Progress 10/01/02 to 09/30/07
Outputs
In June of 2002 the CCPP completed the VI Index on 15 new citrus varieties This is a test for all the known bud transmitted diseases affecting citrus. These new varieties will be released from quarantine and placed in the CCPP Foundation Plantings for evaluation and possible future release for commercial and research purposes. The varieties included two blood oranges, two sweet limes, one lemon, one sweet orange, one tangelo, one tangor, one kumquat and six mandarins. All of these varieties may be of commercial value and will require additional field evaluation. The CCPP now has 128 varieties of citrus still in quarantine. During the period covered by this report the CCPP received 31 new introductions that have begun the testing and cleanup process. Once again all of the citrus on the Lindcove Research and Extension Center (LREC) was tested for tristeza. All trees in the Foundation-Evaluation Block once again tested negative for the virus. The 30,000+ square foot
addition to the CCPP LREC Screenhouse that houses the CCPP Protected Foundation Block was completed with an irrigation system and 100 of the most popular CCPP varieties were planted in the new screenhouse, directly in the ground, and are spaced so that budwood production will be similar to that of field grown trees. These trees are now growing well, and will allow the CCPP to begin discarding container grown trees of these varieties, thus freeing up some space to house new varieties in the protected environment. The CCPP will begin to repropagate the container grown varieties and rotate new young trees into the screenhouse. The small screenhouse that the CCPP had been using for a number of years was moved to the new site adjacent to our large screenhouse and now houses the source trees of the growth modifying Tsn-RNA's. This past fall, winter and spring we again evaluated fruit from our registered trees. The data from these evaluations were averaged into previous evaluation data and
were posted on the CCPP Website (www.ccpp.ucr.edu). Once again this past year we were able to add a number of new images to the website and to improve on the quality of some previous images.
Impacts
Continued availability of disease tested propagation material from the CCPP is essential for the variety of research projects conducted by the University and it is extremely important for the protection of California's citrus industry. Maintaining California in the forefront of high quality fruit production demands the newest varieties and the highest quality propagation material.
Publications
- No publications reported this period
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Progress 01/01/01 to 12/31/01
Outputs
This past year a total of ten new varieties completed all therapy and pre-testing procedures and were entered into the CCPP VI index. This is a test for all the known bud transmitted diseases affecting citrus. If all tests are negative, these new varieties will be released from quarantine and placed in the CCPP Foundation Plantings for evaluation. The varieties included one blood orange, one lime, one lemon, one grapefruit, one sweet orange, one tangelo, one kumquat and three mandarins. All of these varieties may be of commercial value and will require additional field evaluation. We were able to reduce the number of varieties that the CCPP has been holding in quarantine this year. This was possible because the curator of the USDA/ARS National Clonal Germplasm Repository for Citrus and Dates was granted a permit to import and maintain citrus in quarantine. As a result of this the CCPP transferred 52 varieties from our quarantine facility to the USDA facility. The
varieties transferred were primarily imports that will give greater depth to the citrus germplasm collection of USDA and the University of California Citrus Variety Collection and were of no commercial value. This leaves the CCPP with about 75 varieties still in quarantine. Once again all of the citrus on the Lindcove Research and Extension Center (LREC) was tested for tristeza. Several trees were determined to be positive for citrus tristeza and were immediately removed. Fortunately none of these trees were in the Foundation-Evaluation Block. The 30,000+ square foot addition to the CCPP LREC Screenhouse that houses the CCPP Protected Foundation Block was completed this past winter and is ready for use. Approximately 100 of the most popular CCPP varieties were propagated in February and will be planted in the new screenhouse facility as soon as they are ready. These varieties will be planted directly in the ground where they will be spaced so that budwood production will be similar to
that on field grown trees. Once these trees are growing well, the same varieties that we have been holding in containers will be eliminated thus freeing up some space to house new varieties in the protected environment. The small screenhouse that the CCPP had been using for a number of years was moved to the new site adjacent to our large screenhouse. This screenhouse will be used to house the source plants for the growth modifying Tsn-RNA's. Distribution of this material began this June, 2001. This past fall we again evaluated fruit from our registered trees. The results of these evaluations were posted on the CCPP Website (www.ccpp.ucr.edu). We were also able to add a number of new images to the website. We are hoping to complete all the needed images within the next year.
Impacts
Continued availability of disease tested propagation material from the CCPP is essential for the variety of research projects conducted by the University and it is extremely important for the protection of California's citrus industry. Maintaining California in the forefront of high quality fruit production demands the newest varieties and the highest quality propagation material.
