London (July
22nd, 2005) – The consumption of GM foods by hundreds of millions of
people has had no known negative health effects. From an ecological perspective,
present evaluations of GM primarily tend focus on agricultural ramifications
the imagined effects on existing systems which might result from such as gene
drift and the accidental cross-pollination of GM and non-GM crops.
A major factor in some areas remains a fear that non-GM crops could be cross-pollinated
from GM plants. Since such effects could be revealed only by elaborate laboratory
testing, the reason for this fear seems to be not a little irrational. Nevertheless,
it is a real factor at the present time so if a way could be found of guaranteeing
the “purity” of non-GM crops (whatever that might mean), it might
lead to greater acceptance of GM products as a category of food that consumers
have an active choice over whether or not to consume.
Hyperspectral imaging has particular promise for providing data on a crop's
health status, need for irrigation, pest attacks, weed status, soil nutrient
and other previously unquantifiable variables, including gene drift. It might
be used in future to spot the distances between GM and non-GM plantings and
perhaps even the extent of cross-pollination if there were sufficient difference
between the two sorts.
The technique uses a special camera to cut divide a photograph into 120 colour-specific
images, each image with unique characteristics not visible to the human eye.
Various US agencies are attempting to adapt hyperspectral imaging for agricultural
use.
The procedure makes use of the fact that different plants, or plants at different
periods or in different states of health or under attack from pests, might
differ sufficiently in reflectance to be distinguishable spectroscopically.
For example, the spectral reflectance curves of healthy green plants have
a characteristic shape that is dictated by various plant attributes. In the
visible portion of the spectrum, the curve shape is governed by absorption
effects from chlorophyll and other leaf pigments. Chlorophyll absorbs visible
light very effectively but absorbs blue and red wavelengths more strongly
than green, producing a characteristic small reflectance peak within the green
wavelength range. As a consequence, healthy plants appear to us as green in
colour. Reflectance rises sharply across the boundary between red and near
infrared wavelengths to values of around 40 to 50% for most plants.
This high near-infrared reflectance is primarily due to interactions with
the internal cellular structure of leaves. Most of the remaining energy is
transmitted, and can interact with other leaves lower in the canopy. Leaf
structure varies significantly between plant species, and can also change
as a result of plant stress. Thus, species type, plant stress, and canopy
state all can affect near infrared reflectance measurements.
At the end of the growing season leaves lose water and chlorophyll. Near infrared
reflectance decreases and red reflectance increases, creating the familiar
yellow, brown, and red leaf colours of autumn.
The technology could enable the sector to prevent corn pests from developing
resistance. Such resistance might severely limit the continued use of some
new varieties of corn. Thus, the technology could monitor crops and warn producers
of developing pest resistance.
It remains to be seen both what can be distinguished from what, and the resolution
possible from space: whole fields will certainly be possible, and perhaps
a gradient of properties arising from the boundaries of adjacent fields, but
single plants are likely to be too small.
Sources:
1. How to distinguish GM crops from space. Food production Daily
(July 5th, 2005) (http://www.foodproductiondaily.com/news/news-ng.asp?n=61093-how-to-distinguish)
2. Introduction to Hyperspectral Imaging. (http://www.microimages.com/getstart/hyprspec.htm)
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