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    Development of Aster Yellows on Crop and Noncrop Species from the Canadian Prairies
    (The American Phytopathological Society, 2023-04-03) Romero, Berenice; Dumonceaux, Tim; Olivier, Chrystel; Wist, Tyler; Prager, Sean
    Aster yellows phytoplasmas (AYp) are a group of obligate parasites that infect a wide range of plant species, including crops such as canola and cereals and noncrops such as dandelion and wild mustard. In the Canadian Prairies, these microorganisms are mainly transmitted by a migratory species of leafhopper (Macrosteles quadrilineatus Forbes). Although a low incidence of the disease associated with this pathogen has been reported for most years in canola fields, several outbreaks have been documented in this region. A selection of crop and noncrop species commonly found in the Canadian Prairies and Arabidopsis thaliana were used to assess the suitability of these plant species as hosts for AYp (16SrI-B). Symptom expression and phytoplasma levels were examined at different time points following exposure to infective insects.A. thaliana,barley,and canola were susceptible to infection with AYp,yet symptoms differed among these plant species. A. thaliana and canola exhibited symptoms of infection as early as 2 weeks following exposure to infected insects,whereas symptoms in barley were observed at 5 weeks. A lower incidence rate was observed in wheat, and levels of AYp in phytoplasma-infected wheat plants were low.Dandelion and sowthistle tested negative for the presence of AYp at all time points, suggesting that these are unsuitable hosts for these microorganisms. Moreover, we observed a partial disassociation between the plant species that were suitable hosts for AYp and those that had been characterized as more suitable or suitable hosts for aster leafhopper oviposition and nymphal development in previous studies.
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    Do options matter? Settling behavior, stylet sheath counts, and oviposition of Aster leafhoppers (Hemiptera: Cicadellidae) in two-choice bioassays
    (Oxford University Press, 2022-04-22) Romero, Berenice; Olivier, Chrystel; Wist, Tyler; Prager, Sean
    Polyphagous insects are characterized by a broad diet comprising plant species from different taxonomic groups. Within these insects, migratory species are of particular interest, given that they encounter unpredictable environments, with abrupt spatial and temporal changes in plant availability and density. Aster leafhoppers (Hemiptera: Cicadellidae: Macrosteles quadrilineatus Forbes) arrive in the Canadian Prairies in spring and early summer and are the main vector of a prokaryotic plant pathogen known as Aster Yellows Phytoplasma (AYp). Host choice selection behaviour of Aster leafhoppers was evaluated through two-choice bioassays, using domesticated and wild plants species commonly found in the Canadian Prairies. Leaf tissues from these plants were collected and stained to quantify the number of stylet sheaths and eggs. To assess possible effects due to insect infection, two-choice bioassays were repeated using leafhoppers infected with AYp and a subset of plant species. When two domesticated or wild plant species were presented together, similar numbers of uninfected Aster leafhoppers were observed on both plant species in most combinations. In domesticated-wild plant bioassays, uninfected Aster leafhoppers preferred to settle on the domesticated species. There was little to no association between settling preferences and stylet sheath and egg counts. These findings provide a better understanding of AY epidemiology and suggest that after domesticated species germination, leafhoppers could move from nearby wild plants into the preferred cereals to settle on them, influencing the risk of AYp infection in some of these species.
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    Oviposition behavior and development of Aster l eafhoppers ( Cicadellidae) on selected host plants from the Canadian Prairies
    (Entomological Society of America, 2020-09-12) Romero, Berenice; Olivier, Chrystel; Wist, Tyler; Prager, Sean
    Some plant pathogens are capable of manipulating their insect vectors and plant hosts in a way that disease transmission is enhanced. Aster leafhopper (Macrosteles quadrilineatus Forbes) (Hemiptera: Cicadellidae) is the main vector of Aster Yellows Phytoplasma (Candidatus Phytoplasma asteris) in the Canadian Prairies, which causes Aster Yellows (AY) disease in over 300 plant species including cereals and oilseeds. However, little is known about the host range of Aster leafhoppers or their host-choice selection behavior in this geographical region. Several crop and non-crop species commonly found in the Canadian Prairies were evaluated as food and reproductive hosts for Aster leafhoppers through no-choice bioassays. To study possible effects of pathogen infection, AY-uninfected and AY-infected insects were used. Cereals and some non-crops like fleabane were suitable reproductive hosts for Aster leafhoppers, with numbers of offspring observed in treatments using both AY-uninfected and AY-infected insects, suggesting an egg-laying preference on these plant species. Development was similar across the different plant species, except for canola and sowthistle, where growth indexes were lower. Sex-ratios of Aster leafhopper adults did not differ among the plant species or with respect to AY infection. Potential fecundity differed across plant species and was affected by the infection status of the insect. These findings have implications for AY epidemiology and suggest that while cereals can be suitable host plants for Aster leafhopper oviposition and development, some non-crop species could act as alternate hosts for leafhoppers that migrate into the Canadian Prairies before emergence of cereal and canola crops.
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    Characterization of Aphanomyces euteiches pathotypes infecting peas in Western Canada
    (American Phytopathological Society, 2021) Sivachandra Kumar, Nimllash T; Caudillo-Ruiz, Kiela B; Chatterton, Syama; Banniza, Sabine
    Aphanomyces root rot, caused by the soil-borne oomycete Aphanomyces euteiches Drechs., has developed into a serious disease in the pea and lentil-producing areas of the Great Plains of North America. Based on six pea differentials previously used to differentiate 11 pathotypes in France, pathotypes were identified among field isolates from Saskatchewan (14) and Alberta (18). Four isolates from the USA and standard isolates for pathotypes I and III designated in the French study were also included. Each isolate was tested twice in replicated experiments by inoculating French pea differentials Baccara, Capella, MN 313, 902131, 552 and PI 80693, along with the Canadian susceptible pea cultivar CDC Meadow and partially resistant USDA line PI 660736 under controlled conditions. Pea plants grown in vermiculite were inoculated 10 days after seeding by pipetting 5 mL of a suspension containing 1 x 103 zoospores mL-1 to the base of each plant. Root discoloration was scored 10 days post-inoculation using a 0-5 scale. Testing revealed that 38 of the isolates, including standard pathotype I isolate RB84 belonged to pathotype I, 4 isolates including standard pathotype III isolate Ae109 were pathotype III, and USA isolate Ae16-01 was a pathotype II isolate. An alfalfa isolate from Quebec was avirulent on all pea genotypes. These findings indicate that pathotype type I is predominant on the Canadian prairies.