SELECTION OF SEED POTATOES.

Franklin Times, Volume 9, Issue 606, 11 February 1921, Page 5

SELECTION OF SEED POTATOES.

(By W. H. Taylor, Horticulturist, in the Journal of Agriculture.) The selection and treatment of seed potatoes has been the subject - of a great amount of literature as well as carefully carried-out experimental work. There is fairly general agreement on two points—namely,) that immature sets are likely to produce the heaviest crop, and that whole sets about the size of a hen’s egg are better than cut sets or tubers of smaller size.

It is not, however, to be concluded that nothing more is necessary than to plant sets of the size mentioned, taken from an immature crop. A process of selection is necessary, or specially grown seed tubers, else it might well happen—probably would in fact—that such sets would produce a crop inferior to that obtained from sets cut from large tubers. It is well known that potato -varieties deteriorate after -being grown a certain number of years. The length of time they retain original characteristics varies in different varieties, and is greatly affected by the manner of selection for seed purposes. In a field of potatoes there are always found variations in the produce of the different hills. Some will give a good number of small tubers and a very small proportion of large Others yield a small number of tubers, tubers predominating. Both these types are bad, and a sure sign of weakening. Sets taken from such hills might be expected to reproduce themselves in a similar character. < The produce would not be quite the same, but almost surely it would be inferior in character. The life of a variety begins with the first stock of tubers raised from seed. Then commences the increase of the stock from tubers. During this process it is presumed that some selection is carried out, though it. may not be much.- The process is continued until there is a large stock ready for distribution. The value of this stock will depend on the constitution of the variety—that is, how it behaves under the stress of large production. The whole of this large stock had its origin in one seed, and the enormous reproduction from tubers only must have a weakening effect. A strong constitution, combined with care in selection, will maintain vigour in a variety for a long time; but without this care, no matter what the natural strength of a variety may be, it is bound to run out in a comparatively short time, or at least the produce of the field will be varied with some good hills and some bad ones.

The method of saving seed tubers that is most common among fanners and others is to retain for planting tubers that are too small for sale or use as table potatoes, these being taken from the bulk. It follows that hills that produce a preponderance of small tubers are the ones that supply most seed tubers. Hills that produced a small number of tubers of any kind will also be represented. On the other hand, the hills that produced the best crops of good tubers will supply a very small number of sets. It is reasonable to suppose that if large tubers were kept for planting, these being cut to suitable sets, better crops would result, and in most cases it would be so. This, however, depends on several things, the most important perhaps being that a proportion of the large tubers would come from hills of poor production. It is evident that deterioration is hastened by haphazard methods, and there can be no assurance of good crops being obtained in that way.

There are several methods of conserving the desirable characteristics of a variety and enabling the cultivator to reproduce them in his crops. One plan is to use for seed purposes large sets specially selected from good hills, or more roughly, from crops that average good. There are several objections to this method, which need not be considered now. Another plan is to plant large uncut tubers specially to produce seed tubers. The sets being uncut, the expectation is to obtain from them a large number of seed-size tubers. The planting is done late, about Christinas time. This secures tubers that are not over matured, that are lifted late and consequently easily kept till planting time, and that are the direct offspring of high-grade tubers. Quite obviously this is a more economical method than planting cut sets. A third method, and the best, is to go through the growing crop and dig the most promising hills, selecting tubers of the right size, and carefully storing them till planting time. This shoud be done before tfm crop is fully matured, but not until the skin of the tubers is fairly firm. If the skin can be easily rubbed off it is too early to dig them. A disputed point is that regarding the advisability of greening the tubers bv exposing them to the sun. Like most things, the greening process can easily he overdone, but if judiciously carried out it has good

points. It the tubers are lifted at the proper stage the skin will be somewhat tender, and in that state the tubers are easily bruised. A short exposure, just long enough to green the skin, wilt render it tougher and there will then be no danger of rubbing it off or bruising. If, however, the tubers are exposed too long they will be in danger o,f burning, and corky patches may be formed, which would be injurious. Again, in some places where sun-heat is great and the soil is hot they could not be exposed long without suffering injury. It is a matter for the exercise of common sense. Where there is available a cool, airy building of some kind, in which the tubers can ' be placed in a thin layer, exposure to the sun is not necessary.