Publications
- Krueger, R.R., T.L. Kahn, D.J. Gumpf, P.M. Balance, O.J. Bier and J. Bash. 2000. Shoot-tip micro-grafting for the rescue or therapy of field-grown citrus germplasm accessions. IV Congress Intl. Soc. Citriculture. Orlando, Florida.
- Vidalakas, Georgios, D.J. Gumpf and J.S. Semancik. 2001. Efficacy of citrus indexing reactions with mixed infections. 15th Conf. IOCV. Paphos, Cyprus.
- Gumpf, D.J. and M. Polek (eds). 2000. Proceedings of the exotic diseases of citrus workshop. 77p. Citrus Research Board, Visalia, CA.
- Kahn, T.L., O.J. Bier, R. Krueger, M. Roose, and D. Gumpf. 2000. The UC Riverside citrus variety collection, cornerstone of the California citrus genetic resources conservation and utilization system. IV Congress Intl. Soc. Citriculture. Orlando, Florida.
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Progress 01/02/00 to 12/31/00
Outputs
This past year a total of fifteen new varieties completed all therapy and pre-testing procedures and were entered into the CCPP VI index that is a test for all the known bud transmitted diseases affecting citrus. If all tests are negative, these new varieties will then be released from quarantine an place either in the CCPP Foundation Plantings for evaluation or they will be placed in the UCR CVC collection. The varieties included a blood orange, two limes, two lemons and one grapefruit; one pummelo and eight mandarins. All of these varieties may be of commercial value and will require additional field evaluation. Once again all of the citrus on the Lindcove Research and Extension Center (LREC) was tested for tristeza. A number of trees were determined to be positive for citrus tristeza and were immediately removed. None of these trees were in the Foundation-Evaluation Block. It is becoming obvious from these yearly tests that increased spread of tristeza is occurring
in and around the research station and it will be only a matter of time before the disease will begin to be a problem in the CCPP Foundation Block. Fortunately, the second phase of the protected foundation block screenhouse was initiated during this project year. This new screenhouse section will allow us to plant a number of our important scion varieties directly in the field under the protection of this screen. From these trees we will be able to distribute larger numbers of buds than we can from the container grown trees already under protection in the original screenhouse facility. We will be propagating and planting in this new section within the coming year. As in past years we continued our evaluation of fruit collected from our registered trees as well as from a number of newly released varieties that are beginning to fruit for the first time. Our major contribution this year was the development and activation of the CCPP website http://www.ccpp.ucr.edu/. The site still needs
work, particularly photos of the fruit varieties so we will be working hard to complete these deficiencies as soon as possible. The site is very helpful and time saving for us as we can use it to post our yearly fruit evaluations as well as other information from the CCPP that would be of interest to the growers and Nurseries of California.
Impacts
Continued availability of disease tested propagation material from the CCPP is essential for the variety of research projects conducted by the University and it is extremely important for the protection of California's citrus industry. Maintaining California in the forefront of high quality fruit production demands the newest varieties and the highest quality propagation material.
Publications
- Gumpf, D. J. 1999. Citrus quarantine, California. pp. 151-156. In: R. P. Kahn and S. B. Mathur (eds.) Plant pest and pathogen exclusion: containment facilities and safeguards. American Phytopathological Society Press.
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Progress 01/01/99 to 12/31/99
Outputs
This past year a total of fourteen new varieties completed all therapy and testing procedures and was released from quarantine. The varieties included two navel oranges, nine mandarins, a large fruiting Mexican type lime, a sweet lime and a sour orange rootstock. All of these varieties may be of commercial value. We currently have a backlog of approximately 170 varieties still in quarantine. Once again all of the citrus on the Lindcove Research and Extension Center (LREC) was tested for tristeza. Nine trees were determined to be positive for citrus tristeza and were immediately removed. None of these trees were in the Foundation-Evaluation Block. This is, however, the greatest number of infected trees detected on the station during these yearly tests. The CCPP LREC Screenhouse that houses the CCPP Protected Foundation Block, has been operational for 1_ years and contains a complete compliment of the CCPP varieties maintained as container grown trees. No trees were
lost during the December 1998 freeze; however, a number of them did lose their new growth foliage. Particularly hard hit were the lemon varieties. Following pruning late in the spring to remove the frost damaged growth; these trees recovered nicely and are growing vigorously. In fact, they have grown so well that we need to spread the trees further apart. Unfortunately, the screenhouse is completely full. This means that we must begin planning now for the construction of additional protected screenhouse space. This past fall we again evaluated fruit from our registered trees. These evaluations normally continue until about June. We have a large number of newly imported mandarin varieties that are now fruiting and need to be evaluated.
