Seeds that will grow into healthy plants can be distinguished from those
that will die after a few weeks by X-raying them, according to research
from the Netherlands.
Joost van der Burg of the Centre for Plant Breeding and Reproduction
Research in Wageningen says: ‘Selection by hand on basis of X-ray images
halves the percentage of nonproductive plants.’
Van der Burg and fellow researcher Henk Jaling grew hundreds of tomato
plants after X-raying each seed individually. Each seed received an exposure
equivalent to 0.01 millisieverts – too low to harm them, but enough to distinguish
internal features. An average chest X-ray produces an exposure of 0.05 millisieverts.
By comparing the images, they concluded that the easiest tangible determinant
was the so-called ‘free space’ between the plant embryo and the endosperm.
Seedlings most likely to die came from seeds with the most free space. Van
der Burg has designed a computer program that can analyse the amount of
free space in the digitised X-ray image by generating a false-colour image.
Work is also under way on a program which can also analyse more subtle features,
such as the shape of the embryo.
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The success rate for tomato seeds selected by traditional methods –
which include sieving or floating the seeds in water – is 60 per cent.
This is a significant loss, as 1 kilogram of seed, containing about a quarter
of a million seeds, can cost up to 60 000 Dutch guilders ( £21 000),
and seedlings can absorb several weeks’ water and food before dying.
Van der Burg and Jailing’s research may not be easy to apply just yet,
since automation is a prerequisite for commercial use. That needs a video
camera which works in real time, taking about 30 images per second and
resolving details 20 micrometres across, which is 10 times finer than the
best medical X-ray cameras.
