Top of the plant for tip-top seed

When you consider how heavy Irish potatoes are, something is seriously wrong when yields are no more than a miserable 7t/ha. This is less than half the global average and a poor return for the growers in eastern Africa who ought to be getting much better production of this increasingly popular and profitable crop. The problem, as so often with potatoes, is disease.

credit: CIP

Like other vegetatively propagated crops, potato diseases are easily carried forward from generation to generation especially if farmers have no alternative but to use as planting material some of their own crop saved from the previous season. Where 'certified' healthy 'seed' potatoes are scarce or expensive - a situation by no means limited to eastern Africa - farmers can look to the top of the potato plant, rather than the tuber, for safer, healthier planting material. Here they will find true potato seed in the fruits that follow flowering.

True potato seed, like all botanical seed, is generally much less likely to transmit disease. Bacterial wilt, late blight and even the most economically damaging viruses are not transferred within the seed. The only disease so far recognized as being transmitted by true potato seed is spindle tuber virus. The benefits to farmers of starting out with healthy planting material are enormous. Even given that it would be impossible for them to maintain the high standard of management throughout the season necessary for yields of 30 tonnes or more, it should be relatively easy for them to double current yields. The drawback to true potato seed is that it is impossible to achieve the 100% varietal conformity that is achieved by vegetative propagation. This might be a problem if the crop were going for export or processing but for normal market sale there is no disadvantage; the price is as good and yields much higher.

Farmers in the Red River Delta of northern Vietnam, where potatoes are grown mainly in the winter, non-rice growing season, have increased potato yields by nearly 7 t/ha by using true potato seed. The advantages for a country such as India, at 27 million tonnes one of the largest potato markets in the world, are obvious. The 5-10% of tubers saved out of one season's production for next season's planting could be sold and eaten if farmers could use another source of planting material. Recognizing the market potential, an Australian biotechnology company has set up a joint venture with an Indian company based in Delhi to build a 'state of the art' potato seed production facility, with a design capacity of over 18 million seed destined for commercial growers in the region. The company claims ease of handling, transport savings and reduced exposure to field related diseases as some of the benefits. For smaller scale farmers, who are not dependent on producing named varieties for processors, true potato seed offers the same advantages.

At the potato trials being run by CIP at the University of Nairobi's Agricultural Centre, one can look down on to a ground-covering leafy growth of healthy, unblemished, potatoes. These are in strip beds about 1.5 metres wide separated by narrow paths. Kneel down and peer below the canopy and there is a surprise for anyone used to normal potato planting. These true potato seedlings are planted out at 100 plants per square metre. They will produce about 500 small sized tubers per square metre, ready for distribution to farmers for normal planting at 30,000 tubers per acre. As mentioned before, potatoes are heavy. Imagine the saving in transport costs as well as the greatly reduced amount of land needed to produce planting material from true potato seed. And when the alternative is disease-ridden or, at the very least, disease-prone tubers, true potato seed offers a sensible, cheaper and more profitable alternative.

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