Probing Eyespot Resistance & Wheat Quality Clues

Probing eyespot resisitance and wheat quality clues

New part AHDB-funded work to unravel the genetic drivers behind eyespot resistance in wheat should increase plant breeders’ confidence in developing better varieties.

That’s the hope of Paul Nicholson of the John Innes Centre in Norwich who is leading the 42-month £678,303 project*.

Eyespot stem-base disease poses a frequent but often underestimated threat to UK crops being particularly serious in second wheats, says Dr Nicholson.

Even in the absence of lodging it can cut yields by 30%, and despite the use of fungicides it’s estimated to cost growers £12-20m a year.”

 Eyespot is caused by two closely related fungi, Oculimacula yallundae and Oculimacula acuformis, formerly known as the W- and R-types.

 There are only three known sources of genetic resistance in modern wheats, the most effective being the so-called Pch1 gene on a chromosome derived from a wild wheat species, Aegilops ventricosa. This led to the breeding of the first eyespot-resistant variety Rendezvous. The other, less potent, sources came from Capelle Deprez, the UK’s most widely grown variety in the late 1950s and 1960s.

“Varieties with Pch1 are highly resistant to eyespot but unfortunately suffer from ‘linkage-drag’ due to other genes on the same chromosome,” says Dr Nicholson. “So when there’s little or no eyespot pressure they don’t yield as well as varieties susceptible to the disease.

“It’s only relatively recently that Pch1 carrying varieties, such as Skyfall, Grafton and Revelation, have been developed that also possess high yield potential and been placed on the Recommended List.”

However, JIC work has shown that negative yield impact of introducing the whole segment of the wild wheat chromosome which carries Pch1 has been compensated in some of those varieties by factors other than by removing other parts of the segment.

It has also long been known that incorporating that segment boosts grain protein contents by 1-2% which may enhance bread-making potential. But efforts to separate the positive and negative effects of the wild wheat’s insertion were thwarted for two reasons – limited recombination of the genes involved and lack of suitable DNA markers, notes Dr Nicholson.

Recently, however, AHDB-funded work has overcome the recombination problem and identified some useful DNA markers, he says.

“This raises the potential for breeders to select the desirable traits conferred by this segment while removing the deleterious ones from their varieties.”

The latest project aims to sever the links between the positive and negative traits of that segment and develop markers for them all.

“We now have DNA markers that allow us to be convinced that the interval of the chromosome where the Pch1 gene sits is smaller than with our previous efforts.

“Previously we thought that the gene was in a relatively small region that contains around 30 genes, any one of which might actually be Pch1.

“We can now say that the Pch1 is one of 20 or so genes as we have eliminated the others as being possible candidates.

“We’ve also identified a region on the chromosome introduced from Aegilops ventricosa into wheat that increases the protein content of grain, and we’re working to refine its position.”

Recent work with the other two eyespot resistances, Pch2 and QTL5A, from Capelle, has shown that the former is less effective against Oculimacula yallundae than Oculimacula acuformis, but the latter is effective against both species, adds Dr Nicholson.

“We’ve shown that the Pch2 gene is not in exactly the same relative location on the Capelle chromosome as Pch1is on the wild wheat one, so it’s most probably different.

“The materials developed in this project will feed into breeding programmes in the normal fashion and may take six to eight years to become part of varieties on the Recommended List.

“But varieties carrying potent eyespot resistance with no yield penalty shouldn’t require a T1 fungicide and so should improve growers’ profitability. The reduced fungicide need may also have environmental benefits and help growers by increasing the flexibility of their fungicide programmes.”

One recent surprise was an email “out of the blue” from a French colleague, says Dr Nicholson.

“We’ve been extremely fortunate to have developed a great collaboration with a French eyespot expert, Dr Joseph Jahier of INRA.

“He has provided a range of exciting plant materials including lines with very high levels of eyespot resistance and new sources of that resistance. We’re investigating these as far as we are able while focussing on the main project aims.”

Research offers dual benefit:

Eyespot and other stem base diseases are more common than most people believe, says Velcourt Technical Director Keith Norman.

“This project demonstrates that the technology which exists today in terms of unravelling the genetic code of wheat has started to pay dividends.

“Knowing the precise whereabouts of the desirable gene and eliminating some of the ‘baggage’ that goes with the introgression of genes through traditional breeding methods, is a real step forward.”

“The effect on yield is clearly quantified, but one of the main problems is targeting a fungicide on what is a very difficult target. None of the eyespot fungicides have the ability of downward movement in the stem, so penetrating the canopy is a real problem.

“The provision of an improved genetic resistance to eyespot with the additional effect of a small improvement in protein is a win-win for wheat growers.

“The beauty of DEFRA / BBSRC-funded work is that all the results from projects such as this are in the public domain and therefore available for the plant breeders to use.

“I hope we see more of this collaboration between the science and industry in future.”