The environmental basis of the resistance of wheat (Triticum aestivum L. cv. Brigadier) to Stagonospora nodorum Berk

Abstract

The primary aim of the thesis was to identify mechanisms by which the nutritional status
or environmental conditions of wheat influence horizontal resistance to S. nodorum, and
to answer the question: how do changes to the crop's environment affect the nutrients
available to fungal pathogens? The broader aim of the thesis was to find ways to
maximise the expression of horizontal resistance, or to allow plant breeders to select for
traits that improve horizontal resistance, which may result in a reduction in fungicide
requirements. I postulated the hypothesis that resistance of wheat to Stagonospora
nodorum depends on both nitrogen and carbon supply.
The hypothesis was tested by carrying out experiments under controlled conditions
whereby the carbon and nitrogen supply to wheat seedlings (Triticum aestivum L. cv
B1igadier) was manipulated. C supply was altered by shading, and N supply was altered
by growing plants in hydroponics and adjusting the N fom1 and concentration of the
nutrient solution. The growth and reproduction of the fungus in response to forms of Nin
vitro was also investigated. An attempt was made to identify the physiological reasons for
reduction of disease.
Susceptibility of wheat to S. nodorum was increased by supplying moderate and high
concentrations of N compared to low N. Susceptibility was also increased when N was
supplied as ammonium (NH/) compared to nitrate (Non. Leaf physiology was affected
by N supply, and of particular interest was the increased concentration of total amino
acids, proteins and high amounts of asparagine in plants supplied with NH4 +. Pycnidial
production by S. nodorum in vitro was greatest when N was supplied as asparagine. In
shading experiments, disease was generally reduced when light intensity was lowered
between 2 and 4 days after inoculation (dai).
I concluded that the nutritional status of wheat plants is an important factor in modifying
resistance to S. nodorum, and it is perhaps this, rather than the presence of defence
compounds, that determines the success of the pathogen in planta.

Date of Award	May 2004
Original language	English
Awarding Institution	University of Wales, Bangor
Sponsors	Department for Environment, Food and Rural Affairs (Defra), UK
Supervisor	John Farrar (Supervisor)