2024 Agenda & Program

GO1: A KASP assay for detection of SDHI resistance in Stemphylium vesicarium

 

J. Scicluna (1), E. McFaul (1), A. Sedaghatkish (1), B. Gossen (2), M.R. McDonald (1)

(1) Department of Plant Agriculture, University of Guelph, Guelph, ON;

(2) Agriculture and Agri-Food Canada, Saskatoon, SK

 

Stemphylium leaf blight caused by Stemphylium vesicarium is an important foliar disease of onion in Ontario. Management relies on repeated fungicide applications; most registered fungicides contain active ingredients in FRAC group 7 (succinate dehydrogenase inhibitors, SDHI). Resistance to the SDHI active ingredients fluxapyroxad and penflufen has increased since 2012 in Ontario. A Kompetitive Allele Specific PCR (KASP) assay was designed to detect the single nucleotide polymorphisms (SNPs) of the G79R, H134R and C135R mutations in the gene encoding subunit C of succinate dehydrogenase, which have been identified in other regions. The assay was tested on 90 isolates of S. vesicarium collected in Ontario from 2012–2024 previously characterized as sensitive / resistant to fluxapyroxad and penflufen in mycelial growth assays. Resistant isolates were sequenced to detect additional mutations. Mutation C135R was identified in 2% of isolates, G79R in 10%, and H134R in 28% of isolates. An additional mutation, H134N, was detected by sequencing in 18% of isolates. Onion plants were treated with fluxapyroxad and then inoculated with isolates carrying SDHI mutations under controlled conditions. Isolates with the H134R mutation reduced fungicide efficacy by 39% compared to wildtype isolates. The H134R mutation appears to be responsible for most of the SDHI resistance in Ontario. KASP assays can be used to evaluate S. vesicarium populations for mutations early in the growing season as part of an integrated pest management program. This would allow growers to avoid SDHI fungicides that would not be effective against SLB.

 

 

GO2: Evidence for latent infections of American ginseng (Panax quinquefolius L.) by Ilyonectria mors-panacis

 

A. Shi, P. Goodwin

School of Environmental Sciences, University of Guelph, Guelph, ON

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Ilyonectria mors-panacis (IMP) is a fungal pathogen responsible for the root rot of American ginseng and contributes to ginseng replant disease. In vitro experiments revealed that root rot lesions can be activated by both physical (stainless steel pins) and chemical (paraquat) wounding. Lesion areas and the percentage of lesions per wound site were significantly larger in 3-year-old ginseng roots compared to 1-year-old roots. Additionally, roots from replant soil exhibited significantly larger lesion areas and a higher percentage of lesions compared to those from non-replant soil. Out of 18 fungal isolates obtained from wounded roots, 11 were selected for inoculation. By 21 days at 25°C, only IMP induced significantly larger lesions compared to non-inoculated wounded or non-wounded roots. This suggests that IMP is the causal agent, and the other fungi isolated from the lesions are secondary invaders. IMP appears to be a latent pathogen of ginseng roots, potentially persisting in roots for multiple years, and latent infections may be more prevalent in ginseng roots grown in soil previously used for ginseng production. The severity of Ilyonectria is normally based on visible symptoms on roots and shoots, but this underestimates its prevalence. Revealing IMP as a latent pathogen of ginseng should help growers adopt proactive management strategies to mitigate triggering latent infections, such as physical damage or herbicide injury.

 

 

GO3: Assessing the non-target impacts of azadirachtin on a larval parasitoid of emerald ash borer using a novel bioassay technique

 

P. Singh (1), C. MacQuarrie (2), S.M. Smith (1) 

(1) Institute of Forestry and Conservation, University of Toronto, Toronto, ON;

(2) Natural Resources Canada Canadian Forest Service, Sault Ste. Marie, ON

 

Management of invasive insect pests relies on integrated pest management (IPM) using ecosystem-based strategies that focus on long-term prevention and damage mitigation. The interaction between systemic insecticides and biological control agents is critical to understanding the efficacy and sustainability of IPM programs. Emerald ash borer (EAB) is a highly invasive insect that has devastated the ash forests across North America. Systemic insecticides are widely used for EAB management in urban areas, while classical biological control with introduced natural enemies is a key strategy for managing EAB populations in natural forests. Unfortunately, when used in tandem with biological control, systemic insecticides may impact biocontrol agents. We examined the non-target effects of azadirachtin on Tetrastichus planipennisi, an introduced larval parasitoid of EAB. A bioassay protocol was developed by exposing T. planipennisi larvae in EAB to insecticide concentrations resulting in 30% and 50% EAB larval mortality (LC30 and LC50, respectively). EAB larvae were reared on green ash sticks, then briefly transferred to an artificial diet amended with azadirachtin before being returned to green ash sticks for parasitoid exposure. We found that insecticide exposure reduced EAB larval parasitism by T. planipennisi and had profound fitness effects on parasitoid sex ratio, emergence, female body size, potential fecundity, and adult longevity. Our study establishes a methodological framework to test non-target effects of insecticide exposure on larval parasitoids of woodboring insects. Unfortunately, it also suggests that long-term integration of biological and chemical control for EAB management may have unintended consequences on the released agents.

