Volume Number: 1  2  3  4  5  6  7  8  9  10  11  12 

 

GETTING THE MOST OUT OF THE SMALL GRAINS

IMPROVEMENTS IN WHEAT, OATS, BARLEY

No one needs to be told of the part that the small grains take in the scheme of the world's agricultural activities. Their place today is what it has been from the earliest historic periods. Indeed the ethnologists who probe into the prehistoric period tell us that the lake dwellers were cultivators of wheat, and it is known that this plant was under cultivation in Egypt and Mesopotamia at the very earliest period of which there is any record. Then as now the little company of grasses represented by wheat, barley, rye, and oats occupied a preeminent position in supplying man and his domesticated animals with suitable foods. In recent years, to be sure, the American product, Indian corn, has gained supremacy over the small grains as food for domesticated animals, and has attained a notable place as a supplier of food for man himself. But important as this new cereal is, it by no means takes the place of the others. Wheat and rye in particular stand unchallenged as the producers of the chief vegetable foods of mankind throughout the civilized world. Oats constitute the most highly prized food for man's chief helper, the horse; and barley is raised in enormous quantities for purposes of fermentation to produce beverages that retain their popularity generation after generation, whatever may be said as to their wholesomeness. The relatively close relationship of these four grasses is obvious to the most casual observer. Wheat, rye, and barley in particular are so similar that only the practiced eye can distinguish between them with certainty when growing in the field. They are closely related in the eye of the botanist as well, and what may be said of one of them with regard to possibilities of development applies, with minor modifications, to them all. They are plants that, having been for ages under cultivation, have developed many varieties. But, on the other hand, the varieties that assume commercial importance are relatively fixed, owing to the fact that they have always been grown in mass, thus giving no great opportunity for variation, and no necessity for cross-fertilization. These are the good and sufficient reasons why they get few varieties in the field grains and so many in corn and singly cultivated garden vegetables, in which variation is quite evident and varieties are easily segregated. It is obviously necessary that a plant grown from the seed, and for its seed, must reproduce itself accurately from generation to generation; otherwise the agriculturist could have no assurance as to what might come forth when he sows his grain. In point of fact, the numerous varieties have become fixed so that each may be sown with a large measure of assurance that the crop will have the uniform character of the seed. The differences among the different varieties have to do with size of grain, productivity, season of ripening, protein content, quality of so-called hardness, which is important in bread-making, color of grain, peculiarities as to beards, chaff, and the like; and-perhaps most notable of all-condition of susceptibility or immunity to the attacks of the fungus known as rust, which is the chief enemy of the wheat, and a perpetual menace to the crop.

A MICROSCOPIC PEST

There are always penalties associated with any specialized development in a cultivated plant or a domesticated animal. In the case of the small grains, the penalty of specialized breeding in which selection has been made generation after generation with reference to the quality of the seed has been the gradual loss on the part of many varieties of the cereals of the power to ward off the attacks of a fungus pest that finds their stalks its favorite feeding ground. This pest is known to the farmer as "rust," because in many forms it gives to the stalks of the plant, once it is fairly lodged and under development, a blotched, reddish brown appearance suggestive of the scales of rust that appear on a metallic surface. To the botanist the fungus is known as a member of the tribe of so-called Euridineial or Cup Fungi. The most familiar species is known as Puccinia graminis. The precise history of this parasite has been very difficult to trace. It is known, however, that the germinal matter lodges on the stalks of the grain in the form of minute spores, and that these send little rootlets into the substance of the grain cell and sap its vitality. It is further known that at one stage of their career some varieties of rust plant lodge on the leaves of the common barberry and there develop another type of spores. This fact has made the botanist look askance at the barberry, not unnaturally. Yet it is known that rust attacks the wheat in Australia where the barberry does not grow; and experiments have also shown that the rust may be propagated for an indefinite period without passing through the phase of development in which the barberry is its best. So the elimination of the barberry does not constitute the important agency in fighting the rust that the botanist once hoped it might. Nor has any other agency been suggested that will combat the pest. Once its spores have found lodgment, it is obvious that there could be no means of spraying or otherwise giving treatment for their destruction or removal that could be applied to a host plant that is grown not individually or in small clumps, like orchard fruits or garden vegetables, but in fields that aggregate millions of acres. So it has long been recognized that the battle with the rust plant must be fought out along different lines. There could be no hope of eradicating the pest except by making the grain plant itself resistant to the attacks of the enemy.

