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Funded Project

Funding Program: Regional IPM Grants (S-RIPM)

Project Title: Integrated management of anthracnose, botrytis and phytophthora in southeastern strawberry plasticulture systems

Project Director (PD): Frank J. Louws [1]

Lead State: NC Lead Organization: North Carolina State University

Research Funding: $111,338

Start Date: Aug-01-2005 End Date: Jul-31-2007

Summary: Anthracnose ripe fruit rot, Botrytis (gray mold) fruit rot and Phytophthora crown and root rot are the most important diseases of strawberry targeted by frequent fungicide applications in the Southeastern (SE) strawberry production region. The majority of growers have small to moderate sized land holdings and strawberries represent a significant source of income across the SE. Most farms spray intensely to manage Colletotrichum species (anthracnose), Botrytis cinerea, and Phytophthora cactorum. Numerous new fungicides recently included into extension recommendations must now be integrated into an IPM Roadmap context to minimize disease risk, to enhance the cost/benefit of management tactics, and to limit excess dependence on fungicides, not only for environmental purposes but also to limit risk of the development of pathogen resistance. The specific objectives are to: 1) develop and implement a multi-tactic program that includes disease-free strawberry plants, real-time PCR detection, and to initiate host resistance studies to manage anthracnose and Phytophthora problems; 2) develop fungicide use patterns that utilize available and newly generated knowledge of the biology of Colletotrichum and Botrytis to reduce fungicide spray applications by 40% to 50%; 3) perform economic analysis of outcomes as a decision tool growers may utilize to assess risk and optimum IPM strategies. Our research-based recommendations are utilized in the new SE region fruit production guide, the NC production guides, the mid-Atlantic production guide and by most growers in states as far away as Alabama. Thus, we are privileged to be uniquely positioned to develop IPM strategies that will have broad regional impact. Objectives: The specific objectives are to: 1) develop and implement a multi-tactic program that includes disease-free strawberry plants, real-time PCR detection, and to initiate host resistance studies to manage anthracnose and Phytophthora problems; 2) develop fungicide use patterns that utilize available and newly generated knowledge of the biology of Colletotrichum and Botrytis to reduce fungicide spray applications by 40% to 50%; 3) perform economic analysis of outcomes as a decision tool growers may utilize to assess risk and optimum IPM strategies.

Final Report:

