Survival of blackleg pathogen inoculum in canola stubble under simulated flooding conditions
Date
2012-03-13
Authors
Peluola, C.
Fernando, W.D.G.
Huvenaars, C.
Kutcher, H.R.
Peng, G.
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Poster Presentation
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Abstract
Blackleg of canola (Brassica napus), caused by two Leptosphaeria spp, is a significant
constraint to canola production worldwide except in china where only the less virulent L.
biglobosa has been reported. In China, the disease is caused by a less pathogenic species,
L. biglobosa, and there is a concern that importing canola from Canada may introduce the
virulent L. maculans, impacting the crop there negatively. In China, canola (or rapeseed)
production is centered in several eastern and central provinces where winter rapeseed is
often followed by paddy rice that normally is flooded for weeks during late spring and
summer. L. maculans or L. biglobosa in diseased canola stubbles serves as the key
inoculum source to cause blackleg, and it has been questioned if the flooding practice
may help suppress the inoculum. A study was initiated to determine the effect of flooding
temperature (12 to 40°C) and duration (2 to 12 weeks) on survival of blackleg pathogen
in canola stubbles. Experiments were set up on a Thermogradient Plate that is capable of
simultaneously creating 96 independent temperature settings. Diseased stubbles with >
scale-3 level of basal stem-canker symptoms used for the experiments were collected
from a Westar canola plot in Melfort after 2011 harvest. Flooded stubbles were sampled
every two weeks, surface sterilized, and incubated on V8-juice medium amended with
antibiotics for 10 days to observe pycnidia cultures of L. maculans or L. biglobosa as the
evidence of pathogen survival. Two trials were set up in RCBD with four replications,
and pathogen incidence data (based on 25 stubble pieces per replicated) were subject to
ANOVA. Significant reduction (P= 0.01) of pathogen incidence was observed at 2-week
flooding treatment relative to control (non-flooded) and there was no pathogen recovery
after 4weeks of flooding till 12 weeks of experiment. Lower flooding temperatures of
12oC and 16oC appeared to be slightly less effective than higher temperatures (20-40 oC)
in reducing pathogen survival. Stubble tissues degraded sharply after 2weeks (contrast,
P= 0.05) in response to the flooding temperature and the dry weight was reduced more
substantially (40%) at higher temperatures. Virulence of any survived pathogen
propagule after flooding is still intact and survival at any temperature or duration of
flooding does not differentiate between L. maculans or L. biglobosa. High proportion of
survived blackleg pathogen (pycnidia) from flooding were L. maculans (67%) and the
rest L. biglobosa (33.0%) under Westar cotyledon test.
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Keywords
winter rapeseed, patty rice, crop rotation, temperature
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Soils and Crops Workshop