DESTRUCTION WROUGHT BY THE RUST

Experiments in selective breeding, through which new races of wheat have been developed by saving for seeding purposes the grain of plants that proved individually resistant to the rust, have long been carried out more or less systematically. Partly in this way, and partly perhaps through accidental development in regions where the rust does not prevail, some varieties of wheat have been introduced that show a large measure of immunity to the disease. But unfortunately these for the most part have been plants that did not produce grain of very good quality. In general the favorite wheats of the world have remained subject to the attacks of the fungus. Their degree of immunity in any given season has depended upon accidental conditions of weather that interfered with the development or spread of spores of the rust fungus rather than upon any inherent resistance of the cereal itself. Thus it is familiar experience everywhere that the farmer cannot have any full assurance as to the amount of his grain crop until the grain approaches the ripening stage; because at any time the invisible spores of the rust may sweep as a devastating horde across his fields and, finding lodgement on the grain stalks, so devitalize them as greatly to reduce their capacity for seed formation. The attempt has been made many times to estimate the average loss that results to the grain growers of the world-and hence, of course, ultimately to the consumers in every rank of life-from the attacks of this microscopic but all-powerful enemy. It is conservatively estimated, for example, that the loss to the wheat growers of Australia is from ten to fifteen million dollars a year. Yet Australia is relatively free from the pest. In an old wheat country like Prussia, where the rust has gained a more secure foothold, the losses are enormously greater. It has been estimated that in a single season the loss from rust on the various small grains in Prussia alone was not less than $100,000,000. In America the losses from rust vary greatly from year to year; but there is no season when the destruction wrought by this pest would not be calculable in millions of dollars. There are exceptional seasons when in entire regions the wheat crop is almost totally destroyed and other seasons in which the losses amount to a high percentage of the total crop. All in all, the microscopic uredospore must be listed among the most important and most menacing enemies of our race. A pest that perpetually threatens our chief food product must surely be so considered, notwithstanding the individual insignificance of its members.

THE PLANT-DEVELOPER TO THE RESCUE

It is obvious, then, that there is no single task that the plant developer could undertake that would give larger promise of benefit to mankind than the task of rendering the cereals immune to the attacks of the rust fungus. But it is also obvious that the task is one that should be carried out under the auspices of the government, rather than as an individual effort. Nevertheless a very notable beginning has been made in the direction of developing immune races of wheat through the efforts of an individual experimenter, who, however, had the backing of a university position and was therefore not under necessity to have his experiments attain commercial success. The experimenter in question is Professor R. Biffen of the Agricultural Department of Cambridge University, England. His experiments with wheat constitute by far the most satisfactory investigations in plant development that have been carried out under the guidance of the new Mendelian principles of heredity. The investigation through which Professor Biffen was enabled to develop an immune race of wheat in a few generations promises to be of immense economic importance. The story of this development is too important not to be told in some detail. In order to understand Professor Biffen's success in developing an immune race of wheat, it is necessary to review briefly the preliminary studies through which he familiarized himself with the hereditary characteristics of the wheat plant. Professor Biffen had given attention to the development of the wheat through the ordinary methods of selection as early as 1900, and before anything had been heard of the researches of Mendel, which, as we have elsewhere pointed out, were quite unknown to anyone after the death of Mendel himself in 1884 until about the beginning of our new century. But he had not proceeded far before three observers, De Vries, Correns, and Tschermak, independently discovered and made known the forgotten work of Mendel, and, as Professor Biffen himself says, "changed the whole aspect of his problem." It was at once obvious to Professor Biffen that wheat offers opportunity for hybridizing experiments closely comparable to those that Mendel had performed with the pea. Both of these plants are normally self-fertilized, their stamens and pistils being enclosed in receptacles that are never opened and made accessible to insects or subject to wind pollenation. This makes the hand pollenization of the plants a rather tedious and delicate task. But once this is effected, the further experiments are greatly facilitated by the fact that there is no danger of unintended cross-pollenizing-in other words, the plants of the second and subsequent generations will normally inbreed and thus reveal hereditary potentialities without further attention from the experimenter; whereas with most other plants of another habit it is necessary to guard constantly against cross-fertilization.