Results PROGRESS: 2005/08 TO 2008/07 OUTPUTS: Due to the clonal propagation of strawberry plants for new plantation, major disease organisms are brought to the fruiting field with asymptomatic plants. A multi-tactic program that included disease-free strawberry plants, real-time PCR detection, and evaluation of host resistance was implemented. DETECTION ACTIVITY: We have developed real time PCR primer and probe sets to detect and quantify anthracnose causing fungi Colletotrichum acutatum (fruit anthracnose/rot) and C. gloeosporioides (crown anthracnose/rot). This primer set and probe was optimized using a Taqman protocol for Colletotrcichum DNA extracted from pure culture as well as from latently infected strawberry tissue with varied success from different tissues. HOST RESISTANCE ACTIVITY: Plug plants were fall planted each year. Treatments comprised 20 plants in standard fumigated raised mulched beds. Plots were arranged in a checkered pattern between rows and a 5-ft space between plots to ensure no genotype was immediately surrounded by plants of another genotype. Highly anthracnose fruit rot susceptible variety (Chandler)chandler plug plants were inoculated and were then inter-planted in the fall at both ends of the plot to allow natural spread of inoculum throughout the growing season. No fungicides were applied throughout the growing season. Fruits were harvested weekly in the spring. To avoid cross contamination during harvesting, disposable gloves were used between treatments. Disease incidence was determined for each genotype. In field resistance was complemented with detached fruit assays in the lab using the same cultivars. Likewise, whole plant evaluations were conducted in the phytotron to determine the receptivity or resistance of each genotype to the establishment of quiescent infections on green leaves. Berries from all 14 genotypes were also collected from the field at three different stages of maturity such as green, white and white-pink. A composite sample of one gram tissues were cut out from berries of each genotype in three replicates for each berry maturity stage. Samples were immediately frozen and lyophilized and subsequently analyzed for phenolic content and several enzymes to correlate with field and in vitro resistance data. PATHOGEN DIVERSITY: The genetic diversity of C. acutatum and C. gloeosporioides isolates from NC were compared to databased sequences using amplified fragments from the ITS region and Glutamine synthetase gene intron. Replicated field trials were established each year to meet the objective to develop fungicide use patterns that utilize available and newly generated knowledge of the biology of Colletotrichum and Botrytis to reduce fungicide spray applications by 40% to 50%. Isolates from various epidemics were screened for resistance to available fungicides to monitor for resistance. EVENTS: Key personnel spoke at many conferences, agent training and grower sessions. Emphasis was also placed on newsletter articles and research papers. SERVICES: One postdoc and several undergrad students were trained. PARTICIPANTS: Individuals: Mahfuzur Rahman, Postdoctoral scientist. Mike Carnes, Hourly labor. Jim Driver, Technician Partner Organizations: North Carolina Strawberry Growers Association North American Strawberry Growers Association Southern Regional Small Fruit Center Collaborators and contacts: Dr. Jim Ballington, Horticulture, NCSU Dr. Barclay Poling, Horticulture, NCSU Dr. Zvesdana Pesic vanEsbroek, Plant PAthology, NCSU Training or professional development: Southeast Regional Fruit and Vegetable Conference. Savannah, GA. Integrated disease control in strawberries. 11-13 Jan 2008.-- Strawberry disease management, diagnosis and hands-on identification. M. Rahman and F.J. Louws. Sothern Region Small Fruit Center Agent Training. Charlotte, NC. Nov 2-6, 2008.-- Diagnosis and integrated management of Strawberry Diseases. Southeast Strawberry Expo. Charlotte, NC. 7 November, 2008. TARGET AUDIENCES: Primary Targeted Audience: Field agents with strawberry responsibilities. Plasticulture Strawberry Growers in the Southeast USA region. Secondary Audience: Other strawberry growers and agents in North America. Efforts: Field days, agent training programs, presentations at grower conferences. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period. IMPACT: 2005/08 TO 2008/07 DETECTION ACTIVITY: DNA extract from green leaf disks did not amplify the target region of 95 bp at any spore concentration. But extracts from leaf tissues that were subjected to a bio-amplification phase was detected with a very low cycle threshold and in ascending order with the decrease of initial spore load placed on the leaf, indicating the detection of latent infections of Colletotrichum is possible by a Taqman protocol in a quantitative manner. Leaf stage appears to be a significant determinant of successful detection and quantification of latent infection. In spite of inoculation of leaves of different stages, only middle aged leaves showed a meaningful change in cycle threshold value with changes in spore numbers. The real-time PCR protocol was validated using field samples but additional issues need to be addressed. HOST RESISTANCE ACTIVITY: Advanced breeding lines such as NCC 99-13 and NCC 02-63 from the NC anthracnose resistance breeding program had 23.6% and 11.1% anthracnose fruit rot (AFR) incidence compared to the highly susceptible standard cultivar Chandler (70% incidence). Field resistance in 2008 was highly correlated with data generated in 2007 and to in vitro data. Selected breeding lines also showed excellent resistance against quiescent infection incidence and severity. Some genotypes had superior field resistance but low resistance to quiescent infections, others had the opposite trend and a small selection had resistance in both assays - suggesting these are superior lines for future management of AFR. Green strawberries contained higher amounts of phenolics compared to white and pink stages. Phenolic content in the green stage showed a moderate inverse correlation (r2=-0.52) and phenolic content in white and pink stages decreased drastically and did not show any correlation with resistance. Chitinase activity in the strawberry tissue of different genotypes at white to pink stages showed a significant inverse correlation (r2= -0.61) with resistance to AFR. PATHOGEN DIVERSITY: C. acutatum strains from NC epidemics were clustered as compared to a world-wide collection of strains - additional diversity studies are warranted. IPM-FUNGICIDE ACTIVITIES: Gray mold incidence in 2008 was high due to rain and prolonged foliar and floral wetness periods at the beginning of the harvest season. A reduced spray schedule (4 sprays) showed statistically similar efficacy as a season long schedule (9 or 14 sprays), consistent with data from previous years. AFR incidence was also very high due to splashing rain at the beginning of the season. At the end of the season, non-treated control plots had 100% of the fruits infected. Four well timed applications of fungicides starting at 10% bloom provided similar control as a season long program of 9 applications. All isolates evaluated showed sensitivity to current fungicides. Results were effectively extended to agents and growers. The advanced knowledge developed on the biology, ecology and management of strawberry diseases will result in an estimated savings of $20 million per year for plasticulture strawberry growers in the SE-USA (6-15% benefit). Peer reviewed articles are in progress. PUBLICATIONS (not previously reported): 2005/08 TO 2008/07 1. Rahman, M., J.G. Driver and F.J. Louws. 2009. Evaluation of fungicides to control gray mold on strawberry cultivar Chandler, 2008. Plant disease Management Reports. (in press). 2. Rahman, M., J.G. Driver and F.J. Louws. 2009. Evaluation of fungicides to control anthracnose fruit rot on strawberry cultivar Chandler, 2008. Plant disease Management Reports. (in press). 3. Rahman, M., J.G. Driver and F.J. Louws. 2008. Evaluation of standard cultivars and breeding lines for field incidence of anthracnose fruit rot, 2007. Plant disease Management Reports. SMF028. 4. Louws, F.J. and J.G. Driver. 2008. Evaluation of fungicide application methods for anthracnose fruit rot management in strawberry, 2007. Plant disease Management Reports. SMF027. 5. Rahman, M., J.G. Driver and F.J. Louws. 2008. Chemical control of Phomopsis blight of strawberry 2007. Plant disease Management Reports. SMF030. 6. Rahman, M. and F.J. Louws. 2008. Epidemiological significance of C-gloeosporioides infestation of nursery plants on crown rot of strawberry. Phytopathology 98: S129 (abstr). 7. Rahman, M. and F.J. Louws. 2008. Anthracnose resistance in strawberry genotypes for plasticulture systems in the Southeast. Phytopathology 98: S129 (abstr). 8. Louws, F.J. (Section Editor). 2008. Management of Strawberry Diseases. IN Southeast Regional Strawberry Integrated Management Guide. (GA, SC, TN, NC). http://www.smallfruits.org/SmallFruitsRegGuide/Guides/2009/2009Strawb erryIMGFinalNov17.pdf. 9. Louws, F.J. 2008. Summary of fungicide use in strawberries for Botrytis and anthracnose control in the spring. IN: North Carolina Agricultural Chemicals Manual. (Annual Updates). 10. Louws, F.J. 2008. Relative effectiveness of various fungicides for strawberry disease control. IN: North Carolina Agricultural Chemicals Manual. (Annual Updates). 11. Louws, F.J. 2008. Strawberry disease control. IN: North Carolina Agricultural Chemicals Manual. (Annual Updates). 12. Louws, F.J. and M. Rahman. 2008. Strawberry Disease Management: Colletotrichum Crown Rot and Anthracnose Ripe Fruit Rot. In, Stephen J. Toth (ed) North Carolina Pest News. Volume 23 #3.

