Progress 01/01/04 to 12/31/08

Outputs
OUTPUTS: Greenhouse inoculation methods were evaluated for initiating collar rot epidemics (caused by Sclerotinia sclerotiorum) among tobacco seedlings in a float-style greenhouse. One such method was used in a greenhouse collar rot control test to compare development of disease foci after treatment with hydrogen dioxide (trade name Oxidate), Bacillus subtilis QST 713 (trade name Serenade), or B. amyloliquifaciens IN937a and B. subtilis A13 (trade name BioYield) with that in greenhouse trays sprayed with iprodione (trade name Rovral) or azoxystrobin (trade name Quadris). Three further greenhouse trials evaluated alternatives to traditional fungicides for control of damping-off and root and stem rots of tobacco seedlings caused by Pythium spp. Disease development after treatment with hydrogen peroxide, varying rates of BioYield, or a commercial surfactant/soil penetrant (tradename Naiad) was compared to that when the fungicide etridiazole (tradename Terramaster) was applied. Five isolates of plant growth promoting rhizobacteria (PGPR) and four combinations of these isolates were compared with standard treatments for control of tobacco black shank (Phytophthora nicotianae), tobacco blue mold (Peronospora tabacina), target spot of tobacco(Thanatephorus cucumeris), and tobacco cyst nematodes (Globodera tabacum solanacearum - GTS) in multiple greenhouse and field experiments. A graduate research project investigated potential resistance to GTS induced by PGPR in further detail. This project included "split-root" experiments to study whether suppressed GTS reproduction associated with PGPR-amended seedling growth media or application of the commercial biocontrol product acibenzolar-S-methyl (ASM, tradename Actigard) results from induced resistance or some other mechanism. Greenhouse studies also investigated possible interactions between constitutive nematode resistance and resistance induced by PGPR or ASM. Field trials in 2006 through 2008 evaluated reproduction of natural TCN populations on oriental and flue-cured tobacco treated with PGPR. These trials included collaborative field experiments with agribusiness to evaluate GTS reproduction on tobacco seedlings inoculated with different PGPR by varying methods. Research results were shared with scientific colleagues at annual meetings of the USDA-CSREES Multi-State Regional Project S-1015 "Host Resistance as the Cornerstone for Managing Plant-Parasitic Nematodes in Sustainable Agroecosystems" and at Potomac Division and national meetings of the American Phytopathological Society. PARTICIPANTS: Individuals who have worked on this project include: Principal investigator: Charles S. Johnson, Professor, Virginia Tech, Southern Piedmont Agricultural Research and Extension Center and Department of Plant Pathology, Physiology, and Weed Science. Graduate Student: Parkunan Venkatesan, Graduate Research Assistant, Virginia Tech, Southern Piedmont Agricultural Research and Extension Center and Department of Plant Pathology, Physiology, and Weed Science. Partner organizations include Bayer CropScience. Collaborators and contacts include: Dr. David Reed, Tobacco Extension Specialist, Virginia Tech, Southern Piedmont Agricultural Research and Extension Center and Department of Crops, Soils and Environmental Sciences; Dr. Jon Eisenback, Professor, Virginia Tech, Department of Plant Pathology, Physiology, and Weed Science; Dr. Jeremy Pattison, Assistant Professor, Virginia Tech, Southern Piedmont Agricultural Research and Extension Center and Department of Horticulture; and Dr. Kenny Seebold, Department of Plant Pathology, University of Kentucky. TARGET AUDIENCES: This research is intended to provide farmers with effective new methods to control diseases of cultivated tobacco more safely with fewer potential risks to the environment. Results may also apply to producers of other agricultural commodities that face similar problems, particularly in greenhouse seedling production and in crop production in fields infested by plant-parasitic nematodes. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