MENDELIAN CLUES

The essential facts of Mendelian discovery with regard to "unit" characters and their grouping into pairs, in which one character is dominant and one recessive, have been more than once called to our attention and have been illustrated again and again with instances drawn from my own plant experiments. The cases of the black and white blackberries, the thorny and thornless blackberry, and of stone bearing and stoneless plums, among others, will be recalled. But we have also observed cases in which the characters of two parents seemed to be blended in the offspring, there being no clear dominance of one character over another. Such was the case, for example, with the Sunberry, the Primus berry, and the Plumcot. Now it is peculiarly interesting to note, in the light of our experiments with various fruits and flowers of widely different orders, that Professor Biffen was able to analyze the diverse qualities of the various wheats with which he experimented and to discover that different groups of unit characters operated differently in heredity. Some of the pairs showed dominance and recessiveness; others showed an irregular or partial dominance; while other pairs showed the blending of characters, so that the offspring was intermediate between the parents, there being no apparent tendency to dominance or recessiveness. Yet all of these characters, whether manifesting the phenomena of dominance in the hybrid of the first generation or not, showed the same tendency to segregation in the succeeding generation, and to segregation along the familiar Mendelian lines; that is to say, one offspring in four would reveal the first character only, the second and third offspring were mixed as to the pair of characters, and the fourth would show only the second character. It was necessary only to plant the individual grains of wheat in plots by themselves, and to note the qualities of the grains of each (that is to say, the qualities of the offspring of the first filial generation) to make sure as to the position of each individual in the Mendelian scale (whether pure or mixed in its heredity as to its given factor), and thus to be able to select pure types that would breed true; and, what is perhaps equally important, to eliminate the impure types that would not breed true.

DOMINANT AND RECESSIVE CHARACTERS

It will be of interest to note a few characters that Professor Biffen particularly studied and the groups into which they fall. As to characters that show the phenomena of pure dominance and recessiveness, the following among others were clearly revealed: Beardless ears of grain are dominant to the bearded ears; keeled glumes to round glumes; lax ears to compact ears; red chaff to white chaff; red grain to white grain; thick and hollow stem to thin and solid stem; rough leaf surface to smooth leaf surface; bristles on the stem to a smooth stem; hard, translucent endosperm (central grain substance) to soft opaque endosperm; and, finally, susceptibility to the attacks of yellow rust was dominant to immunity to yellow rust. This implies, as the reader is aware, that in each case of those just listed, when two plants represented by the opposite characters are crossed, the offspring will show the first-named character to the exclusion of the other in the first generation, but the excluded character will reappear in one fourth of the offspring of the second generation. Breeding a wheat with beardless ears and white grain, for example, with a wheat having bearded cars and red grain, all the progeny will be beardless and red-grained; but bearded ears and white grain will reappear, in various combinations, in one fourth of the progeny of the second generation. It is never safe for the plant developer to draw exact inferences as to the hereditary tendencies of one plant from observation of a quite different plant. Nevertheless it is of interest to observe certain analogies between the wheat grains as studied by Professor Biffen and certain of our plant developments already cited. In particular we may note that red grain is dominant to white grain, suggesting what we have said as to the dominance of black blackberries over white blackberries. Again, the rough leaf surface and bristly stem of the wheat proved dominant to the smooth leaf and smooth stem, suggesting the case of our thorny stemmed briars in which the thorns proved dominant to smoothness of stem. But doubtless the most important revelation made by Professor Biffen's investigation was the fact that susceptibility to rust was dominant to immunity to rust. This means that when a susceptible type of wheat is crossed with an immune one, all the offspring will be susceptible. But it means also that the recessive quality of immunity will reappear in one fourth of the offspring of the second generation. And thereby hangs the tale of Professor Biffen's great achievement, as will appear in a moment.

