Location: Crop Diseases, Pests and Genetics
2008 Annual Report
Objective 1: Determine the epidemiology of exotic, emerging, re-emerging, and invasive diseases in California, including (but not necessarily limited to) Xf-caused diseases of horticultural, agronomic, and ornamental crops. Objective 2: Determine the nature and mechanism(s) of susceptibility/resistance to Xf infection and subsequent disease development in horticultural and agronomic crops, including (but not necessarily limited to) Vitis species and Prunus species. Objective 3: Develop effective, economical, environmentally sound strategies to manage exotic, emerging, re-emerging, and invasive diseases, including (but not necessarily limited to) xylella diseases.
Limited research also has been conducted on Huanglongbing (HLB) disease of citrus. As HLB associated bacteria, classified as “Candidatus Liberibacter” spp. are non-culturable, listed as select agents, and do not occur in California, research has been limited to DNA based genomic studies and development of PCR detection assays. Genome-walking approaches have resulted in cloning and sequencing of “Ca. Liberibacter” spp. genome fragments. PCR assays for the 16S rDNA region have been developed that amplify DNA of all three “Ca. Liberibacter” spp. associated with HLB disease.
6. High-throughput detection of X. fastidiosa from plant tissues. Xylella fastidiosa is responsible for Pierce’s disease of grapevines and almond leaf scorch disease. Although the pathogen may be cultured from diseased plants, isolation of the pathogen from field samples is difficult and not suitable for evaluation of large sample sizes needed for epidemiological studies. A rapid and simple procedure for X. fastidiosa DNA extraction from diseased almond tissue was developed by ARS scientists in the Crop Diseases, Pests and Genetics Research Unit in Parlier, CA, and found to be both reliable and suitable for high throughput PCR analysis. The technique will facilitate epidemiological studies in which X. fastidiosa infection status for a large number of samples are required to track pathogen spread and disease progression in the field. This project contributes to National Program 303 (Plant Diseases); Component 2 (Biology, Ecology, Epidemiology, and Spread of Plant Pathogens and Their Relationships with Hosts and Vectors); Problem Statement 2C (Population Dynamics, Spread, and Epidemiology of Pathogens). 7. Characterization of ribosomal RNA genes from “Candidatus Liberibacter” associated with citrus Huanglongbing (HLB) disease. HLB disease of citrus represents a serious threat to the US citrus industry. The disease is associated with an unculturable bacterium, “Candidatus Liberibacter” spp. Sequencing of ribosomal RNA genes of the bacterium facilitated development by ARS scientists in the Crop Diseases, Pests and Genetics Research Unit in Parlier, CA, of an improved PCR assay for detection of the bacterium. The assay will be useful in studies designed to evaluate the association of the bacterium with HLB disease. This project contributes to National Program 303 (Plant Diseases); Component 2 (Biology, Ecology, Epidemiology, and Spread of Plant Pathogens and Their Relationships with Hosts and Vectors); Problem Statement 2A (Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen).
8. Immunocytochemical protocols developed for detection of Xylella fastidiosa and glassy-winged sharpshooter (GWSS) watery saliva in grape tissue. The mechanism by which the Pierce’s disease bacterium, Xylella fastidiosa, is inoculated (injected into plants) by sharpshooters is presently unknown. Evidence to date supports that bacteria are carried into the plant by injected watery saliva, which is invisible in classically stained plant tissues. Immunocytochemical protocols were developed by ARS scientists in the Crop Diseases, Pests and Genetics Research Unit in Parlier, CA, for confocal microscopy to separately localize in grape tissue either X. fastidiosa cells or the primary enzymatic constituent of GWSS watery saliva, a type of cellulase called beta 1,4-glucanase. These new methods will enable testing of the role of salivation in the inoculation mechanism, and may result in potential targets for disruption of pathogen transmission to grapes. This project contributes to National Program 303 (Plant Diseases); Component 2 (Biology, Ecology, Epidemiology, and Spread of Plant Pathogens and Their Relationships with Hosts and Vectors); Problem Statement 2B (Plant-Microbe-Vector Interactions). 9. Morphological evidence for viruses (phages) in Xylella fastidiosa. As with many bacteria, the genome of Xylella fastidiosa has integrated prophage DNA sequences but it is unknown whether these sequences are nonfunctional remnants or competent to produce active phage infections able to destroy bacterial cells. X. fastidiosa was cultured under stress, by ARS scientists in the Crop Diseases, Pests and Genetics Research Unit in Parlier, CA, in an attempt to induce active phage reproduction. Senescent cultures of X. fastidiosa produced low levels of virus-like particles which, based on transmission electron microscopy, resemble particles of phages known to occur in other bacteria. X. fastidiosa phages hold promise as both a means of disease control and as tools for introduction of foreign DNA to X. fastidosa. This project contributes to National Program 303 (Plant Diseases); Component 2 (Biology, Ecology, Epidemiology, and Spread of Plant Pathogens and Their Relationships with Hosts and Vectors); Problem Statement 2A (Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen).
