Identification of aster yellows phytoplasma in garlic and green onion by PCR-based methods

Phytoplasma diseases of plants: molecular diagnostics and way forward

Phytoplasmas are obligate phytopathogenic bacteria associated with devastating diseases in hundreds of crops across the world. They have been responsible for huge economic losses in many crop plants for decades now. Isolation and establishment of axenic culture of phytoplasma in complex media is a recent progress in phytoplasma research. Earlier methods for phytoplasma disease detection included symptom profiling, microscopy, serology and dodder transmission studies. With advancement in the field of molecular biology, phytoplasma diagnostics and characterisation witnessed radical improvement. Starting from PCR amplification which often necessities a nested PCR on account of low titre of phytoplasmas, to the closed tube quantitative PCR assays and then the ddPCR, an array of diagnostics have been developed for phytoplasma. The isothermal diagnostic platforms are the latest addition to this and the Loop Mediated Isothermal Amplification (LAMP) assay has been applied for the detection of phytoplasma from several hosts. The futuristic approach in phytoplasma detection will be very likely provided by an integration of nanotechnology and molecular diagnostics. Phytoplasma disease management majorly relies on early detection, vector control, use of disease free planting materials and cultivation of resistant varieties. Hence understanding the molecular mechanism of phytoplasma-host interaction is as important as timely and accurate detection, in the management of phytoplasma diseases. Further, the changing climatic scenario and global warming may lead to an upsurge in the phytoplasma diseases spread and severity across the world, making disease management even more challenging.

Detection and molecular characterization of an aster yellows phytoplasma in poker statice and Queen Anne's lace in Alberta, Canada

Queen Anne's lace and poker statice plants were found with a yellows-type disease with typical phytoplasma symptoms in an experimental farm near Brooks, Alberta in 1996. Phytoplasma bodies were detected by transmission electron microscopy in phloem cells of symptomatic plants, but not in healthy plants. The presence of a phytoplasma was confirmed by analysis with the polymerase chain reaction. Using a pair of universal primer sequences derived from phytoplasma 16S rRNA, an amplified product of the expected size (1.2 kb) was observed in samples from infected plants, but not in asymptomatic plants. Sequence analysis of the PCR products from the 16S/23S rDNA intergenic spacer region indicated that the two phytoplasma isolates in Queen Anne's lace and poker statice are genetically closely related to the western aster yellows phytoplasma.