Bromus catharticus striate mosaic virus: a new mastrevirus infecting Bromus catharticus from Australia.

Although monocotyledonous-plant-infecting mastreviruses (in the family Geminiviridae) are known to cause economically significant crop losses in certain areas of the world, in Australia, they pose no obvious threat to agriculture. Consequently, only a few Australian monocot-infecting mastreviruses have been described, and only two have had their genomes fully sequenced. Here, we present the third full-genome sequence of an Australian monocot-infecting mastrevirus from Bromus catharticus belonging to a distinct species, which we have tentatively named Bromus catharticus striate mosaic virus (BCSMV). Although the genome of this new virus shares only 57.7% sequence similarity with that of its nearest known relative, Digitaria didactyla striate mosaic virus (DDSMV; also from Australia), it has features typical of all other known mastrevirus genomes. Phylogenetic analysis showed that both the full genome and each of its probable expressed proteins group with the two other characterised Australian monocot-infecting mastreviruses. Besides the BCSMV genome sequence revealing that Australian monocot-infecting mastrevirus diversity rivals that seen in Africa, it has enabled us, for the first, to time detect evidence of recombination amongst the Australian viruses. Specifically, it appears that DDSMV possesses a short intergenic region sequence that has been recombinationally derived from either BCSMV or a close relative that has not yet been identified.

Abacá mosaic virus: a distinct strain of Sugarcane mosaic virus

Abacá mosaic virus (AbaMV) is related to members of the sugarcane mosaic virus subgroup of the genus Potyvirus. The ~2 kb 3′ terminal region of the viral genome was sequenced and, in all areas analysed, found to be most similar to Sugarcane mosaic virus (SCMV) and distinct from Johnsongrass mosaic virus (JGMV), Maize dwarf mosaic virus (MDMV) and Sorghum mosaic virus (SrMV). Cladograms of the 3′ terminal region of the NIb protein, the coat protein core and the 3′ untranslated region showed that AbaMV clustered with SCMV, which was a distinct clade and separate from JGMV, MDMV and SrMV. The N-terminal region of the AbaMV coat protein had a unique amino acid repeat motif different from those previously published for other strains of SCMV. The first experimental transmission of AbaMV from abacá (Musa textilis) to banana (Musa sp.), using the aphid vectors Rhopalosiphum maidis and Aphis gossypii, is reported. Polyclonal antisera for the detection of AbaMV in western blot assays and ELISA were prepared from recombinant coat protein expressed in E. coli. A reverse transcriptase PCR diagnostic assay, with microtitre plate colourimetric detection, was developed to discriminate between AbaMV and Banana bract mosaic virus, another Musa-infecting potyvirus. Sequence data, host reactions and serological relationships indicate that AbaMV should be considered a distinct strain of SCMV, and the strain designation SCMV-Ab is suggested.

Host range, symptom expression and RNA 3 sequence analyses of six Australian strains of Cucumber mosaic virus

We have characterised six Australian Cucumber mosaic virus (CMV) strains belonging to different subgroups, determined by the sequence of their complete RNA 3 and by their host range and the symptoms they cause on species in the Solanaceae, Cucurbitaceae and on sweet corn. These data allowed classification of strains into the known three CMV subgroups and identification of plant species able to differentiate the Australian strains by symptoms and host range. Western Australian strains 237 and Twa and Queensland strains 207 and 242 are closely related members of CMV subgroup IA, which cause similar severe symptoms on Nicotiana species. Strains 207 and 237 (subgroup IA) were the only strains tested which systemically infected sweet corn. Strain 243 caused the most severe symptoms of all strains on Nicotiana species, tomato and capsicum and appears to be the first confirmed subgroup IB strain reported in Australia. Based on pair-wise distance analysis and phylogeny of RNA 3, as well as mild disease symptoms on Nicotiana species, CMV 241 was assigned to subgroup II, as the previously described Q-CMV and LY-CMV.

Bats: Important reservoir hosts of emerging viruses

Bats (order Chiroptera, suborders Megachiroptera and Microchiroptera) are abundant, diverse, and geographically widespread. These mammals provide us with resources, but their importance is minimized and many of their populations and species are at risk, even threatened or endangered. Some of their characteristics (food choices, colonial or solitary nature, population structure, ability to fly, seasonal migration and daily movement patterns, torpor and hibernation, life span, roosting behaviors, ability to echolocate, virus susceptibility) make them exquisitely suitable hosts of viruses and other disease agents. Bats of certain species are well recognized as being capable of transmitting rabies virus, but recent observations of outbreaks and epidemics of newly recognized human and livestock diseases caused by viruses transmitted by various megachiropteran and microchiropteran bats have drawn attention anew to these remarkable mammals. This paper summarizes information regarding chiropteran characteristics and information regarding 66 viruses that have been isolated from bats. From these summaries, it is clear that we do not know enough about bat biology, that we are doing too little in terms of bat conservation, and that there remain a multitude of questions regarding the role of bats in disease emergence.

