Improving crop resistance to fungi
To ensure there is enough food for a rapidly growing world population, crop plants need to produce more from diminishing land area. Yields can be improved by making crops more resistant to pests and pathogens, and less susceptible to climate change-induced environmental stresses. The EU-funded DURABLE RESISTANCE (Understanding factors affecting durability of crop resistance genes) project used canola and a fungal pathogen as a model to understand how disease resistance in a crop can break down. In an evolutionary defence and counter-defence strategy, plants and fungi have co-evolved matching genes that allow fungi to attack and plants to defend against disease. For example, fungi have avirulence (avr) genes that produce proteins called effectors, which allow the fungus to infect a plant. Plants, meanwhile, have evolved resistance (R) genes that recognise the fungus' corresponding avr gene to trigger the plant's defence system. By rapidly changing its avr genes, fungi can escape recognition by the plant's R genes, leading to a breakdown in the plant's resistance. This happened to canola crops in Australia in 2003, when the country experienced widespread resistance breakdown during a fungal epidemic. When studying the genetics of the resistance-breaking fungus, researchers discovered that mutations in its avr genes rendered the pathogen 'invisible' to the plants' defences. To counteract such breakdown, DURABLE RESISTANCE showed that resistance could be improved by adding secondary minor R genes during breeding. These minor genes alone do not confer resistance, but prevent the fungus from evolving a way to break the R gene's resistance. Researchers also found that the environment has an effect on how durable and stable the resistance is. In a warming world, it is concerning that R genes are less effective at high temperatures while fungal effectors can better suppress host defences. Finally, DURABLE RESISTANCE discovered proteins that bind to fungal effectors and may be used in breeding programmes to improve resistance in canola and other crops. The work of this project will help prevent future fungal outbreaks in crop plants.
Keywords
Crop resistance, fungal disease, environmental stresses, resistance genes, canola, avirulence