THE Australian grains industry must remain vigilant in monitoring mutations within plant disease, according to Australian National University senior lecturer in plant pathology Celeste Linde.
Dr Linde, who specialised in plant disease resistance break down, said the industry must tailor its responses to plant disease according to how each disease evolves.
Farming practices play a large role in keeping a lid on crop diseases, which costs the Australian grains industry $60 million annually, and could have an impact of up to $300 million should control practices not be implemented.
Speaking at a plant disease workshop for agronomists in Horsham last week, Dr Linde said some diseases break down resistance far quicker than others.
“Something like stripe rust could break down the plant resistance in two to five years, whereas with cereal cyst nematode (CCN), the resistance could be effective for up to 20 years,” she said.
She told agronomists attending the session that when resistance was overcome, it was not a result of the resistance gene failing, rather it was a change in the disease pathogen.
Generally speaking, Dr Linde said diseases with the ability to move large distances over a relatively short period of time, such as fungal disease, which travel through the air as spores, will mutate far quicker than other crop diseases, such as soil-bound diseases like crown rot and take-all.
Disease life cycle also has a big role in resistance break-down. A disease like CCN only cycles once every year, meaning it will be slower to mutate and overcome plant resistance than a plant that has several cycles in a year.
The issue of timeliness has an impact on the breeding industry. In the case of rusts and the like, the development of a major blocking gene may take more time than the resistance actually lasts before the pathogen mutates, meaning there is a focus on constantly updating partial resistance genes.
Minor disease resistance is generally made up of a number of different, partially effective genes.
From a breeding perspective, Dr Linde said one of the difficult issues was assessing which particular resistance was protecting a crop from disease where there was more than one form of resistance.
“Identifying which kind of resistance is working against which strain of the disease and which one is failing due to a disease mutation can be difficult,” she said.
She said disease levels could be kept low by controlling inoculum build-up.
To do this, farmers can look to management practices such as volunteer control, to cut down on the green bridge which helps rusts establish the following season, or by strategic fungicide applications, which protect crop during the season and prevent the build-up of fungal disease.
Training agronomists to make the timely and correct identification of crop disease was crucial.
“Treating crops on time is the most important thing.”
Dr Linde said more fungal disease had been noted through south-eastern Australia this year due to the cool and wet conditions.
She said there was still the potential for pulses to be impacted by fungal disease due to the late and cool finish to the season.
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