No control methods are currently registered for collar rot (Sclerotinia sclerotiorum), among the most damaging diseases in transplant production greenhouses. Collar rot levels were similarly lower among seedlings grown in a medium amended with two plant growth promoting rhizobacteria or PGPR (Bacillus amyloliquifaciens IN937a and B. subtilis A13 - tradename BioYield) compared to plants treated with the fungicides iprodione and azoxystrobin. Unfortunately, disease pressure in these experiments was very low. Consequently, more research is needed on the reliability of BioYield as a potential control method for collar rot in tobacco greenhouses. Losses in usable transplants due to Pythium are increasingly common in tobacco greenhouses. Neither hydrogen peroxide or BioYield reduced disease damage caused by Pythium, but a collaborative trial with Dr. Kenny Seebold of the University of Kentucky incorporated a commercial surfactant into the "float water" upon which tobacco seedlings were grown, lowering Pythium damage similarly to use of the fungicide etridiazole (tradename TerraMaster). This new approach to managing Pythium in tobacco greenhouses could significantly reduce fungicide use in tobacco transplant production. Approximately one-third of Virginia's flue-cured tobacco acreage is treated routinely with nematicides to control a tobacco cyst nematode (Globodera tabacum solanacearum - GTS). Application of disease-resistance inducing products such as Actigard and PGPR could enable growers to reduce or eliminate nematicide use, saving as much as 175 dollars per acre and increasing yield by approximately 15 percent. Reducing production costs is particularly critical for Virginia growers facing a highly competitive global market driven by intense pressure to minimize expenses. In addition to improved farm safety and reducing potential negative impacts on the environment, the estimated yield increase could increase the value of Virginia's flue-cured tobacco crop, based upon 2007 records, by approximately $10,000,000. Among four PGPR combinations tested in greenhouse studies, BioYield suppressed GTS reproduction most consistently. Application of acibenzolar-S-methyl (ASM) also reduced final numbers of GTS cysts, but caused chlorosis, stunting, and lowered plant fresh weight. BioYield suppressed GTS reproduction on both resistant and susceptible flue-cured tobacco cultivars more consistently than ASM. When oriental tobacco seedlings were grown in a BioYield-amended medium, a single application of 200 mg ASM/L one week after transplanting significantly suppressed GTS reproduction in the field without phytotoxicity. Collaborative field trials with Bayer CropScience found periodic yield increases with suppressed GTS reproduction associated with PGPR treatments. Further research is necessary to improve the consistency of these effects. Identification of alternatives to nematicides is critical given 2008 proposals by EPA to cancel Virginia's label for aldicarb on tobacco and to dramatically increase regulation of soil fumigants, severely restricting current nematicide use.

