Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2009
Publication Date: June 1, 2009
Citation: Lee, I., Bottner, K.D., Sun, M. 2009. An emerging potato purple top disease caused by a new 16SrIII group phytoplasma in Montana. Plant Disease. 93:574-583. Interpretive Summary: Potato purple top wilt (PPT) and similar diseases have caused tremendous damage to potato tuber production and processed products, such as French fries and potato chips, in South America, Mexico, the US and elsewhere. Many of these diseases are caused by uncultured small bacteria, termed phytoplasmas. PPT diseases appear to be caused by diverse phytoplasmas. In the U.S., PPT and related diseases have been reported to occur in Washington, Oregon, Texas, Nebraska, and North Dakota. Several distinct phytoplasma strains belonging to three phytoplasma groups, 16SrVI, 16SrI, and 16SrXVIII, are the culprits that inflict theses PPT diseases occurring in various regions. In 2007, sporadic diseased potato plants exhibiting PPT symptoms were found in an isolated potato field in Montana. In this study, we identified a new phytoplasma strain belonging to a new group, 16SrIII, as the causal agent of this newly emerging PPT disease. This phytoplasma also is able to cause disease in tomato. The information is important for regulatory agents to implement quarantine regulations for preventing further spread of this new disease, and will help extension workers and plant diagnosticians to determine how to combat the disease.
Technical Abstract: Potato purple top (PPT) is a devastating disease that occurs in the United States, Canada, Mexico, Russia, and elsewhere. There are at least seven distinct phytoplasma strains belonging to five different phytoplasma groups (16SrI, 16SrII, 16SrVI, 16SrXII, and 16SrXVIII) that were reported to cause purple top and related symptoms in potato. A new disease with symptoms similar to PPT was recently observed in an isolated potato field in Montana. A new phytoplasma strain was detected and identified in all symptomatic plants. Based on analysis of PCR-amplified 16S rDNA sequences, this new phytoplasma is distinct and most closely related to milkweed yellows phytoplasma strain MW1 belonging to X-disease phytoplasma group (16SrIII), subgroup 16SrIII-F. Pathogenicity of this new phytoplasmas was demonstrated in potato as well as in tomato. The phytoplasma is tuber transmissible. This is the first report of 16SrIII group phytoplasmas causing diseases in potato.