Assessment of the effects of novel insecticides on green peach aphid (Myzus persicae) feeding and transmission of Turnip mosaic virus (TuMV)

BACKGROUND

Laboratory bioassays using treated leaf disks of peach were conducted to determine the efficacy of nine insecticides against the green peach aphid (GPA), Myzus persicae (Sulzer). The effects of these insecticides on aphid feeding behaviors and rates of transmission of Turnip mosaic virus (TuMV) to potted rutabaga plants were also determined.

RESULTS

Median lethal concentration (LC₅₀ ) values after 48 h feeding varied considerably, ranging from lows of 1.5 and 4.6 μg a.i./L for sulfoxaflor and λ-cyhalothrin, respectively, to 97.2 and 167.9 μg a.i./L for flonicamid and spirotetramat. LC₅₀ values were lowest and roughly equivalent for λ-cyhalothrin (1.2) acetamiprid (2.1), sulfoxaflor (0.23) and flupyradifurone (2.3) after 72 h feeding. Electrical penetration graph (EPG) recordings showed modest effects on feeding behaviors for certain insecticides, with sulfoxaflor, spirotetramat, and acetamiprid non-significant reduction in feeding duration and number of pathway and potential drop phases occurring during the first 5 min compared with the control. However, greenhouse experiments carried out to investigate the effect of these insecticides on rates of transmission of TuMV, which is transmitted non-persistently by GPA, resulted in only modest non-significant reductions in infection rates for acetamiprid, pymetrozine, λ-cyhalothrin, and flonicamid of 27%, 23%, 20%, and 17%, respectively.

CONCLUSION

All test materials were efficacious to GPA at differing levels, and some such as sulfoxaflor and acetamiprid non-significantly reduced the duration and number of pathways and potential drop phases of feeding within the first 5 min. None, however, resulted in significant reductions in rates of transmission of TuMV. © 2020 Her Majesty the Queen in Right of Canada. Pest Management Science © 2020 Society of Chemical Industry.

Aphid Transmission of the Ontario Isolate of Plum Pox Virus

Utilization of timed virus acquisition access probes in studies of plum pox virus (PPV) transmission by aphids demonstrated that endemic species transmitted the virus readily from plum, Prunus domestica (L.) Batsch; peach, P. persica (L.); or dwarf flowering almond, P. glandulosa Thunberg., to peach seedlings. The green peach aphid, Myzus persicae (Sulzer), was shown to be the most efficient vector. Acquisition of virus by green peach aphids from infected peach leaves resulted in 18-28% infected peach seedlings, while aphids previously fed on infected leaves of plum transferred virus to 36% of peach seedlings. Although the spirea aphid, Aphis spiraecola (Patch), was a less efficient vector than M. persicae it is perhaps more important for the spread of PPV due to its greater abundance and occurrence earlier in the season when peach trees are thought to be more susceptible to infection. Virus transmission rates varied depending on the virus source and healthy test plant species. In contrast to many previous studies, aphid inoculation of the experimental host Nicotiana benthamiana Domin occurred at a low rate, never exceeding 4%. Acquisition of PPV by M. persicae from infected peach fruit was greatly reduced compared with acquisition from leaves. The results of this research indicate that the Ontario isolate of PPV-D is readily transmissible by aphids to peach and natural spread of the virus needs to be considered in future management or eradication programs.

First Report of Aster Yellow Phytoplasmas ('Candidatus Phytoplasma asteris') in Canadian Grapevines

