Analysis of the Transcriptome of the Infective Stage of the Beet Cyst Nematode, H. schachtii.

The beet cyst nematode, Heterodera schachtii, is a major root pest that significantly impacts the yield of sugar beet, brassicas and related species. There has been limited molecular characterisation of this important plant pathogen: to identify target genes for its control the transcriptome of the pre-parasitic J2 stage of H. schachtii was sequenced using Roche GS FLX. Ninety seven percent of reads (i.e., 387,668) with an average PHRED score > 22 were assembled with CAP3 and CLC Genomics Workbench into 37,345 and 47,263 contigs, respectively. The transcripts were annotated by comparing with gene and genomic sequences of other nematodes and annotated proteins on public databases. The annotated transcripts were much more similar to sequences of Heterodera glycines than to those of Globodera pallida and root knot nematodes (Meloidogyne spp.). Analysis of these transcripts showed that a subset of 2,918 transcripts was common to free-living and plant parasitic nematodes suggesting that this subset is involved in general nematode metabolism and development. A set of 148 contigs and 183 singletons encoding putative homologues of effectors previously characterised for plant parasitic nematodes were also identified: these are known to be important for parasitism of host plants during migration through tissues or feeding from cells or are thought to be involved in evasion or modulation of host defences. In addition, the presence of sequences from a nematode virus is suggested. The sequencing and annotation of this transcriptome significantly adds to the genetic data available for H. schachtii, and identifies genes primed to undertake required roles in the critical pre-parasitic and early post-parasitic J2 stages. These data provide new information for identifying potential gene targets for future protection of susceptible crops against H. schachtii.

The global trade in fresh produce and the vagility of plant viruses: a case study in garlic.

As cuisine becomes globalized, large volumes of fresh produce are traded internationally. The potential exists for pathogens infecting fresh produce to hitchhike to new locations and perhaps to establish there. It is difficult to identify them using traditional methods if pathogens are novel, scarce, and/or unexpected. In an attempt to overcome this limitation, we used high-throughput sequencing technology as a means of detecting all RNA viruses infecting garlic (Allium sativum L.) bulbs imported into Australia from China, the USA, Mexico, Argentina and Spain, and those growing in Australia. Bulbs tested were grown over multiple vegetative generations and all were stably infected with one or more viruses, including two species not previously recorded in Australia. Present in various combinations from 10 garlic bulbs were 41 virus isolates representing potyviruses (Onion yellow dwarf virus, Leek yellow stripe virus), carlaviruses (Shallot latent virus, Garlic common latent virus) and allexiviruses (Garlic virus A, B, C, D, and X), for which 19 complete and 22 partial genome sequences were obtained, including the first complete genome sequences of two isolates of GarVD. The most genetically distinct isolates of GarVA and GarVX described so far were identified from Mexico and Argentina, and possible scenarios explaining this are presented. The complete genome sequence of an isolate of the potexvirus Asparagus virus 3 (AV3) was obtained in Australia from wild garlic (A. vineale L.), a naturalized weed. This is first time AV3 has been identified from wild garlic and the first time it has been identified beyond China and Japan. The need for routine generic diagnosis and appropriate legislation to address the risks to primary production and wild plant communities from pathogens spread through the international trade in fresh produce is discussed.

A single tube, quantitative real-time RT-PCR assay that detects four potato viruses simultaneously.

A high throughput, real-time multiplex, single tube RT-PCR assay was developed for simultaneous detection of Potato leafroll virus (PLRV), Potato virus X (PVX) and Potato virus S (PVS) in potato leaves and tubers, and Tomato spotted wilt virus (TSWV) in potato tubers and tomato leaves. The test uses four different fluorescently labelled TaqMan probes. Limits of detection sensitivity were established using a range of virus transcript copy numbers (8 x 10(1) to 8 x 10(9) copies of PVX and PVS, 1 x 10(2) to 1 x 10(10) copies of PLRV and 1 x 10(3) to 1 x 10(10) copies of TSWV). For each individual assay, the inter-assay reproducibility was high, with a coefficient of variation of the combined assays of <2%. Total RNA was extracted rapidly and efficiently from bulked samples equivalent to 300 dormant tubers to detect single infections of PLRV, PVX, PVS and TSWV simultaneously in a single assay. The multiplexed assay was validated in blind studies with leaves and tubers. This high-throughput test is accurate and sensitive, and provides seed potato industries with a cost-effective diagnostic tool to detect viruses reliably in bulked samples of dormant potato tubers.