HEREDITY FACTOR

Manawatu Standard, Volume LVI, Issue 168, 17 June 1936, Page 6

HEREDITY FACTOR

PLANT BREEDING SCIENCE NO MASS PRODUCTION (By R. A. Calder, Plant Research Bureau.) “Like tends to beget like.” This is the foundation stone upon which the structures of both plant and animal breeding are erected. A grower of prize sweet peas may be a little doubtful as to whether a particular plant will g've rise to another with blooms as good as its own, but he lias at least the satisfaction of knowing that it will not produce Californian thistles. If it could, and if all other living material could act; similarly what a chaos there would be! But no, Nature has certain laws, and one of the most important is that of heredity. Individuals tend very closed to resemble their ancestors.

Tlie “tend” is significant. There fire seldom any perfect resemblances. Tlie behaviour of the reproductive mechanism is distinct from that of a modern motor manufacturing concern. It is opposed to mass production; every unit is a different unit and may be either an improvement or not over Tne previous one. The differences are termed variations and are of many kinds and due to many causes. These two processes) then, heredity and variation, have been responsible for the gradual development both of “cabbages and kinds’’ from llieir prehistoric beginnings to their present day accomplishments. PRIMITIVE DAY PROBLEM. Man began his existence more or less as an individualist but, subsequent to animal domestication, soon came to realise tlie advantages to be gained by forming communities; had he foreseen some of lho modern disadvantages he may have hesitated liefore imposing such a mode of living upon his descendants. These communities roved as tribes, moving their animals from feeding ground to feeding ground and living chietly on fish, flesh, and some of the wild forms of plant life. Ultimately, settlements were formed in some of the more fertile river valleys. Here plant growth was more abundant, being sufficient to supply the needs for both man and his stock. “The story of the ancient empires (Egypt and Lower Mesopotamia) may be 6aid to begin with the discovery of agriculture. Before the early peoples could live in organised communities and established centres of commerce and administration they had to solve the problem of food production. It was necessary that they should be relieved of the necessity of migrating periodically from limiting ground to minting ground and of devoting the greater part of each day to catching fish and following the chase. When, however, they began to cultivate cereals and root crops which could he stored in quantities adequate to their needs between the harvests, fixed settlements became not only possible, but necessary and a beginning was made in building up the fabric of civilisation.” EARLY PLANT MODELS. Judging from the appearance of tlie wild forms existing to-day, these cereals and roots of our ancestors were rather different from similar exhibits seen in an agricultural shows. Yet they formed, as it were, the early models. Variations in shape and size appeared naturally and, gradually, by eoinmonsenso selection and breeding methods, •• improved . introductions appeared. Wallowing in the luxuries of modern civilisation we are inclined, not unnaturally, to claim lor ourselves most of the credit for the excellence of our agricultural crops, hut it has been chiefly due to the efforts of our forefathers that they are what they are. Selection and hybridisation, like marriage, are ancient customs and, though they were adopted in complete ignorance of the underlying principles, yet, perhaps, just as groat advances were made as, nowadays, when the relation between cause and effect is better understood. Down the centuries contributions towards tlie more exact interpretation of reproduction, heredity, and variation were added periodically by advanced thinkers, but it has been within the last 100 years that the greatest strides have been made. Many renowned scientists have assisted in lifting the veil of misunderstanding and many plant breeders, aided by clearer vision, have seized the advantage and have introduced many improved forms, both agricultural and horticultural. The names of these men may lie unfamiliar to most but their achievements made such a “splash” that the ripples, directly or indirectly, affect all. increases in tne output of farm and garden ciops, improvement in quality of flowers, fruits, roots, and seeds, resistance to diseases, and even the production ot entirely new forms have been their bucks and mortar in the edifice of civilisation. THE GAMBLE MINIMISED.

Consequent upon their endeavours, plant breeding lias been raised almost to the level of an exact science; it is no longer cpiite the same gamble as formerly. New. methods and wider knowledge ensure predictable results — sometimes. The new methods, however, are all based on the two systems used by oiir forebears namely, selection and hybridisation. These ape sthl, fundamentally, the two highways along which is made the approach to plant improvement.

“Like tends io baget like.” A good plant will probably produce belter progeny than a poorer plant. This is the principle upon which selection is based. Very few crops are absolutely uniform and, .-veil if they are, they will not remain so foi long; variations inevitably arise. Selection, then, consists in choosing irom a mixed population tho most desirable plants. Some improvement may be attained simply by using these plants for further propagation, but tlie method is unreliable. The value of a selected individual depends not so much upon its own behaviour as upon the type of offspring it can produce. Modern breeding methods depend on progeny tests for the true evaluation of selected material. If the “children” are worthy either they or their “parents” may he used to form the foundation stock for the construction of improved strains. VALUE OF SELECTION. It has been the various adaptations of this method that have led to the differentiation and establishment of the numerous breeds of animals and varieties of plants which are now utilised by farmers. “Selection is responsible for the high producing dairy cow of the present times, for the speed of our race horses, the strength of the draught horse, the high egg laying capacity of our breeds of fowls, the wool production of sheep, etc. .Selection has transformed the common beet with an average sugar content of about 10 per cent, into the sugar beet with an average yield run of 15 per cent, and an average content of over 20 pei cent, in highly selected stocks. it lias lengthened tlie fibre of cotton and increased its strength, and it has operated in many other ways to augment the value of animal and plant forms for practical and ornamental purposes.” HYBRIDISATION METHODS. Despite its usefulness selection has its limitations. It merely chooses the best from what is already present; it cannot create anything new. This can be accomplished onh* by hybridisation, which is able to bring together qualities scattered among different forms, to effect their rearrangement, and to bring about their higher development in original directions. Hybridisation, or the crossing of different types, has been practised since early times, and although some remarkable results were achieved it was not until 1900, when Mendel’s classic investigations were rediscovered, that the actual mechanics of the process began to be understood. Since then additional contributions have further clarified the position and results can now be predicted with mathematical precision. Bv means of hybridisation the particular features of two distinct types can be sorted out and recombined to form further distinct types. Thus: (1) Crosses between pure races give first generation progenies as uniform as the parent types.

(2) Variation is greater in the second generation than in the first. (3) When a sufficient number of individuals are obtained the grand-par-ental type are recovered. (4) Variations which exceed the extremes of either parental race are sometimes obtained because new combinations are brought about, and some of these may cause a greater or less development of certain characters than that produced by either parent. (5) Different lines descended from second generation individuals differ in their variability and the length of tim6 necessary to reduce them to uniformity and constancy, because some combinations, are composed of like elements and, therefore, remain constant, while others are made up of unlike elements and again segregate. These are the chief reactions consequent upon hybridisation, and it is through such liehaviour that many improved forms of plant and animal life have been evolved.

At the Plant Research Station such methods of selection and hybridisation have been adopted by the Field Crop Section in an attempt to secure improved forms of lucerne, rape, peas, oats, turnips, and swedes. The results to date have been quite encouraging, and it is to be hoped that the end products will outlive introduced material. Although commercial importations have been remarkably satisfactory, nevertheless, strains and varieties selected or bred in the environment in which they are to he grown should prove to be of even greater value.