Submitted to: Annals of Applied Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2015
Publication Date: 1/2/2016
Citation: Wei, W., Wu, W., Davis, R.E., Lee, I., Zhao, Y. 2016. Development of biomarkers and a diagnostic tool for investigation of coinfections by and interactions between potato purple top and potato witches’-broom phytoplasmas in tomato. Annals of Applied Biology. 168:133-141. doi: 10.1111/aab.12248.
Interpretive Summary: In nature, plants are often infected by two or more germs simultaneously. Interactions between the coexisting germs inside the affected plants may result in unpredictable biological consequences: some may lead to more serious diseases and others may change the way diseases spread (for example, changes in insect vectors and/or plant host specificity). Therefore, correct diagnosis of mixed infections and identification of coexisting germs are essential to developing proper disease control measures. Phytoplasmas are a group of tiny bacteria that lack a cell wall. These bacteria are genetically diverse and have overlaps in their insect vectors and in ranges of plant host species, making mixed infections inevitable in natural environment. In the present study, we identified molecular markers and devised a sensitive diagnostic tool for rapid detection of mixed infections by two phytoplasmas that are harmful to potato, tomato, and many other agriculturally important crops. The diagnostic tool can also monitor changes in relative abundance of the two coexisting phytoplasmas, and therefore infer different fitness levels of the two pathogens in their host plants. Findings and the diagnostic tool from our work will be of interest to scientists, students, and university professors who are studying pathogen-host interactions. This report will also be of interest to growers, extension personnel, and agricultural economists who are concerned with plant disease management and food security.
Technical Abstract: Columbia Basin potato purple top (PPT) phytoplasma and Alaska potato witches’-broom (PWB) phytoplasma are two closely-related but mutually distinct pathogenic bacteria that infect potato and other vegetable crops. Inhabiting phloem sieve elements and being transmitted by phloem-feeding insect vectors, both pathogens are affiliated with ‘Candidatus Phytoplasma trifolii’ and are members of the clover proliferation phytoplasma group (16SrVI). The polyphagous nature and wide geographic distribution of their insect vectors make mixed infection inevitable. In the present study, we experimentally constituted a simultaneous PPT and PWB phytoplasma infection in tomato (Solanum lycopersicum) and developed a sensitive diagnostic tool to investigate mixed infections by and in planta interactions of the two phytoplasmas. The distribution and relative abundance of the two co-infecting phytoplasmas were monitored over a 45-day post-infection time course and for three serial passages in planta. Our results revealed that co-infection of the two phytoplasmas induce a new symptom unseen in infection by either phytoplasma alone. Our results also raised an interesting question as to whether the two phytoplasmas differ in ability of competitive dominance under co-infection conditions. The biomarkers and the diagnostic tool devised in the present study should be useful for further investigations of the interactions between the two closely-related phytoplasmas in their hosts.