Maturation of resting spores of Plasmodiophora brassicae does not require a living host. F. AL-DAOUD, 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 and Development Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada
Plasmodiophora brassicae Woronin, cause of clubroot on canola (Brassica napus L.) and other brassicas, is an obligate pathogen that survives in soil as long-lived resting spores. Factors affecting maturation of resting spores have not been examined. To determine if a living host is required for spore maturation, the effect of the following four treatments was assessed under controlled conditions on inoculated 1-week-old seedlings of a susceptible canola line: (1) plant shoot removed at 4 weeks post inoculation (wpi) and clubs collected at 8 wpi, (2) clubs removed at 4 wpi, frozen for 3 days, reburied and collected at 8 wpi, (3) plants exposed to drought conditions by withholding water after 4 wpi and harvesting clubs at 8 wpi, and (4) clubs harvested from control plants at 8 wpi. Spore maturity was assessed using propidium monoazide-assisted qPCR, in which amplification of immature spore DNA is inhibited. The majority of spores collected from intact plants at 8 wpi were mature (91 ± 6%), and the proportion of mature spores did not differ among the treatments (shoots removed = 97 ± 3%, frozen clubs = 94 ± 6%, drought-stressed plants = 89 ± 11%). This result demonstrates that maturation of resting spores does not require a living host after 4 wpi.
In search of chemicals for the control of stem and bulb nematode (Ditylenchus dipsaci) in the Canadian garlic (Allium sativum L) industry. L. IVES, M. CELETTI, K. JORDAN AND M. R. MCDONALD. Department of Plant Agriculture, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada; and (M.C.) Ontario Ministry of Agriculture and Food and Ministry of Rural Affairs, University of Guelph, Guelph, ON N1G 2W1, Canada
The stem and bulb nematode, Ditylenchus dipsaci, is one of the most destructive nematodes of garlic worldwide and is a problem in Ontario. This nematode can cause total yield loss and decrease the availability of seed cloves for successive planting. There are no garlic cultivars with resistance to D. dipsaci and no nematicides are registered for use on garlic seed cloves in Canada. Field trials were conducted on two different soils, mineral (5% organic matter) and muck (80% organic matter), to evaluate products and application methods to control the nematode. The treatments were: abamectin, flufensulfone, fluopyram, thyme oil and a seed fumigant, phosphine. The seed cloves were infested with an average of 832 nematodes gram−1. Abamectin, flufensulfone, fluopyram and thyme oil were applied to cloves by soaking for 4 h and as a drench over the cloves at seeding, while phosphine was applied as a seed fumigant prior to seeding. An untreated check and a check of clean seed were also included. The most effective product was fluopyram applied as a drench. Marketable yield for the treated plots were 1003 g and 871 g per plot on muck and mineral soil, respectively, as compared with 55 g and no marketable yield on the untreated infested check, and 400 g and 55 g of the garlic grown from non-infested seed. Fluopyram applied as a soak was also effective in reducing disease incidence and increasing marketable yield. There was no advantage to combining an in-furrow drench and seed soak of fluopyram.
Impact of different intensities of supplemental top lighting using far red light-emitting diodes on the development of powdery mildew of pepper in a greenhouse trial. G. MARCHAND AND X. HAO. Harrow Research and Development Centre (HRDC), Agriculture and Agri-Food Canada (AAFC), 2585 County Road 20, Harrow, ON N0R 1G0, Canada
Powdery mildew [Leveillula taurica (Lév.) G. Arnaud] has been a significant production issue for cultivated peppers (Capsicum annuum L.) grown in the greenhouse (GH) in Canada for almost 20 years. Fungicides are routinely used to control this disease, given that other integrated pest management tools may not provide full control. Concurrently, the use of light-emitting diodes (LEDs) is gaining momentum for GH production. There is a limited body of reports on the impact of various wavelengths on pathogens of GH crops, but it has been shown that far red light can reduce infestations of downy mildew on basil. The objective of this study was to evaluate the impact of different doses of top lighting using far red LEDs on powdery mildew of greenhouse pepper. A trial was performed at the HRDC in the autumn of 2016 and winter of 2017. Overhead lighting was provided by high-pressure sodium (HPS) lights (180 μmol m−2 s−1) supplemented with four different rates (0, 8, 16 and 24 μmol m−2 s−1) of far red (725–750 nm) light provided by LEDs. No statistically significant differences in powdery mildew development as measured by the area under the disease progress curve were observed between the different treatment intensities of supplemental far red top lighting, although a numerical reduction of 20–25% was observed in the top tier of the crop for all three treatments supplemented with far red light compared with the control (HPS alone).