Analysis of the serological variability of Lettuce mosaic virus using monoclonal antibodies and surface plasmon resonance technology

A panel of 19 monoclonal antibodies (mAbs) was used to study the immunological variability of Lettuce mosaic virus (LMV), a member of the genus Potyvirus, and to perform a first epitope characterization of this virus. Based on their specificity of recognition against a panel of 15 LMV isolates, the mAbs could be clustered in seven reactivity groups. Surface plasmon resonance analysis indicated the presence, on the LMV particles, of at least five independent recognition/binding regions, correlating with the seven mAbs reactivity groups. The results demonstrate that LMV shows significant serological variability and shed light on the LMV epitope structure. The various mAbs should prove a new and efficient tool for LMV diagnostic and field epidemiology studies.

Emerging Viruses: Coming in on a Wrinkled Wing and a Prayer

The role that bats have played in the emergence of several new infectious diseases has been under review. Bats have been identified as the reservoir hosts of newly emergent viruses such as Nipah virus, Hendra virus, and severe acute respiratory syndrome–like coronaviruses. This article expands on recent findings about bats and viruses and their relevance to human infections. It briefly reviews the history of chiropteran viruses and discusses their emergence in the context of geography, phylogeny, and ecology. The public health and trade impacts of several outbreaks are also discussed. Finally, we attempt to predict where, when, and why we may see the emergence of new chiropteran viruses.

Cucumber mosaic virus infection of kava (Piper methysticum) and implications for cultural control of kava dieback disease

Cucumber mosaic virus (CMV) was found by reverse transcription polymerase chain reaction (RT-PCR) to be not fully systemic in naturally infected kava (Piper methysticum) plants in Fiji. Twenty-six of 48 samples (54%) from various tissues of three recently infected plants were CMV-positive compared with 7/51 samples (14%) from three long-term infections (plants affected by dieback for more than 1 year). The virus was also found to have a limited ability to move into newly formed stems. CMV was detected in only 2/23 samples taken from re-growth stems arising from known CMV infected/dieback affected plants. Mechanical inoculation experiments conducted in Fiji indicate that the known kava intercrop plants banana (Musa spp.), pineapple (Ananas comosus), peanut (Arachis hypogaea) and the common weed Mikania micrantha are potential hosts for a dieback-causing strain of CMV It was not possible to transmit the virus mechanically to the common kava intercrop plants taro (Colocasia esculenta), Xanthosoma sp., sweet potato (Ipomoea batatas), yam (Dioscorea alata), papaya (Carica papaya) or the weed Momordica charantia. Implications of the results of this research on a possible integrated disease management strategy are discussed.

Carrot as a natural host of Watermelon mosaic virus

Carrot was confirmed as a new natural and experimental host of Watermelon mosaic virus by serology, host reactions and sequence comparisons of the coat protein.

Developing and communicating strategies for controlling virus diseases in vegetable cucurbit crops

Virus diseases cause serious yield and quality losses in field grown cucurbit crops worldwide. In Australia, the main viruses of cucurbits are Papaya ringspot virus (PRSV), Squash mosaic virus (SqMV), Watermelon mosaic virus (WMV) and Zucchini yellow mosaic virus (ZYMV). Plants infected early have severely distorted fruit. High infection incidences, of ZYMV and PRSV in crops cause losses of marketable fruit of up to 100% and infected crops are often abandoned. Two new alternative hosts of ZYMV were identified, the native cucurbit Cucumis maderaspatanus and wild legume Rhyncosia minima. No new alternative hosts of PRSV, SqMV or WMV were found in Western Australia or Queensland. Seed transmission of ZYMV (0.7%) was found in seedlings grown from ZYMV-infected fruit of zucchini but not of pumpkin. None was detected with PRSV or SqMV in zucchini or pumpkin seedlings, respectively. ZYMV spread to pumpkins by aphids was greater downwind than upwind of a virus source. Delaying sowing by 2 weeks decreased ZYMV spread. Millet non-host barriers between pumpkin plantings slowed ZYMV infection. Host resistance gene (zym) in cucumber cultivars was effective against ZYMV. Pumpkin cultivars with resistance gene (Zym) became infected under high virus pressure but leaf symptoms were milder and infected plants higher yielding with more market-acceptable fruit than those without Zym. Most zucchini cultivars with Zym developed severe leaf and fruit symptoms. ZYMV, PRSV, WMV and SqMV spread readily from infected to healthy cucurbit plants by direct leaf contact. ZYMV survives and remains infective on diverse surfaces for up to 6 hours but can be inactivated by some disinfectants. Phylogenetic analysis indicates at least three separate introductions of ZYMV into Australia, with new introductions rarely occurring. ZYMV isolates clustered into three groups according to collection location i) Kununurra, ii) Northern Territory and iii) Carnarvon, Qld and Vic. A multiplex Real-Time PCR was developed which distinguished between the three groups of Australian isolates. Integrated disease management (IDM) strategies for virus diseases of vegetable cucurbit crops grown in the field were improved incorporating the new information gathered. These strategies are aimed at causing using minimal extra expense, labour demands and disruption to normal practices.

