Agriculture Reference
In-Depth Information
3.8
3.6
3.4
3.2
3.0
2.8
winter wheat,
triticum aestivum,
cultivar Ritmo,
fertilized with a standard
or modified Hoagland solution
2.6
0.0
1
2
3
days after inoculation
Fig. 11.7
Effects of nitrogen supply and inoculations by powdery mildew -
Blumeria graminis
-
on the ratio of blue to green fl uorescence (From Bürling et al.
2011
, altered)
infected by leaf blotch (
Rhynchosporium secalis
), leaf rust (
Puccinia hordei
)
and powdery mildew (
Erysiphe graminis
). However, the effects on the
red edge
infl ection point indices
were much higher for the nitrogen rates than for the
mode of fungicide application. The red edge infl ection point indices thus repre-
sented mixed effects from nitrogen as major contributor and fungi as minor
participants.
Mixed effects
of nitrogen and fungi may also be hidden in fl uorescence signals.
However, the weighting of the contributors nitrogen and fungi for the sensed index
might be reversed (Bürling et al.
2011
). In Fig.
11.7
, the sensing index is the ratio of
the blue to green fl uorescence emission amplitudes (Fig.
11.4
bottom, blue curve).
The results were obtained in a laboratory and refer to wheat leaves from plants that
were artifi cially infected or not by powdery mildew and either fully or only partially
supplied with nitrogen. There is an effect of the nitrogen supply on the fl uorescence
index, yet it is small. The infl uence of the fungal infections on the index is much
more pronounced.
So regarding refl ectance sensing by a red edge infl ection index, the signals rep-
resent predominantly the nitrogen supply, whereas instead with the blue to green
fl uorescence index mainly the fungal infections matter. In the experiments by
Bürling et al. (
2011
) this held not only for powdery mildew (
Blumeria graminis
) but
for leaf rust (
Puccinia triticina
) as well. The discrimination among the infected and
