Southwestern Ontario Regional Meeting, 2015/Réunion régionale du-oust de l’Ontario, 2015

Differentiating viable/non-viable and mature/immature Plasmodiophora brassicae resting spores using propidium monoazide-assisted qPCR. F. AL-DAOUD, B. D. GOSSEN AND M. R. MCDONALD. Department of Plant Agriculture, Crop Science Building, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada; and (B.D.G.) Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada

Soil-borne resting spores (RS) of Plasmodiophora brassicae Woronin, the causal agent of clubroot of canola (Brassica napus L.) and other Brassicas, can remain viable for years. Soil spore load can be quantified using quantitative polymerase chain reaction (qPCR); however, qPCR amplifies DNA from viable and non-viable RS. Propidium monoazide (PMA) has been used in conjunction with qPCR (PMA-PCR) to prevent amplification of DNA from non-viable microorganisms. The objective of this study was to assess the potential of PMA-PCR to differentiate RS based on viability and maturity. Relatively immature and mature RS were isolated from younger and older clubs, respectively, and heat-treated at 80°C to produce a mixture of viable and non-viable spores. The spores were then treated with PMA (40–120 µM) followed by qPCR analysis. PMA-PCR indicated that almost all of the non-heat-treated mature RS were viable whereas only 26% of non-heat-treated immature RS were viable, when compared with qPCR without PMA. After exposing mature and immature RS to the heat treatment, PMA-PCR detected a decrease of up to 98% in viable RS, when compared with qPCR without PMA. Bioassays on susceptible canola plants confirmed the ability of non-heat-treated and mature RS to produce more clubroot than most of the heat-treated and immature RS, respectively. Collectively, these data indicate that PMA-PCR was able to differentiate between viable and non-viable as well as mature and immature RS. Current research is assessing various protocols for use with PMA-PCR on soil samples.

Effectiveness of organic fungicides in reducing the prevalence of Venturia inaequalis in ‘McIntosh’ apples. A. HALDAR, C. JACKSON, A. ZWIEP, F. BETANCOURT, L. KRZYWDZINSKI, M. PARCEY, K. SCHNEIDER AND D. ERRAMPALLI. London Research and Development Centre, Agriculture and Agri-Food Canada, 4902 Victoria Avenue North, Vineland Station, ON L0R 2E0, Canada

Apple scab disease is a common problem in apple growing regions in the world, including Ontario, Canada and also causes economic losses to apple orchards. This disease is caused by the fungal pathogen Venturia inaequalis (Cooke) Wint. whose spores are spread to leaves and the developing fruit through rainfall. The development of fungicide resistance by V. inaequalis and the precise timing of application often make apple scab disease hard to manage leading to reduced apple yields. This study aims to examine the effect of organic fungicides against V. inaequalis in reducing the development of apple scab in ‘McIntosh’ apples in the orchard. During the summers of 2014 and 2015, apples were sprayed with three organic fungicides, a water control and a chemical control (N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide). The three organic fungicides used were Sulphur (Kumulus), a 0.25% Reynoutria sachalinensis (Regalia #1) and 0.25% pre-bloom and 0.75% post-bloom R. sachalinensis (Regalia #2). A disease rating scale was used to take observations of the presence of apple scab on ‘McIntosh’ leaves and fruits. Observations on apple scab disease were made over a period of 3 months in 2014 and in 2015 which showed a gradual increase in disease progression. Two-way ANOVA tests were also performed to determine any statistical differences between and among all five treatments. Results indicated that the Sulphur treatment was the most effective organic fungicide followed by R. sachalinensis in reducing apple scab disease in ‘McIntosh’ apple leaves and fruits.

Identification of boron tolerant canola cultivars and assessment of clubroot [Plasmodiophora brassicae] severity following a drench application of boron. A. MCLEAN, B. D. GOSSEN AND M. R. MCDONALD. Department of Plant Agriculture, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada; and (B.D.G.) Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada

Clubroot substantially reduces seed yield and oil content in infected canola (Brassica napus L., B. rapa L.). Resistant cultivars limit clubroot severity, however few chemical treatment options exist. Previous studies have demonstrated that concentrations of boron above 4 kg ha⁻¹ significantly reduce clubroot but also induce phytotoxicity in canola. Our research sought to identify boron tolerant canola cultivars and assess clubroot severity among tolerant and intolerant cultivars. A total of 150 canola cultivars were seeded and grown in a greenhouse for 3 weeks in May 2015. Seedlings from 88 cultivars were hand transplanted into organic soil infested with Plasmodiophora brassicae Woronin, in Bradford Ontario. Cultivars received a drench application of 8 kg ha⁻¹ boron delivered at a rate of 1500 L ha⁻¹. Phytotoxicity was assessed 5 days after boron application with a visual scale (0–3) based on the extent of leaf cupping and marginal burning. Mean cultivar phytotoxicity was calculated using a phytotoxicity index. Plants were harvested 9 weeks after seeding and clubroot severity assessed using a scale (0–3) based on the total proportion of root galling. Mean cultivar clubroot severity was calculated using a disease severity index. Fresh and dry top weights were recorded in cultivars demonstrating the highest and lowest boron tolerance. Cultivars with highest boron tolerance showed a significant reduction in clubroot severity compared with boron susceptible cultivars in both treated and untreated plots. No significant difference was found between the mean top weights of boron tolerant and susceptible cultivars when compared with their untreated counterparts.

