Progress 07/01/10 to 06/30/13
Outputs
Target Audience: Research and extension plant pathologists, Plant disease diagnosticians, Agricultural and horticultural extension agents, Nursery and greenhouse producers, Chemical industry personnel, Conservation biologists and educators, and Policy-makers Changes/Problems: Phytophthora diseases are a major limiting factor affecting the profitability and sustainability of the ornamental horticulture industry in the Southern region and nationwide. To protect this multi-billion dollar industry from these destructive diseases, chemical control often is indispensable. However, use of oomyceiticides such as Subdue Maxx (mefenoxam) will provide no control of these diseases caused by insensitive populations of Phytophthora species. As a result, a window of opportunity for chemical protection is lost, so may be the entire crops. As Phytophthora diseases affect a huge variety of ornamental crops, the potential economic losses of such an incident could be hundred and million dollars for the industry in the southern region alone and could be many times of this number nationwide. This project provided the essential data, efficient tools (multiwell plate assays) and alternative chemistries for farmers to formulate site-specific mefenoxam resistance and Phytophthora disease risk mitigation programs to prevent such incidents from occurring. These programs are crucial to improving the profitability and sustainability of the ornamental horticulture industry while reducing the unnecessary hazards to the public and environments. Additionally, the multiwell plate assays developed in this project will be a robust research and diagnostic tools for evaluating Pythium resistance to these compounds. They are readily applicable to populations of both genera from other crops as well as the natural environment. What opportunities for training and professional development has the project provided? Two postdoctoral associates (Olson and Cafa) and one graduate student (Yang) worked on this project at Virginia Tech and developed expertise and practical experience in oomyceticide resistance research and education programming. This project also provided a unique opportunity for them to interact with farmers and ornamental plant pathologists at collaborating institutions. Additional associates were trained at the collaborating institutions. How have the results been disseminated to communities of interest? Four articles have been published in Plant Disease and Plant Disease Management Reports, respectively, and one invited presentation was given at the 18th Ornamental Workshop on Diseases and Pests in Kanuga Conference Center in Hendersonville, NC on September 26, 2012 to communicate the results of this project with research and extension communities as well as policy-makers and general public. Data from the fitness trials and additional fungicide evaluation trials are being prepared fornew publications. The implications of these data and recommendations on mefenoxam resistance and Phytophthora disease management have been communicated with growers and landscapers via numerous local and regional extension venues including presentations, Field Days, on-site visits, disease diagnostic reports. A fact sheet incorporating the final results from the recent field trials is being developed for regional distribution. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Mefenoxam and phosphorous acid (or phosphite) are two most widely-used compounds for control of Phytophthora diseases, a major limiting factor for the multi-billion dollar ornamental horticulture industry. Understanding whether Phytophthora populations have developed resistance to these oomyceticides at a regional level is crucial to mitigating the potential risk of crop devastation caused by these pathogens because they are frequently moved via interstate stock plants materials. A multiwall plate assay was developed to provide robust screening of Phytophthora isolates for insensitivity to mefenoxam and phosphorous acid, respectively. A total of 1,526 isolates were evaluated for sensitivity to 100 a.i. mefenoxam/ml usingthe multiwell plate assay. These isolates included 518 from plants, 696 from irrigation water, and 312 from streams. The plant isolates belong to 20 species, while the irrigation and stream isolates are from 25 and 16 species, respectively. Mefenoxam insensitivity was detected in 8% of the plant isolates belonging to four species, 9% of the irrigation isolates from eight species, and 4% of the stream isolates from three species. Eighty-five percent of mefenoxam insensitive plant isolates identified in this project was P. nicotianae, of which 86% were recovered from