Fig. 1. Bacterial wilt on tomato caused by Ralstonia solanacearum (race 1, biovar 1).
Tim Momol, Jeff Jones, and Steve Olson, University of Florida, IFAS, NFREC, Quincy, and Plant Pathology Department, Gainesville, Florida
Contact person: tmomol@ufl.edu
O6/13/03 UPDATE - (from USDA, APHIS, PPQ) May 28, 2003: "As of May 21, APHIS confirmed detections of Ralstonia solanacearum race 3, biovar 2 on geraniums in 27 States and 127 establishments (excluding the MI and NH rooting stations), primarily in geraniums from Kenya. The number of positive testing facilities in each state is tallied as follows: AL (9), AR (2), CO (1), DE (1), GA (2), ID (1), IL (4), IN (4), IA (6), KS (3), KY (1), MD (3), ME (1), MI (13), MN (4), MO (6), NH (1), NJ (1), NY (3), NC (13), OH (7), PA (8), SC (8), TN (1), TX (7), VA (10), and WI (7). All of the 921 affected nurseries have been released. APHIS is in the process of following up on suspect geraniums linked to a few shipments from Guatemala that tested positive."
03/14/03 UPDATE: on Ralstonia solanacearum race 3, biovar 2; Source; USDA, APHIS, PPQ "March 12, 2003 - New detections of Ralstonia solanacearum race 3 biovar 2 continue with additional states having positive testing facilities. The totals now stand as follows, with the number of nurseries in each state in parenthesis: Delaware (1), Georgia (2), Illinois (1), Indiana (3), Iowa (1), Kansas (2), Maryland (2), Michigan (3), Missouri (2), North Carolina (2), Tennessee (1), Virginia (3) and Wisconsin (2)." Details are available at: http://www.aphis.usda.gov/ppq/ep/ralstonia/.
Introduction. Diseases caused by Ralstonia (previously named Pseudomonas) solanacearum continue to be the most serious bacterial diseases worldwide and causes great economic losses. The species is very complex and highly variable. Strains of R. solanacearum are grouped into five races according to the host or hosts primarily affected and five biovars according to the use of selected biochemical properties (Hayward, 1991). Bacterial wilt on tomato (Fig. 1) caused by Ralstonia solanacearum (race 1, biovar 1) causes wilt by infecting plants through roots and colonizing stem vascular tissue. Although diseased plants can be found scattered in the field, bacterial wilt usually occurs in foci associated with water accumulation in lower areas. Under natural conditions, the initial symptom in mature plants is wilting of upper leaves in hot days followed by recovery throughout the evening and early hours of the morning. Under hot humid conditions favorable for disease, complete wilting occurs and the plant will die. The vascular tissues in the lower stem of the wilted plants usually show a brown discoloration. R. solanacearum (race 1, biovar 1) is endemic in Southeastern U.S. Race 1 has a wide host range (solanaceous and other plants). Southern wilt of geranium (Fig. 2 and 3) was reported in North Carolina (Strider et al., 1981). The endemic strain of R. solanacearum (race 1, biovar 1) was detected in 2001 in geraniums in Florida and reported in 2002 (Pradhanang et al, 2002) (http://pestalert.ifas.ufl.edu/tmm-0607.htm)
Until 1999 race 3, biovar 2 strains of R. solanacearum were not detected in U.S. This new introduction of race 3, biovar 2 in 1999 to U.S. was reported in 2002 on geraniums in Wisconsin and South Dakota (Williamson et al, 2002) and in New Jersey, New York and Pennsylvania (V.S. Malik, USDA-APHIS-PPQ, ISPM http://www.aphis.usda.gov/ppq/ispm/potato/ralstonia/).
Recently, a new outbreak of R. solanacearum (race 3, biovar 2) in several states, have been traced to shipments from rooting stations in Michigan and New Hampshire. These facilities were apparently received infected geraniums from a facility in Kenya (See http://pestalert.ifas.ufl.edu/usda-rs3-actionplan-v4.pdf, USDA, APHIS, PPQ, Action Plan, January 16, 2004 version 4). R. solanacearum race 3 is listed on USDA Agricultural Bioterrorism Act of 2002, as a serious pathogen of potatoes and other plants. R. solanacearum (race 3, biovar 2) is not reported in Florida. Host range of this group (race 3, biovar 2) is mainly limited to potato, tomato, other solanaceous plants (including weeds), geraniums, stinging nettle, and some other plants. Infected plants, contaminated irrigation or surface water, and contaminated soil or potting mixture could be the primary source of inoculum.
Information could be found on the following web sites to learn more and to monitor your crops:
Disease Alert: Ralstonia solanacearum by M. Daughtrey, Cornell University http://www.growertalks.com/ralstonia/ralstonia1.asp
Ralstonia solanacearum, Race 3 Biovar 2 found in U.S. Greenhouses by A. Hammer and K. Rane, Purdue University. http://www.ppdl.purdue.edu/ppdl/hot03/02-24.html
Update on Ralstonia race 3, biovar 2 from North Carolina State University, Plant Disease and Insect Clinic. http://www.ces.ncsu.edu/depts/ent/clinic/ralstonia/ralstonia.htm
USDA 2004 Action Plan for Ralstonia solanacearum race 3, biovar 2 found in nursery facilities. http://pestalert.ifas.ufl.edu/usda-rs3-actionplan-v4.pdf
Recently discovered bio-fumigants against Ralstonia solanacearum (race 1, biovar 1). Due to the limited efficacy of the current integrated management strategies, bacterial wilt continues to be economically important for field grown fresh market tomato production in the southeastern United States and many subtropical and tropical areas of the world. Cultural practices, crop rotation and host resistance could provide a limited success.
