hypothesis is correct. Outputs are being made available to community through peer-reviewed publications, presentations at scientific meetings and to the agricultural community.
Publications
- 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 98: 743-748.
- 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 74: 3690-3701.
- 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.
- 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.
- 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.
- Chatterjee, S., Almeida, R.P.P. and Lindow, S.E. 2008. Living in two worlds: the plant and insect lifestyles of Xylella fastidiosa. Annual Review of Phytopathology 46: 243-271.
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Progress 01/01/07 to 12/31/07
Outputs
We have summarized our outputs in three sections, based on the objectives of our project.One of our goals was to generate information on how the bacterium Xylella fastidiosa interacts with sharpshooter vectors at the molecular level. Although this has been assumed to be a complex association, so far it remains poorly understood. Based on our studies, we have created a model for the X. fastidiosa-vector interactions that can be explored for the development of strategies to disrupt these interactions. For example, our experiments demonstrated that certain sugar-binding proteins on the surface of X. fastidiosa cells are important for initial pathogen adhesion to vectors. We hope to use this information to look for proteins or other compounds with similar binding activity to test if we can saturate these receptors in vectors so that X. fastidiosa cells have nowhere to attach in sharpshooters, resulting in no transmission to plants. The determination of how X. fastidiosa
interacts with vectors will open new venues to control disease spread, as understanding how pathogen and vector interact may lead to strategies to block the transmission of X. fastidiosa to plants.Another objective was to determine the relative importance of different parameters on X. fastidiosa transmission to plants by sharpshooters. This process is fundamental to any scientific understanding of the epidemiology of X. fastidiosa diseases in California and elsewhere. We conducted research to fill in this knowledge gap on the biology of X. fastidiosa transmission by quantifying some of the ecological factors believed to be important for disease spread. Our results illustrate how the number of infective insects on a plant, the number of infection events, and temperature affect X. fastidiosa transmission. We have also begun to use these experimental measurements to parameterize a mathematical model which allows forecasting of the rates of PD spread under different ecological scenarios.
This information is critical for developing ecologically sound and economically practical methods of managing PD.Lastly, we are also studying the ecology of an emerging grapevine diseases and its invasive vector, namely Grapevine leafroll-associated viruses (GLRaV) and the vine mealybug. Our current work is focused on essential first steps in understanding GLRaV transmission. So far, our results havegenerated biological information that can be incorporated into disease management practices. For example, only first instars of vine mealybug vector GLRaV; vine mealybug acquires and inoculates virus quickly; transmission efficiency increases with longer plant access time; vine mealybug loses acquired virus and its infectivity a couple of days after leaving infected grapevines; GLRaV is transmitted by the vine mealybug in a semi-persistent manner. Outputs are being made available to community through peer-reviewed publications, presentations at scientific meetings and to the agricultural
community.
Impacts
We have summarized our outcomes/impacts in three sections, based on the objectives of our project.Vector transmission of X. fastidiosa is an essential, albeit neglected, aspect of the epidemiology of this leafhopper-borne pathogen. Currently, there is little information on how X. fastidiosa cells interact with the cuticle of sharpshooter vectors. We have used a multidisciplinary approach to address this question and have demonstrated that initial attachment of cells to vectors, or the first step of sharpshooter colonization, is mediated by carbohydrate-binding proteins on the cell surface. We have also tested in vitro and in vivo all other X. fastidiosa gene mutants available that were assumed to be important for transmission. Results from those experiments suggest that X. fastidiosa colonization of vectors is a complex, stepwise process, much like the formation of biofilms. We generated a framework for the community to analyze how cells interact with vectors and,
importantly, it provides new opportunities for the development of means to disrupt Pierce's disease spread that are pathogen-vector specific. The dynamics of vectored diseases are governed by the interplay of a variety of biotic and abiotic factors. We studied some of these factors that are expected to be important to the epidemiology of Pierce's disease in California vineyards. We conducted a series of greenhouse transmission experiments to quantify how sharpshooter species, sharpshooter number, inoculation period, and temperature affect transmission of X. fastidiosa to grapes and Pierce's disease symptom development. For the blue-green sharpshooter, acquisition and inoculation access periods had similarly strong effects on infection rate. Interestingly, larger numbers and longer inoculation periods increased the onset of Pierce's disease symptoms. However, while the number of glassy-winged sharpshooter increased infection rate, inoculation period did not. These results suggest that
high sharpshooter loads may not only increase transmission rate but also decrease incubation period - presumably because of a larger inoculum. We expect that high vector densities and temperatures will increase the rate of disease cycling, which is particularly relevant to disease prevalence in this system.The introduction of the vine mealybug 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. 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 and a 1-h inoculation access period. Mealybugs lost GLRaV-3 and infectivity 4 days after virus acquisition. In addition, GLRaV-3 was not transovarially transmitted. Transmission parameters of GLRaV-3 by the vine mealybug indicate that transmission of this virus occurs in a
semipersistent manner.
Publications
- Borth, W.B., Fukuda, S.K., Hamasaki, R.T., Hu, J.S. and Almeida R.P.P. 2006. Detection, characterisation and transmission by Macrosteles leafhoppers of watercress yellows phytoplasma in Hawaii. Annals of Applied Biology 149: 357-363.
- Robson, J.D., Wright, M.G. and Almeida, R.P.P. 2006. Within-plant distribution and binomial sampling plan of Pentalonia nigronervosa (Hemiptera, Aphididae) on banana. Journal of Economic Entomology 99: 2185-2190.
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