Outcomes N/A

Impacts From report submitted by the PI to USDA CRIS report system DETECTION ACTIVITY: DNA extract from green leaf disks did not amplify the target region of 95 bp at any spore concentration. But extracts from leaf tissues that were subjected to a bio-amplification phase was detected with a very low cycle threshold and in ascending order with the decrease of initial spore load placed on the leaf, indicating the detection of latent infections of Colletotrichum is possible by a Taqman protocol in a quantitative manner. Leaf stage appears to be a significant determinant of successful detection and quantification of latent infection. In spite of inoculation of leaves of different stages, only middle aged leaves showed a meaningful change in cycle threshold value with changes in spore numbers. The real-time PCR protocol was validated using field samples but additional issues need to be addressed. HOST RESISTANCE ACTIVITY: Advanced breeding lines such as NCC 99-13 and NCC 02-63 from the NC anthracnose resistance breeding program had 23.6% and 11.1% anthracnose fruit rot (AFR) incidence compared to the highly susceptible standard cultivar Chandler (70% incidence). Field resistance in 2008 was highly correlated with data generated in 2007 and to in vitro data. Selected breeding lines also showed excellent resistance against quiescent infection incidence and severity. Some genotypes had superior field resistance but low resistance to quiescent infections, others had the opposite trend and a small selection had resistance in both assays - suggesting these are superior lines for future management of AFR. Green strawberries contained higher amounts of phenolics compared to white and pink stages. Phenolic content in the green stage showed a moderate inverse correlation (r2=-0.52) and phenolic content in white and pink stages decreased drastically and did not show any correlation with resistance. Chitinase activity in the strawberry tissue of different genotypes at white to pink stages showed a significant inverse correlation (r2= -0.61) with resistance to AFR. PATHOGEN DIVERSITY: C. acutatum strains from NC epidemics were clustered as compared to a world-wide collection of strains - additional diversity studies are warranted. IPM-FUNGICIDE ACTIVITIES: Gray mold incidence in 2008 was high due to rain and prolonged foliar and floral wetness periods at the beginning of the harvest season. A reduced spray schedule (4 sprays) showed statistically similar efficacy as a season long schedule (9 or 14 sprays), consistent with data from previous years. AFR incidence was also very high due to splashing rain at the beginning of the season. At the end of the season, non-treated control plots had 100% of the fruits infected. Four well timed applications of fungicides starting at 10% bloom provided similar control as a season long program of 9 applications. All isolates evaluated showed sensitivity to current fungicides. Results were effectively extended to agents and growers. The advanced knowledge developed on the biology, ecology and management of strawberry diseases will result in an estimated savings of $20 million per year for plasticulture strawberry growers in the SE-USA (6-15% benefit). Peer reviewed articles are in progress.

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