Publications

• Johnson, C.S., Wernsman, E.A., and LaMondia, J.A. 2009. Effect of a chromosome segment marked by the Php gene for resistance to Phytophthora nicotianae on reproduction of tobacco cyst nematodes. Plant Disease 93: 309-315.

Progress 10/01/07 to 09/30/08

Outputs
OUTPUTS: Two greenhouse trials evaluated alternatives to traditional fungicides for control of damping-off and root and stem rots of tobacco seedlings caused by Pythium spp. Disease development after treatment with hydrogen peroxide, varying rates of BioYield, or a commercial surfactant/soil penetrant (tradename Naiad) was compared to that when the fungicide etridiazole (tradename Terramaster) was applied. A graduate research project continued investigating potential resistance to Globodera tabacum solanacearum (GTS) induced by plant growth promoting rhizobacteria (PGPR) in detail. "Split-root" experiments studied whether suppressed GTS reproduction associated with PGPR-amended seedling growth media or application of the commercial biocontrol product acibenzolar-S-methyl (ASM, tradename Actigard) results from induced resistance or some other mechanism. Greenhouse studies also investigated possible interactions between constitutive nematode resistance and resistance induced by PGPR or ASM. Field trials in 2008 evaluated reproduction of natural TCN populations on oriental and flue-cured tobacco treated with PGPR. These trials included collaborative field experiments with agribusiness to evaluate GTS reproduction on tobacco seedlings inoculated with different PGPR by varying methods. Research results were shared with scientific colleagues at the 2008 meeting of the Potomac Division and the 2008 national meeting of the American Phytopathological Society. PARTICIPANTS: Individuals who have worked on this project include: Principal investigator: Charles S. Johnson, Professor, Virginia Tech, Southern Piedmont Agricultural Research and Extension Center and Department of Plant Pathology, Physiology, and Weed Science. Graduate Student: Parkunan Venkatesan, Graduate Research Assistant, Virginia Tech, Southern Piedmont Agricultural Research and Extension Center and Department of Plant Pathology, Physiology, and Weed Science. Partner organizations include Bayer CropScience. Collaborators and contacts include: Dr. David Reed, Tobacco Extension Specialist, Virginia Tech, Southern Piedmont Agricultural Research and Extension Center and Department of Crops, Soils and Environmental Sciences; Dr. Jon Eisenback, Professor, Virginia Tech, Department of Plant Pathology, Physiology, and Weed Science; Dr. Jeremy Pattison, Assistant Professor, Virginia Tech, Southern Piedmont Agricultural Research and Extension Center and Department of Horticulture; and Dr. Kenny Seebold, Department of Plant Pathology, University of Kentucky. TARGET AUDIENCES: This research is intended to provide farmers with effective new methods to control diseases of cultivated tobacco more safely with fewer potential risks to the environment. Results may also apply to producers of other agricultural commodities that face similar problems, particularly in greenhouse seedling production and in crop production in fields infested by plant-parasitic nematodes. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Losses in usable transplants due to Pythium are increasingly common in tobacco greenhouses. Hydrogen peroxide or BioYield (Bacillus amyloliquifaciens IN937a and B. subtilis A13) did not reduce disease damage caused by Pythium, but a collaborative trial with Dr. Kenny Seebold of the University of Kentucky incorporated a commercial surfactant into the "float water" upon which tobacco seedlings were grown, lowering Pythium damage similarly to use of the fungicide etridiazole (trade name TerraMaster). This new approach to managing Pythium in tobacco greenhouses could significantly reduce fungicide use in tobacco transplant production. Approximately one-third of Virginia's flue-cured tobacco acreage is treated routinely with nematicides to control a tobacco cyst nematode (Globodera tabacum solanacearum - GTS). Application of disease-resistance inducing products such as Actigard and PGPR could enable growers to reduce or eliminate nematicide use, saving as much as 175 dollars per acre and increasing yield by approximately 15 percent. Reducing production costs is particularly critical for Virginia growers facing a highly competitive global market driven by intense pressure to minimize expenses. In addition to improved farm safety and reducing potential negative impacts on the environment, the estimated yield increase could increase the value of Virginia's flue-cured tobacco crop, based upon 2007 records, by approximately $10,000,000. When oriental tobacco seedlings were grown in a medium amended with the PGPR product BioYield, a single application of 200 mg ASM/L one week after transplanting significantly suppressed GTS reproduction in the field without phytotoxicity. A collaborative field trial with Bayer CropScience found increased yield associated with several PGPR treatments. Further research is necessary to improve the consistency of these effects. Identifying alternatives to traditional nematicides is critical given 2008 proposals by EPA to cancel Virginia's label for aldicarb on tobacco and to dramatically increase regulation of soil fumigants, severely restricting current nematicide use.

Publications

• Johnson, C.S., Pattison, J.A., Clevinger, E.M., Melton, T.A., Fortnum, B.A., and Mila, A. 2008. Clarifying the source of black shank resistance in flue-cured tobacco. Online. Plant Health Progress doi:10.1094/PHP-2008-0618-02-RS
• Parkunan, V., Johnson, C.S., Eisenback, J.D., Tolin, S. A., and Pattison, J. 2008. Variations in induced resistance response among cultivated tobacco types. http://www.apsnet.org/meetings/2008/abstracts/a08ma637.htm

