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Fresno, WA, United States

Saqib M.,Murdoch University | Nouri S.,Murdoch University | Cayford B.,Murdoch University | Jones R.A.C.,Agricultural Research Western Australia | Jones M.G.K.,Murdoch University
Australasian Plant Pathology

In the Ord River irrigation area near Kununurra in the Kimberley region of Western Australia, symptoms suggestive of Bean common mosaic virus (BCMV) were found in a common leguminous weed, Macroptilium atropurpureum (siratro). Virus from one M. atropurpureum plant and an isolate from Phaseolus vulgaris (common bean) identified previously as BCMV based on genome fragment sequencing and host range, were both transmitted to Nicotiana benthamiana, Chenopodium amaranticolor and C. quinoa by sap inoculation, giving symptoms typical of BCMV. Reciprocal inoculations with infective N. benthamiana sap indicated that both source plants contained the same virus species and reproduced field symptoms consistent with BCMV in both original hosts. Complete (10054 nucleotide) and partial (∼8400 nucleotide) sequences were determined for two sub-isolates MS1 and NWA-1, respectively, using reverse transcriptionpolymerase chain reaction assays. Both sub-isolates were from a N. benthamiana plant containing a BCMV isolate originally from a single M. atropurpureum plant. Their nucleotide sequences were aligned with those of four complete and three partial BCMV genome sequences, and their coat protein amino acid sequences were aligned with those of 17 other BCMV isolates. The results from the genomic and coat protein analyses show that the two M. atropurpureum sub-isolates were closely related to BCMV isolates reported previously from North and South America. © 2010 Australasian Plant Pathology Society. Source

Coutts B.A.,Agricultural Research Western Australia | Webster C.G.,Agricultural Research Western Australia | Webster C.G.,U.S. Department of Agriculture | Jones R.A.C.,Agricultural Research Western Australia | Jones R.A.C.,University of Western Australia
Crop and Pasture Science

Eighteen Brassica napus (canola) genotypes were examined for their responses to infection with Beet western yellows virus (BWYV) and infestation by Myzus persicae (green peach aphid) in a field experiment and in a series of pot experiments under controlled-environment conditions. When exposed to infection with BWYV in the field, plants of cvv. Tranby and Trigold remained uninfected with BWYV. Only 25% of plants of cvv. Stubby and Banjo became infected, but infection incidence was 1423% in cvv. Tanami and Jade, and reached 4565% in 12 other commercial cultivars or advanced breeding lines of B. napus. Once plants became infected, the sensitivity rankings for most genotypes were 23: mild to moderate symptoms consisting of plant stunting and reddening of lower leaves. When plants of cvv. Tranby, Trigold, Stubby, and susceptible control cv. Pinnacle growing in pots were exposed to spread of BWYV by viruliferous winged M. persicae flying from an infested cv. Pinnacle plant infected with BWYV, similar numbers of aphids colonised each of the different cultivars. Thus, no aphid feeding preference was apparent among the different B. napus cultivars. However, all 18 plants of cv. Pinnacle became infected with BWYV, but only 1, 2, and 5 plants of cvv. Trigold, Tranby, and Stubby became infected, respectively. When 68 plants each of cvv. Tranby, Trigold, and Stubby were each inoculated with 110 viruliferous aphids/plant, only 1 of cv. Trigold, 3 of cv. Tranby, and 6 of cv. Stubby became infected with BWYV despite infection of 45 plants of cv. Pinnacle. This shows that cvv. Tranby, Trigold, and Stubby have resistance to infection with BWYV by aphid transmission. In 2 experiments when viruliferous M. persicae were placed on plants of B. napus grown from seed treated with imidacloprid (240ga.i./100kg seed), they infested 72% of plants grown from treated seed and transmitted BWYV to 62% of them regardless of the growth stage inoculated. Aphids colonised 100% of plants grown from untreated seed but 0% of plants sprayed with imidacloprid (2ga.i./L water), and infection with BWYV was diminished markedly by the foliar spray. This suggests that insufficient insecticide adhered to most of the dressed seeds to kill the aphids and prevent BWYV transmission. B. napus cultivars found to have infection resistance to BWYV can be used in conjunction with imidacloprid seed dressings (if applied effectively) as components of an integrated disease management strategy for control of BWYV in B. napus crops. © CSIRO 2010. Source

