Abstract :
Leptosphaeria maculans, the causal agent of blackleg of
canola, produces polygalacturonases during infection.
Stem extracts of spring and winter canola cultivars contained
a water-soluble inhibitor of the polygalacturonase
activity of L. maculans. The polygaiacturonase inhibitor
material had different characteristics dependent upon the
cuitivar. Some canola cultivars had a polygalacturonase
inhibitory compound(s) which was heat liable, low molecular
weight and required divalent cations, and other cultivars
had a heat stable, low molecular weight
compound(s). The cuitivar Maluka had a unique polygalacturonase
inhibitory compound(s) that was heat
labile, low molecular weight and did not need divalent
cations. The level of the polygalacturonase inhibitory
activity in the stem extracts was significandy related to
the resistance of the cultivars to L. maculans as measured
by the rate of lesion elongation, but was less related
to the rate of stem girdling. The significant correlation
between levels of polygalacturonase inhibitor activity and
stem resistance in canola cultivars indicates that polygalacturonase
inhibitors may be involved in the resistance
of stems to blackleg. The two quantitative measures of
stem resistance, rate of lesion elongation and rate of
stem girdling, were significantly correlated to cotyledon
resistance and to each other.
