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South Perth, Australia

Potato tubers infected with Potato virus S (PVS), Potato leaf roll virus (PLRV) or Potato virus X (PVX) and ELISA were used to study effects of three tissue sampling positions, primary and secondary infection, cultivar, three storage temperatures and different storage durations on virus detection (tuber numbers found infected), concentration (A405 values) and distribution within tubers. Numbers of detections were highest in tissue samples from the rose (PVS), heel (PLRV), and, depending on the period of storage, either the heel or rose end (PVX). With all 3 viruses, detection was least reliable and A405 values lowest in central core tissue. PVS was detected most readily in tuber samples of cvs Mondial, Royal Blue, Ruby Lou and White Star, but less readily in cv. Nadine and poorly in cv. Atlantic samples. Its detection was unaffected by whether infection was primary or secondary. In cv. Nadine tubers, PVS detection was poorer at 4° and 10° (but not at 20°) after 5 and 13 weeks storage than after 21 weeks storage at 4°, 0° and 20°. After >1 weeks storage, PVS A405 values were generally low to very low regardless of storage temperature or duration, lowest values occurring with cv. Atlantic. Numbers of tuber samples in which PLRV was detected were highest in cvs Mondial and Atlantic, intermediate in cvs Nadine and White Star, and poorest in cv. Ruby Lou. However, the number of tuber samples in which PLRV was detected was unaffected by storage temperature or duration, or whether infection was primary or secondary. Higher PLRV A405 values were generally obtained with tuber samples of cvs Mondial and Nadine than of cvs Atlantic, Ruby Lou or White Star. No overall differences in PVX detection occurred resulting from cultivar, different storage durations or temperatures or whether infection was primary or secondary. However, in secondarily infected tubers, detection in tissue from the central core was least reliable at 20°, but most reliable at 10°. In cv. White Star tubers only, mean PVX A405 values at 20° were generally the lowest, while those at 10° were highest. Testing sprouts detected PVS in more tubers than direct tuber testing, especially with cv. Atlantic, and generally resulted in higher A405 values than testing tubers stored for >1 week. In some cultivars, testing sprouts for PLRV gave slightly lower detection efficiencies than testing tubers directly, but sprout A405 values were usually higher. With PVX, testing sprouts gave comparable detection and A405 values to testing tuber tissue. When tuber tissue samples tested by ELISA were also tested by RT-PCR, PVS and PLRV were detected in many more or several more tubers, respectively, and PCR bands were obtained with rose, core and heel tissue. © 2011 Australasian Plant Pathology Society Inc. Source


Saqib M.,Murdoch University | Gadja B.E.,Crop Protection Branch | Jones M.G.K.,Murdoch University | Jones R.A.C.,Murdoch University | Jones R.A.C.,University of Western Australia
Crop and Pasture Science | Year: 2011

Plants of 212 accessions from the core collection of model legume species Medicago truncatula were inoculated with infective sap containing Alfalfa mosaic virus (AMV, isolate EW), Bean yellow mosaic virus (BYMV, isolate MI) or Cucumber mosaic virus (CMV, isolate SN-1). A diverse range of systemic symptoms were obtained that varied widely in severity depending on the combination of virus isolate and accession, or, especially with AMV, some accessions became infected but did not display symptoms. The delay between virus inoculation and symptom appearance normally varied from 1 to 4 weeks, but with CMV it took up to 8 weeks in two accessions. Five (AMV), 59 (BYMV) and 22 (CMV) core accessions remained uninfected systemically. Plants of most of these accessions, and some that died or gave susceptible phenotypes, were then inoculated with two additional isolates of AMV (eight accessions), or two distinct strains of BYMV (58 accessions) and CMV (21 accessions). Plants of accession 11715 remained uninfected by CMV isolates CP (CMV subgroup 1) and LW (CMV subgroup 2), but those of all other previously uninfected accessions became infected systemically by all three viruses. All accessions inoculated with AMV isolates Aq and Hu, and most inoculated with BYMV isolate LKoj1-NN (generalist strain), BYMV isolate LP-1 (lupin strain), and CMV isolates CP and LW developed typical susceptible phenotypes. However, systemic hypersensitive phenotypes developed with BYMV LKoj1-NN and LP-1 in plants of 4456, or with LKoj1-NN only in 774, 1526, 4327, 14829, 15268, 22922 and 25654; 15268 and 25654 had developed this phenotype previously with MI (generalist strain). Similarly, plants of 21362 developed this phenotype with CMV CP and LW, while plants of 1526, 2748 and 31443 developed it with CP; 2748, 21632 and 31443 had developed it previously with SN-1 (mixture of subgroups 1 and 2). Once the genetic bases of the BYMV and CMV resistances found in M. truncatula are understood, they may prove useful in future virus resistance breeding among crop and pasture legumes. © CSIRO 2011. Source


