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Only a few plants in a crop are generally thought to become infected by abiotic soil transmission. In glasshouse experiments we have induced almost total infection in tomatoes growing in soil with infective debris, but levels of infection are dependent upon certain conditions. We found that as the inoculum concentration decreased (i) a greater percentage of the infections were either latent (symptomless) or restricted to roots and (ii) infection levels decreased. Thus, apparent infection (based on symptoms) of 0. 10% was in reality 0 60–70% based on enzyme-linked immunosorbent assay and immunoelectron microscopy testing of roots and leaves. This occurred whether seedlings or seed were planted into infected mix. Under conditions in which minimal root damage was caused (planting seed) or roots were mechanically inoculated only once, almost all systemically infected plants were symptomless.

Mycelial extracts of Pythium irregulare were processed using CF-11 chromatography and analysed by gel electrophoresis for double-stranded RNA (dsRNA) content. DsRNA molecules of between 1 and 6 kb were found in 33 of 39 isolates tested. The dsRNA profiles of individual isolates remained unchanged after repeated subculturing of hyphal tips, after storage under water for 2 years, or when single zoospores were used to generate subcultures. However, dsRNA profiles varied between isolates, and even within individual populations; in the one case eight different dsRNA types were recovered upon testing 17 isolates from a single wheatfield. Isometric virus-like particles (VLPs) of approximately 45 nm were found in isolates containing dsRNA, while no such particles could be found in isolates in which dsRNA was not detected. Electrophoretic profiles of dsRNA extracted from partial purifications of VLPs were identical to those of dsRNA extracted from whole mycelium, suggesting that the dsRNA is at least partially encapsidated. Attempts to transmit dsRNA between isolates by hyphal anastomosis or by coinfection in wheat plants were unsuccessful, with only parental types being recovered. Analysis of 29 isolates representing 14 other Pythium species failed to detect dsRNA, even when co-isolated with P. irregulare known to contain dsRNA

We studied the behaviour of tomato mosaic tobamovirus (ToMV) in a recirculating nutrient solution. Particles of tomato mosaic virus were found in the nutrient solution 3 days after leaf inoculation of plants and we demonstrated that the level could increase to a concentration readily detectable by electron microscopy. Virions remained infective in nutrient solution for at least 6 months, could infect bait plants and induced systemic symptoms within 10 days. This is the first report of measurement of infective virions in recirculating nutrient solutions. Hydroponic producers should be aware of the potential for rapid spread of virus diseases in soilless growing systems as one infected plant can serve as a source of inoculum that can ultimately result in an epidemic.

Electrophoresis on 5% polyacrylamide was used to analyze dsRNAs of 26 cucumber mosaic virus isolates propagated in Nicotiana tabacum. There was variation between isolates in the migration of each of the dsRNAs 1, 2, and 3. Comparison of the dsRNA profiles enabled each isolate to be allocated to 1 of 7 distinct dsRNA profile types. Two distinct and readily distinguishable isolates were mixed in planta and dsRNA from these infected plants compared with in vitro mixtures of them. All bands from both types were present, indicating that the differences were real and reproducible. This method is of value as a means of classifying cucumber mosaic virus isolates, as it more closely reflects a range of biological characteristics than do other methods currently used.

