Natural host range, thrips and seed transmission of distinct Tobacco streak virus strains in Queensland, Australia

Diseases caused by Tobacco streak virus (TSV) have resulted in significant crop losses in sunflower and mung bean crops in Australia. Two genetically distinct strains from central Queensland, TSV-parthenium and TSV-crownbeard, have been previously described. They share only 81% total-genome nucleotide sequence identity and have distinct major alternative hosts, Parthenium hysterophorus (parthenium) and Verbesina encelioides (crownbeard). We developed and used strain-specific multiplex Polymerase chain reactions (PCRs) for the three RNA segments of TSV-parthenium and TSV-crownbeard to accurately characterise the strains naturally infecting 41 hosts species. Hosts included species from 11 plant families, including 12 species endemic to Australia. Results from field surveys and inoculation tests indicate that parthenium is a poor host of TSV-crownbeard. By contrast, crownbeard was both a natural host of, and experimentally infected by TSV-parthenium but this infection combination resulted in non-viable seed. These differences appear to be an effective biological barrier that largely restricts these two TSV strains to their respective major alternative hosts. TSV-crownbeard was seed transmitted from naturally infected crownbeard at a rate of between 5% and 50% and was closely associated with the geographical distribution of crownbeard in central Queensland. TSV-parthenium and TSV-crownbeard were also seed transmitted in experimentally infected ageratum (Ageratum houstonianum) at rates of up to 40% and 27%, respectively. The related subgroup 1 ilarvirus, Ageratum latent virus, was also seed transmitted at a rate of 18% in ageratum which is its major alternative host. Thrips species Frankliniella schultzei and Microcephalothrips abdominalis were commonly found in flowers of TSV-affected crops and nearby weed hosts. Both species readily transmitted TSV-parthenium and TSV-crownbeard. The results are discussed in terms of how two genetically and biologically distinct TSV strains have similar life cycle strategies in the same environment

Watermelon Mosaic Virus Of Pumpkin (Cucurbita Maxima) From Sulawesi: Identification, Transmission, And Host Range

A mosaic disease of pumpkin (Cucurbita maxima) was spread widely in Sulawesi. Since the virus had not yet been identified, a study was conducted to identify the disease through mechanical inoculation, aphid vector transmission, host range, and electron microscopic test. Crude sap of infected pumpkin leaf samples was rubbed on the cotyledons of healthy pumpkin seedlings for mechanical inoculation. For insect transmission, five infective aphids were infected per seedling. Seedlings of eleven different species were inoculated mechanically for host range test. Clarified sap was examined under the electron microscope. Seeds of two pumpkin fruits from two different infected plants were planted and observed for disease transmission up to one-month old seedlings. The mosaic disease was transmitted mechanically from crude sap of different leaf samples to healthy pumpkin seedlings showing mosaic symptoms. The virus also infected eight cucurbits, i.e., cucumber (Cucumis sativus), green melon (Cucumis melo), orange/rock melon (C. melo), zucchini (Cucurbita pepo), pumpkin (Cucurbita maxima), water melon (Citrulus vulgaris), Bennicosa hispida, and blewah (Cucurbita sp.). Aphids transmitted the disease from one to other pumpkin seedlings. The virus was not transmitted by seed. The mosaic disease of pumpkin at Maros, South Sulawesi, was associated with flexious particles of approximately 750 nm length, possibly a potyvirus, such as water melon mosaic virus rather than papaya ringspot virus or zucchini yellow mosaic virus

Mosaic Disease of Maize Caused by Sugarcane Mosaic Potyvirus in Sulawesi

Mosaic disease of maize and grasses is commonly found in Sulawesi. The symptoms resemble the common mosaic symptoms of virus infection, but the pathogen has not been identified. The objective of this study was to identify the causal agent of the mosaic disease of maize and grasses in Sulawesi. Transmissions of the virus were studied by mechanical inoculation and the insect vector aphid. Serological study was done by using enzyme linked immunosorbent assay (ELISA). Results of mechanical inoculation showed that the disease was caused by a virus which was transmitted from diseased maize and grasses to healthy sweet corn seedlings. The disease was also transmitted by aphid (Rhopalosiphum maidis). Serological study indicated that the virus was closely related to the sugarcane mosaic virus (SCMV). Based on these results, it can be concluded that the maize and grass mosaic disease was caused by SCMV

