Protecting cereal crops from eyespot fungal disease

Eyespot is a fungal disease of cereals, affecting the stem base and causing large yield losses, making it economically important, especially in areas such as North West Europe and North West USA where mild damp autumns are ideal for its growth. Chemical control using fungicides, as well as being environmentally unsound, is often not cost effective for farmers, so crop varieties with higher levels of resistance are needed to help combat this disease

Dr Paul Nicholson, funded by the Biotechnology and Biological Sciences Research Council, has been working with the Home-Grown Cereals Authority (HGCA) and the plant breeding company RAGT Seeds, through a CASE studentship awarded to Chris Burt, to understand the disease and identify new sources of resistance.

Very little variation in genetic resistance to eyespot exists in commercially-grown wheat varieties. In most instances, any moderate resistance in varieties was thought to derive from a single gene, Pch2, bred in from a French wheat, Cappelle Desprez in the 1950s.

Eyespot is caused by two different, co-existing fungal species, Oculimacula yallundae and Oculimacula acuformis, and recent research from the John Innes Centre is now suggesting that the resistance derived from Pch2 is differentially effective against the two species. Publishing in the journal Plant Pathology, Dr Paul Nicholson and his group have shown that the Pch2 gene is significantly less effective against O. yallundae than against O. acuformis.

"In all probability this resistance is not, as previously supposed, responsible for the partial resistance observed in many varieties," said Dr Nicholson. "We have now characterised a source of genetic resistance that is effective against both eyespot pathogens, and it is this, rather than Pch2, that we believe confers the partial protection observed in moderately eyespot-resistant commercial wheat varieties."

The group looked at a second reported component of the resistance in Cappelle Desprez, but on a different chromosome to the Pch2 gene. Publishing in the journal Theoretical and Applied Genetics they found that this confers significant resistance to both eyespot pathogens, and at both the seedling and adult stage, making it much more effective than Pch2 alone.

"Breeders thought that they were working with Pch2 while, in fact, if they had moderate eyespot resistance it was most probably coming from this other gene in Cappelle Desprez," said Dr Nicholson.

"This suggests that using Pch2 as the sole source of genetic resistance may not provide adequate protection against eyespot where the predominant cause of eyespot is O. yallundae. Currently, in the UK, O. acuformis predominates but there is evidence that a shift in the type of fungicide used may be reducing this prevalence in favour of O. yallundae."

"In the search for genetic resistance against eyespot, it is going to be critical that we test any potential candidates for resistance against both species."

The group have found nearby genetic markers, which can be used by plant breeders to breed this resistance into commercial wheat varieties.

Sarah Holdgate, lead cereal Pathologist for RAGT Seeds, added: "although eyespot is a globally important fungal pathogen, conventional approaches to the identification of resistant lines are time consuming and costly. This research, through dissection of resistance components and identification of linked markers, will clearly facilitate breeding of naturally resistant varieties."