 

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GO4: Influence of ginsenosides on the pathogenicity of Ilyonectria

 

A. Colo, M. Bernards

Biology Department, Western University, London, ON

 

American ginseng, Panax quinquefolius L., is an economically valuable crop used in Traditional Chinese Medicine; however, its yield is negatively impacted by ginseng replant disease (GRD). GRD is characterized as a root-rot due to the fungus Ilyonectria mors-panacis, resulting in decreased growth of healthy ginseng roots grown in soil where ginseng was previously grown. GRD is thought to be influenced by ginsenosides, the chemical compounds produced by ginseng that give the roots their value in Traditional Chinese Medicine. Previous literature has discovered that ginsenosides increase the growth of I. mors-panacis. To have an effect on I. mors-panacis growth in a ginseng garden, ginsenosides have to be present in the soil. In this research, it was found that ginsenosides accumulate in ginseng soils over the first three and a half years of cultivation, decrease by time of harvest, and are barely present in soils a year later. Since ginsenosides do not persist in ginseng soils post-harvest, they cannot be a direct cause of GRD. To understand if ginsenosides influence I. mors-panacis and related species, the pathogenicity of Ilyonectria on ginseng was examined when Ilyonectria was exposed to ginsenosides in our lab. A species similar to I. mors-panacis, known as Ilyonectria rufa, became more harmful to ginseng following exposure to ginsenosides. This research suggests that Ilyonectria fungi may become more harmful when exposed to ginsenosides in soils while ginseng is grown, making them more able to infect ginseng the next time it is planted in the same garden.

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GO5: Soil microbiome and soil properties associated with the risk of cavity spot on carrots in high organic matter soils

 

U. Ilyas (1), L. Du Toit (2), M. Kalischuk (1), M.R. McDonald (1)

(1) Department of Plant Agriculture, University of Guelph, Guelph, ON;

(2) Department of Plant Pathology, Washington State University, Mount Vernon, WA, USA.

 

Cavity spot is an economically important disease caused by several species of Pythium and Globisporangium. The disease appears as superficial lesions on carrot roots impacting quality. Diagnostic tools are unavailable to identify fields with high-risk for cavity spot. It is hypothesized that the soil microbiome and soil properties, in addition to soilborne inoculum, influence disease development. Bulk muck soil (organic matter 40–80%) was collected soon after seeding from thirty carrot fields in the Holland Marsh, Ontario, 2020–23. These fields were grouped as low or high-risk based on cavity spot severity assessed in previous years by the local integrated pest management program. Metagenomic analysis showed that microbial communities were different in the soils with high and low-risk of cavity spot. The relative abundance of the following taxa was significantly greater in low-risk soils compared to high-risk soils in both years; fungi in Aspergillaceae, Helotiales, Hypocreales, and Mortierellaceae; bacteria in Burkholderiales, Chitinophagaceae, and Rhizobiales; and the oomycetes Albugo, Saprolegnia, and Phytopythium. The abundance of Globisporangium was greater in high-risk soils. Soil nutrient analysis showed low-risk soils had significantly less organic matter (~59%) and higher pH (~7) and calcium content (~83%) compared to high-risk soils (70% organic matter, pH ~6, and 70% calcium content). Envfit analysis showed that the composition of microbial communities in both low and high-risk soils was influenced by soil properties, with bacterial communities having the greatest influence. This information will help to identify fields with greater risk of cavity spot, enabling growers to avoid high-risk fields.

 

 

GO6: Unicorn Poop and Crown Royal: The effect of cultivar and temperature on the management of cannabis aphid on cannabis cultivated in controlled environments

 

J. Lemay, C. Scott-Dupree

School of Environmental Sciences, University of Guelph, Guelph, ON

 

Cannabis aphid (Phorodon cannabis) (CA) is a major pest of cannabis (Cannabis sativa), particularly when cultivated in controlled environments. The economic damage caused by CA is predominantly by contaminating the harvestable flowers rather than direct crop losses. We compared the concentration of major cannabinoids in harvested cannabis flowers with and without CA and found no differences in any of the cannabinoids across multiple cultivars. However, the novelty of cannabis as a legal crop has resulted in a paucity of information on CA life history and management strategies. Growers rely primarily on biological control to manage insect pests in cannabis. To address knowledge gaps in CA life history, we assessed the development and fecundity of CA at temperatures from 20-28 °C on four different cultivars using leaf disk and rooted cutting assays. The time to reproductive maturity was shortest at 24 °C (7.7 days) and increased by 36.4% at 28°C (10.5 days). Fecundity differed between cultivars as CA produced significantly more offspring on cv. Unicorn Poop. We then photographed different plant tissues from the four cannabis cultivars and quantified the area covered by trichomes, which varied by tissue type and cultivar. In fecundity assays using rooted cuttings, the cultivar with the greatest trichome coverage on its leaves had the lowest fecundity. We also evaluated five different parasitoid species to identify the most effective management option for CA and then tested the effect of cultivar on their performance. This will provide growers with strong recommendations for biological control strategies to manage CA.

