Taxonomy

Domain	Bacteria
Phylum	Proteobacteria
Class	Betaproteobacteria
Order	Burkholderiales
Family	Comamonadaceae
Genus	Acidovorax

Scientific Name

Acidovorax konjaci

Common Name

Acidovorax bacteria

Author:Tom Creswell, Purdue University

Reviewed by: J.B. Jones, University of Florida

Pathogen

Acidovorax konjaci is a gram-negative, rod-shaped, motile bacterium with a single polar flagellum that causes leaf spot in several host plants. The bacterium was first described in Japan by Goto as Pseudomonas pseudoalcaligenes subsp. konjaci. He described the bacterium as Gram-negative rods measuring 0.5 x 1.8-2.3 µm. Colonies are white, round, transparent, smooth and slightly convex on YP agar. The colony size is 0.8 to 1.0 mm in diameter at 48 hours on YP agar and 2-3 mm within 5 days at 28 degrees C. The pathogen was transferred by Willems in 1992 to the genus, Acidovorax , and designated Acidovorax konjaci.

Symptoms and Signs

Symptoms produced by Acidovorax konjaci can vary widely depending on the host plant. On konjac leaf lesions begin as small, dark brown, angular, water-soaked spots between the veins. Under humid conditions the lesions coalesce causing severe blighting of the entire leaf. The bacterium continues to move down the petiole and eventually may cause a soft rot of the roots and corm. On petunia and calibrachoa, leaf spots begin as small dark brown spots but under wet conditions may quickly become blighted with large areas having a water-soaked appearance and eventually decaying. On verbena the spots are usually angular and light brown, with less water-soaking than on other hosts.

Geographic Distribution

Acidovorax konjaci was first described in Japan from leaves konjac (Amorphophallus konjac). Subsequent reports have indicated it causes leaf spots and brown to black discoloration of radish roots in Korea. It has been identified causing leaf spots and rapid blighting of petunia cuttings and seedlings and leaf spots on verbena in commercial greenhouse production in the US. The full distribution has not been documented but it is suspected to appear sporadically in the greenhouse trade.

Management

Management of diseases caused by Acidovorax konjaci is largely dependent on prevention by good sanitation. The pathogen has not been documented to be disseminated by seed; however, long distance spread is likely by trade in contaminated propagation material in production of greenhouse ornamentals. Local spread within a planting is by splashing water and contaminated pots, tools or handling. Copper based compounds may help reduce spread but are generally of marginal efficacy. Consult your local extension specialist or agent for recommendations relevant to your particular host and state. Remember: the label is the law.

Diagnostic procedures

In addition to the characteristics given in the introduction the following characteristics help identify Acidovorax konjaci: The bacterium produces a water-soluble brown pigment in King’s medium B, is oxidase positive, and elicits a hypersensitive reaction in tobacco . The Biolog™ bacterial identification system generally produces a solid match with this bacterium but for confirmation on a new host or when additional evidence is needed the isolate should be identified by sequencing the 16S rRNA gene and comparing with the known sequence.

Resources and References

GOTO, M. 1983. Pseudomonas pseudoalcaligenes subsp. konjaci subsp. nov., the Causal Agent of Bacterial Leaf Blight of Konjac (Amorphophalus konjac Koch.). International Journal of Systematic Bacteriology, 33, 539-545. doi:10.1099/00207713-33-3-539
HAYASHI, N. 1989. Survival of Pseudomonas pseudoalcaligenes subsp. konjaci, the causal agent of bacterial leaf blight of Konnyaku (Amorphophallus konjaci), in residues of diseased leaflets, on corms and in soil. Annals of the Phytopathological Society of Japan, 55, 609-614.
MYUNG, I. S., LEE, Y. K., JEONG, I. H., MOON, S. Y., LEE, S. W. & SHIM, H. S. 2010. A new disease, bacterial black rot of Korean radish, caused by Acidovorax konjaci. New Disease Reports, 22, Article 26.
SADDLER, G. S. 1994. Acidovorax konjaci. Descriptions of Fungi and Bacteria. IMI Descriptions of Fungi and Bacteria, Set 122, Sheet 1214.

8WILLEMS, A., GOOR, M., THIELEMANS, S., GILLIS, M., KERSTERS, K. & LEY, J. D. 1992. Transfer of several phytopathogenic Pseudomonas species to Acidovorax as Acidovorax avenae subsp. avenae subsp. nov., comb. nov., Acidovorax avenae subsp. citrulli, Acidovorax avenae subsp. cattleyae, and Acidovorax konjaci. International Journal of Systematic Bacteriology, 42, 107-119.

Acknowledgements