In North America, elm yellows, aster yellows (AY), and X-disease phytoplasmas have been detected in American grapevines (1), and recently, Bois noir was detected in Canadian vineyards from British Columbia (BC) and Ontario (ON) (2). Typical symptoms of grapevine yellows (GY) include leaf rolling and chlorosis, uneven or total lack of lignification of canes, flower abortion or berry withering, and stunting. In 2006 and 2007, independent surveys were conducted by the Canadian Food Inspection Agency (CFIA) and Agriculture and Agri-Food Canada (AAFC) to detect phytoplasmas in Canadian vineyards containing different cultivars in BC, ON, Québec (QC), Nova Scotia, New Brunswick, and Prince Edward Island. The CFIA collected and tested 651 fresh leaf samples from recently imported grapevines and older grapevines in the same or neighboring blocks displaying symptoms typical of those associated with disease caused by phytoplasmas. Many vineyards were surveyed only once. AAFC collected and tested 3,485 samples from symptomatic and asymptomatic grapevines from established vineyards in ON, BC, and QC. The same vineyards were sampled in ON and BC both years; QC vineyards were only sampled in 2007. AAFC-collected leaf samples were freeze dried and stored at -20°C before processing. CFIA samples were tested by a modified real-time PCR assay and TaqMan probe targeting the 16S ribosomal RNA gene that detects a wide range of known phytoplasmas (2). Positive samples were confirmed by conventional PCR using the phytoplasma-specific primers P1/P7 (3) and the resulting ~1,800-bp fragment was cloned and sequenced as previously described (2). DNA extracted by AAFC was amplified by nested PCR technology with universal phytoplasma specific primer pairs P1/P6 and R16R2/R16F2 (3) and the resulting 1,200-bp fragment was cloned and sequenced. Two plants, one located in ON in 2006 and the other in BC in 2007, were found to be infected with an AY-like phytoplasma by the CFIA. The phytoplasmas detected in both infected plants had a 99.9% nt sequence identity with AY phytoplasma sequences from GenBank (Accession Nos. AF222063 and AY665676, respectively), with the BC isolate also showing 100% identity to a strain of AY, ash witches'-broom phytoplasma (GenBank Accession No. AY566302). AAFC detected phytoplasma DNA in both years in a total of 17 symptomatic plants and 21 asymptomatic plants from different vine varieties in ON, BC, and QC. Positive samples were found to have a 99.0% nt sequence identity to AY subgroup 16SrI-A (GenBank Accession No. AY180956). Sequences were exchanged for confirmation of phytoplasma identity and were deposited in Genbank under Accession Nos. FJ659844 and FJ824597. Phytoplasma strains were identified for all plants in which phytoplasmas were detected. Results show that AY is present in vineyards in the provinces of ON, BC, and QC. To our knowledge, this is the first report of AY being detected in grapevines in Canada. References: (1) E. Boudon-Padieu. Bull. O I V, 79:299, 2003. (2) M. Rott et al. Plant Dis. 91:1682, 2007. (3) E. Tanne et al. Phytopathology 91:741, 2001.

Transfection of Arabidopsis protoplasts with a Plum pox virus (PPV) infectious clone for studying early molecular events associated with PPV infection

The development of novel strategies against plant viral diseases relies on a better understanding of molecular virus-host interactions. Here, we report an easy, efficient and reproducible protocol for Arabidopsis protoplast isolation and transfection to study the infection and replication of a potyvirus, Plum pox virus (PPV). Macerozyme and cellulose were used to release protoplasts from Arabidopsis leaf tissues, and polyethylene glycol-mediated DNA uptake was employed for transfection of a PPV infectious clone. Protoplast viability was monitored by fluorescein diacetate staining, and transfection efficiency was estimated by transient expression of the green fluorescent protein. The protocol allowed production of 95% viable mesophyll protoplasts and a successful transfection rate of 35%. The system was used further in a time-course experiment to investigate PPV viral RNA accumulation. It was found that 3 h post-transfection (hpt) in the transfected protoplasts viral RNA increased by about 150-fold and progressively accumulated to reach the maximum at 12 hpt. Viral RNA then decreased dramatically at 24 hpt reaching 40% of its peak level. Considering the availability of the whole genome microarrays, and other genomic resources of Arabidopsis, the synchronized single-cell (protoplast) infection system will be useful for elucidating early molecular events associated with PPV infection.

Distribution of Plum pox virus in Residential Sites, Commercial Nurseries, and Native Plant Species in the Niagara Region, Ontario, Canada

Extensive surveys of native weed populations in peach orchards heavily infected with Plum pox virus strain D (PPV-D) in the Niagara Region quarantine area, Ontario, Canada, failed to identify natural infection in any of the species examined. Surveys of rural and urban residential properties within areas of high PPV incidence did not detect widespread infection of susceptible hosts, with infected Prunus glandulosa (dwarf flowering almond) being found only at one site. The prominent color-breaking observed in blossoms of PPV-infected P. glandulosa would make this an excellent sentinel species for early detection of virus in Prunus orchards. Surveys of susceptible ornamental Prunus spp. in Niagara nurseries failed to demonstrate PPV infection in any of the nursery field plantings.