CHARACTERS THAT Do NOT "MENDELIZE"

Before following this let us glance at the other groups of unit characters which Professor Biffen found not subject clearly to the rules of dominance and recessiveness. These groups include fewer characters than those in the dominant list, partly perhaps because it is obviously more difficult to study characters that do not show the clear phenomena of dominance and recessiveness. But these groups are highly interesting none the less. The unit characters that showed what Professor Biffen speaks of as irregular dominance as studied in this investigation, were only two, namely: (1) felted glumes versus glabrous glumes; and (2) gray colored glumes versus red or white glumes. The glume, perhaps it should be explained, is a bract that has no particular interest for anyone except the botanist, but which may serve admirably in checking the results of experimental breeding. The glumes have practical significance for the agriculturist, because their character determines to some extent the readiness with which the grain is shelled out in the thresher. The interest in the different types of glumes as to smoothness and of color, in the present connection, centers about the fact that neither parent showed dominance in the first generation of the hybrid, the individual hybrids differing indefinitely. In some cases there would be almost pure dominance; in others a blend of the characters. But in the second generation the characters were segregated just as if they had shown the typical phenomena of dominance and recessiveness in the first generation. The third group of characters, in which there was uniform blending in the first generation of hybrids, with no tendency whatever to manifestation of dominance of one character over the other, found representation in the following pairs of unit characters: (1) lax ears versus tense ears; (2) large glumes versus small glumes; (3) long grains versus short grains; (4) early habit of ripening versus late habit of ripening. As to each of these pairs of characters, the hybrids of the first generation were intermediate between the parents. For example, if a wheat having long grains was crossed with one having short grains, the hybrid bore wheat neither long nor short but intermediate; and if a wheat that ripened early was crossed with one that ripened late, the hybrid offspring ripened their grain at an intermediate season, later than their early parent but earlier than their late one. Yet here again-and this perhaps is most significant of all--there was segregation of characters in the second generation along the usual Mendelian lines. That is to say, the first generation hybrids that bore grain of medium length will produce offspring one fourth of which bear long grain and one fourth short grain, the other half bearing intermediate grain; and similarly the first generation hybrids that ripened their grain at an intermediate season, produce progeny one fourth of which ripened their grain early and one fourth late, the other half ripening their grain at the intermediate season. The importance of this observation is that it shows that the Mendelian principle of the segregation and recombination of unit characters in second generation hybrids follows the same rule whether or not the characters show clear dominance in the first generation. And if we look a little beneath the surface it will appear that there are hundreds or perhaps thousands of unit characters that for one reason or another do not show the phenomena of dominance in the first generation and hence are exceedingly difficult to trace, and yet which reappear segregated in new and varied combinations in the second generation, thus accounting for the extraordinary diversity of second generation hybrids to which our attention has been called again and again. It is interesting to note that Professor Biffen found such conspicuous conditions as long grain and short grain to fail to manifest the phenomena of dominance and recessiveness. Considering that tallness of vine had shown itself to be dominant over shortness of vine in Mendelian peas, it might perhaps have been expected, reasoning from analogy, that long grains of wheat would be dominant to short grains. But I have already suggested that it is unwise to attempt to predict the hereditary tendencies of one plant from observation of another; and in particular it should be said that the stems of plants, as regards their fixity of hereditary tendency, are likely to be on a different plane from the flowers or fruit, or any other new characters. The particular arrangement of floral envelope that characterizes the plant of today is of relatively recent development, and may be expected to be subject to greater fluctuations, or in other words to show greater plasticity under the disturbing influences of hybridization. Professor Biffen even found that there was a difference in the manifestation of dominance and recessiveness with regard to certain characteristics between different varieties of wheat. Thus in the matter of the glumes, where the parent that bore a felted glume was the variety known as "rough chaff," the felted glume proved dominant over the smooth glume. But where the felted parent was the variety known as rivet wheat, the phenomena of dominance were irregularly manifested, or manifested not at all. So hybrids of the rivet wheat were listed in the class of irregular dominants, as above outlined.