Effect of ginsenosides on the growth of Clonostachys rosea and Fusarium oxysporum. J. L. MARTIN, G. E. M. TANABE, K. I. SCHNEIDER AND D. ERRAMPALLI. London Research and Development Centre, Agriculture and Agri-Food Canada, Vineland Research Farm, 4902 Victoria Avenue North, P.O. Box 6000, Vineland, ON L0R 2E0, Canada
Ginseng replant disease is a complex problem that prevents ginseng from being replanted in previous sites as it results in root diseases such as rusty root and root rot. In order to understand the potential involvement of fungal pathogens, one must take into consideration the contribution of the saponins the ginseng produces, which are called ginsenosides. Ginsenosides have been shown to affect the growth of various foliar and root fungal pathogens. The purpose of this study was to determine the growth in vitro of a biocontrol agent, Clonostachys rosea, and a known ginseng pathogen, Fusarium oxysporum, when exposed to different concentrations of ginsenoside extract. The ginsenoside extract was obtained using methanol extraction from ginseng roots. A standard in vitro disc diffusion assay was conducted using sterilized RO water as the control and concentrations of 10 mg mL−1, 50 mg mL−1, 100 mg mL−1 and 200 mg mL−1 crude ginsenoside root extract to assess the growth of the two fungi. A pathogenicity assay was conducted using both fungi on ginseng roots. Significant inhibition of colony growth was observed in the presence of the ginsenoside extract. The ginsenoside extract at a concentration of 200 mg mL−1, inhibited 40.8% and 15.7% of the colony growth of F. oxysporum and C. rosea respectively. The pathogenicity assay showed that F. oxysporum was pathogenic. This indicates that the antifungal properties of ginsenosides may not affect the capabilities of F. oxysporum to act as an effective pathogen.
Control of stripe rust in Ontario winter wheat in 2017. L. TAMBURIC-ILINCIC AND A. TENUTA. Department of Plant Agriculture, University of Guelph, Ridgetown Campus, 120 Main Street East, Ridgetown, ON N0P 2C0, Canada; and (A.T.) Ontario Ministry of Agriculture and Food and Ministry of Rural Affairs, 120 Main Street East, Ridgetown, ON N0P 2C0, Canada
Stripe rust (Puccinia striiformis f. sp. tritici Erikss.) was the most important disease in Ontario winter wheat in 2016 when high yield losses were reported. The disease was not an issue in Ontario for a couple of decades. Breeding resistant cultivars and fungicides application are considered the most effective ways to control the disease. The objectives of this study were: (1) to evaluate the effect of different fungicides for stripe rust control in cultivars with different levels of resistance, (2) to evaluate the effect of seeding rates. The experiment was conducted at Ridgetown in 2017. The winter wheat cultivars were: ‘Gallus’ (resistant to stripe rust), ‘UGRC Ring’ (moderately resistant), ‘OAC Flight’ (moderately susceptible) and ‘Venture’ (susceptible). The fungicides azoxystrobin plus propiconazole (Quilt), trifloxystrobin plus propiconazole (Stratego) and prothioconazole plus tebuconazole (Prosaro) were tested in four replicates in a randomized complete block design, using 400, 500 and 600 seeds m−2. Stripe rust severity (scale 0–9), yield and test weight were recorded. The highest yield and test weight, and the lowest stripe rust severity, across the cultivars and seeding rates, were recorded after Prosaro applications. ‘UGRC Ring’ had the highest yield, while ‘Gallus’ had the lowest stripe rust severity and the highest test weight, across the fungicides and seeding rates. Seeding rate did not influence stripe rust severity in 2017. The experiment will be repeated in 2018 at two locations. The results from this study will help growers to have the best management strategies for stripe rust including fungicides, seeding rate and resistant cultivars.
Isolation and DNA sequence based characterization of fungi from soils with ginseng replant disease. G. TANABE, J. MARTIN, K. E. SCHNEIDER AND D. ERRAMPALLI. London Research and Development Centre, Agriculture and Agri-Food Canada, Vineland Research Farm, 4902 Victoria Avenue North, P.O. Box 6000, Vineland, ON L0R 2E0, Canada
Canada is one of the world’s largest producers and exporters of North American ginseng (Panax quinquefolius L.), which is a highly valuable herb crop used for its medicinal properties. The conditions required for ginseng growth and the decreased soil diversity caused by continual cropping are conducive to ginseng replant disease, which is thought to be caused by fungal pathogens, such as Fusarium, Pythium and Ilyonectria. In this study, 39 fungal isolates collected from 2015 soil and 80 fungal isolates collected from 2016 soil were characterized through morphological and molecular methods to determine which fungi are present in ginseng replant soil. The dominant fungal species found in 2015 replant soil was Clonostachys rosea with a relative abundance of 20.7%. In 2016 replant soil the dominant species were Fusarium solani (11.1% relative abundance) and Fusarium oxysporum (7.4% relative abundance). The Shannon diversity index was used to measure the fungal diversity of 2015 and 2016 soils and revealed that replant soil had the highest diversity in both years. A pathogenicity test revealed that a C. rosea isolate from 2016 was non-pathogenic and a F. solani isolate from 2016 was weakly aggressive. The species-specific primers ITS-Fu2 and CLOX amplified 14 isolates as F. solani and four isolates as F. oxysporum, respectively, from 2016 ginseng soils. Identifying fungi involved in replant disease and confirming their pathogenicity is important for developing better detection methods for specific fungi in the soil. This may allow ginseng growers to better assess soil health and manage replant disease.