Pests and diseases

Background

Crown rot and barley yellow dwarf virus are major diseases of Australian cereal crops, causing significant losses in the grains industry. The industry faces considerable uncertainty around how elevated carbon dioxide (eCO₂), higher temperatures and extreme climate events will influence pathogen prevalence, insect behaviour and interactions with the crop.

Project outline

Crown rot

Wheat lines were grown at the AGFACE facility under ambient CO₂ (384 mol/mol) and eCO₂ (550 mol/mol) to determine if eCO₂ influenced the severity of the fungal disease crown rot (CR), the resistance to the disease across genotypes, and disease interactions with grain yield and quality.

Barley yellow dwarf virus

A series of experiments were conducted in growth chambers, greenhouses and the AGFACE facility to determine the impact of eCO₂ on the aphid Rhopalosiphum padi (R. padi), which is the main vector of barley yellow dwarf virus (BYDV) in southern Australia.

Results

Crown rot

Crown rot will remain a significant challenge to wheat production and may become more severe under eCO₂ conditions:

• Stem browning and CR severity were increased under eCO₂ but this varied across genotypes
• Frequency of highly aggressive strains of the CR fungal pathogen increased under eCO₂
• Grain yield of infected plants was reduced more under eCO₂ than under current ambient conditions
• The level of the fungal mycotoxin deoxynivalenol in wheat crowns was increased under eCO₂, potentially providing health risks to stock feeding on infected grains
• Partially resistant wheat lines remained resistant under eCO₂ indicating that resistance traits will still be useful in the future when developing new resistant varieties adapted to higher atmospheric CO₂ conditions.

Barley yellow dwarf virus

BYDV and its aphid vector are expected to increase in severity under future climates with increased CO₂ and temperatures:

• Plant leaf nitrogen content decreases under eCO₂, making plants less nutritious for aphids, causing them to compensate by feeding longer
• Under eCO₂ BYDV infected plants do not lose as much nitrogen from leaves as non-infected plants, making these plants more attractive to the aphids, increasing the chances of virus transmission to non-infected plants
• The amount of virus in the plants was greater in eCO₂ than under ambient CO₂, indicating potentially greater transmission efficiency of the virus.

Next steps

Crown rot

Overall, the results suggest that crown rot severity will increase with rising CO₂, reducing yields and potentially increasing the severity of more aggressive strains. Breeding programs for resistant lines will need to continue but current practices appear to be effective under future eCO₂ conditions.

Further research is required to address the following questions:

1. How will the combined effect of warming and eCO₂ impact on CR pathogens and host-plant resistance
2. How will the gradual rise in CO₂ and temperature interact with drought to influence yield and quality of CR-infected crops?
3. How will pathogens behave and evolve in farming systems under warming and eCO₂ over several seasons of monoculture / rotation?

Barley yellow dwarf virus

These results may have important implications for the epidemiology of BYDV under future climates in Australia. Ongoing studies in the AGFACE and in chambers incorporate wheat cultivars with different tolerances to BYDV hosts as well as temperature interactions. Future research should also include other cereal crops and different agronomic practices to better understand the pest and disease interactions.

Related resources

Title	Excerpt
AGFACE fact sheet (2014)	Fact sheet profiling the project Australian Grains Free Air Carbon dioxide Enrichment program.
Piotr Trebicki - AGFACE results: pests and diseases	Presented by Piotr Trebicki, DEPI, at the AGFACE Crop Science Workshop.
Piotr Trebicki - BYDV and climate change: why important? (poster)	Presented by Piotr Trebicki, DEPI, at the AGFACE Crop Science Workshop