Progress 10/01/06 to 09/30/07

Outputs
OUTPUTS: Greenhouse inoculation methods were evaluated in 2007 for initiating collar rot epidemics caused by Sclerotinia sclerotiorum among tobacco seedlings in a float-style greenhouse. One such method was used in a greenhouse collar rot control test comparing development of disease foci after treatment with hydrogen dioxide (trade name Oxidate), Bacillus subtilis QST 713 (trade name Serenade), or B. amyloliquifaciens IN937a and B. subtilis A13 (trade name BioYield) with that in greenhouse trays sprayed with iprodione (trade name Rovral) or azoxystrobin (trade name Quadris). My doctoral graduate student conducted 3 greenhouse experiments and 2 field tests in 2007 on induced resistance to Globodera tabacum solanacearum (tobacco cyst nematode - TCN). One of Mr. Parkunan Venkatesan's greenhouse studies evaluated TCN reproduction on 4 flue-cured tobacco cultivars to investigate possible interactions between constitutive nematode resistance and resistance induced by PGPR or ASM. He also conducted 2 "split-root" experiments to study whether suppressed TCN reproduction associated with PGPR-amended seedling growth media or ASM application results from induced resistance or some other mechanism. Mr. Venkatesan's field work in 2007 evaluated reproduction of natural TCN populations on flue-cured and oriental tobacco treated with PGPR or ASM. I also conducted a collaborative field trial with Bayer CropScience in 2007 to evaluate TCN reproduction on tobacco seedlings grown in media amended with 4 different PGPR (plant growth-promoting rhizobacteria) treatments. These early research results were shared with scientific colleagues at the annual meeting of the USDA-CSREES Multi-State Regional Project S-1015 "Host Resistance as the Cornerstone for Managing Plant-Parasitic Nematodes in Sustainable Agroecosystems." PARTICIPANTS: Individuals who have worked on this project include: Principal investigator: Charles S. Johnson, Professor, Virginia Tech, Southern Piedmont Agricultural Research and Extension Center and Department of Plant Pathology, Physiology, and Weed Science. Graduate Student: Parkunan Venkatesan, Graduate Research Assistant, Virginia Tech, Southern Piedmont Agricultural Research and Extension Center and Department of Plant Pathology, Physiology, and Weed Science. Partner organizations include Bayer CropScience. Collaborators and contacts include: Dr. David Reed, Tobacco Extension Specialist, Virginia Tech, Southern Piedmont Agricultural Research and Extension Center and Department of Crops, Soils and Environmental Sciences. Dr. Jon Eisenback, Professor, Virginia Tech, Department of Plant Pathology, Physiology, and Weed Science. Dr. Jeremy Pattison, Assistant Professor, Virginia Tech, Southern Piedmont Agricultural Research and Extension Center and Department of Horticulture. TARGET AUDIENCES: This research is intended to provide farmers with effective new methods to control diseases of cultivated tobacco more safely with fewer potential risks to the environment. Results may also apply to producers of other agricultural commodities that face similar problems, particularly in greenhouse seedling production and in crop production in fields infested by plant-parasitic nematodes.

Impacts
Disease pressure was generally extremely low after inoculation of a greenhouse test with Sclerotinia sclerotiorum, but mortality rates appeared similarly lower among seedlings grown in a medium amended with a combination of two PGPR (Bacillus amyloliquifaciens IN937a and B. subtilis A13) compared to plants treated with the fungicides iprodione and azoxystrobin. No control methods are currently registered for the collar rot disease caused by S. sclerotiorum, which is among the most damaging diseases occurring on tobacco seedlings in transplant production greenhouses. Identification of an effective biocontrol method for collar rot would significantly improve transplant production efficiency. Reductions in tobacco cyst nematode reproduction were associated with PGPR treatments and ASM application in 2007 greenhouse and field results, but these reductions weren't consistent. Further work is needed to verify these associations. Results from the collaborative field trial with Bayer CropScience suggested associations between PGPR treatments and suppressed TCN reproduction, but the effects were not as great as that of the standard control treatment (soil fumigation with 1,3-dichloropropene). Tobacco cyst, root-knot, and lesion nematodes can reduce tobacco yields up to 50% under Virginia conditions. If confirmed, the 2007 PGPR-TCN results could be critical to avoiding crop losses to nematodes, as EPA recently recommended canceling the tobacco registration for aldicarb (the last remaining non-fumigant nematicide available) and the pending cluster re-registration of soil fumigants may further limit the set of effective pesticides to control nematodes. This work needs to be repeated to verify whether or not the PGPR really possess significant potential as alternatives to standard nematicides. However, nematicides are expensive and pose significant environmental and applicator safety risks. Identification of an effective biocontrol alternative for control of plant-parasitic nematodes could significantly reduce nematicide use.

Publications

• V. Parkunan, Johnson, C.S., and Eisenback, J.D. 2007. Induced resistance to Globodera tabacum solanacearum in tobacco. Abstract published online: http://www.apsnet.org/meetings/div/po07abs.asp

