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Effects of colonizing and non-colonizing mycorrhizal fungi on clubroot of canola.

Al-Daoud, F., Gossen, B.D., Lee, S.H., Zwiazek, J.J., and McDonald, M.R. 2016. Effects of colonizing and non-colonizing mycorrhizal fungi on clubroot of canola. Can. J. Plant Pathol. 38: 542.


Clubroot of canola (Brasscia napus L.), caused by Plasmodiophora brassicae Woronin, is managed through use of resistant cultivars. However, resistance is breaking down at many locations and alternative management strategies are not available. The objective of this study was to examine the effect of inoculation with colonizing and non-colonizing fungi on clubroot severity in the susceptible ACS-N39 line. Four treatments were compared: (1) seed treatment with a canola-colonizing endophyte, Piriformospora indica Verma; (2) seed inoculated with spores of a non-colonizing mycorrhizal fungus, Glomus intraradices Schenk and Smith (AGTIV, Premier Tech); (3) drench application of a formulation of 18 non-colonizing mycorrhizal fungi (Root Rescue Environmental Products Inc.); and (4) a non-treated control. Seedlings from bare seed and seed coated with P. indica were inoculated with resting spores of P. brassicae (0, 105, 106 or 107 spores mL−1). The G. intraradices and Root Rescue treatments were inoculated with only 105 spores mL−1. Five-week-old plants were rated for clubroot severity (0–3 scale) and a disease severity index (DSI) was calculated. There were no differences in severity among the treatments inoculated with 106 or 107 spores mL−1. In treatments inoculated with 105 spores mL−1, severity in plants treated with G. intraradices (81 ± 1%) did not differ from the non-treated controls (82 ± 3%), but severity was reduced slightly but significantly by the P. indica (69 ± 7%) and Root Rescue (66 ± 6%) treatments. This result indicates that both colonizing and non-colonizing fungi may reduce clubroot severity under moderate disease pressure.

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