Speaking about the importance of genetic resistance to help slow septoria development in winter wheat at Wednesday’s tillage conference, Steven Kildea of Teagasc indicated that current resistance ratings seem increasingly fragile.
Reminding growers of the collapse in resistance that occurred here on Cellule, he said this was based on a single gene that had become overcome.
Isolates known to have overcome resistance in this variety were tested on a range of other new varieties thought to have good septoria resistance
Subsequent research found that when other Cellule plants were inoculated with isolates taken from the same variety, these proved very aggressive, while Cellule remained largely resistant to isolates taken from another variety.
Follow-up research found a similar problem relating to an older variety, Cougar. Isolates known to have overcome resistance in this variety were tested on a range of other new varieties thought to have good septoria resistance, but they proved highly susceptible to these Cougar isolates. Many of these had Cougar in their parentage, but others did not.
These finding indicate that a variety’s resistance rating could change dramatically if exposed to a different specific isolate that had previously overcome genetic resistance. They also tell us that we need a much better understanding of the basis of genetic resistance in each variety to ensure continued confidence in our resistance ratings.