Agriculture Reference
In-Depth Information
Chapter 7
Crop tolerance of foliar
pathogens: possible mechanisms
and potential for exploitation
Ian Bingham
1
and Adrian Newton
2
1
Scottish Agricultural College, Edinburgh, UK
2
Scottish Crop Research Institute, Invergowrie, Dundee, UK
7.1
Host defence against fungal pathogens encompasses three key processes: disease
avoidance (sometimes known as escape), resistance to infection and tolerance of infec-
tion (Lovell
et al.
, 2004; Brown & Handley, 2006). Disease avoidance refers to the ability
of a crop to restrict spore transfer within the canopy, thereby limiting the spread of the
pathogen. Resistance mechanisms, on the other hand, limit the growth of the pathogen
within the host following successful transfer and germination of spores. Tolerance refers
to the ability of the host to maintain growth and yield in spite of pathogen infection and
disease.
In practice it is resistance, and to a lesser extent avoidance, mechanisms that have been
exploited most effectively in the management of crop disease. By contrast, tolerance is
poorly understood and has not been exploited commercially even though it has potential
for reducing the impact of pathogens on yield and the need for fungicides. Recently there
has been a revival in interest in tolerance, stimulated by the recognition that crop produc-
tion must become more sustainable (Brown & Handley, 2006). Unlike most major resis-
tance genes and fungicides, tolerance is a potentially durable form of defence because it
places little or no selection pressure on pathogen populations. In this chapter we consider
briefl y why progress in understanding and improving tolerance of infection in crops has
been slow, before discussing which crop traits might confer greater tolerance and the
prospects for their exploitation in the future. Successful exploitation will require progress
in three areas. Firstly, quantifying intra-specifi c variation in tolerance and its heritabil-
ity, secondly, identifying the underlying mechanisms and traits responsible, and thirdly,
developing suitable methods for selecting the desirable traits in breeding programmes.
We focus on tolerance of foliar pathogens, although similar principles will also apply to
tolerance of stem base and root pathogens.
Introduction
7.2
It has been recognised for many years that genotypes can differ in their yield response
to a given severity of infection and reported examples include some as early as 1894
Concepts and defi nitions - a historical perspective
