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Biology and genetics of durable resistance to biotrophic pathogens of cereals - AR0712

Description
The powdery mildew and rust fungi are highly successful pathogens that pose a constant threat to UK cereals where infection may drastically reduce grain quality and yield. Amongst the rusts, yellow rust of wheat offers a major threat, having caused major epidemics over recent decades. The fungi are biotrophic, feeding on living plant cells, depriving the plant of nutrients and causing premature leaf senescence. Genetic host resistance offers disease control that is potentially far more desirable than the application of fungicides. Defra recognises the potential contribution of resistance to sustainable crop production and management systems. However, the rapid evolution of pathogen virulence has nullified many single genes for resistance that have been deployed in UK cereal cultivars. Durable resistance is available, but it is generally under complex genetic control, and therefore difficult to exploit. The proposed project is aims towards increasing understanding of the basis of durable resistance to cereal powdery mildews and wheat yellow rust in order to facilitate its exploitation through plant breeding.
While a great deal is known about the basic biology of powdery mildew disease, very little indeed is known about wheat yellow rust. Thus, investigations proposed here will have different emphases for the different systems. For powdery mildew, this proposal builds on current understanding of quantitative, durable resistance where we know that its polygenic control is reflected in a complex of cellular resistance mechanisms acting at different stages during pathogen development to halt or reduce the rate of pathogenesis by the attacking fungal population. We are therefore in a position to explore the heritability of these individual mechanisms and assess the ease with which they may be incorporated into desirable agronomic backgrounds. At the same time, we will investigate the pathogen's ability to adapt to and overcome individual resistance mechanisms present in modern cvs with quantitative, adult plant resistance. This will inform on the stability of quantitative resistance selected empirically by plant breeders. Building on past investigations, we will also use pharmacological intervention to gain understanding of local induced resistance that can have important effects on epidemic development in crops with quantitative resistance. Finally, we will use experimental crosses between Lolium and Festuca grasses to investigate the role of leaf wax components in the earliest stages of powdery mildew spore germination and development.
For wheat yellow rust we have very little understanding of the basic biology of the disease. However, we do have a number of older and more recent cvs collected by Dr Roy Johnson because their field performance indicated that they possess durable resistance. We will examine this collection to select cvs that maintain their resistance when attacked by pathogen populations that have developed complex virulence, and show the type of quantitative, adult plant resistance that is often associated with durability. These selections will provide material for genetic analysis and for future studies of the biological processes that lead either to resistance or susceptibility. Furthermore, we will perform detailed studies of germination and germling development by the yellow rust fungus with a view to understanding the processes that control the means by which germ tubes locate and respond to plant stomata. This will give us understanding of how to manipulate the pathosystem for future studies histological studies aimed at understanding the complete range of pre- and post-infection mechanisms contributing to durable yellow rust resistance.
Objective

01. Create and assess of a range of recombinant inbred lines for oat powdery mildew resistance based on crosses between the cv. Maldwyn that has proven, durable mildew resistance and modern, susceptible cvs. The ultimate aim is to test the heritability of resistance mechanisms that reduce penetration efficiency (via papilla deposition), prevent colony establishment due to low-frequency host cell death, and reduce colony growth rates and sporulation capacity. Initial crosses will be made with the help of Dr JM Leggett (oat cytogeneticist, Non-Forage Crop Team, IGER, currently funded under Defra CE0xxx). To be performed at IGER.
02. Test the durability of powdery mildew resistance mechanisms in modern barley cvs that express high levels of partial field resistance. An extension of work started under CE0154 (milestone 03/05) to identify individual mechanisms contributing to the partial resistance of two selected cvs and test their continued efficacy as fungal isolates are grown on them continuously ('trained') and so provided the opportunity to adapt to the resistances. To be performed at IGER.
03. Investigate the physiologic basis of locally induced resistance (inaccessibility) and susceptibility (accessibility) to cereal powdery mildew. As a means to assess the potential for enhancing levels and extent of induced resistance and to facilitate plant breeding for its use in cv production. This objective to pursued principally at IGER in collaboration with Dr E Prats funded under a Marie Curie Fellowship. It will, however, involve close collaboration with Dr M Lyngkjaer, Risø, Denmark, Dr L. Mur, UWA, Aberystwyth, and Prof H. Kunoh, Mie University, Japan, with some related investigations being performed by these workers.
04. Explore the role of Graminaceous epicuticular leaf wax components in disrupting germling development by the powdery mildew fungus. Towards exploiting the natural resistance of the abaxial surface of Lolium spp in other species of the Gramineae. To be performed at IGER in close collaboration with the Molecular and Applied Genetics Group and exploiting their experimental Lolium-Festuca introgression lines.
05. Characterise a collection of wheat cvs for durable resistance to populations of wheat yellow rust carrying complex virulence. Exploiting the collection made by Dr Roy Johnson and held at JIC, trials will confirm their continued resistance and examine the histological and genetic basis of resistance in selected cvs. To be performed at JIC.
06. Define the effects of pre-inoculation lighting treatments on predisposition of wheat to infection by yellow rust. Test the hypothesis that effects are mediated via host characteristics that affect fungal responses during the pre-appressorial stage of development. Towards identifying a novel form of resistance for exploitation by plant breeding. Mainly to be performed at JIC but with some scanning electron microscopy at IGER.

Project Documents
• Final Report : Biology and genetics of durable resistance to biotrophic pathogens of cereals   (876k)
Time-Scale and Cost
From: 2003

To: 2007

Cost: £914,053
Contractor / Funded Organisations
Institute of Grassland and Environment Research (IGER)
Keywords
Arable Farming              
Cereal Production              
Crop Diseases              
Farming              
Natural Resource Use              
Sustainable Farming and Food              
Sustainable Production              
Fields of Study
Arable Crops