 

 

GO7: Effect of tillage on Pratylenchus spp. (root lesion nematode) and soil health conditions in corn soybean production

 

J. Akanwari (1,2), T. Sultana (2)

(1) Agriculture and Agri-Food Canada, Vineland, ON

(2) Department of Biological Sciences, Brock University, St. Catharines, ON

 

Soil management practices, such as tillage, can substantially influence soil processes and quality. Long-term effect of tillage on soil nematode communities have generated interest, as nematodes provide insights into nutrient cycling and decomposition pathways within soil food webs, serving as indicators of soil health. Is this study, high‐throughput amplicon sequencing is used to investigate the effect of different types of tillage systems on agricultural practices; no tillage (NT), minimum tillage (MT) and conventional tillage (CT); and depth of sampling on Pratylenchus genera and soil health conditions in corn soybean rotation integrated with winter cover crops. The findings revealed that tillage significantly influenced plant-parasitic nematodes, with the highest abundance observed in the CT system (66.3% in CT, 20.0% in MT, and 13.7% in NT). For a targeted plant parasitic nematode species, Pratylenchus, the relative abundance was higher (>80%) at 5-20cm than at the 0-5cm depth. Relative abundance of Pratylenchus was also highest on CT system in both depth, compared to MT and NT. This was positively correlated with cation exchange capacity (CEC) and negatively correlated with total organic carbon. Soil health under MT and NT was characterized by high nutrient availability, minimal disturbance, and decomposition pathways dominated by bacterial and fungal pathway. In contrast, CT soils shifted from high-nutrient conditions in 2021 to low-nutrient, with fungal-dominated decomposition pathways. We conclude that tillage is a key soil management practice that can significantly impact plant-parasitic nematodes in the soil and influence overall soil health conditions.

 

 

GO8: Effect of pH and calcium base saturation on clubroot severity, Holland Marsh, 2023-2024.

 

K. Holy (1), B. Gossen (2), M.R. McDonald (1)

(1) Department of Plant Agriculture, University of Guelph, Guelph, ON;

(2) Agriculture and Agri-Food Canada, Saskatoon, SK

 

Plasmodiophora brassicae (Woronin) is the causal agent of clubroot on brassica crops. The disease can be suppressed with calcium-based soil amendments, but calcium amendments also often alter soil pH, which suppresses clubroot. A field trial was conducted using InVigor L233P canola on high organic matter soil (~70%) at the Ontario Crops Research Centre – Bradford in 2023 and 2024. Four soil amendments were assessed for suppression of  P. brassicae in relation to changes in pH and calcium base saturation (CBS). Gypsum (CaSO4) was used to increase soil calcium content and CBS without changing pH, while potassium bicarbonate (KHCO3) was used to increase pH without adding calcium. A combination treatment of gypsum and potassium bicarbonate was evaluated compared to hydrated lime (Ca(OH)₂) and Wollastonite (CaSiO3), which raised both pH and calcium, and a nontreated control. The treatments successfully elevated pH (7.2–7.7); only small fluctuations in CBS occurred (84–86%). All amendments except gypsum reduced plant wilting and clubroot severity relative to the control. The combination of potassium bicarbonate and gypsum produced slightly higher plant biomass compared to all other treatments. There was a strong correlation (r = -0.84) between DSI and soil pH, but a weak correlation (r = 0.27) between CBS and DSI. The most effective treatments were hydrated lime, potassium bicarbonate, and the combination treatment. The results demonstrate that only increasing pH produced a significant reduction of clubroot severity in organic soils.

 

 

GO9: Understanding ginseng replant disease through ginsenoside mobility in ginseng garden soil

 

A. Rabas (1), M. Bernards (1)

Biology Department, Western University, London, ON

 

American ginseng (Panax quinquefolius) is a highly valued perennial herbaceous plant in traditional Chinese medicine. However, ginseng growers face the significant challenge of ginseng replant disease (GRD), characterized by the enduring negative effects of ginseng cropping on subsequent plantings, regardless of intervals, extending beyond normal pathogen carryover. Alongside pathogens, it is speculated that ginsenosides, secondary metabolites produced by ginseng, may contribute to GRD as they possess phytotoxic properties that inhibit ginseng seed germination and influence pathogen growth. Although ginsenosides are known to be released into the surrounding soil, their fate in the soil remains unclear. This study investigates the behaviour of ginsenosides in ginseng garden soil. Five different concentrations of ginsenosides were applied to ginseng garden soil packed into columns and eluted with water. Ginsenosides in the initial flowthrough (i.e. unbound ginsenosides) and subsequent washings were processed using LCMS. After ten weeks, each soil column was segmented, and the distribution of ginsenosides within the soil column established through extraction and LCMS analysis. In general, protopanaxatriols (PPT) were more mobile in the soil than protopanaxadiols (PPD), with most ginsenosides eluting within the first four weeks. PPD bound more to the upper soil layers at lower concentrations, while at higher concentrations, they were distributed throughout the entire column. These findings provide insight into ginsenoside dynamics in soil and allow a better understanding of their potential role in ginseng garden soils and their contribution to GRD.