A major development in potato growing

Press, 10 June 1977, Page 6

A major development in potato growing

By

D. L. Fyfe

Ihe potato section of the Crop Research Division of the Department of Scientific and Industrial Research at Lincoln has devised a method of producing potato seed that gives promise of greatly reducing the cost of growing the crop.

It involves the use of what is known as true genetic seed, which comes from the berries produced by potatoes. There can be some 50 to 300 tiny seeds in these berries. Dr A. S. Bedi, the leader of the potato section at the division, says that to grow a hectare of potatoes instead of 2,5 tonnes of conventional seed only 2.5 to 3.75 kg of seed would be required.

It is expected that the big reduction in seed cost that will result from adoption of this technique will reduce the cost of growing potatoes commercially by as much as 50 per cent. This should be of benefit to consumers as well as growers.

It is also expected to greatly facilitate the export of seed and to be a major advance in promoting the growing of potatoes in underdeveloped countries and in helping to overcome the world food problem.

The technique, too, will speed up the process of developing new varieties of potatoes. Dr Bedi savs that it could cut two or three years off the time taken using existing methods.

As far as he was aware this was the first time that production of potatoes in the field from genetic seed had been attempted anywhere in the world, and this had been done successfully with yields being obtained that were comparable with conventional crops. Dr Bedi said that the application of the new technique to potato growing would depend on how quickly industry took it up and developed it. Normally potatoes were grown from seed potatoes, which is a vegetative form of plant reproduction.

At about the turn of the century it was found that potatoes were degenerating due to virus diseases transmitted chiefly by aphids. To overcome that problem seed certification schemes were introduced and these had been very successful in advanced countries, in which potatoes were a major part of the diet.

But in recent years with efforts being made to increase yields, seed pro-

duction had become extion had been become expensive, so, for example, group one seed of any variety now cost at least twice if not three times as much as non-certified seed.

And in an endeavour to improve the health status of seed still further, path o g e n-tested seed schemes had been launched in Scotland, the Netherlands and Australia. Pathogen-tested seed when initially developed was free of all viral, fungal and bacterial disease, some of which were in a latent form and escaped detection during seed certification. Blackleg and mild forms of mosaic were two such diseases.

The seed that was made available to growers under such schemes, according to Dr Bedi, was more healthy and while it was still debatable whether there was an increase in yield, it certainly cost more than group one seed. The Lincoln team’s development was initially the result of the keen observation of the director of the division Dr H. C. Smith, who noted seedling potatoes growing in ground in his garden in which no potatoes had been grown for four years. Dr Bedi inspected them and found that they had originated from true genetic seed and not from potatoes which had been lying in the ground since the earlier crop.

True genetic seed is ftr.nd In the berry of the plant. Dr Bedi says that it is the result of sexual fusion between the male and female parts in the flower. This seed can result either from selfing, when the pollen of the flower fertilises the female part of the same flower, or as a result of fusion with pollen from other potato plants.

The variety Rua with its abundance of berries is an examph of selfed seed.

However some varieties set flowers but have no berries. Ham Hardy is such a variety but in this case berry production can be achieved by using the abundant pollen produced by varieties like Katahdin or Chippewa to provide the male element with

role. Some varieties set no flowers at all and a variety like Red King Edward also poses a problem in that it sets flowers but they refuse to stay on the plant. To encourage plants to flower various techniques have to be employed. On October 29 five tria's were sown using true genetic seed from some 16 varieties and these were harvested on May 23. The best line of these produced a yield comparable with that obtained from potatoes produced from conventional seed, according to Dr Bedi. A line of 50 plants in a

Ham Hardy in the female metre spacing between rows produced on average 892 grams of tubers, with the best plant giving 3.4 kg. These were from a cross between a domestic potato and a South American wild species. In the light of the encouraging results obtained Dr Bedi said that work was continuing to further simplify the technique and to develop varieties of potatoes that were most suited to this method of propagation. The next step would be to identify better lines of potatoes that would give still better yields. At present Dr Bedi said that New Zealand was not able to export potato seed because of poor shipping, which was also expensive, and also because this country’s geographical position meant that as far as the northern hemisphere was concerned the growing seasons clashed.

But with the new technique and suitable varieties, he said it would be reasonable to consider exporting true genetic seed of potatoes to virtually anywhere in the world at any time. Perhaps those who would stand to benefit most from this development would be those living in the underdeveloped countries, where food production was a problem.

There, he said, there was a lack of facilities for handling conventional seed, such as adequate transport and proper storage and seed certification schemes. For this reason growing potatoes as a food crop had not really developed on a large scale in these countries. But in the future he said he could see a great potential for the export of New Zealand-grown true

genetic seed of potatoes to these countries. No longer would there be major storage or transportation problems. As far as could be seen, Dr Bedi said that there would be big savings in crop production, because the cost of producing seed was one of the biggest single factors in the costs of potato production. In the last two years when prices of potatoes had been as low as they had been 25 years ago, planting costs had risen four to six times and perhaps even more so a reduction in the cost of seed would certainly be a great benefit to the industry and also the housewife. For the industry, Dr

Bedi said that a reduction in production costs was equivalent to an increase in yield.

Dr Bedi said that the true genetic seed, like that of other crops like cereals, brassicas and onions, could be kept for long periods without any appreciable loss of vigour in the plants that were subsequently grown. He had a reference of where true genetic seed was kept for more than 20 years with very little reduction in subsequent germination. There was also no disease present in New Zealand that would be transmitted through genetic seed. Hence it could be saved from crops grown anywhere in New Zealand. There would be no need to wash seed to free it of potato cyst nematode, as it was not transmitted by this means.

An immense advantage, of course, was the smallness of the amount of seed required — about I to 1.5 kg compared with one tonne of conventional seed. One hundred true genetic seeds weighed 6.0534 grams and to grow potatoes with the rows 81 centimetres (32in) apart and 25 centimetres (lOin) apart in the row with about 49,000 plants to the hectare, 2.616 kg of seed would be required per ha or 1.3 kg per acre.

Where true genetic seed was exported overseas

there would also be far less quarantine restrictions than with conventional vegetative seed.

Dr Bedi said that a cone seeder had been used to sow the seed in trials but a commercial machine would be required to do this job. Attempts would be made this winter to develop a prototype machine for field plantings next spring.

A very important part of the technique, he said, was that it would enable new varieties to be developed more quickly — two to three years could be cut off the time now taken.

With the new technique he said it would be possible to grow the seedlings in the field and make se-

lections from these instead of having to grow seedlings in the glasshouse. Where seedlings were grown from the true seed it would be possible to harvest the entire production of tubers which could amount to 30 to 50 from a single plant. It would be possible to bulk up and test out much more quickly. Whereas in the glasshouses, with available manpower, it was not possible to grow more than 20,000 seedlings and sometimes far less than that, with the new technique it was hoped to raise up to 100,000 seedlings. The possibility of selecting dasirable varieties was far greater when there was a much bigger selection of material to choose from.

In the trials in the most recent season the Lincoln workers were looking at the most suitable depth to place the seed, the possible relationship between seed weight and germination and subsequent vigour, and different kinds of mulches and the effect of viruses and diseases on different varieties. The results are now being analysed. And in the future they will be looking at such characteristics as uniformity of shape of the tubers, their size, maturity, and disease resistance and processing quality.