5.Significant Activities that Support Special Target Populations
2008 PWA Summer Intern Program: Mentored one female Hispanic student on project concerning molecular characterization of phages from Xylella fastidiosa.
Chen, J., Civerolo, E.L., Tubajika, K.M., Livingston, S., Higbee, B. 2008. Hyper-variation of Tandem Repeats at the PD0218 (pspB) locus of Xylella fastidiosa Almond Leaf Scorch and Grape Pierce’s Disease Strains. Applied and Environmental Microbiology. 74:3652-3657.
Deng, X., Chen, J., Luo, Z., Feng, Z., Li, H., Civerolo, E.L. 2008. First report of graft-transmission and PCR detection of Candidatus Liberibacter asiaticus from Atalantia buxifolia in Guangdong, China. Plant Disease. 92: 314.
Doddapaneni,, H., Lin, H., Walker, M., Yao, J., Civerolo, E.L. 2008. vitisExpDB: A database resource for grape functional genomics. Biomed Central (BMC) Plant Biology.8:23doi:10.1186/1471-2229-8-23
Nadel, H., Seligmann, R., Johnson, M.W., Hagler, J.R., Stenger, D.C., Groves, R.L. 2008. Effects of citrus and avocado irrigation and nitrogen-form soil amendment on host selection by adult Homalodisca vitripennis. Environmental Entomology. 37(3):787-795.
Gassmann, A.J., Stock, P.S., Sisterson, M.S., Carriere, Y., Tabashnik, B.E. 2008. Synergistic interactions between entomopathogenic nematodes and Bt crops: integrating biological control and resistance management. Journal of Applied Ecology 45:957-966.
Chen, J., Civerolo, E.L. 2008. Morphological evidence for phages of Xylella fastidiosa. Virology Journal. 5:75.
Habibi, J., Coudron, T.A., Backus, E.A., Brandt, S.L., Wagner, R.M., Wright, M.K., Huesing, J.E. 2008. Morphology and histology of the alimentary canal of Lygus hesperus Knight (Heteroptera: Cimicomoropha: Miridae). Annals of the Entomological Society of America. 101(1):159-171.
Sisterson, M.S., Chen, J., Civerolo, E.L., Ledbetter, C.A., Groves, R.L. 2008. Effects of Almond Leaf Scorch Disease on Almond Yield and Implications for Management. Plant Disease 92:409-414.
Sisterson, M.S. 2008. Effects of Insect Preference for Healthy or Infected Plants on Spread of an Inspect Vectored Plant Pathogen: Insights from a Model. Journal of Economic Entomology 101: 1-8.
Chen, J., Groves, R.L., Zheng, Y., Civerolo, E.L., Viveros, M., Freeman, M. 2007. Colony morphology of almond leaf scorch strains of xylella fastidiosa and its epidemiological application. Canadian Journal of Plant Pathology. 29:225-231.
Chen, J., Livingston, S., Groves, R.L., Civerolo, E.L. 2008. High throughput PCR detection of Xylella fastidiosa directly from almond tissues. Journal of Microbiological Methods. 73:57-61.
Deng, X., Chen, J., Feng, Z., Shan, Z., Guo, H., Li, H., Civerolo, E.L. 2007. Identifiction and Characterization of Huanglongbing Bacterium in Pummelo [citrus grandis (L.) Osbeck] from Multiple Locations in Guangdong, P.R. China. Plant Disease. 92:513-518.
Deng, X., Chen, J., Shan, Z., Zhou, G., Li, H., Civerolo, E.L. Identification of Candidatus Liberibacter asiaticus from Foshou (Citrus medica) in China. Plant Pathology. New Disease Report, 15:Article July 2007. Available: http://www.bspp.org.uk/ndr/july2007/2007-66.asp
Lin, H., Doddapaneni, H., Takahashi, Y., Walker, A. 2007. Comparative analysis of est's involved in grape responses to Xylella fastidiosa infection. Biomed Central (BMC) Plant Biology 2007, 7:8, doi:10.1186/1471-2229-7-8
Fritschi, F., Cabrera-La Rosa, J.C., Groves, R.L., Lin, H., Johnson, M.W. 2007. Behavioral Responses of Homalodisca vitripennis (Hemiptera: Auchenorrhyncha: Cicadellidae) on Four Vitis Genotypes. Environmental Entomology. Vol. 36, Issue 4, pp. 926-936.
Sisterson, M.S., Carriere, Y., Dennehy, T.J., Tabashnik, B.E. 2007. Non-target effects of bt crops: implications of source-sink population dynamics. Environmental Entomology. 36:121-127.
Sisterson, M.S., Biggs, R.W., Manhardt, N.M., Carriere, Y., Dennehy, T.J., Tabashnik, B.E. 2007. Effects of Transgenic Bt Cotton on Insecticide Use and Predatory Insect Abundance. Entomologia Experimentalis et Applicata. 124:305-311.