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Plant Viruses Threaten Crops as Climate Warms

An aphid is tethered by a gold wire

An aphid is tethered by a gold wire to a penetration electrode to measure feeding behaviour and virus transmission.

By Piotr Trebicki

Climate change will exacerbate the spread of a virus that reduces the yield of infected wheat by 70%.

Barley yellow dwarf virus is an important pathogen that reduces the yield and grain quality of important food crops such as wheat, barley, oats and corn. We have found that the virus thrives when wheat is grown in the laboratory at higher carbon dioxide (CO2) levels, resulting in greater plant damage. Our findings suggest that as CO2 concentrations rise to levels predicted by climate change modellers, food crop plants such as wheat can be badly affected.

Barley yellow dwarf virus is spread by aphids, which acquire it from the sap of an infected plant. As the aphids feed on other plants, they transmit the virus through their saliva. At least 25 species of aphids can successfully transmit this virus between plants, but the major vector is the bird cherry-oat aphid (Rhopalosiphum padi), which is found across Australia and other parts of the world.

A high concentration of the virus in plants causes earlier and more pronounced symptoms in susceptible varieties. As insects are attracted to infected plants by sensing changes in plant colour and odour, this can increase the probability that the virus will spread.

Wheat plants are most vulnerable to viral infection at the early growth stage. Infection of wheat with barley yellow dwarf virus when the plants are a couple weeks old can result in yield losses of up to 70%. In Australia, this virus affects yields across all cereal-growing regions of south-west and south-east Australia, as well as south-east Queensland. Factors such as weather conditions and virus concentrations in weeds and aphids will alter its impact, but even sporadic outbreaks of barley yellow dwarf virus can increase the incidence of the virus and therefore reduce crop yields.

Although plant viral diseases are a serious threat to food production, only a few studies have investigated how plants and viruses interact under conditions of elevated CO2 concentrations or increased temperatures. Instead, most plant studies have focused on disease-free plants under elevated CO2 scenarios, often without considering temperature increases.

These studies show both positive and negative effects. Positive effects have included increased yield and improved rates of photosynthesis, greater light use efficiency and higher water-use efficiency due to the partial closure of stomata. However, increased CO2 concentrations can also cause serious changes to plant biochemistry, including an increase in carbon:nitrogen ratios due to a reduction in nitrogen in the foliage and an increase in carbon produced by higher photosynthetic rates.

Reduced nitrogen levels in plants and grains are a serious concern, as nitrogen is a crucial building block of amino acids. Hence lower nitrogen levels will reduce the protein concentration in the grain, decreasing the nutritional value, baking quality and other important characteristics of flour.

Under future climate conditions in the semi-arid wheat-growing regions of southern Australia, the net simulated effect of increasing atmospheric CO2 and hotter and drier spring conditions are expected to reduce the average yield by 3–13%.

While many studies have explained the effects of climate change on plant physiology, we still don’t fully understand how future climate will impact plant pathogens. For example, there are knowledge gaps concerning the biology of barley yellow dwarf virus and its aphid vectors, and it’s essential to fill in these gaps if we are to mitigate the negative effects of this disease in wheat crops under future climate conditions.

We have been attempting to redress this by investigating the effects of increased CO2 on plants infected with barley yellow dwarf virus. We grew virus-infected plants in a controlled laboratory setting under current and elevated CO2 levels, and used molecular techniques to determine the amount of virus within the plant tissue.

We found that plants grown under elevated CO2 levels had significantly higher viral loads. The reason behind this 35% increase in virus concentration is not well understood, but cannot be explained by the plants’ stimulated growth rate. Our unique study has been published in Global Change Biology (

As aphids are responsible for spreading the virus to and within a food crop, it’s also important to understand how elevated CO2 levels will affect the insect. Therefore we are conducting further research on the interactions between the insect, wheat and virus under future climate conditions to understand possible mechanisms across different wheat cultivars that can inhibit or eliminate the spread of the disease.

Aphids use their stylet to pierce plant tissue and feed on the plant’s sap. Since this process is fully contained within the plant, we are implementing different methods to understand how aphids feed and how efficient the virus transmission can be in plants grown under future climate conditions.

Since the global human population will continue to rise, there will be even greater pressure on our agriculture and available land to grow crops. It’s extremely important to understand how future climate and an increase in CO2 concentration in the atmosphere will affect our food production and agricultural pests and diseases. We need to know how future climate conditions will affect plant growth and yield, and how we can prevent crop loss if the severity of pests and diseases increases.

Understanding how this climate will affect interactions between pests and diseases will provides scientists with a great opportunity to also find solutions to sustain or even improve current food production levels.

Piotr Trebicki is a Research Scientist for the Victorian Department of Economic Development, Jobs, Transport and Resources in Horsham, Victoria.