herbaceous annual crops in a limited number of nursery and greenhouse locations/states. The other mefenoxam insensitive plant isolates belonged to P. undulata (3 cultures), P. palmivora (1) and P. taxon “PgChlamydo” (1). P.t. “PgChlamydo”, a taxon yet to be formally described; and P. undulata, whose taxonomic status is yet to be settled, are weak pathogens to ornamental crops at the most. In the greenhouse trials with annual vinca and petunia, applications of Subdue Maxx (mefenoxam) at the label rate 4 days prior to inoculation controlled the Phytophthora diseases of both crops caused by sensitive isolates but not those by any of the insensitive isolates. The fitness of mefenoxam-insensitive isolates of P. nicotianae to survive in greenhouse crop production was tested by introducing an insensitive isolate (either SO845 or SO846) at one end of a planted tray of snapdragon opposite a mefenoxam-sensitive isolate (S1103) of the pathogen at the other end of the tray. After Phytophthora root rot had developed, the root system was cut into short segments and re-mixed with the soilless mix in the tray. The tray was then replanted with healthy snapdragon seedlings and disease allowed to develop naturally. After the third replanting when disease incidence was near 100%, root isolations were made for Phytophthora from each individual snapdragon. Recovered isolates were tested for mefenoxam sensitivity at 100 ppm. Mefenoxam insensitive isolates SO845 and SO846 were recovered from 98% and 90% of the infected snapdragon plants in the respective treatments. In addition, 115 isolates (mostly insensitive to mefenoxam) were evaluated for sensitivity to 500 ppm of phosphite and compared to a lab-generated insensitive isolate of P. capsici from the Coffey Lab at the University of California, Riverside. These ornamental isolates belong to P. cryptogea, P. drechsleri, P. gonapodyides, P. hydropathica, P. megasperma, P. nicotianae, P. pini and P. tropicalis and they were from both greenhouse and nursery production facilities in North Carolina and Virginia. The reference isolate of P. capsici was insensitive as expected while all ornamental isolates assessed were sensitive. These findings constitute significant changes in the knowledge regarding the oomyceticide resistance: • Multiple resistances to mefenoxam and phosphite were not detected. • Mefenoxam insensitivity is an issue of limited scope, e.g., mostly one species (P. nicotianae) from annual crops in some locations. • Based on the insensitivity detected among the irrigation and stream isolates, it was proposed that repeated applications of Subdue Maxx (mefenoxam) may have selected the insensitive populations that already are in nature rather than induced resistant mutations. • Insensitivity to mefenoxam does not impose a fitness penalty on survival and infection. • A variety of new chemistries including some nonregistered ones were identified as promising alternatives which could be used for rotation with mefenoxam for resistance management.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Olson, H. A., Jeffers, S. N., Ivors, K. L., Steddom, K. C., Williams-Woodward, J. L., Mmbaga, M. T., Benson, D. M., and Hong, C. X. Diversity and mefenoxam sensitivity of Phytophthora spp. associated with ornamental crops in the southern US. Plant Disease 97:86-92
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Yang, X., Kong, P., and Hong, C. X. Evaluation of fungicide drenches for control of Phytophthora root rot of petunia, 2012. Plant Disease Management Reports 7:OT002
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Yang, X., Richardson, P. A., and Hong, C. X. Evaluation of nonregistered fungicide for control of rose downy mildew, 2012. Plant Disease Management Reports 7:OT001
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Yang, X., Richardson, P. A., Kong, P., and Hong, C. X. Fungicidal control of Phytophthora aerial blight on annual vinca in Virginia, 2012. Plant Disease Management Reports 7:OT005
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Progress 07/01/11 to 06/30/12
Outputs