Progress 10/01/05 to 09/30/06

Outputs
As in 2005, burley cultivars KT204LC, NC5, and NC7 were more susceptible to target spot (Thanatephorus cucumeris) than KY14xL8 and blue-mold resistant NC2000. Genetically engineering burley tobacco TN90 reduced target spot damage to that cultivar. Induced resistance from application of acibenzolar-S-methyl reduced target spot severity on lower leaves prior to first harvest of flue-cured tobacco. However, disease levels were lowest throughout the harvest period when azoxystrobin was applied three times on a 14 day interval over the four week period prior to harvest. Delaying the initial spray until either of two threshold levels was reached hindered disease control on bottom leaves, but improved late season control on upper leaves. Although tobacco cyst nematode (TCN - Globodera tabacum solanacearum) reproduction was lower on all released burley tobacco cultivars compared to susceptible standard flue-cured tobacco cultivar K326, significant differences were also observed among burley cultivars. All entries in the 2007 flue-cured tobacco Regional Farm Test were TCN-resistant except ULT219, SP229, and XP257. Control of TCN from metam sodium was best when the nematicide was applied as a row treatment or when broadcast treatments were incorporated with a power-tiller versus a disc or field cultivator. Final incidence of bacterial wilt (Ralstonia solanacearum) was again similar among released burley tobacco cultivars, but 3 breeding lines were identified with improved resistance (comparable to moderately susceptible flue-cured cultivar NC71). Bacterial wilt incidence was significantly lower on six new flue-cured tobacco cultivars versus NC71. Significant resistance to black shank (Phytophthora parasitica var. nicotianae) was also noted among burley tobacco cultivars and breeding lines. Combining use of imidacloprid with mefenoxam improved black shank control for burley tobacco, probably due to improved control of flea beetle larvae. Applying phosphorus acid in addition to imidacloprid mefenoxam reduced black shank damage even further.

Impacts
My target spot control research facilitated the registration of a new fungicide that was applied to an estimated 13% of Virginia's 2006 tobacco crop, saving tobacco farmers between 285,000 and 1,225,440 dollars during this growing season alone. Characterizing resistance to nematodes, black shank, and bacterial wilt is enabling Virginia's tobacco growers to significantly reduce use of soil pesticides, potentially reducing production costs by 150 to 370 dollars per acre. Improved disease resistance could range from 59 percent for black shank on flue-cured tobacco to 73 percent for bacterial wilt in burley tobacco. Reducing yield losses and production costs is particularly critical for Virginia producers, who face a highly competitive global market. Improving disease control is a critical component in empowering Southside Virginia farmers in offsetting lost income through increased production of burley tobacco production. Increased use of traditionally-developed resistant cultivars, as well as that developed through transgenic technology or induced by application of resistance-activating products such as Actigard, will also improve farm safety and reduce any potential negative impacts of agriculture on the environment.

Publications

• Johnson, C. S. and Reed, T. D. 2006. Host resistance to target spot in Virginia, 2005. B&C Tests 21:FC029.
• Johnson, C. S., Reed, T. D., and Clarke, C. T. 2006. Host resistance to Granville wilt in Virginia, 2005. B&C Tests 21:FC027.
• Johnson, C. S. 2006. Efficacy of various nematicides against tobacco cyst nematodes in Virginia, 2005. F&N Tests 61:N004.
• Johnson, C. S. 2006. Efficacy of fungicides for target spot control for flue-cured tobacco in Virginia, 2005. F&N Tests 61:FC087.
• Johnson, C. S. and Clarke, C. T. 2006. Granville wilt control in Virginia using soil fumigation, 2005. F&N Tests 61:FC045.
• Johnson, C. S. and Reed, T. D. 2006. Host resistance to black shank in Virginia, 2005. B&C Tests 21:FC026.
• Johnson, C. S. and Reed, T. D. 2006. Tobacco cyst nematode resistance in burley tobacco cultivars in Virginia, 2005. B&C Tests 21:FC028.

Progress 10/01/04 to 09/30/05

Outputs
Use of acibenzolar-S-methyl or plant growth promoting rhizobacteria (PGPR) to induce resistance to target spot (Thanatephorus cucumeris) did not protect tobacco as well in 2005 as in 2004. Five isolates of plant growth promoting rhizobacteria (PGPR) and four combinations of these isolates were again compared with standard treatments. In contrast to 2004 results, leaf area damage was similar in PGPR-treated tobacco to untreated controls, perhaps due to the very late onset of the disease. As in 2004, application of azoxystrobin significantly reduced disease damage. Other 2005 field experiments noted differences in susceptibility to target spot among burley tobacco cultivars, but all burley cultivars tested were more susceptible than flue-cured tobacco varieties K 326 and NC 71. Blue mold damage was equivalently low on two burley tobacco cultivars (NC 2000 and NC 2002) and two breeding lines compared to a fungicide-protected control in a collaborative on-farm trial conducted in Southwest Virginia. Survival of burley cultivars KT 205 and NC 7 was significantly higher than the standard black shank resistant cultivar TN 90, but lower than flue-cured tobacco cultivar NC 71, in a field infested by races 0 and 1 of the black shank pathogen (Phytophthora parasitica var. nicotianae). Survival of the most resistant burley cultivars (BXP 05 and NC BH129) in a field infested by the bacterial wilt pathogen (Ralstonia solanacearum) was no greater than the susceptible flue-cured cultivars K 326 and NC 71. Survival of flue-cured tobacco cultivars in the same field was highest for NC 810, Sp 168 and Sp 220 and was significantly higher than that of NC 71. Although preplant fumigation with chloropicrin products or metam sodium increased yield of flue-cured tobacco cultivar NC 71, reductions in incidence of bacterial wilt were greater from use of host resistance than from soil fumigation. Use of metam sodium in a strip-tillage cultivation system also resulted in significant fumigant injury under the cool, wet spring conditions in 2005.

