Transgenic approaches to combat fusarium head blight in wheat and barley

Fusarium head blight (FHB) and contamination with deoxynivalenol (DON) produced by the primary pathogen Fusarium graminearum Schwabe [teleomorph Gibberella zeae (Schwein.)] have caused devastating losses to wheat (Triticum aestivum L.), durum (Triticum turgidum L. ssp. durum Desf.Husr.), and barley (Hordeum vulgare L.) growers across the USA since the early 1990s. Evaluation of barley, wheat, and related germplasm yielded only a few accessions with partial resistance. This resistance appears, in most cases, to be under polygenic control, making the development of resistant cultivars with suitable agronomic and quality traits a challenge. The insertion of individual antifungal and antitoxin genes via genetic transformation has the potential to aid in development of resistant wheat and barley cultivars. Although wheat and barley transformation has been achieved in several laboratories, the development of a high throughput wheat and barley transformation systems has been slowed by genotype effects on plant regeneration, low transformation efficiencies, somaclonal variation, and problems with transgene inheritance and stability of expression. Among the antifungal genes targeted to combat FHB are coding sequences for proteins that degrade fungal cell walls, disorganize fungal membranes, bolster the host defense response systems, and interfere with fungal protein synthesis, pathogenesis, and/or accumulation of DON. Promoter sequences have been selected that confer high levels of expression to the antifungal constructs, particularly in the spike tissues which are susceptible to FHB. As more antifungal genes are inserted into wheat and barley, field and greenhouse evaluation will show whether transgenes achieve their potential in the fight against FHB.