BUMPER harvests of sweet potatoes are in store for some of the world鈥檚
poorest farmers, thanks to an easy screening technique which ensures plants are
free of harmful viruses. Developed by the International Potato Center (CIP) in
Lima, Peru, the method has already helped Chinese farmers boost yields of the
crop by up to 40 per cent.
Sweet potatoes are a staple crop for many farmers in developing countries.
The red, parsnip-sized potatoes are used to make noodles, feed livestock and
provide starch for industrial applications.
But harvests can be decimated by harmful viruses, such as the sweet potato
feathery mottle virus, which disrupts photosynthesis in the plants. 鈥淵ou end up
with shrivelled leaves and plants,鈥� says Tom Walker, an economist at CIP who
played a key role in the development of the new procedure.
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The researchers tested the screening procedure in China, where 85 per cent of
the world鈥檚 sweet potatoes are grown. Farmers in the Shandong and Anhui
provinces, where the method was pioneered, last year produced 30 million tonnes
of virus-free potatoes on 800,000 hectares of farmland. 鈥淭he difference in yield
was 30 to 40 per cent,鈥� says Walker.
Sweet potato plants are grown from cuttings rather than seeds. CIP鈥檚
screening process starts with lab cultures of meristems鈥攕hoot tips
cultured in a standard cocktail of nutrients. To establish which are free of
viruses, the researchers expose each in turn to mixtures of antibodies extracted
from rabbits that have been inoculated with the plant viruses. Any shoots that
trigger an antibody response are rejected, and the rest are grown into mature
plants. Walker says the technique is extremely simple, and could be done in any
small laboratory. In China, much of the practical work was done at the Shandong
Academy of Agricultural Sciences in Jinan.
He says that within two years, a single virus-free plant can produce enough
cuttings to plant 25,000 hectares of farmland. But he warns that the selected
strains begin to succumb to viruses again after three or four years, so the
whole screening process has to be repeated.