Agriculture Reference
In-Depth Information
In species of natural vegetation there is some evidence of a trade-off between the evolution
of resistance to herbivory and evolution of tolerance (Meijden
et al.
, 1988; Fineblum &
Rausher, 1995). This may arise because the biosynthesis of defence compounds (resis-
tance) and regrowth following defoliation (tolerance) both represent a demand on a limited
supply of carbon skeletons and energy reserves. It is conceivable, therefore, that a similar
trade-off may occur between resistance to and tolerance of pathogen infection. If genetic
improvement in induced resistance leads to a greater biosynthesis of defence compounds,
it could be at the expense of assimilates used for yield formation in diseased crops.
7.7
Role of modelling
Crop growth models are useful tools for predicting the effects of pests and pathogens
on crop growth and for investigating the interactions between specifi c mechanisms of
damage and the prevailing climatic conditions (Rossing
et al.
, 1992). Such an approach
has been used in a range of pathosystems to determine which component of damage con-
tributes most to the yield response to disease (Rabbinge
et al.
, 1985; Rossing
et al.
, 1992;
Bastiaans & Kropff, 1993). For example, modelling the effects of rice blast on canopy
photosynthesis indicated that the reduction in rate was the result of adverse effects of
lesions on leaf photosynthetic rate and to shading of healthy leaf area by dead leaf tis-
sue (Bastiaans & Kropff, 1993). Other uses of modelling include estimating the effects
on crop growth of infection by two or more pathogens at the same time (Robert
et al.
,
2004). In the same way, modelling can be used to estimate the relative effects of different
k
0.3-0.9
LAI 2-8
Flag size 0.5-1.5
Pmax flag 16-30
beta 0.5-1.5
6.00
5.00
4.00
3.00
2.00
1.00
0.00
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.00
Relative change
Figure 7.4
Output from a sensitivity analysis of the response of above ground growth rate (dry matter
gain) to foliar disease in spring barley just prior to booting. Graph shows predicted effects of changing the
canopy light extinction, the light extinction coeffi cient (
k
), canopy size (LAI, of leaf plus stem), the ratio of
virtual lesion to actual lesion size (
), compensatory changes in size of the fl ag leaf (fl ag size) and light saturated
rate of photosynthesis of the fl ag leaf (Pmax fl ag). Values in the key indicate the range over which the variable
was altered; the default value was the mid-point in the range (relative change = 1.0). When a particular vari-
able was altered, others were held at their default value. Flag leaf size is in units of LAI, and Pmax in units of
μ
β
mol CO
2
m
−2
s
−1
; other variables are dimensionless (Bingham
et al.,
unpublished data).