OUTPUTS: Mefenoxam and phosphorous acid (or phosphite) are two most widely-used compounds for control of oomycete diseases including downy mildews, Phytophthora and Pythium. The primary objectives of this collaborative project among seven laboratories in six southern states (GA, NC, SC, TN, TX, VA) were to assess how widespread and how bad is the mefenoxam insensitivity issue in the ornamental horticulture industry at a regional level, to develop a hypothesis on the underlying mechanism of mefenoxam insensitivity, and to investigate whether a similar problem also has emerged with phosphite. Phytophthora species were used as a model system in this project. To date, a total of 1,526 isolates have been evaluated for sensitivity to 100 a.i. mefenoxam/ml using a multiwell plate assay. These isolates included 518 from plants, 696 from irrigation water, and 312 from streams. The plant isolates belong to 20 species, while the irrigation and stream isolates are from 25 and 16 species, respectively. Mefenoxam insensitivity was detected in 8% of the plant isolates belonging to 4 species, 9% of the irrigation isolates from 8 species, and 4% of the stream isolates from 3 species. Eighty-five percent of mefenoxam insensitive plant isolates identified in this project was P. nicotianae, of which 86% were recovered from herbaceous annual crops in a limited number of nursery and greenhouse locations/states. The other mefenoxam insensitive plant isolates belonged to P. undulata (3 cultures), P. palmivora (1) and P. taxon "PgChlamydo" (1). P.t. "PgChlamydo", a taxon yet to be formally described and P. undulata, whose taxonomic status is yet to be settled, are weak pathogens to ornamental crops at the most. In the greenhouse trials with annual vinca and petunia, applications of Subdue Maxx at the label rate 4 days prior to inoculation controlled the Phytophthora diseases of both crops caused by sensitive isolates but not those by any of the insensitive isolates. These results indicated that mefenoxam insensitivity is an issue of limited scope, e.g., mostly one species (P. nicotianae) from annual crops in some locations. Based on the insensitivity detected among the irrigation and stream isolates, it was proposed that repeated applications of Subdue Maxx (mefenoxam) may have selected the insensitive populations that already are in nature rather than induced resistant mutations. In addition, 115 isolates (mostly insensitive to mefenoxam) were evaluated for sensitivity to 500 ppm of phosphite and compared to a lab-generated insensitive isolate of P. capsici from the Coffey Lab at the University of California, Riverside. These ornamental isolates belong to P. cryptogea, P. drechsleri, P. gonapodyides, P. hydropathica, P. megasperma, P. nicotianae, P. pini and P. tropicalis. The reference isolate of P. capsici was insensitive as expected while all ornamental isolates assessed were sensitive. These data have been written for publication in Plant Disease and was recently presented to a national group of extensional plant pathologists and diagnosticians at the 18th Ornamental Workshop on Diseases and Pests in Kanuga Conference Center in Hendersonville, NC. PARTICIPANTS: Olson, H. A., Postdoc Associate, Virginia Tech; Jeffers, S. N., Co-Principal Investigator, Clemson University; Ivors, K. L., Co-Principal Investigator, North Carolina State University; Steddom, K. C., Co-Principal Investigator, Texas A & M University; Williams-Woodward, J. L., Co-Principal Investigator,University of Georgia; Mmbaga, M. T., Co-Principal Investigator, Tennessee State University; Benson, D. M., Co-Principal Investigator, North Carolina State University; and Hong, C. X., Principal Investigator, Virginia Tech TARGET AUDIENCES: Research and extension plant pathologists, Plant disease diagnosticians, Extension agents (agriculture and horticulture), Nursery and greenhouse crop producers, Chemical company representatives, Conservation biologists, and educators PROJECT MODIFICATIONS: We have requested a no cost 1-year extension for this project to continue looking into how mefenoxam-insensitive isolates live with those sensitive isolates in the absence of this compound while screening new cultures from other projects.
Impacts
Phytophthora diseases are among the single most significant factors affecting the productivity, profitability and sustainability of the ornamental horticulture industry in the Southern region and nationwide. To protect this multi-billion dollar industry from these destructive diseases, chemical control often is indispensable. However, use of oomyceiticides such as Subdue Maxx (mefenoxam) and Aliette or Alude (phosphite) will provide no control of these diseases caused by insensitive populations of Phytophthora species. As a result, a window of opportunity for chemical protection is lost, so may be the entire crops. As Phytophthora diseases affect a huge variety of ornamental crops, the potential economic losses of such an incident could be hundred and million dollars for the industry in the southern region alone and could be many times of this number nationwide. This project provided the essential data for farmers to prevent such incidents from occurring, improving the profitability and sustainability of the green industry while reducing the unnecessary hazards to the public and environments.
