Interaction of pH and temperature affect infection and symptom development of Plasmodiophora brassicae in canola

Figures & data

Fig. 2. Effect of temperature and pH on the mean proportion of primary plasmodia and sporangia of Plasmodiophora brassicae in root hairs of canola seedlings at 12 days after inoculation (repetition 2 only). Capped lines represent standard error.

Fig. 1. The effect of temperature and pH on root hair infection and subsequent clubroot severity in canola inoculated with Plasmodiophora brassicae under controlled conditions. Only those treatments that were assessed in both repetitions of these studies are presented.

Fig. 3. Effect of pH and temperature on mean incidence (A) and severity (B) of clubroot in canola, and the best-fit regression lines at 20 and 25 °C across two repetitions of the study under controlled conditions. Very little clubroot developed at 15 °C, irrespective of pH.

Table 1.  Correlation between clubroot incidence (%) and severity (based on the disease severity index, DSI) with soil pH in clubroot-infested commercial canola fields in Alberta, 2005–2010

	No. of	Soil pH	Incidence	r	DSI	r
Year	fields	Mean (range)	Mean (range)	P-value	Mean (range)	P-value
2005	25	6.3 (4.8–7.7)	54.9 (1–100)	−0.43	40.3 (1–92)	−0.46
				0.03		0.02
2006	68	6.4 (4.8–7.5)	57.6 (1–100)	−0.33	44.3 (1–100)	−0.34
				0.006		0.005
2007	49	6.6 (4.8–7.8)	46.9 (2–100)	−0.42	32.8 (1–100)	−0.45
				0.003		0.001
2008	14	5.6 (5.0–7.4)	76.7 (10–100)	−0.58	63.4 (4–100)	−0.60
				0.03		0.02
2009	48	6.4 (5.6–7.1)	38.7 (2–100)	0.09	25.9 (2–80)	0.07
				0.56		0.64
2010	63	6.4 (5.1–7.5)	47.8 (2–100)	0.04	31.7 (1–84)	0.02
				0.75		0.87
Total	267	6.4 (4.8–7.8)	50.7 (1–100)	−0.30	36.5 (1–100)	−0.33
				< 0.0001		< 0.0001

Fig. 4. Correlation of soil pH with clubroot incidence (A) and severity (B) in 267 clubroot-infested commercial canola fields in Alberta, 2005–2010.