Scientists at the John Innes Centre in Norwich believe they have discovered why plant breeders have found it difficult to produce wheat varieties which combine high yield and good resistance to septoria.
Professor James Brown and his colleague Dr Lia Arraiano traced the problem back to decisions made nearly sixty years ago after analysing resistance and susceptibility to septoria in wheat varieties grown in the UK between 1860 and 2000. Using a technique called association genetics, they found that the gene with the biggest effect on increasing susceptibility to septoria is very closely linked to one that increases yield and grain size.
Prof Brown says: “As we studied a historical set of varieties covering more than a century of wheat breeding, we discovered where the small region of the genome that increases both septoria and yield came from. We traced it back to a variety called Heines Peko, which was used to breed for yield and rust resistance in the late 1950s.”
Heines Peko was crossed with Cappelle Desprez, the major wheat variety in Britain at the time. This cross was so influential that all modern wheats bred in Britain are descended from it.
Professor Brown suggests that as wheat breeders selected ever more strongly for higher yield, susceptibility to septoria ‘hitch-hiked’ along with it.
“My group is now trying to find out if the connection between the two traits can be broken,” he adds.
While resistance to septoria has improved in recommended varieties over the last ten years, the lack of knowledge about the relationship between yield and susceptibility to the disease has hindered progress, says Prof Brown.
“It’s surprising that a decision made so long ago has had such a long-lasting effect,” he says.
Ed Flatman, head of European wheat breeding at Limagrain says: “Professor Brown and Dr Arraiano’s work has helped us to understand the past history of breeding for resistance to septoria.
“We have now taken James’ results and built on them by identifying novel septoria resistances in current, high yielding elite varieties.”
The research also points to a way of rising to the challenge of combining yield and septoria resistance. The scentists found ten other genes scattered throughout the genome with smaller effects on septoria. They also found that nearly half the variation in septoria was controlled by genes with effects that were too small to identify individually.
“We know the genes are there,” says Prof Brown, “but we don’t know where they are.”
However, he is confident breeders can make durable advances in septoria resistance with this knowledge.
“With the pressures of restrictions on pesticide use added to septoria becoming insensitive to most fungicides, farmers need varieties which combine yield and quality with resistance to septoria and other diseases. Our breakthrough should accelerate progress in developing these new varieties.”
The research was funded by Defra, with support from AHDB, Elsoms Seeds, Limagrain, Sejet, SW Seed and Syngenta, and by the Biotechnology and Biological Sciences Research Council.