Impacts
Continued availability of disease tested propagation material from the CCPP is essential for the variety of research projects conducted by the University and it is extremely important for the protection of California's citrus industry. Maintaining California in the forefront of high quality fruit production demands the newest varieties and the highest quality propagation material.
Publications
- No publications reported this period
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Progress 01/01/98 to 12/01/98
Outputs
This past year a total of fourteen new varieties completed all therapy and testing procedures and was released from quarantine. The varieties included three navel oranges, two late valencia oranges, five mandarins, a sweet lemon, a sour orange, a tangelo and CITRUS YUZU. All of these varieties may be of commercial value. We currently have a backlog of approximately 150 varieties still in quarantine. No tristeza-infected trees were detected in the Foundation Block nor in the CCPP Cultivar Block this past year. This year as an added precaution, the entire Lindcove station was tested for tristeza. This was done to give us an idea of the level of tristeza immediately surrounding our Foundation Block. One tree on the station tested positive for tristeza and was removed. This year the new screenhouse, which will house the CCPP Protected Foundation Block, was completed. An irrigation system complete with fertilizer proportioner and timer was also installed. Throughout the
summer months the new trees that had been propagated for the new screenhouse were transplanted into 20-gallon pots and placed in the new screenhouse. In all approximately 350 trees representing about 200 different varieties were transplanted into the new facility.
Impacts
(N/A)
Publications
- SEMANCIK, J.S., A.G. RAKOWSKI, J.A. BASH, and D.J. GUMPF. 1997. Application of selected viroids for the dwarfing and enhancement of production of 'Valencia' orange. J. Hort. Science 72: 563-570.
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Progress 01/01/97 to 12/01/97
Outputs
Citrus scion material that tests free of all known bud-transmitted diseases and is true-to-name is necessary for the continued productivity and growth of the California citrus industry. Diseases now present in California as well as those that have been excluded so far, could be disastrous to the citrus industry without a program to systematically eliminate diseases and provide a source of tested budwood. Budsports, chimeras and other spontaneous genetic disorders are frequent in citrus and can result in serious commercial losses if left unchecked. Careful inspection and elimination of these natural mutations from budwood source trees must also be an integral part of any budwood program. Citrus cultivars important to California are "cleaned up" and established in the CCPP Foundation-Evaluation Block and the new CCPP Lindcove Quarantine Screenhouse. To provide a source of citrus propagation material which is tested for all known bud-transmitted diseases, these trees are
maintained in healthy condition by appropriate care, periodic indexing for disease, yearly inspections of trees and evaluation of fruit produced by either budwood source trees or trees propagated from these protected sources. Trees in the Foundation-Evaluation Block and in the Quarantine Screenhouse are registered with the CDFA following their guidelines for establishing a registered budwood source tree. The CCPP is vital for the production of California citrus from new diseases that could be introduced along with the importation of new varieties from other citrus growing areas of the world as well.
Impacts
(N/A)
Publications
- NIKOLAEVA, O.V., KARASEV, A.V., GUMPF, D.J., LEE, R. F., and GARNSEY, S.M. 1995. Production of polyclonal antisera to the coat protein of citrus tristeza virus expressed in ESCHERICHIA COLI: application for immunodiagnosis. Phytopathology.
- GUMPF, D.J. 1995. The California citrus clonal protection program. Subtropical Fruit News 3:10.
- GUMPF, D.J. 1995. The California citrus clonal protection program. IN: Lee, R., M. Rocha-Pena, C.L. Niblett, F. Ochoa, S.M. Garnsey, R.K. Yokomi and R. Lastra (eds.). Proceedings of the 3rd International Workshop on CTV and BrCA.
- NIKOLAEVA, O.V., KARASEV, A.V., POWELL, C.A., GUMPF, D. J., GARNSEY, S.M. and LEE, R.F. 1996. Mapping of epitopes for citrus tristeza virus-specific monoclonal antibodies using bacterially expressed coat protein fragments. Phytopathology 86.
- GUMPF, D.J. 1996. Citrus Greening. University of California Center for Exotic Pest Research Bulletin.