Impacts
Accurately identifying burley and flue-cured tobacco cultivars resistant to nematodes, black shank, and bacterial wilt will enable growers to significantly reduce use of soil fumigants and fungicides, potentially reducing production costs by 150 to 200 dollars per acre. Reducing production costs is particularly critical for Virginia growers facing a highly competitive global market driven by intense pressure to minimize expenses in order to achieve and maintain profitability. Increased use of disease resistant tobacco cultivars will also increase yield in infested fields, increasing the value of the tobacco crop in Virginia by 2,000,000 to 6,000,000 dollars annually, and decrease risks to farm safety and environmental degradation associated with pesticide use. Identifying efficient disease management practices for burley tobacco produced in the Piedmont regions of Virginia will enable farmers in that area to respond to increased demand for this crop and to offset income lost to reduced production of flue-cured and dark-fired tobacco. Identification of effective fungicides to manage blue mold and target spot could save Virginia tobacco farmers an estimated 8,455,000 dollars annually. Replacing traditional pesticides with disease-resistance inducing products such as Actigard and plant growth promoting rhizobacteria (PGPRs) would also improve farm safety and reduce any potential negative impacts of agriculture on the environment.

Publications

• Johnson, C. S., Way, J. A., and Barker, K. R. 2005. Nematode parasites of tobacco. In: Luc, M., R. A. Sikora, and J. Bridge (eds). Plant Parasitic Nematodes in Subtropical and Tropical Agriculture. CABI Publishing, Wallingford, Oxford, UK. 675-708.
• Syracuse, A. J., Johnson, C. S., Eisenback, J. D., Nessler, C. L., and Smith, E. P. 2004. Intraspecific variability within Globodera tabacum solanacearum using random amplified polymorphic DNA. Journal of Nematology 36:433-439.
• Peek, D. R., Johnson, C. S., and Jerrell, H. L. 2005. Burley tobacco resistance to black shank and blue mold in Southwest Virginia, 2004. B&C Tests 20:FC018.
• Peek, D. R., Johnson, C. S., and Miller, R. D. 2005. Host resistance to blue mold in burley tobacco in Virginia, 2004. B&C Tests 20:FC020.
• Johnson, C. S. 2005. Nematicides and induced resistance activators against tobacco cyst nematodes in Virginia, 2004. F&N Tests 60:N001.
• Johnson, C. S. 2005. Fungicides and induced resistance for control of target spot on flue-cured tobacco in Virginia, 2004. F&N Tests 60:FC106.
• Johnson, C. S. and Clarke, C. T. 2005. Host resistance to Granville wilt in Virginia, 2004. B&C Tests 20:FC021.
• Johnson, C. S. and Wright, L. 2005. Induced resistance and fungicides for blue mold control on burley tobacco in Southwest Virginia, 2004. B&C Tests 20:FC019.
• Johnson, C. S., Reed, T. D., and Semtner, P. J. 2005. Effects of Actigard, Admire, and tomato spotted wilt virus on flue-cured tobacco in Virginia, 2004. F&N Tests 60:FC089.