Field evaluation of tolerance to Tobacco streak virus in sunflower germplasm, and observations of seasonal disease spread

Strong statistical evidence was found for differences in tolerance to natural infections of Tobacco streak virus (TSV) in sunflower hybrids. Data from 470 plots involving 23 different sunflower hybrids tested in multiple trials over 5 years in Australia were analysed. Using a Bayesian Hierarchical Logistic Regression model for analysis provided: (i) a rigorous method for investigating the relative effects of hybrid, seasonal rainfall and proximity to inoculum source on the incidence of severe TSV disease; (ii) a natural method for estimating the probability distributions of disease incidence in different hybrids under historical rainfall conditions; and (iii) a method for undertaking all pairwise comparisons of disease incidence between hybrids whilst controlling the familywise error rate without any drastic reduction in statistical power. The tolerance identified in field trials was effective against the main TSV strain associated with disease outbreaks, TSV-parthenium. Glasshouse tests indicate this tolerance to also be effective against the other TSV strain found in central Queensland, TSV-crownbeard. The use of tolerant germplasm is critical to minimise the risk of TSV epidemics in sunflower in this region. We found strong statistical evidence that rainfall during the early growing months of March and April had a negative effect on the incidence of severe infection with greatly reduced disease incidence in years that had high rainfall during this period

The development of an improved PCR-based marker system for Sw-5, an important TSWV resistance gene of tomato

Sw-5 is an important disease resistance gene of tomato, providing broad resistance to Tomato spotted wilt virus TSWV). A cleaved amplified polymorphic sequence (CAPS) marker, losely linked to the gene, has been reported. Although the Sw-5 locus has been characterised, a gene-specific marker has not been developed. This paper presents a PCR-based marker-system that consists of the co-amplification of a dominant marker representing the Sw-5 gene sequence, and the modified CAPS marker as a positive control and indicator of genotype

Natural host range and thrips transmission of capsicum chlorosis virus in Australia

The orthotospovirus, capscium chlorosis virus (CaCV) was shown to be common and widespread in the weed host Ageratum conyzoides in eastern coastal regions of Queensland, Australia with up to 92% of plants infected. This is the first report of A. conyzoides being an important host of CaCV in Australia. CaCV was also found as natural infections of Arachis hypogaea (peanut), Ananas comosus (pineapple), Sonchus oleraceus, Tagetes minuta and Emilia sonchifolia. This is the first report of CaCV infecting pineapple and being associated with severe disease symptoms. Thrips palmi, Frankliniella schultzei and Microcephalothrips abdominalis were shown to transmit CaCV while no transmission was achieved using F. occidentalis

A preliminary assessment of sweet potato cultivars for sweet potato feathery mottle virus (SPFMV)

Four cultivars of sweet potato (Ipomoea batatas) at the Gatton Research Station (Queensland) were screened for sweet potato feathery mottle virus (SPFMV). Both mother stock and field grown material were indexed by grafting to the indicator plant Ipomoea setosa. Within the limitations of our testing procedures, virus was not detected in mother stock of cw. Rojo Blanco (27 grafts), Resisto (20 grafts), LO-323 (22 grafts) and Red Abundance (23 grafts). Four of 35 grafts made with field-grown material were positive suggesting that virus infection of commercial planting material is more likely to occur by infection during field multiplication than from infected mother stock. Virus infection was detected by symptoms on and the presence of flexuous, filamentous particles in sap extracts of I. setosa. The virus was identified as sweet potato feathery mottle potyvirus by serology