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Progress 01/01/96 to 12/30/96
Outputs
This past year a total of sixteen new varieties completed all therapy and testing procedures and were released from quarantine. The varieties include a number of late navels that will undergo field testing here in California. Also include in this years released introductions were three new satsumas, two Tangelos, three lemons and a seedless Nagami kumquat. We still have over 50 additional varieties under quarantine in various stages of therapy and testing. No tristeza infected trees were detected in the Foundation Block nor in the CCPP Cultivar Bank. All tristeza testing was performed using the serological reagents resulting from the research reported in the publications list. The production of these reagents was a significant contribution because of its specificity, lack of healthy reaction and the quantities available. This year as an added precaution, the entire Lindcove station was tested for tristeza. This was done to give us an idea of the level of tristeza
immediately surrounding our Foundation Block. The results of this extensive test revealed that there were no infected trees on the entire station. This information will be useful as the special CRB Subcommittee debates alternatives to the field planted Foundation Block. This past year the CCPP maintained a booth at the Tulare Farm and Equipment Show in February and the Visalia Citrus Expo in March. Different citrus varieties were displayed and information about the program and its benefit to California Agriculture was also made available.
Impacts
(N/A)
Publications
- NIKOLAEVA, O.V., KARASEV, A.V., GUMPF, D.J., LEE, R. F., and GARNSEY, S.M. 1995. Production of polyclonal antisera to the coat protein of citrus tristeza virus expressed in ESCHERICHIA COLI: application for immunodiagnosis. Phytopathology.
- GUMPF, D.J. 1995. The California citrus clonal protection program. Subtropical Fruit News 3:10.
- GUMPF, D.J. 1995. The California citrus clonal protection program. IN: Lee, R., M. Rocha-Pena, C.L. Niblett, F. Ochoa, S.M. Garnsey, R.K. Yokomi and R. Lastra (eds.). Proceedings of the 3rd International Workshop on CTV and BrCA.
- NIKOLAEVA, O.V., KARASEV, A.V., POWELL, C.A., GUMPF, D. J., GARNSEY, S.M. and LEE, R.F. 1996. Mapping of epitopes for citrus tristeza virus-specific monoclonal antibodies using bacterially expressed coat protein fragments. Phytopathology 86.
- GUMPF, D.J. 1996. Citrus Greening. University of California Center for Exotic Pest Research Bulletin.
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Progress 01/01/95 to 12/30/95
Outputs
This past November, (16) new citrus varieties entered our variety introduction index. This index will be completed in May, at which time the varieties testing negative for all the known bud-transmitted diseases will be released from quarantine. Included in this years index are, several new satsumas, a late navel from South Africa, three lemon varieties, a seedless nagami and the giant Key lime from Florida. We are still holding 61 cultivars under quarantine where they are undergoing "clean up" and disease testing. Starting the first week of October 1995, we again initiated our annual evaluation and testing of fruit from our Foundation Block trees. This process is necessary to insure that these trees are performing to the highest possible standards and that they are not producing fruit that is "off type" or producing large numbers of chimeras or other spontaneous mutations. As in past years, this information was made available to any interested growers. We also held a
fruit display in Visalia in conjunction with the farm advisors fall citrus meeting. In November, budwood from all the registered trees in field 56 of the Foundation Block was collected and used as inoculum for a Mexican lime test. The Mexican lime test is part of our routine testing of this block for tristeza and other bud-transmitted diseases. The rest of the Foundation Block, field 55, will be given a Mexican lime test in May of 1996. A Foundation Block walk through open to all interested nurserymen and growers was held in early January 1996.
Impacts
(N/A)
Publications
- No publications during this time period.
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Progress 01/01/94 to 12/30/94
Outputs
During the five year period of this project, there were several important and significant changes made on this project which resulted from research performed either directly or indirectly under this project. First of all, the entire project was shifted so that it is now totally under the direction of the Department of Plant Pathology. This has greatly improved the efficiency and the productivity of the project. Secondly, all citrus viroid testing done on this project is now done using a combination of laboratory procedures including sequential poly acrylamide gel electrophoresis and polymerase chain reaction tests. These techniques were developed by Semancik and have greatly improved our ability to diagnose and identify the viroids infecting citrus. This technique requires only about 2-3 months to complete as opposed to our previous method which required a lengthy incubation period of at least 2 years. A third major contribution during this reporting period is that we
have successfully cloned and sequenced the coat protein gene of citrus tristeza virus. The cloned gene was then translated in vitro and a fusion protein including the coat protein was produced. This protein was used for the production of specific high quality polyclonal antisera which has greatly enhanced our tristeza ELISA testing. The antisera is of such quality that it is being used by other labs and is considered the standard by which other tristeza antisera must be evaluated.