Glasshouse production of capsicums in the Sunraysia district of NSW and Victoria is severely limited by infection with a range of viruses. Aphid transmission tests, electron microscopy and serological assays have shown that one of the viruses involved is a luteovirus – the frst record of a naturally occurring luteovirus in glasshouse capsicum. The relationship of this virus to other luteoviruses known to infect solanaceous hosts is examined, and data presented to show that it is most probably a capsicum strain of potato leafroll virus. ZusammenfassungCapsicum yellows — eine Krankheit, die durch Luteoviren bei Paprikapfianzen (Capsicum annuam) im Gewachshaus in Australien verursacht wird Die Gewachshausproduktion von Capsicum im Sunraysia-Distrikt von NSW und Victoria wird sehr stark limitiert durch Infektionen mit einer Reihe von Viren. Blattlausubertragungstests, elektronenmikroskopische Untersuchung sowie seroiogische Prufungen habcn gezeigt, das eines von den ve rant wort lichen Viren ein Luteovirus ist — der erste Bericht iiber ein naturlich vorkommendes Luteovirus in Gewachshaus-Capsium. Das Verhaltnis von diesem Virus zu anderen Luteoviren, die bekanntlich Solanaceae-Wirtspflanzen haben, wurde festgestdlt, und es werden Ergebnisse wiedergegeben, die zeigen, dafi das Virus wahrscheinlich ein Capsicum-Sts.mm des potato leafroll virus ist.

A carlavirus was found to be widespread in commercial passionfruit (Passiflora edulis) plantings in New South Wales and Queensland. The particles observed were flexuous rods with mean dimensions of 651 × 12 nm. The particles often occurred in cells as aggregates but were never associated with pinwheel inclusion bodies, as is typical with passionfruit woodiness potyvirus. The particles showed a strong affinity (by immunoelectron microscopy) for antiserum prepared against Passiflora latent carlavirus (PLV) from Germany but increasingly less affinity for antisera against potato viruses S and M and PLV from the United States. Survey results indicated that PLV has been present in Australian passionfruit for more than 10 years and is widespread in most commercial cultivars in New South Wales and Queensland. The virus was twice found in wild Passiflora suberosa, once in wild P. subpeltata, and once in a feral seedling of P. edulis near an infected planting of P. edulis.

Fusarium wilt of the Canary Island Date Palm (Phoenix canariensis) caused by Fusarium oxysporum f. sp. canariensis was recorded for the first time in several locations in Victoria. The identity of the fungus was substantiated using a polymerase chain reaction-based technique with primers specific for this particular pathogen.

Fusarium wilt of basil, caused by Fusarium oxysporum f. sp. basilici, occurs worldwide but has not been officially recorded in Australia. Fourteen isolates of F. oxysporum were collected from diseased basil from a number of locations in Australia. A PCR diagnostic test previously shown to react only with isolates of F. oxysporum f. sp. basilici was used to identify the isolates and Koch’s postulates were performed for a subset of isolates to confirm pathogenicity. Two techniques, vegetative compatibility grouping and DNA fingerprinting using enterobacterial repetitive intergenic consensus (ERIC) targeted primers, were used to analyse all isolates. Diagnostic PCR confirmed that 11 of the isolates were F. oxysporum f. sp. basilici and they were shown to belong to a single VCG and to have a single ERIC profile, indicating that the population is essentially clonal. This is the first report of this pathogen in Australia.

Fusarium wilt of Phoenix canariensis (Canary Island Date Palm) is caused by Fusarium oxysporum f. sp. canariensis (Foc). The disease occurs worldwide, including Australia where hundreds of palms have been killed. Isolates of Foc were collected from fronds of diseased palms at sites around Sydney and different parts (non-frond) of individual palms within a site. Three techniques were used to assess diversity of these isolates; vegetative compatibility groupings, PCR testing for a sequence previously shown to be associated with pathogenicity and DNA fingerprinting using ERIC primers. The combined methods divided the isolates into one major and four minor groups, with two of the minor groups showing some bridging characters. ERIC PCR showed these groups to be different from six overseas isolates of Foc, five of which belonged to VCG 0240. A minority of isolates did not fall into any group and are presumed saprophytes. Some discrepancies in the expected correlation between the techniques occurred for the non-frond isolates; this has implications for appropriate tissue selection for disease diagnosis. The number of groups and the differences between them indicate a degree of diversity comparatively higher than that shown in other studies for this forma specialis and may have important consequences for disease management.

