Epidemiology and Control of Ranunculus Bacterial Blight Progress Reports — June 1999
Project Progress Report Cover Page & Requirements
11 Glen-Ed Professional Park, Glen Carbon, Illinois 62034 Telephone: 618.692.0045 Fax: 618.692.4045 Email: bstoeckl@endowment.org
Annual Report Deadline:
Reports must be received no later than June 1
Reporting Media:
An original hard copy and computer copy must be submitted.
- Submit 30 copies of the report by mail and
- An MSWord computer copy — two media options exist:
(1) Submit on 3.5″ diskette or (2) attach file to email.
Report Content:
Progress reports must include this cover sheet (fully completed). Do not exceed four typed pages (minimum font size = 11). Reports must (1) review industry needs addressed and project objectives, (2) summarize work conducted since inception outlining results and specific benefits to the industry especially new information identified, (3) outline next steps and future for project and anticipated industry benefit(s).
Purpose of Progress Report:
Progress reports enable the board and industry to keep abreast of the work accomplished in each project receiving AFE funding. They provide a tool to evaluate whether the work is meeting industry needs and original objectives. They are also used as a resource to develop publicity for AFE funded research.
IMPORTANT NOTE:
Information provided will be used as needed for publicity purposes unless the investigator indicates otherwise. If the material is confidential, an appropriate summary must be included that can be publicized, so the status of all projects can be released to industry.
Date: 6/2/99
Title of Project: Epidemiology and Control of Ranunculus Bacterial Blight
Institution(s): University of California, Riverside
AFE Grant Amount: $23,936 Grant Period: 09/98 to 08/99
Project Completion Date (as indicated on proposal application) 08/99
Project Leader: Donald A. Cooksey
Title: Professor and Chair
Address: Department of Plant Pathology, University of California, Riverside, CA 92521
Telephone: 909-787-4115 Fax: 909-7887-4294 Email: Cooksey@ucrac1.ucr.edu
Additional Researchers (Names): Albert O. Paulus, Extension Plant Pathologist, UCR Karen Robb, UCCE Advisor, San Diego Co.
PROJECT PROGRESS REPORT
Epidemiology and Control of Ranunculus Bacterial Blight
Donald A. Cooksey
University of California, Riverside
May 29, 1998
This project follows our recent description of a new Ranunculus disease caused by the bacterium Xanthomonas campestris. In addition to causing symptoms of blight on leaves and stems, the bacterium was shown to move systemically into root tubers and to infest seed. It is likely that the bacterium is spread in the industry in infested seed and tubers, and disinfestation of these materials should be key to preventing the disease during Ranunculus selection and propagation. All seed lots tested were infected with this pathogen, which has become widespread and severe in the major Ranunculus-growing region of Southern California. Infested seed lots have a lower percentage of viable seeds than noninfested seed lots, and infested tubers also show signs of necrosis. Infested tubers have resulted in diseased plants appearing in homeowners gardens. This proposal is to test seed and tuber treatment methods for eliminating the bacterial pathogen and to follow disease progression during two growing seasons at a commercial Ranunculus production site. The second season is nearing completion under funding from the American Floral Endowment.
Objectives:
1. Test the efficacy of seed and tuber treatments for removing Xanthomonas campestris, and measure effects on Ranunculus seed and tuber viability.
2. Quantify the severity and systemic spread of Xanthomonas campestris in field plots established with treated and nontreated Ranunculus seed and tubers.
3. Assess the role of weeds or other plant hosts as reservoirs of inoculum.
Progress to date:
-
Objective 1.
Ongoing laboratory tests have refined seed treatment methods that optimize the elimination of Xanthomonas campestris from seed lots, while minimizing the loss of seed viability. In 1996-97, we worked with both chlorine bleach and hot water treatments, and combinations of the two, but the chlorine treatments were consistently more effective, and as discussed below, more likely to be readily adopted by industry. During 1997-98, we used different durations of chlorine bleach treatment for our field trials. Subsequently, three new experimental chemical disinfectants were brought to our attention, and we have incorporated these into our laboratory and field experiments. Their effectiveness is still under evaluation with our 1998-99 field trials still in progress, but preliminary results are discussed below.
-
Objective 2.
Following a preliminary field trial at a commercial Ranunculus production site in Carlsbad, California, during the 1996-1997 growing season, our proposal under AFE funding was to conduct our experiments during two seasons beginning with a fall planting in 1997.
