|Polymyxa graminis isolates from Australia: identification in wheat roots and soil, molecular characterization and wide genetic diversity |
B. A. Cox (1), H. Luo (2), R. JONES (3). (1) University of Western Australia, Crawley, Australia; (2) Deaprartment of Agriculture and Food Western Australia, South Perth, Australia; (3) Univ of Western Australia, South Perth, WA, Australia
<i>Polymyxya graminis</i> is an important virus vector in cereal crops. In 2011-12, it was identified in wheat root samples from southwest Australia. It’s presence was detected by PCR, and confirmed by DNA sequencing of transcribed regions of its ribosomal RNA genes and observing sporosori of characteristic morphology and size in wheat roots. When soil samples were collected from 2/3 locations where <i>P. graminis </i>was found and wheat bait plants grown, <i>P. graminis</i> was detected in their roots by PCR. Ribosomal DNA sequences of six southwest Australian isolates from wheat roots, and one northeast Australian isolate from barley roots were obtained. When these sequences were compared with others from Genbank, three south-west Australian isolates were classified as <i>P. graminis</i> f. sp. <i>temperata </i>(ribotypes Ia and Ib), and three as f. sp. <i>tepida</i> (ribotypes IIa and IIb). The <i>P. graminis</i> isolate from northeast Australia was placed into new ribotype VI. When wheat leaf samples from 67 field crops and soil bait plants from two locations with <i>P. graminis</i> were tested by RT-PCR for <i>Soil-borne wheat mosaic virus</i>, <i>Soil-borne cereal mosaic virus</i>, <i>Wheat spindle streak mosaic virus</i> and furoviruses, no virus was found. This study suggests that soil-borne cereal viruses are likely to become established should they become introduced to Australia.