Proc. of
Integrated Control of Phytophthora Root Rot using Strain TW of Myrothecium roridum
M.D. Coffey and R. Gees
Department of Plant Pathology,
Abstract. Potential antagonists of Phytophthora cinnamomi were
evaluated from among 36 fungi and 100 bacteria isolated from the rhizosphere of avocado roots growing in a soil suppressive
to Phytophthora where P. cinnamomi had been present for 40 to 50
years. Strain TW of Myrothecium roridum proved to be the most active antagonist in
controlling P. cinnamomi in repeated greenhouse pot tests with highly
susceptible seedlings of Persea indica inoculated
with P. cinnamomi. M. roridum was grown on a
wheat-bran medium and introduced into a peat-perlite
mixture at 2.5% (w/v) 2 weeks before inoculation with P. cinnamomi. In a
UC mixture with P. indica inoculated with
zoospores of P. cinnamomi, M. roridum suppressed
root infection by 50 to 94% compared with uninoculated
controls. In the same experiments there was no significant difference in the
level of control achieved by either M. roridum or
the fungicide potassium phosphonate (2.5 mg/pot). In
three naturally-infested field soils, root infection ranged from 12 to 54% in
the presence of M. roridum compared with 58 to
93% for controls over the same 4-wk period. On a selective medium containing carbendazim a fungicide-resistant mutant of strain TW,
TWm14, was isolated consistently from the root tips of P. indica growing in infested soil 4 weeks after transfer,
demonstrating the apparent rhizosphere competence of
this strain in the three soils. Preliminary work using bran-alginate
formulations of these biocontrol fungi indicate that
they have a good shelf life comparable to some fungicides. In combination with
suitable organic amendments, such formulated biocontrol
agents may possibly permit a significant reduction in fungicide usage. However,
this has yet to be tested in actual field practice in a Californian avocado
grove.