1997-98 season.
Two infested seed lots (two separate cultivars) of Ranunculus were treated with chlorine bleach at two treatment levels. Our earlier work had included hot water treatments, but chlorine bleach was more effective. In addition, the effective temperature range for hot water treatment without damaging seed viability was quite narrow, and this method therefore did not seem as likely to be adopted by industry. Control seeds were soaked in water only. Seeds were planted in prepared beds at a commercial Ranunculus production site in Carlsbad, CA in a randomized complete block design with four replicates per treatment. Sampling and disease assessments were conducted at regular intervals through the growing season. Early season samplings indicated again that our seed treatments with chlorine bleach were successful in reducing or eliminating bacterial inoculum and establishment of the bacterium in field plots. However, as this season progressed, we had unusually severe El Nino rains and wind-driven moisture across the plots. Our later sampling dates indicated that the pathogen had spread across border rows to infest our treated plots. All plots became diseased, in spite of our early data that the seed treatments were successful. The final harvest was scheduled in June of 1998, but our grower-cooperator mistakenly destroyed our plots along with adjacent plantings before the agreed-upon harvest date. We were therefore not able to collect final data on seed and tuber infestation for the 1997-98 season.
1998-99 season.
More extensive field trials were conducted during the 1998-99 season with more seed treatment methods, with both drip and overhead irrigation, and at two different sites to minimize problems from unexpected weather or improper management of plots by cooperators. The Carlsbad commercial site was again used, and identical plots were established at the University of California South Coast Field Station in Santa Ana, CA. Unfortunately, unusually destructive winds at the Santa Ana site destroyed our beds the day after planting. Our experiments at the Carlsbad site are still in progress and are scheduled for final harvest later this month.
Treatments during this season included three new promising experimental chemicals as potential seed disinfestation methods. Preliminary laboratory experiments were conducted to determine optimum concentrations and durations of the new chemicals, and chlorine bleach was again used at two treatment durations. Control seeds were soaked in water only. Six total treatments were planted in randomized complete block designs with four replicates per treatment on 11/30/98 at Carlsbad and on 12/4/98 at Santa Ana. Each replicate consisted of 15 ft of commercial bed with two rows of plants and drip irrigation in the center of the beds. Approximately 225 plants were grown in each replicate plot. Border rows of plants free of the pathogen were interspaced between treatment plots. At each site, the entire experiment was duplicated, and the second set of plots was sprinkler irrigated to favor bacterial growth in the event of a dry season. Every month, plant samples were taken for bacterial isolation, and visual disease ratings were made for each plot. At harvest, isolations will be made from seeds and tubers to enumerate bacterial spread to these propagative materials.
While the sampling and analysis of data from this season are still in progress, our results to date show that chlorine bleach and an experimental chemical DBNPA, which is used in water treatment, were the most effective in reducing populations of Xanthomonas campestris on seed and reducing the establishment of the pathogen in our plots.
-
Objective 3.
Within our field plots, 19 different species of weeds were detected during the 1997-98 growing season, and all were assayed for the presence of Xanthomonas campestris by washing plant parts and plating on selective media. No disease symptoms were observed on weeds, but epiphytic populations were detected on five species overall. Two grasses were the most common weeds harboring significant epiphytic populations of Xanthomonas campestris. The bacterium was also recovered infrequently on three other species, including two clovers and common cheeseweed. Our work suggests that weeds can be a significant source of residual inoculum.
Next steps and anticipated industry benefit:
The final harvest will be conducted later this month, followed by extensive sampling from the plants, seed, and tubers collected. The graduate student supported on this project is also conducting further tests in growth chambers and attempting to optimize both seed treatment procedures and PCR-based detection of low levels of the pathogen in seed, tubers, and plants.
The information gained from this project will be disseminated through a peer-reviewed journal and Cooperative Extension publications directed toward both the floriculture industry and homeowners. The PI has also given several talks on this subject during the past two years to growers, pest control advisors, and horticultural scientists. The results are expected to provide practical solutions to this disease problem during Ranunculus selection and propagation, as well as improve the quality of Ranunculus in commercial and home gardens. Our recent finding that weeds may harbor significant epiphytic populations of X. campestris will be confirmed and incorporated into disease management recommendations.
