Supposed Degeneracy of the Potato.

Waikato Argus, Volume XXV, Issue 3850, 3 August 1908, Page 2

Supposed Degeneracy of the Potato.

Sir W. T. Thistleton Dyer, K.C.M.G., F. R.S., contributed to the ! April number of the Journal of the Board of Agriculture some interesting notes on this subject. He says:— “The undoubted difficulties which now occur in the cultivation of at any rate some kinds of potatoes present a , problem which is obviously of great I practical importance as well as of scientific interest. It is not, however, I satisfactorily disposed of when attributed to degeneracy. The potato plant has not been run out, but too much has been demanded of it, and it has broken down in the attempt to respond. I think a little further light may be thrown on the subject by examining rather more closely what happens in a potato under natural and healthy conditions. I “A potato tuber is an underground I branch which towards the end of the growing season, becomes swollen out laterally and filled with accumulated nutriment for the purpose of giving its buds a vigorous start in the following year. This nutriment is stored up for the most part in the form of starch. Now this is insoluble and is not available to support growth till it has been converted into something—a sugar—which is soluble. This conversion is affected by a ferment or enzyme called diastase. It can be extracted from the potato tuber, and it will do its work quite as effectively outside as inside; it has been found, however, that if an extract be made from an ordinary healthy potato it has, at first, no action on starch; but, after standing for a few days, attacks it energetically. “The explanation is that diastase is not present as such in a potato tuber, but is the result of the decom- ■ position of another substance called 1 a zymogen, a word which merely I

means “ferment producer.” Before the starch in a potato tuber can be made available to support growth two things have to take place; 1. Decomposition ‘of the zymogen to produce diastase; 2. conversion of the starch into sugar by its action. Until they do take place there will be no growth from the tuber. “When, therefore, a tuber fails to grow it is not a sufficient explanation of the failure to say that the plant is degenerate, or that diastase is wanting. Both explanations are conclusively disproved by the interesting experiments of the Curator of Kew in exposing the sluggish tubers to a higher temperature. They then sprouted vigorously and, after planting, produced a normal crop. It is clear that what was really amiss was that the diastase remained locked up in the zymogen and was not available to do its work. It is known that the production of diastase requires the access of oxygen from the air; it also needs some amount of warmth and is probably stimulated by light. “When a sluggish tuber is plan'.el, it either remains completely dormant or sends up a feeble growth which utilises little of the accumulated starch. On the other hand, the shoot manufactures more, and this is transferred to the tuber which actually increases in size. What is now complained of seams to be only an extreme form of a state of things which has long been known to cultivators. In Gloucestershire the remedy recommended is ‘greening’ the tubers. The method is described in Leaflet No. 173 pp. 4, 5, issued by the board. The tubers ‘are placed in the autumn in shallow boxes containing no soil or other material, and stored throughout the winter in tiers in a cool, well ventilated and well lighted shed.’ Under the influence of light the dormant surface of the tuber becomes active and green. This means that chemical action takes place; diastase will be set free, starch will be made available for growth, and sprouting follows. It was found in Yorkshire in 1903 that with Up to Date, ‘an advantage of two tons per acre followed the use of boxed seed. ’ “As far as any general conclusions | can be drawn from the facts as stated it can hardly be said that the potato is in any intelligible sense degenerate, but it appears to have become sluggish in starting into growth, and to require the stimulus of a higher temperature than formerly. It must be remembered that the modern potato is a highly artificial product. It has been induced by continual selection to load itself with starch to a point for in excess of any natural requirements of the plant. It may be that, as already suggested, too much is demanded of it and that the machinery for the processes of growth has reached its breaking point. The tuber desirable for food may not be one which is prompt to start into growth without increased stimulus from heat and light. We can control nature in altering the constitution of a plant; but eventually a barrier is reached beyond which it is impossible to go. The case of the sugar beet is instructive. Beginning with 8 to 10 per cent of its weight of sugar, it has been brought up by selection to 16 to 18 per cent. But H. L. de Vilmorin informed me this was the limit. ‘Beet roots containing more than 18 per cent sugar cease to vegetate properly and die.’ (Kew Bulletin, 1897, p. 317.) If a similar limit has been reached in the potato, growers must be content with sturdier but perhaps from a culinary point of view', less desirable kinds.”