Publications
- Olson, H. A., Jeffers, S. N., Ivors, K. L., Steddom, K. C., Williams-Woodward, J. L., Mmbaga, M. T., Benson, D. M., and Hong, C. X. 2012. Diversity and mefenoxam sensitivity of Phytophthora spp. associated with ornamental crops in the southern US. Plant Disease 96 (in press)
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Progress 07/01/10 to 06/30/11
Outputs
OUTPUTS: Resistance to mefenoxam, a fungicide frequently used for the management of Phytophthora diseases in the ornamental industry, has been identified as a growing concern within the industry. In order to efficiently screen large culture collections, a high-throughput assay using 48-well culture plates was developed to evaluate sensitivity to mefenoxam. Phytophthora isolates were collected from ornamental plants, irrigation water, and natural streams and soil in the southeastern United States. To date, 1,030 isolates of Phytophthora from Georgia (GA), North Carolina (NC), South Carolina (SC), Tennessee (TN), Texas (TX), and Virginia (VA) have been identified to species and screened for sensitivity to 100 ppm of mefenoxam. These isolates belonged to 23 species, and 95 of them were insensitive to mefenoxam. These insensitive isolates were identified from P. citricola, P. drechsleri, P. gonapodyides, P. hydropathica, P. insolita, P. megasperma, P. nicotianae, P. PgChlamydo, and P. pini. The insensitive isolates originated predominantly from ornamental plants and irrigation water; however, nine isolates of P. gonapodyides from GA and one isolate of P. hydropathica and one isolate of P. megasperma from VA collected from streams also were insensitive to mefenoxam. Additional isolates have been screened for mefenoxam insensitivity; however, their identities are yet to be determined. To validate the mefenoxam insensitivity assay, isolates of P. nicotianae collected from annual vinca identified as insensitive and sensitive to mefenoxam were inoculated onto annual vinca plants treated with the label rate of mefenoxam (Subdue Maxx). Only mefenoxam-insensitive isolates caused significant foliar blight on annual vinca plants treated with mefenoxam, supporting the in vitro mefenoxam assay. In many plant pathogens, pesticide resistance reduces the fitness of the organism in the absence of the pesticide. The fitness of mefenoxam-insensitive and mefenoxam-sensitive isolates of P. nicotianae in the absence of mefenoxam was evaluated. After three subsequent plantings of snapdragons into potting mix infested with the isolates, the population structure of this pathogen isolated from the snapdragon roots was comprised of 88 to 100% mefenoxam-insensitive isolates, suggesting that mefenoxam-insensitive isolates are more fit and better able to compete for infection sites than mefenoxam-sensitive isolates. The mefenoxam-screening assay was adapted to evaluate isolates for sensitivity to 500 ppm of phosphorous acid, another extensively used compound for Phytophthora disease management. A lab-generated phosphite-insensitive isolate of P. capsici was obtained for the insensitive control. Initially, 28 mefenoxam-insensitive Phytophthora isolates from VA were screened during the assay development. Of these, three isolates of P. pini were insensitive. Currently, all participating research labs are assessing the phosphorous acid-screening protocol. PARTICIPANTS: PD: Dr. Chuan Hong, Virginia Polytechnic Institute and State University, Virginia Beach, VA 23455, email: chhong2@vt.edu; Co‐PD: Dr. D. Michael Benson, North Carolina State University, Raleigh, email: mike_benson@ncsu.edu; Co‐PD: Dr. Steven Jeffers, Clemson University, Clemson, SC 29634, email: sjffrs@clemson.edu; Co‐PD: Dr. Kelly Ivors, North Carolina State University, Mills River, NC 28759, email: kelly_ivors@ncsu.edu; Co‐PD: Dr. Karl Steddom, Texas A&M University, Overton, TX 75684, email: k‐steddom@tamu.edu; Investigator: Dr. Heather Olson, Virginia Polytechnic Institute and State University, Virginia Beach, VA 23455, email: heather.a.olson@gmail.com; Cooperator: Dr. Margaret Mmbaga, Tennessee State University, McMinnville, TN 37110, email: mmmbaga@tnstate.edu; Cooperator: Dr. Jean Williams‐Woodward, University of Georgia, Athens, GA 30602, email: jwoodwar@uga.edu. Web conferences involving all project individuals have been held every three months to discuss project results. TARGET AUDIENCES: Extension activities targeting crop consultants and crop producers within the ornamental horticulture industry have focused on emphasizing the potential for mefenoxam resistance and the importance of crop rotation for mitigating resistance development in Phytophthora. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The ornamental horticulture industry involves extensive plant movement between production facilities within a state and between states. This plant movement allows the spread of Phytophthora throughout the industry. By studying mefenoxam resistance at a regional level, the spread of mefenoxam-resistant isolates of Phytophthora can be reduced. Identifying the scope and degree of mefenoxam resistance in the ornamental horticulture industry has been crucial in directing proper use of this compound for disease management and improving its overall efficacy. It has helped avoid reapplication of this compound where resistant populations have been identified, mitigating crop loss risk while preventing its unnecessary release into the environment. By rotating with new chemistries, crop health risk is lessened and oomyceticide resistance development is slowed. Most importantly, growers better understand the importance of resistance management strategies and avoid repeated use of the same compounds, thus reducing the risk of Phytophthora developing resistance to new chemicals.
Publications
- No publications reported this period
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