Breeding for resistance to Fusarium head blight (FHB) is challenging because of the polygenic nature of resistance and interactions with environmental and host factors such as plant height and flowering time. While most research into Fusarium head blight (FHB) is understandably focussed on increasing resistance through introducing beneficial genes it is becoming clear that removing deleterious ones may provide an alternative approach.

Investigations of wheat, barley and Brachypodium distachyon have shown how various phytohormones affect susceptibility and resistance to FHB. The relationships between particular pathways and susceptibility are not always clear-cut, possibly because of the hemi-biotrophic nature of the interaction between Fusarium graminearum and wheat. It appears that F. graminearum may be exploiting certain pathways to prevent the plant from mounting an effective defence. This view is supported by the finding that isolates of F. graminearum are capable of producing some of the core phytohomones and these may be used to persuade the plant to maintain growth at the cost of defence.

The negative association between plant height and FHB has long been recognised. Curiously, despite having similar effects on plant height, the semi-dwarfing gene/allele Rht-D1b has a more serious impact than Rht-B1b in winter wheat varieties. Our findings suggest that this is not a pleiotropic effect but is due to the introduction of a gene close to Rht-D1 from the spring wheat donor.

While the majority of wheat varieties lack the ability to prevent the spread of the fungus once it enters the spike, barley varieties have high levels of this so-called Type 2 resistance. We examined wheat barley chromosome addition/substitution lines to determine whether barley chromosomes could provide Type 2 resistance to wheat. Surprisingly, the most potent effect derived from the substitution of chromosome 4D with 4H suggesting that the susceptibility of wheat is due, in large part, to the presence of a susceptibility factor(s) on 4D rather than the absence of resistance factor(s). Work to identify the causal gene will be described.

While resistance to FHB and DON mycotoxin accumulation in agronomically adapted varieties can undoubtedly be enhanced by the introduction of resistance from various sources it is also possible that resistance can be increased through the elimination of susceptibility factors. The challenge in both cases is to provide robust FHB resistance without compromising other important agronomic characteristics required by breeders and growers.

 Acknowledgment

This work was funded by the BBSRC [BB/P016855/1], BB/J004588/1] and AHDB [RD-2007-3453].