Cox B.A.,Bentley Delivery Center | Cox B.A.,University of Western Australia | Luo H.,Crop Protection Branch | Jones R.A.C.,Crop Protection Branch | Jones R.A.C.,University of Western Australia
Plant Disease | Year: 2014

Polymyxa graminis is an obligate parasite of roots and an important vector of viruses that damage cereal crops in different parts of the world. In 2011 and 2012, P. graminis was identified infecting 11 wheat root samples from three widely dispersed locations in southwest Australia. Its presence was detected by polymerase chain reaction (PCR) and confirmed by DNA sequencing of the transcribed regions of its ribosomal RNA genes (rDNA) and observing sporosori of characteristic morphology and size in stained wheat roots. Also, when soil samples were collected from two locations where P. graminis was found and wheat bait plants grown in them, P. graminis was detected in their roots by PCR. Ribosomal DNA sequences of six southwest Australian isolates were obtained from wheat roots, and one northeast Australian isolate from barley roots. When these seven P. graminis sequences were compared with others from GenBank by phylogenetic analysis, three southwest Australian isolates were classified as P. graminis f. sp. temperata (ribotypes Ia and Ib), and three as f. sp. tepida (ribotypes IIa and IIb). P. graminis f. sp. temperata and tepida both occur in temperate growing regions of other continents and are associated with transmission of soil-borne viruses to cereal crops. The P. graminis isolate from northeast Australia was sufficiently distinct from the five existing sequence groups for it to be placed into a newly proposed grouping, ribotype VI, which also included an isolate from tropical West Africa. However, when randomly collected wheat leaf samples from 39 field crops from 27 widely dispersed locations, 21 individual wheat plant samples collected from low lying areas within 21 fields at 11 locations, and wheat bait plants growing in five soil samples from two locations were tested by reverse transcription (RT)-PCR for the presence of Soil-borne wheat mosaic virus, Soil-borne cereal mosaic virus, Wheat spindle streak mosaic virus, and furoviruses in general, no virus infection was detected. These findings suggest at least three P. graminis introductions into Australia, and the occurrence of f. sp. temperata (ribotype I) and f. sp. tepida (ribotype II) suggests that, if not already present, soil-borne cereal viruses are likely to become established should they become introduced to the continent in the future. © 2014 The American Phytopathological Society. Source


Nyalugwe E.P.,University of Western Australia | Jones R.A.C.,University of Western Australia | Barbetti M.J.,University of Western Australia | Kehoe M.A.,Crop Protection Branch
Plant Pathology | Year: 2015

Turnip mosaic virus (TuMV) causes crop losses worldwide. Eight Australian TuMV isolates originally obtained from five different species in two plant families were inoculated to 14 plant species belonging to four families to compare their host reactions. They differed considerably in virulence in Brassicaceae crop species and virus indicator hosts belonging to three other families. The isolates infected most Brassica species inoculated, but not Raphanus sativus, usually causing systemic mosaic symptoms, so they resembled TuMV biological host type [B]. Whole genome sequences of seven of the Australian isolates were obtained and had lengths of 9834 nucleotides (nt). When they were compared with 37 non-recombinant TuMV genomes from other continents and another whole genome from Australia, six of them formed an Australian group within the overall world-B phylogenetic grouping, while the remaining new genome sequence and the additional whole genome from Australia were part of the basal-B grouping. When the seven new Australian genomes and the additional whole genome from Australia were subjected to recombination analysis, six different recombination events were found. Six genomes contained one or two recombination events each, but one was non-recombinant. The non-recombinant isolate was in the Australian grouping within the overall world-B group while the remaining recombinant isolates were in the basal-B and world-B phylogenetic groups. © 2015 British Society for Plant Pathology. Source

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