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| Rural Industries |
Objective
To explore whether potassium phosphonate or a derivative prepared from it could be developed as the basis of control of panama disease in bananas.
Background
Potassium phosphonate is now used widely within Australia
to control diseases caused by members of the genus Phytophthora,
for example P. cinnamoni the cause of avocado root rot
and eucalypt die back. The full spectrum of activity of potassium
phosphonate is not known and there have been scattered reports
which suggested that it could control diseases caused by other
classes of fungi and by bacteria.
These reports included one in which some control of Panama disease in bananas had been obtained following stem injection with phosphonate. Given that there is presently no suitable chemical control for F. oxysporum var Cubense and only limited banana varietal resistance against race 4, it is important to follow any lead that might give rise to cost-effective chemical controls.
Research
The effects of potassium phosphonate on the growth and metabolism of F. oxysporum grown in culture were examined. The methods used allowed its effects on a wide variety of metabolic pathways to be observed.
Outcome
The study showed that potassium phosphonate strongly
inhibited growth of F. oxysporum var Cubense (Race 4),
but only under conditions where phosphate was present in very
low (non-physiological) conditions. Under conditions where growth
of the organism was inhibited by phosphonate, the alternations
in phosphate metabolism characteristic of phosphonate effects
in Phytophthora spp. were not observed.
However, subsequent to the study, new methods have shown that phosphonate does alter the production and distribution of polyphosphates in F. oxysporum var Cubense. This suggests that there is at least one site of action common to the different organisms and increases the probability of developing an effective control based on phosphonate derivatives. Novel phosphonate compounds which are assimilated more rapidly by F. oxysporum var Cubense in the presence of phosphate were synthesised and have been shown to be effective inhibitors in the presence of physiological concentrations of phosphate.
Implications
Research showed that Fusarium oxysporum var
Cubense is sensitive to phosphonate, but that the compound is
not assimilated at the concentrations of phosphate found in plants.
Since there appears to be at least one site of phosphonate action
common to both Fusarium and Phytophthora it will
be possible to synthesise compounds based on phosphonate but which
can be readily assimilated under physiological conditions. However,
a great deal of developmental work will need to be done to determine
whether these compounds can be developed into commercial agrochemicals.
RIRDC Project No: UM-12A
RESEARCHER: Bruce Grant
ORGANISATION: University of Melbourne
PARKVILLE VIC 3052PHONE: 03 344 5938
FAX: 03 347 7730
Last updated: 10 October 1996
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