Improved resistance of bentgrasses to Microdochium nivale under climate change. S. STRICKER, T. HSIANG AND A. BERTRAND. School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada; and (A.B.) Soils and Crops Research and Development Centre, Agriculture and Agri-Food Canada, 2560 Hochelaga Boulevard, Quebec City, QC G1V 2J3, Canada

Microdochium nivale (Fries.) Samuels & Hallett causes Microdochium Patch and attacks many Poaceae spp. including wheat and various turfgrasses. If atmospheric CO₂ concentration levels continue to increase they could double before the end of the century, and Canada is projected to experience a temperature increase between 1.5 and 4°C within the next 50 years. A detailed study is needed on the effects of increased CO₂ concentrations on plant pathogens and their interactions with hosts. Management of plant diseases now includes disease resistance activators, which are non-toxic to plants and fungi, but can activate a plant’s natural resistance responses. This project tested the efficacy of a mineral oil-based product, Civitas/Harmonizer™ (C/H), to activate resistance against M. nivale under two CO₂ concentrations. Eight turfgrass cultivars were grown in chambers under 400 and 800 ppm CO₂ at 15°C. After 10 weeks, the grass was treated with 5% Civitas and 0.3% Harmonizer. A week later they were inoculated with M. nivale, and yellowing was rated over 2 weeks. The C/H treatment reduced disease symptoms up to 75%, and higher CO₂ concentration decreased disease severity from 34% to 17% yellowing. This could mean a decline in Microdochium Patch in the field as atmospheric CO₂ concentrations continue to rise. Cultivars varied in their inherent resistance, and there were differential responses to activation, indicating diversity in existing disease resistance genes. This research will be useful to provide recommendations on the selection of turfgrass cultivars for golf courses and on sustainable management practices to face climate change.

Trichothecene mycotoxin levels in winter wheat in Ontario. L. TAMBURIC-ILINCIC. University of Guelph, Ridgetown Campus, 120 Main Street East, Ridgetown, ON N0P 2C0, Canada

Fusarium head blight caused by Fusarium graminearum Schwabe is a serious disease of wheat (Triticum aestivum L.). Deoxynivalenol (DON) is the mycotoxin most commonly detected in contaminated wheat grain in Ontario. The objective of this study was to evaluate the level of trichothecene mycotoxins in winter wheat grain in Ontario from 2009, 2010, 2013 and 2014. The harvested grain was sampled to determine DON, 15-acetyl DON, 3-acetyl DON, nivalenol (NIV), T-2 and HT-2 toxins using a GC‐MS system with a detection limit of 0.06, 0.05, 0.05, 0.12, 0.06 and 0.04 µg g⁻¹, respectively. The average DON level was 0.7 µg g⁻¹, 0.3 µg/g, 3.3 µg g⁻¹ and 0.2 µg g⁻¹ in 2009, 2010, 2013 and 2014, respectively. NIV was not detected in any sample in 2009, 2010 and 2014 while it was detected just in one sample in 2013 at level 0.14 µg g⁻¹. T-2 and HT-2 toxins were detected in one sample in 2009 at level 0.07 µg g⁻¹ and 0.06 µg g⁻¹, respectively, while they were not detected in 2010 and 2014. In 2013, T-2 and HT-2 ranged from 0.08 µg g⁻¹ to 0.14 µg g⁻¹ and from 0.04 µg g⁻¹ to 0.80 µg g⁻¹, respectively. In 2013, DON level was high in general, but lower mean levels of DON were detected in hard red wheat than in soft white wheat (1.5 vs. 4.1 µg g⁻¹, 3.3 vs. 11.8 µg g⁻¹ and 5.2 vs. 19.8 µg g⁻¹ at Ridgetown, Inwood and Centralia, respectively). 15-acetyl DON and 3-acetyl DON were not detected in 2009 and 2010 in Ontario. In 2013, 15‐acetyl DON were detected at all three locations, while 3‐acetyl DON were detected in soft white winter at one or two locations. Several times higher average levels of DON were detected in 2013 compared with previous years, with some winter wheat lines showing a level of tolerance to mycotoxins accumulation. DON level was low in general in 2014, and the highest in cv. ‘Wentworth’ at Ridgetown (1.6 µg g⁻¹). Accumulation of other mycotoxins was below detection limit. We recommend future monitoring of trichothecene mycotoxins in winter wheat in Ontario.