Climate change affects plant disease risk

Climate change could change the nature and severity of plant pests and diseases affecting agriculture, according to a senior CSIRO scientist.

Speaking at a symposium on cereal rust diseases organised by the NSW Centre for Animal and Plant Biosecurity, Dr Sukumar Chakraborty said realistic pest risk analyses for agriculture must take into account the impact of elevated atmospheric CO2 levels.

Dr Chakraborty said it had been assumed that higher CO2 could be good for plants, by having a ‘fertiliser effect’ which enlarged canopies by 30% and resulted in increased yields.

“However, none of this research has considered pests or pathogens”, he said.

Rust diseases, which are caused by fungi, are regarded as a serious threat to world food supplies.

Dr Chakraborty has reviewed research on 27 different plant diseases and found that the severity of the majority of diseases is higher with elevated CO2 levels; however, many of the changes are specific to the host plant and pathogen.

“At this stage we cannot generalise”, he said.

“We know that changing temperature can also tip the balance between pathogen species and that climate change can activate ‘sleeper’ pathogens, whilst others may cease to be of economic importance.”

Dr Chakraborty said that higher CO2 can increase the fertility of fungi, which may produce more spores, and that once they penetrate plant tissue they grow much faster.

“The number of spores can be up to 15 to 20 fold higher, leading to a massive increase in the pathogen.

“You may get new strains developing, with adaptation occurring faster. Evolution may be accelerated”, he said.

Of the 27 diseases examined under elevated CO2 levels, 13 caused higher crop losses than expected. Ten of the diseases had a reduced impact, and four had the same effect as they do now.

Speakers at the symposium pointed out that the impact is likely to vary with different sites and cultivars – and be worse where crops were under stress.

Dr Chakraborty said the physical location of infrastructure like silos and roads would make it difficult for agriculture to move to where the climate was more conducive.

“This means many crops will be grown under chronic stress situations, which is likely to make them more vulnerable to pathogens.”

Dr Chakraborty said risk assessment tools were available, and these needed to be used to ensure climate change was taken into account when assessing the future risks of pests.

The NSW Centre for Plant and Animal Biosecurity is a partnership between the NSW Department of Primary Industries and the University of Sydney.