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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