Ten Fusarium graminearum isolates from China were screened for dsRNA mycoviruses. Five dsRNAs (2.4 to 3.5 kbp) were purified from isolate China 9, cloned, and sequenced. BLAST analysis showed that the proteins encoded by dsRNA1 possess motifs that are conserved in RNA-dependent RNA polymerases, dsRNA2 resembles the hypothetical protein encoded by dsRNA3 of Magnaporthe oryzae chrysovirus 1, dsRNA4 shares no significant similarity to any published protein, and dsRNA5 has a C2H2 zinc finger domain. Tandem mass spectrophotometry, surface protein labeling of virus-like particles, SDS-PAGE, and protein BLAST results supports the notion that three of the virus segments code for structural proteins, of which dsRNA3 possibly codes for the capsid protein. Relative quantitative RT-PCR studies of the 5 dsRNAs suggested that the segments are encapsidated separately in unequal amounts. Genomic structure and phylogenic studies support the possibility that this virus may be a candidate for the type species of a novel genus in the family Chrysoviridae.

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Some (perhaps all) plant viruses transmitted in a circulative manner by their insect vectors avoid destruction in the haemolymph by interacting with GroEL homologues, ensuring transmission. We have previously shown that the phloem-limited begomovirus tomato yellow leaf curl virus (TYLCV) interacts in vivo and in vitro with GroEL produced by the whitefly vector Bemisia tabaci. In this study, we have exploited this phenomenon to generate transgenic tomato plants expressing the whitefly GroEL in their phloem. We postulated that following inoculation, TYLCV particles will be trapped by GroEL in the plant phloem, thereby inhibiting virus replication and movement, thereby rendering the plants resistant. A whitefly GroEL gene was cloned in an Agrobacterium vector under the control of an Arabidopsis phloem-specific promoter, which was used to transform two tomato genotypes. During three consecutive generations, plants expressing GroEL exhibited mild or no disease symptoms upon whitefly-mediated inoculation of TYLCV. In vitro assays indicated that the sap of resistant plants contained GroEL-TYLCV complexes. Infected resistant plants served as virus source for whitefly-mediated transmission as effectively as infected non-transgenic tomato. Non-transgenic susceptible tomato plants grafted on resistant GroEL-transgenic scions remained susceptible, although GroEL translocated into the grafted plant and GroEL-TYLCV complexes were detected in the grafted tissues.

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For the detection of microbial plant pathogens, like fungi, bacteria, viruses and viroids, methods based on nucleic acids have gained importance as the availability of sequence information increased. This requires well-established extraction procedures that are cheap, non-laborious, safe and reliable. The paper cards introduced by Flinders Technology Associates, acronym FTA Ò cards, offer a simple tool to sample and preserve nucleic acids from many kinds of biological specimen and have been already tested for their potential to sample and process several plant pathogens in PCR and RT-PCR. We have tested FTA cards for the sample preparation of a broader range of plant pathogens with different NA contents and subsequent amplification by PCR, RT-PCR as well as multiplex PCR.