DNA fingerprints, based on Enterobacterial Repetitive Intergenic Consensus (ERIC) sites, were investigated as an alternative technique to Vegetative Compatibility Grouping (VCG) in studying populations of Fusarium oxysporum Schlecht. emend. Snyd. & Hans. Isolates of F. oxysporum were recovered from orchids displaying visible signs of root rot. Fifty-two isolates were collected and analysed using both the ERIC DNA fingerprinting technique and Vegetative Compatibility Grouping. Isolates were divided into 17 ERIC groups and 37 VCG groups. Based on its lower level of sensitivity and its rapid and reproducible result, the ERIC DNA fingerprinting was found to be a more appropriate technique for studying diverse populations of F. oxysporum.

Fusarium wilt of the Canary Island Date Palm (Phoenix canariensis), caused by Fusarium oxysporum f.sp. canariensis, was recorded for the first time in South Australia. The identity of the fungus was substantiated using a polymerase chain reaction-based technique with primers specific for this particular pathogen.

Transgenic tobacco plants expressing the coat protein (CP) of an Australian isolate of cucumber mosaic cucumovirus (CMV) were resistant to infection with the homologous and two heterologous CMV strains. The level of resistance observed in CP-expressing plants was related to the virulence of the challenging CMV isolate and not to the similarity between the CP expressed by the transgenic plant and the CP of the challenging virus.

This paper records the occurrence of an antigen produced in plants infected by potato leafroll virus (PLRV), which is copurified with the virus and induces an immune response in rabbits used for virus antiserum production. The antigen also appeared to be produced in uninfected but physiologically stressed potato plants. These plants reacted with antisera to PLRV in ELISA tests, thereby giving false positive results. We refer to the compound as virus-stress antigen (VSA). The importance of this finding, not only to serological testing for PLRV, but also as a possible explanation for some false-positive reactions that occur with other host-virus combinations, is discussed. The necessity of having detailed information on plants from which samples are taken for testing is emphasized.

Virus disease limit glasshouse production of capsicums in the Supraysia District of New South Wales. Symptoms develop on plants about 4 weeks after planting; and up to 83° of plants are infected. The major virus is cucumber mosaic (CMV) with some pepper mild niottle (PMMV) also present. Evidence is presented to show that the primary source of intection of both viruses is most likely to be debris from previous crops remaining in the soil. It demonstrates a previously unconsi-dered mechanism tor survival and spread of labile viruses such as CMV and the ecological ecological consequence of these results are considerable. Zusammenfassung Die Rolle nicht-vektorbedingter Bodenubertragung als Hauptursache von Infektionen durch Pepper Mild Mottle und Gurken-Mosaik-Virus bei im Gewachshaus gezogenem Capsicum in Australien Virtiskrankheiten beentrachutigen die Gewachshaus. sproduktion von Capsieum-Arten im Sunraysia- Bezirk von Neusudwales. Vier Wochen nach dem Auspflanzen treten die ersien Symptome auf etwa 80 % der Pflanzen sind befallen. Hauptsaehlieh tritt der Gurken-Mosaik Virus auf CMV), aber auch etwds Pepper Mild Mottle (PMMV). Die Studie liefert Beweise dafur. das die Hauptiniektionsquelle durch beide Virusarten in Uberresten fruherer Bepflanzung liegt, die in der Erde verblieben sind. Die Arbeit beschreibt einen bislang nicht beobachtenen Uberlebensmechanismus sowie die Ausbreitungsweise von labilen Virusarten wie CMV, deren okologischie Auswirkungen beitratlich sind.

Cuttings of the Wollemi Pine, Wollemia nobilis, were inoculated with Phytophthora cinnamomi, Botyosphaeria sp., Rhizoctonia sp., Fusarium oxysporum and F. solani. P. cinnamomi and the Botyosphaeria sp. were pathogenic causing plant death over a period of up to 5 weeks. None of the other fungi caused significant disease although two out of nine plants inoculated with F. oxysporum died during the experimental period. The results confirm the necessity to maintain strict hygiene and entry controls on the site where this extremely rare plant is found.