|Lee, Ing Ming|
|Du Toit, Lindsey - WSU MOUNT VERNON WA|
|Crosby, Todd - MERCER RANCH PROSSER WA|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 2, 2006
Publication Date: March 2, 2006
Citation: Lee, I., Bottner, K.D., Munyaneza, J.E., Davis, R.E., Crosslin, J., Du Toit, L., Crosby, T. 2006. Carrot purple leaf: a new carrot disease associated with spiroplasma citri and phytoplasmas in Washington State. Plant Disease.90-989-993. Interpretive Summary: Plant pathogenic spiroplasmas and phytoplasmas are small, cell wall-less bacteria. These bacteria cause several hundred economic diseases in plants worldwide. New diseases caused by these bacteria emerge from time to time. During 2003/2004 a new carrot disease outbreak occurred in several carrot fields located in south central Washington State. The affected carrots exhibited symptoms similar to but distinct from those caused by aster yellows disease, the most common phytoplasmal disease in carrot. Our extensive survey indicated that Spiroplasma citri, a causal agent of citrus stubborn disease in California, is the primary cause of this new carrot disease, termed carrot purple leaf. This is the first report that S. citri causes carrot disease in nature. The information will aid implementation of quarantine regulation and it will help extension workers and plant diagnosticians to combat this new disease.
Technical Abstract: During 2003/2004 a new disease outbreak occurred in several carrot fields located in south central Washington. In the fall, the affected carrot plants exhibited extensive purple or yellowish purple leaf discoloration; general stunting of shoots and tap roots; and formation of bunchy, fibrous secondary roots. PCR assays using primers specific to phytoplasmas and to plant pathogenic spiroplasmas were employed for the detection of putative causal agents. RFLP analyses of PCR-amplified 16S rDNA sequences reveled that all the symptomatic plants showing characteristic purple leaf symptoms (about 81%) tested positive for Spiroplasma citri. Plants showing mild purple discoloration symptoms tested positive for a phytoplasma strain (about 13%) belonging to the clover proliferation group (16SrVI), subgroups 16SrVI-A, and for another phytoplasma strain (about 1%) belonging to the aster yellows group (16SrI), subgroup 16SrI-A. Nucleotide sequence analysis of cloned 16Sr DNA confirmed the identification based on RFLP analysis. Several symptomatic plants were doubly infected by both S. citri and one of the two phytoplasma strains.