MacCarone L.D.,University of Western States | Barbetti M.J.,University of Western States | Barbetti M.J.,Agricultural Research Western Australia | Sivasithamparam K.,University of Western States | And 2 more authors.
Plant Disease

Lettuce plants showing symptoms of lettuce big-vein disease were collected from fields in the Perth Metropolitan region of southwest Australia. When root extracts from each plant were tested by polymerase chain reaction (PCR) using primers specific to the rDNA internal transcribed spacer (ITS) region of Olpidium brassicae and O. virulentus, only O. virulentus was detected in each of them. The nucleotide sequences of the complete rDNA ITS regions of isolates from five of the root samples and 10 isolates of O. virulentus from Europe and Japan showed 97.9 to 100% identities. However, with the six O. brassicae isolates, their identities were only 76.9 to 79.4%. On phylogenetic analysis of the complete rDNA-ITS region sequences of the five Australian isolates and 10 others, the Australian isolates fitted within two clades of O. virulentus (I and II), and within clade I into two of its four subclades (Ia and Id). Japanese isolates had greatest sequence diversity fitting into both clades and into all of clade I subclades except Ib, while European isolates were restricted to subclades Ib and Id. When the partial rDNA-ITS region sequences of two additional southwest Australian isolates, four from Europe, and four from the Americas were included in the analyses, the Australian isolates were within O. virulentus subclades Ia and Id, the European isolates within subclade Ic, and the American isolates within subclades Ia and Ib. These findings suggest that there may have been at least three separate introductions of O. virulentus into the isolated Australian continent since plant cultivation was introduced following its colonization by Europeans. They also have implications regarding numbers of different introductions to other isolated regions. Lettuce big-vein associated virus and Mirafiori lettuce big-vein virus were both detected when symptomatic lettuce leaf tissue samples corresponding to the root samples from southwest Australia were tested using virus-specific primers in reverse transcription-PCR, so presence of both viruses was associated with O. virulentus occurrence. © 2010 The American Phytopathoiogicai Society. Source

Maling T.,Agricultural Research Western Australia | Maling T.,University of Western Australia | Diggle A.J.,Agricultural Research Western Australia | Diggle A.J.,University of Western Australia | And 4 more authors.
Crop and Pasture Science

A hybrid mechanistic/statistical model developed previously to predict vector activity and epidemics of vector-borne viruses was modified to simulate virus epidemics in the Beet western yellows virus (BWYV) Brassica napus pathosystem. BWYV, which is persistently aphid-borne, spreads to B. napus crops from external sources and causes substantial yield losses when there is widespread infection of young plants. Risk that such losses may occur depends on the magnitude and availability of viral inoculum in the external source, the amount of biomass available to support aphid vectors, its duration before crop emergence, and the time of arrival of vector aphids in the crop. The model uses daily rainfall, temperature, and evaporation data from over 450 sites in the grainbelt of south-western Australia to track biomass levels throughout the growing season. This information is then used to simulate aphid vector populations and virus incidence, initially in the external source environment, then in the crop, and ultimately to provide risk forecasts. The model predicted BWYV spread successfully for 10 of 12 different datasets from 3 years of field observations on B. napus blocks at 4 sites representing different rainfall and geographic zones of the grainbelt. Sensitivity analysis was used to determine the relative importance of the main parameters that describe the pathosystem and to predict which control measures are likely to be useful. An analysis of timing of predictions v. their accuracy was also done to establish optimum timing of forecasts for BWYV epidemics in B. napus crops. © CSIRO 2010. Source

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