Impacts
(N/A)
Publications
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Progress 01/01/93 to 12/30/93
Outputs
During the period covered by this report, 18 varieties completed all cleanup andtesting and were released from quarantine. Forty additional citrus cultivars remain under quarantine where they are undergoing various cleanup and testing procedures. Ten of the most recent introductions were part of the budwood Early Release program. These included the Cara Cara pink navel, and two new Clementine mandarins from morocco and the variegated pink fleshed Eureka lemon. These varieties in particular have received a great deal of attention during our fruit displays and as a consequence budwood demand was greater than we were able to supply. The intensive testing of the foundation block for tristeza continues as a high priority. This year the block was tested 3 times by ELISA prior to budwood cutting and an additional time by inoculation to Mexican lime. No citrus tristeza was detected by our tests. Of added importance that past year we have expressed the coat protein gene of
citrus tristeza virus (CTV) and have developed an in vitro translation system for the production of this protein. This protein has then been used to produce both rabbit polyclonal and mouse monoclonal antisera. We have tested the polyclonal antiserum against a wide range of CTV isolates from around the world and it has detected everything we have tried thus far. The desirability of this in vitro system is that it eliminates the need for repeated purifications of CTV from infected tissue which is a very difficult task and yields are low.
Impacts
(N/A)
Publications
- KARASEV, A. V. and D. J. GUMPF. 1993. Rapid screening of the genome of clostero-like viruses by PCR with degenerate primers. Abstract. American Society for Virology, 12th Annual Meeting, July 10-14, 1993.
- PAPPU, H. R., A. V. KARASEV, E. J. ANDERSON, S. S PAPPU, R. F. LEE, U. V. DOLJA, E.V. KOONIN, D. J. GUMPF, and C. L. NIBLETT. 1993. Citrus tristeza virus potentially encodes HSP70- and HSP90-like proteins. Abstract. 9th International Cong.
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Progress 01/01/92 to 12/30/92
Outputs
During the Period covered by this summary, there have been some major changes and significant improvements made in the Citrus Clonal Protection Program. All virus testing, clean up and maintenance and release of citrus budwood from the Foundation Block is now under the direction of Plant Pathology. This year required a great deal of time to be spend propagating and registering new materials to be placed in the Foundation Block which had not been completed for two years under the previous system of divided responsibility. The newly registered trees entered into the program this year numbered 102. In addition 47 new imported varieties completed all clean up and testing and were released from federal quarantine and can now be propagated. Thirty-one additional imports are still under quarantine at various stages of clean up and testing. Our most significant accomplishment beside the reorganization this past year was the success of our viroid testing. We were able to test
259 varieties for the presence of viroids. Translated into time saved by using this sPAGE procedure it amounts to 3 years of greenhouse testing. Once again we continued our intensive testing of the Foundation Block for the presence of tristeza. The entire block was tested three times by ELISA just prior to budwood cutting and once during the year by inoculation to Mexican Lime. Following budwood harvest composite samples of the actual budwood distributed to nurseries was also tested by ELISA. No citrus tristeza virus was detected in any of our tests.
Impacts
(N/A)
Publications
- No publications reported this period.
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Progress 01/01/91 to 12/30/91
Outputs
During the period covered by this report, some real changes from past Citrus Clonal Protection Program (CCPP) procedures were implemented because of a possible threat of tristeza (CTV) contamination of our foundation trees. Therefore, no budwood was released from any of the registered field trees, but we did release limited quantities of budwood from trees that were in protected screenhouses and greenhouses. In our effort to supply the highest quality virus-tested budwood from our foundation block, we performed four CTV indexes on these foundation trees. Three of these indexes were ELISA tests and the fourth was the standard Mexican lime index. The first test run in October of 1990 revealed the presence of one infected tree which was immediately pulled. A second ELISA was run on collections made from the foundation block in December of 1990, which again turned up positive trees, this time three which were likewise pulled and destroyed. After the second ELISA turned
up three positive trees, a decision was made to index all the citrus on the Lindcove Field Station since any infected trees could serve as a source of further spread. This index was done by ELISA and completed by June 1991 with only a single infected tree discovered. The foundation block was tested again by ELISA in June of 1991 and the results were all negative. In June budwood from half of the foundation block was also collected and tested for CTV by the Mexican lime index. The results of this test were likewise negative.