Developing molecular diagnostics for the detection of strawberry viruses

Developing molecular diagnostics for the detection of strawberry viruses.

Phylodynamic evidence of the migration of turnip mosaic potyvirus from Europe to Australia and New Zealand

Turnip mosaic virus (TuMV) is a potyvirus that is transmitted by aphids and infects a wide range of plant species. We investigated the evolution of this pathogen by collecting 32 isolates of TuMV, mostly from Brassicaceae plants, in Australia and New Zealand. We performed a variety of sequence-based phylogenetic and population genetic analyses of the complete genomic sequences and of three non-recombinogenic regions of those sequences. The substitution rates, divergence times and phylogeographical patterns of the virus populations were estimated. Six inter- and seven intralineage recombination-type patterns were found in the genomes of the Australian and New Zealand isolates, and all were novel. Only one recombination-type pattern has been found in both countries. The Australian and New Zealand populations were genetically different, and were different from the European and Asian populations. Our Bayesian coalescent analyses, based on a combination of novel and published sequence data from three nonrecombinogenic protein-encoding regions, showed that TuMV probably started to migrate from Europe to Australia and New Zealand more than 80 years ago, and that distinct populations arose as a result of evolutionary drivers such as recombination. The basal-B2 subpopulation in Australia and New Zealand seems to be older than those of the world-B2 and -B3 populations. To our knowledge, our study presents the first population genetic analysis of TuMV in Australia and New Zealand. We have shown that the time of migration of TuMV correlates well with the establishment of agriculture and migration of Europeans to these countries.

Associations between exposure to viruses and bovine respiratory disease in Australian feedlot cattle

Bovine respiratory disease (BRD) is the most important cause of clinical disease and death in feedlot cattle. Respiratory viral infections are key components in predisposing cattle to the development of this disease. To quantify the contribution of four viruses commonly associated with BRD, a case-control study was conducted nested within the National Bovine Respiratory Disease Initiative project population in Australian feedlot cattle. Effects of exposure to Bovine viral diarrhoea virus 1 (BVDV-1), Bovine herpesvirus 1 (BoHV-1), Bovine respiratory syncytial virus (BRSV) and Bovine parainfluenza virus 3 (BPIV-3), and to combinations of these viruses, were investigated. Based on weighted seroprevalences at induction (when animals were enrolled and initial samples collected), the percentages of the project population estimated to be seropositive were 24% for BoHV-1, 69% for BVDV-1, 89% for BRSV and 91% for BPIV-3. For each of the four viruses, seropositivity at induction was associated with reduced risk of BRD (OR: 0.6–0.9), and seroincrease from induction to second blood sampling (35–60 days after induction) was associated with increased risk of BRD (OR: 1.3–1.5). Compared to animals that were seropositive for all four viruses at induction, animals were at progressively increased risk with increasing number of viruses for which they were seronegative; those seronegative for all four viruses were at greatest risk (OR: 2.4). Animals that seroincreased for one or more viruses from induction to second blood sampling were at increased risk (OR: 1.4–2.1) of BRD compared to animals that did not seroincrease for any viruses. Collectively these results confirm that prior exposure to these viruses is protective while exposure at or after feedlot entry increases the risk of development of BRD in feedlots. However, the modest increases in risk associated with seroincrease for each virus separately, and the progressive increases in risk with multiple viral exposures highlights the importance of concurrent infections in the aetiology of the BRD complex. These findings indicate that, while efficacious vaccines could aid in the control of BRD, vaccination against one of these viruses would not have large effects on population BRD incidence but vaccination against multiple viruses would be expected to result in greater reductions in incidence. The findings also confirm the multifactorial nature of BRD development, and indicate that multifaceted approaches in addition to efficacious vaccines against viruses will be required for substantial reductions in BRD incidence.

Induced Resistance: Potential for Control of Postharvest Diseases of Horticultural Crops

Fortunately, plants have developed highly effective mechanisms with which to defend themselves when attacked by potentially disease-causing microorganisms. If not, then they would succumb to the many pathogenic fungi, bacteria, viruses, nematodes and insect pests, and disease would prevail. These natural defence systems of plants can be deliberately activated to provide some protection against the major pathogens responsible for causing severe yield losses in agricultural and horticultural crops. This is the basis of what is known as ‘induced’ or ‘acquired’ disease resistance in plants. Although the phenomenon of induced resistance has been known amongst plant pathologists for over 100 years, its inclusion into pest and disease management programmes has been a relatively recent development, ie. within the last 5 years. This review will discuss very briefly some of the characteristics of the induced resistance phenomenon, outline some of the advantages and limitations to its implementation and provide some examples within a postharvest pathology context. Finally some approaches being investigated by the fruit pathology team at DPI Indooroopilly and collaborators will be outlined.