Effects of the Lr34 and Lr46 rust resistance genes on susceptibility to hemibiotrophic and necrotrophic diseases of wheat

Lead Research Organisation: John Innes Centre
Department Name: Contracts Office

Abstract

The rust diseases of wheat are among the greatest challenges facing agriculture in developing countries (DC). In the last decade, races of yellow rust adapted to high temperatures have spread world-wide while Ug99 races of stem rust have spread into Asia. Brown rust continues to be a persistent threat to wheat yields.

Genes for durable disease resistance are especially valuable in plant breeding. Unlike gene-for-gene resistance, durable resistance remains effective for a long time over a large area, even in areas conducive to the disease, helping greatly to provide farmers with food security and economic stability.

Wheat breeders need to understand and control all diseases which are significant in the local environment, not just rusts. Septoria tritici blotch (STB) is the most important foliar disease of wheat in many DC regions while Fusarium head blight (FHB) produces toxic fungal metabolites and is a threat to yield in hot, humid environments.

There is mounting evidence for trade-offs between responses to different diseases and pests. In particular, resistance to biotrophic pathogens may increase susceptibility to necrotrophs. Recent research has shown that certain important genes for rust resistance alter the responses of wheat seedlings to STB, increasing susceptibility to virulent isolates of STB and suppressing resistance to avirulent isolates.

The significance of this effect for control of STB in the field will be determined, because all current data are from seedlings. To understand the full implications for wheat breeding, however, the effects of these genes on other necrotrophic and hemibiotrophic fungi will be studied. Understanding the mechanism by which rust resistance genes affects responses to STB will help pathologists to predict their effects on diverse diseases, while the relationship of STB-susceptibility to resistance to rusts and mildew will be investigated.

Publications

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Description In wheat seedlings, certain genes for partial resistance to biotrophic fungi increased susceptibility to Septoria tritici blotch (STB), caused by Zymoseptoria tritici, in near-isogenic lines. There was variation in the strength of this effect between different recurrent backgrounds. A similar effect was observed in adult plants with artificial inoculation in polytunnels. The role of leaf age in resistance to mildew and susceptibility to STB, controlled by these genes, was tested. It was hypothesised that enhanced senescence can make leaves more resistant to biotrophs but more susceptible to necrotrophs. In young leaves, LB was less susceptible to STB than NILs bearing the resistance genes. The opposite pattern was observed in older leaves. There was higher expression of genes associated with senescence and cell death in plants bearing one of the biotroph-resistance genes, indicating that it may enhance senescence. Metabolites associated with senescing leaves accumulated to a higher level in Z.tritici-infected plants with the biotroph-resistance gene than with the susceptibility allele. In seedlings, the biotroph-resistance genes favoured the non-biotrophic fungi Magnoporthe grisea, the wheat blast pathogen, and Ramularia collo-cygni, the Ramularia leaf spot pathogen of barley. They reduced spot blotch (Cochliobolus sativus) in field trials but no conclusive results were obtained for tan spot (Pyrenophora tritici-repentis) or Fusarium head blight (FHB; Fusarium graminearum).
Exploitation Route These results presented indicate that there may be significant consequences for the use of these biotroph-resistance genes to control rust and mildew in areas where necrotrophic diseases are prevalent, including some which have not previously been economically significant on wheat, and that plant breeding strategies to control multiple diseases simultaneously are required. They also indicate that the potential to breed varieties in which the adverse effects of these genes are mitigated.
Sectors Agriculture, Food and Drink

 
Description The results have been communicated to the International Centre for Maize and Wheat Improvement (CIMMYT), which was a partner in the project. They are incorporating the results into their plans for breeding and selecting for broad-spectrum disease resistance in diverse countries and environments.
First Year Of Impact 2014
Sector Agriculture, Food and Drink
Impact Types Societal,Economic