Impacts
(N/A)
Publications
- NO PUBLICATIONS REPORTED THIS PERIOD.
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Progress 01/01/90 to 12/30/90
Outputs
More than 450,000 buds have been distributed from the Citrus Clonal Protection Program (CCPP) since its inception. There are presently over 360 trees representing 135 selections of citrus maintained in the protected CCPP foundation block. Nine new selections were entered into the CCPP this past year, all from heat treated and/or shoot-tip grafted plants. All foundation budwood trees were indexed on Mexican lime for citrus tristeza virus. Each tree was also carefully inspected and the fruit evaluated. Inspections of both trees and fruit are made three times each year, in October, December and April, so that each variety can be sampled and evaluated in its peak season. Also, registered budwood source trees are retested for exocortis every 3 years, for psorosis every 6 years, and for cachexia every 10 years. Limited quantities of budwood from six new selections were distributed this year from the early budwood release program. These selections include Cara Cata pink navel
and Flame grapefruit from Florida, Delta Valencia from South Africa, Henderson Ruby and Ray Ruby grapefruit from Texas and Limonero Fino lemon from Spain. Training of personnel from the CCPP in the laboratory procedures for detection of the cachexia agent by polyacrylamide gel electrophoresis (PAGE) has been completed. The PAGE procedure has proven to be not only faster but also more accurate and reliable than the previously used Parson Special mandarin bioassay.
Impacts
(N/A)
Publications
- PERMAR, T. A., GARNSEY, S. M., GUMPF, D. J. and LEE, R. F. 1990. A monoclonal antibody that discriminates strains of citrus tristeza virus. Phytopathology 80:224-228.
- NAUER, E. M., CARSON, T. L., GUMPF, D. J. and BASH, J. A. 1990. The varietal outlook. Citrograph 75:181-185, 188-190.
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Progress 01/01/89 to 12/30/89
Outputs
Since its inception, more tha 415,000 buds have been distributed from this Citrus Clonal Protection Program (CCPP). Most commercial orchards planted in California in the last 25 years have been established with nursery trees using budwood originating directly or indirectly from the virus-free budwood sources developed by the CCPP. There are presently over 400 trees reprensenting 122 selections of citrus maintained in the protected CCPP foundation block. Nineteen new selections were entered into the CCPP this past year, all but five from heat-treated or shoot-tip grafted plants. All functional budwood trees were indexed on Mexican lime for citrus tristeza virus. Each tree was also carefully inspected and the fruit evaluated. Inspections of both trees and fruit are made three times per year, in October, December and April, so that each variety cn be sampled and evaluated in its peak season. Also, registered budwood source trees are re-tested for exocortis every 3
years, for psorosis every 6 years, and for cachexia every 10 years. The first budwood to be distributed from the CCPP Early Budwood Release Program occurred this year. Over 3,000 buds of Rio Red grapefruit were released from screenhouse-grown container plants. This coming year three additional varieties will be available for early release.
Impacts
(N/A)
Publications
- MARCO, G.M., SEMANCIK, J.S. and GUMPF, D.J. 1989. Isometric viral particles recovered from tatter leaf-citrange stunt complex infected plants. 11th Conf. IOCV.
- MARCO, G.M. and GUMPF, D.J. 1989. A simple technique for the production of highly specific polyclonal antisera for citrus tristeza virus. 11th Conf. IOCV.
- LEVY, L.L. and GUMPF, D.J. 1989. Psorosis virus of citrus: host range, dsRNA analysis, purification, and initial characterization of the rod-shaped particle associated with the disease. 11th Conf. IOCV.
- YOKOMI, R.K., GARNSEY, S.M., CIVEROLO, E.L. and GUMPF, D.J. 1989. Transmission of exotic citrus tristeza virus isolates by a Florida colony of aphis gossypii. Plant Disease 73:552-556.
- LEE, J.G., SAKOVICH, N.J., DODDS, J.A., GUMPF, D.J. and MENGE, J.A. 1989. Troyer decline in Ventura County. Citrograph. 74:252-254.
- SEMANICK, J.S., GUMPF, D.J. and BASH, J.A. 1989. Interactions among group II citrus viroids: a potential for protection from the cachexia disease. 11th Conf. IOCV.
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