A group of scientists (Tim Momol, Prakash Pradhanang, Jeff Jones and Steve Olson), from University of Florida, IFAS, NFREC and Plant Pathology Department, have conducted greenhouse experiments to determine the effectiveness of plant essential oils as soil bio-fumigants to manage bacterial wilt in tomato. Potting mixture ("soil") infested with Ralstonia solanacearum (race 1, biovar 1) was treated with the essential oils at 400 mg or ml and 700 mg or ml per L soil in greenhouse experiments. R. solanacearum population densities were determined just before and 7 days after treatment. Populations declined to undetectable levels in thymol, palmarosa oil and lemongrass oil treatments at both concentrations, whereas tea tree oil had no effect. Tomato seedlings transplanted in soil treated with 700 mg/L thymol, 700 ml/L palmarosa oil and 700 ml/L lemongrass oil were free from bacterial wilt and 100% of the plants in thymol treatments were free of R. solanacearum. Soil amendment with fresh leaves of essential oil producing plants did not reduce bacterial wilt incidence compare to untreated inoculated control. Some thyme oil producing plants such as thyme (Thymus vulgaris) cv. German winter, Creeping thyme (Thymus serpyllum), and Greek oregano (Origanum vulgare subsp. hirtum), while remaining symptomless, became systemically infected by R. solanacearum and were therefore identified as hosts of R. solanacearum (Pradhanang et al, 2003).
The U.S. Food and Drug Administration lists thymol as a food additive and the U.S. Environmental Protection Agency (EPA) lists it as a "Generally Recognized as Safe (GRAS)" compound. The first thymol product registered as pesticide in the U.S was in 1964. EPA is not aware of any adverse effects of thymol to humans or the environment when it is used in a manner consistent with the label (Liu et al, 2002). Our results indicate that thymol, palmarosa oil and lemongrass oil have the potential to suppress R. solanacearum populations in soil and reduce bacterial wilt incidence in greenhouse pot experiments. However, further research is needed in order to determine the effectiveness and economics of plant essential oils under production conditions to manage bacterial wilt of tomato and other crops.
Literature Cited:
Daughtrey, M. Disease Alert: Ralstonia solanacearum. http://www.growertalks.com/ralstonia/ralstonia1.asp
Hammer, A and Rane, K. 2003. Ralstonia solanacearum, Race 3 Biovar 2 found in U.S. Greenhouses. http://www.ppdl.purdue.edu/ppdl/hot03/02-24.html
Hayward, A. C. 1991. Biology and epidemiology of bacterial wilt caused by Pseudomonas solanacearum. Annu. Rev. Phytopathol. 29:65-87.
Janse, J. D. 1996. Potato brown rot in Western Europe - History, presence, occurrence and some remarks on possible origin, epidemiology and control strategies. EPPO Bull. 26:679-985.
Liu, W. T., Chu, C. L., and Zhou, T. 2002. Thymol and acetic acid vapors reduce postharvest brown rot of apricots and plums. HortScience 37: 151-156.
Malik, V.S. Potato Diseases: Ralstonia Program Information. http://www.aphis.usda.gov/ppq/ispm/potato/ralstonia/
Momol, M.T. and Pradhanang, P. M. 2002. Occurrence of Southern Wilt Caused by Ralstonia solanacearum (race 1, biovar 1) on Geranium in Florida. http://pestalert.ifas.ufl.edu/tmm-0607.htm
Pradhanang, P.M., Momol, M.T., Olson, S.M., and Jones, J.B. 2003. Effects of plant essential oils on Ralstonia solanacearum population density and bacterial wilt incidence in tomato. Plant Disease 87: (In press).
Pradhanang, P.M., Momol, M.T., Dankers, H., Momol, E.A., and Jones, J.B. 2002. First report of southern wilt caused by Ralstonia solanacearum on geranium in Florida. Online. Plant Health Progress doi:10.1094/PHP-2002- 0611-01-HN. http://www.plantmanagementnetwork.org/pub/php/brief/geranium/
Strider, D.L., Jones, R.K., and Haygood, R.A. 1981. Southern bacterial wilt of geranium caused by Pseudomonas solanacearum. Plant Disease 65:52-53.
USDA, APHIS, PPQ. 2004. Action plan for Ralstonia solanacearum race 3, biovar 2 found in nursery facilities, January 14, 2004 version 4.. http://pestalert.ifas.ufl.edu/usda-rs3-actionplan-v4.pdf
Williamson, L., Nakaho, K., Hudelson, B. and Allen, C. 2002. Ralstonia solanacearum race 3, biovar 2 strains isolated from geranium are pathogenic on potato. Plant Disease 86:987-991. http://www.apsnet.org/pd/search/2002/0715-01r.asp