First Report of Onion Yellow Dwarf Virus in Ontario

Onion yellow dwarf virus (OYDV) (1) was identified in a commercial planting of garlic (Allium sativum L.) near Delhi, Ontario, in 1998. Infected plants exhibited mild mosaic symptoms that became less noticeable by mid-July. Many plants were co-infected with garlic latent virus (GLV) (4), which was mechanically transmitted to leek (A. porrum L.). Since leek is not susceptible to OYDV (3), it is an appropriate host for the differentiation of GLV and OYDV. OYDV was transmitted nonpersistently by Myzus persicae (Schultz) from garlic to garlic and onion (A. cepa L.). Infected onion exhibited yellow striping, leaf curling, and pronounced stunting. Necrotic lesions were not present on inoculated leaves of Chenopodium amaranticolor Coste & Reyn. and C. quinoa Willd., which are often associated with co-infection with leek yellow dwarf virus (2). The isolate reacted strongly in enzyme-linked immunosorbent assay with OYDV antisera (from M. Fukami, Chiba Prefectural Agric. Exp. Stn., Chiba 266, Japan; D. Z. Maat, DLO Research Instit., Plant Prot., Wageningen, The Netherlands). Electron microscopic observations of negatively stained preparations of infected leaf tissues revealed virus particles averaging 765 ± 45 nm with typical pinwheel inclusions. References: (1) L. Bos. CMI/AAB Descrip. Plant Viruses no. 158, 1976. (2) K. Graichen. Nachrichtenbl. Pflanzenschutz DDR 32: 245, 1978. (3) K. Graichen and H. U. Leistner. Arch. Phytopathol. Pflanzenschutz 23:165, 1987. (4) L. W. Stobbs et al. Plant Dis. 80:343, 1996.

Occurrence of Turnip Yellow Mosaic Virus on Oriental Cruciferous Vegetables in Southern Ontario, Canada

Turnip yellow mosaic virus (TYMV) has been reported throughout Europe, New Zealand, and Australia. In 1994, this virus was identified in two field plantings of Bok Choi and one planting of Pak Choi (Brassica campestris Chinensis group var. communis) in Durham and Haldimand-Norfolk counties, respectively. In early October, approximately 25% of the plants were infected at each site. Both the striped flea beetle (Phyllotreta striolata (F.)) and the crucifer flea beetle (P. Cruciferae(Goeze)), reported vectors of the virus (1), were present at each site. Infected plants exhibited bright yellow to yellow-green mosaic mottling and often showed chlorotic lesions on the lower leaves. Vein clearing was also seen on several plants. Plants were often coinfected with turnip mosaic virus. Four symptomatic plants were taken from each field site for testing. Spherical virus particles (28 nm) were identified as TYMV by electron microscopy following post-antibody decoration and enzyme-linked immunosorbent assay with the TYMV Agdia test kit. Symptoms were reproduced on both Bok and Pak Choi by mechanical inoculation into healthy plants. Extended host range susceptibility tests with 14 differential hosts were consistent with those reported in the VIDE database (1). This virus, in the presence of the flea beetle vectors, may pose a threat to susceptible traditional cruciferous vegetables grown extensively in this area. Reference: (1) A. A Brunt et al., eds. Plant Viruses Online: Descriptions and Lists from the VIDE Database. Version: 16th January 1997.

Construction of a simple, inexpensive multiple enzyme-linked immunosorbent assay microdilution plate washer

In this paper, plans are given for the construction of an inexpensive enzyme-linked immunosorbent assay plate washer from readily available materials. The wash unit uses an intermittent wash cycle based on a wash manifold cycling over the microdilution plates for a predetermined time. Laboratory tests showed that the unit provided reliable, rapid washing of plates with tap water, with no detectable contamination between wells. Substrate absorbance values for test samples from machine-washed plates were equal to or greater than absorbance values for corresponding samples from plates washed manually by an accepted protocol, by using either enzyme-linked immunosorbent assay wash buffer or tap water.