RESEARCH & EVENTS
From page 40 2 . Detoxification of the fungicide . 3 . Increased expression of the target site so that the fungicide is ineffective .
4 . Exclusion or expulsion of the fungicide from the cell . Some resistant individuals have reduced fitness without the fungicide present so do not readily survive without continuous application of the fungicide .
How to reduce the risk of fungicide resistance
How is fungicide resistance detected ? Resistance is often determined by measuring fungal growth , such as colony diameter , spore germination or germ tube growth rate , in assays on agar media amended with different concentrations of a fungicide to determine the dose that inhibits growth by 50 % ( EC50 ). Large numbers of isolates are tested to account for natural variability and to determine the frequency of resistance in the pathogen population . Sometimes , initial screening is done at a single discriminating dose , followed by further tests if potential resistance is found . Rarer cases may be detected by field baiting sentinel plants with fungicide application , where a small plot of trees treated with up to twice the standard fungicide rate is set up to capture potential resistant isolates . DNA tests are available in some cases that are specific to certain fungi and fungicide activity groups and detect known mutations . DNA tests for fungicide sensitivity are rapid and cost effective compared to agar plate testing . Overseas studies clearly show that fungicide resistance has developed to many products that are currently used in Australia . It is timely that the sensitivity of Australian fungal and bacterial pathogens is determined to enable optimisation of spray strategies and implementation of effective and sustainable disease management practices .
Fungicide resistance testing As part of Hort Innovation funded AL22002 An Integrated Disease Management program for the Australian almond industry - Phase
2 , Agriculture Victoria researchers will undertake testing of three key pathogens causing anthracnose , hull rot and bacterial spot ( Figure 1 ). Isolates collected during project surveys will be used as well as
Figure 2 . Culture plate for assessment of chemical sensitivity in Xanthomonas arboricola pv . pruni .
historical specimens from culture collections . Preliminary experiments have trialled agar plate methods for the pathogens of anthracnose and bacterial spot ( Figure 2 ).
industry . australianalmonds . com . au
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