Progress 10/01/03 to 09/30/04

Outputs
Five isolates of plant growth promoting rhizobacteria (PGPRs) and four combinations of these isolates were compared with standard treatments for control of tobacco black shank (Phytophthora parasitica var. nicotianae), tobacco blue mold (Peronospora tabacina), target spot of tobacco (Thanatephorus cucumeris), and tobacco cyst nematodes (Globodera tabacum solanacearum) in 2004. Two PGPR isolates reduced percent leaf area damaged by target spot on bottom leaves 62 days after transplanting, and all of the PGPR treatments reduced target spot damage on middle leaves. However, no PGPR isolates or combinations of isolates were associated with improved control of tobacco black shank, blue mold, or tobacco cyst nematodes (at mid-season). Induction of systemic acquired resistance (SAR) by use of acibenzolar-S-methyl (ASM) in the field did not reduce mid-season population densities of G. t. solanacearum. Application of ASM to tobacco seedlings was associated with a slight reduction in plant stand, but this effect appeared to be mitigated by simultaneous use of imidicloprid and/or supplemental applications of ASM after transplanting. However, field sprays with ASM significantly reduced target spot damage, as did foliar applications of azoxystrobin and iprodione. A dry flowable formulation of dimethomorph provided equivalent blue mold control compared to the wettable powder formulation. Two burley tobacco cultivars (NC 2000 and NC 2002) and five breeding lines provided equivalent blue mold control compared to regular application of dimethomorph plus mancozeb to burley cultivar Clays 403. Bacterial wilt (Ralstonia solanacearum) was significantly lower on flue-cured tobacco cultivars Speight 168, Speight 179, and NC 810 compared with NC 71. Parasitism by G. t. solanacearum was significantly lower on flue-cured tobacco lines containing the Ph gene, and on several breeding lines with partial resistance to Meloidogyne arenaria, compared to susceptible flue-cured tobacco cultivars.

Impacts
Planting nematode-resistant flue-cured tobacco cultivars enables growers to reduce or eliminate nematicide use, saving as much as 200 dollars per acre (494 dollars/ha) and increasing yield by approximately 10 percent. Improved control of black shank, bacterial wilt, and nematodes through better resistant varieties should increase the value of tobacco in Virginia by 2,000,000 to 6,000,000 dollars annually. Identification of effective fungicides and blue mold resistance and/or tolerance is saving the Virginia tobacco industry an estimated 1,000,000 to 2,000,000 dollars annually. Replacing traditional pesticides with disease-resistance inducing products such as Actigard and plant growth promoting rhizobacteria (PGPRs) would improve farm safety and reduce any potential negative impacts of agriculture on the environment.

Publications

• Johnson, C. S. 2004. Host resistance and use of Telone products to control tobacco cyst nematodes in Virginia, 2003. F&N Tests 59:N002.
• Johnson, C. S., and Clarke, C. T. 2004. Host resistance and chloropicrin to control Granville wilt in Virginia, 2003. F&N Tests 59:FC029.
• Johnson, C. S., and Clarke, C. T. 2004. Host resistance and nematicides to control tobacco cyst nematodes in Virginia, 2003. F&N Tests 59:N003.
• Johnson, C. S., and Clarke, C. T. 2004. Host resistance and two rates of Telone C-17 to control tobacco cyst nematodes in Virginia, 2003. F&N Tests 59:N004.
• Johnson, C. S., and Clarke, C. T. 2004. Host resistance and Telone C-17 for control of tobacco cyst nematodes in Virginia, 2003. F&N Tests 59:N005.
• Johnson, C. S., and Wright, L. 2004. Blue mold severity on selected burley tobacco cultivars in Virginia, with and without Acrobat, 2003. B&C Tests 19:FC007.
• Peek, D. R., and Johnson, C. S. 2004. Host resistance, Acrobat MZ, and Actigard for blue mold control in burley tobacco in Virginia, 2003. B&C Tests 19:FC031.
• Peek, D. R., and Johnson, C. S. 2004. Effect of Actigard application strategies on blue mold severity in burley tobacco in Virginia, 2003. F&N Tests 59:FC028.
• Johnson, C. S., Way, J. A., and Barker, K. R. 2004. Nematode parasites of tobacco. In: Luc, M., R. A. Sikora, and J. Bridge (eds). Plant Parasitic Nematodes in Subtropical and Tropical Agriculture. CABI Publishing, Wallingford, Oxford, UK. In press.
• Syracuse, A. J., Johnson, C. S., Eisenback, J. D., Nessler, C. L., and Smith, E. P. 2004. Intraspecific variability within Globodera tabacum solanacearum using random amplified polymorphic DNA. Journal of Nematology 36:In press.
• Johnson, C. S. 2004. Host resistance for control of tobacco cyst nematodes in flue-cured tobacco in Virginia, 2003. B&C Tests 19:FC006.
• Johnson, C. S. 2004. Relative efficacy of various nematicides against tobacco cyst nematodes in Virginia, 2003. F&N Tests 59:N001.