STOCK-BREEDING.

Press, Volume LXVI, Issue 20038, 20 September 1930, Page 16

STOCK-BREEDING.

INHERITANCE OF PRODUCTIVITY. [By Dr. O.' H. Frankel, geneticist to the Wheat Eesearch Institute, in the Journal of the Canterbury A. and P. Association.] It is the stock-breeder's aim, just as it is the plant-breeder's, to choose for his breeding stock individuals of n high economic productivity, which character he expects to bo passed on to their progenies. Professor Alexander has drawn attention in the Journal to the large range of variation in productivity between animals of the same stud flock, and in consequence stressed the importance of breeding for production itself rather than for external characters usually associated with productivity. Now, the problem arises whether these differences in productivity, tho occurrence of which is undeniable, v.ould be inhorited; whether a sheep yielding l4lb of wool were to produce sheep again yielding 141b, or at least more than the average yield of wool. ■ In an ordinary wheat crop, one can easily pick out plants with a larger number of grains; that is, a. higher productivity than others. If the variety is pure, such differences would not bo passed on to the progeny, being entirely due to different external conditions; for example, differences in the soil. On the other hand, if the variety is impure or the changed characteristics derived from hybridisation, some of the difference in productivity again will be due to external circumstances; others, however, will be truly transmitted on to the progeny, and may serve for tho establishment of new varieties with increased productivity. Now, it is impossible to distinguish by mere eye-inspection a wheat plant which owes its higher'production to external circumstances only from another one truly, possessing a valuable inheritance. Both will show up equally. It is only through testing their individual progenies, side by side, undor equal conditions, that those truly possessing a higher productivity could be picked out from the rest. The progeny test only can reveal the "internal" characters; that means those characters which determine the stability and the economic value of the breed. * Our domestic animals never are, and probably never will be, as pure as are thoroughbred varieties of wheat or barley. This is not by any means duo to a difference between animals on the one side and plants on the other. It would be, for similar biological reasons, almost as difficult to establish an absolutely pure strain of red clover as of sheep, or pigs, or cattle. In consequence, there is certain to be a largo scope for individual selection for productivity, pven among bur purer races of live stock. Now, every animal is the combined product of two parent animals, both or' which contribute an equal share to itc make-up. In consequence, the inheritable characters of the ewe, the cow, the sow, or the hen, are of exactly the same importance for the progeny as are those of the male parent. In sheep-breeding it will appear that tho ewe does not receive an appropriate attention, as compared with the ram. If the best results are to be aimed at, the principle of testing both parents, male and female, by their respective progenies, and selecting only those individual lines which proved, in fairly close in-breeding, of high and stable performance through several generations,, will have to bo established as the fundamental rule of breeding for production. Considerations of space will not allow, on this occasion, to dwell on any details of the suggested schemo. It must suffice to state that scales and other instruments largely will have to take tho place of mere eye-judgment; that the results recorded in the progeny testa can be appreciated only under application of the principles of statistics, which have proved of fundamental '•value in plant-breeding and variety testing; that only the expert, trained in the modern principles of heredity, would be able to apply inbreeding, in its closest form so highly beneficial for the establishment of pure breeds, and to overcome its injurious consequences; and that only the expert could make the best use of th<) results obtained from progeny tests, for the selection of the very best types obtainable from our breeding stock. But even further advance is well feasible. We know, in plants, that by dossing two varieties with equal yields new varieties may be produced outyielding both parents. Furthermore, characteristics derived from different parents may be combined and stabilised in the progeny. In plant breeding hybridisation on scientific lines has been practised for the last thirty years with startling success, as in Sweden, where crossbred varieties have increased the annual output of wheat by 50 per cent., or in Canada, where the wheat belt was extended by hundreds pf miles. In New Zealand we have started, at the Plant Breeding Station ■of the Wheat Research Institute, to combine high yield with high baking and milling qualities, by means of crossing. Similar attempts at combining useful characters, such as meat and milk, or meat and wool, by means of crossing, are numerous in the history of animal breeding, but the stabilisation in every case took a very long time. In many instances, such as the Corriedale, it has not been achieved up to this day. This doubtless is due to the fact that the phenomena appearing after crossing are biologically very complicated. However, the rules which they follow are well known to as now, and their application surely would-not only considerably shorten the period required for stabilisation; it might even allow to aim at objects of breeding which appeiar out of reach for the breeder at present. The application to plant breeding of the laws of inheritance since their discovery, thirty years ago, proved of enormous benefit to the farming communities all the over. Modern agriculture is unthinkable without modern varieties of crop plants, practically all of which were produced on scientific lines. If anyone wore to aim at crop improvement without consideration for these principles, he would be lilce an engineer ignorant of the laws of physics. In animal breeding instinct and sound experience of centuries have achieved marvellous results, so far practically without the application of scientific principles, which have been proved to apply to animals just as well as to plants. Still, there is much scope for further progress if practical experience were to make use of modern scientific' methods.