PRACTICAL APPLICATION OF THE NEW KNOWLEDGE

Having thus analyzed his wheat plants and made himself familiar with their hereditary possibilities, Professor Biffen was ready to make application of his knowledge to the improvement of existing varieties of wheat. In particular he desired to produce a variety of wheat that would be immune to rust, yet would at the same time produce a good head of wheat having the quality described by the miller as "hardness"-a quality that is essential to the making of high grade flour, yet which some otherwise excellent wheats altogether lack. Material was at hand for crossing experiments in that there was a race of wheat known to be immune to the yellow rust which had not hitherto been thought of as solving the rust problem because it bore grain of very poor quality. To Professor Biffen, armed with his new knowledge, it appeared that it should be possible to combine this immune wheat of poor quality with susceptible races of wheat bearing a good grain in such a way as to secure a new race that would present the good qualities of each parent and eliminate the bad qualities. So he crossed a race of wheat that bore a grain susceptible to rust with the immune variety that bore the grain of poor quality, and developed a generation of crossbreds all of which were-quite as he had expected-susceptible to the attacks of the rust. To the untrained plant experimenter it would have appeared that this experiment should be carried no further. Progress was apparently being made in the wrong direction; for whereas half the parents were immune to rust, all of the children were susceptible. But Professor Biffen knew, as we have already seen, that susceptibility and immunity constituted a Mendelian pair of hereditary factors. So he knew that in the next generation one fourth of the hybrid plants would be immune to rust. And this expectation was justified by results. The second generation hybrids showed diverse combinations of various other qualities that were under consideration, and a certain proportion of them revealed the combination of the desired quality of grain with the stems immune to the attacks of the rust fungus. As immunity to rust is a recessive factor, it follows that the second generation hybrids that show such immunity will breed true to that character. Their offspring will be immune. But as regards certain other qualities, notably hardness, it was necessary to continue the experiment through a third generation, in order to discover which of the plants that were individually hard were pure dominants as regards the quality of hardness. To ascertain this it was necessary only to plant the grains showing the desired quality in plots by themselves. The individuals that produced only hard-grained offspring in the next generation were thus shown to be pure dominants for that quality. They constituted a fixed race and could be depended upon to breed absolutely true. Thus the clear recognition of the qualities of Mendelian segregation, as applied to the different pairs of unit characters representing respectively desirable and undesirable qualities of the wheat, enabled Professor Biffen to produce in the third generation a fixed race of wheat having the desired qualities of grain and a plant stem that is immune to the yellow rust. The seeds of this new variety being multiplied as rapidly as possible, a wheat was produced that promises to be of enormous importance to the grain growers of England. It is obvious that a similar line of experiment should enable the plant developers of other countries to produce new varieties of wheat that will be immune to the various rusts, and thus to rid the agriculturist of one of the pests that of all others has hitherto rendered his calling precarious.

POSSIBLE AID FROM THE WILD WHEAT

The greatest difficulty, doubtless, will be to secure varieties of wheat that are immune to the various rusts to utilize in crossbreeding. Much further investigation will be needed before we can make sure as to the material that is available. But peculiar interest attaches to the investigations recently made by Mr. 0. F. Cook, the biometrist in charge of crop acclimatization and adaptation of the U. S. Department of Agriculture, with reference to the wild wheats of Palestine, which were discovered by Mr. Aronson, a native of Palestine. Mr. Cook's researches have shown that there are races of wheat growing wild in Southwestern Asia that are prototypes of the cultivated wheat. The resemblance of northern wild forms to the cultivated varieties is striking. Yet the differences are also conspicuous. The wild wheat has a looser, less compact head, and some varieties have the peculiarity of shedding the spikelets that hold the grain individually, each spikelet being provided with a barbed shaft which serves the purpose of helping the grain to attach itself or even to bury itself in the soil. All of which would be expected in a wild wheat, which is found also in the wild oats and rye as well as in rice. The kernels of some wild wheats are not large, but some of them are of more or less edible quality. A chief interest in the plant centers about its seeming immunity to rust. And the question at once arises as to whether it may not be possible to hybridize these wild wheats with the cultivated ones to secure resistance to disease as well as unusual variation, vigor, and hardiness. Tests calculated to discover possibilities in this direction are now being made, and there is every reason to hope that they will have valuable results. It may be added that the wild wheat is not universally self-fertilized. The stamens and pistils of its flowers sometimes protrude and permit cross fertilization by the aid of the wind or insects. This may to some extent facilitate the hybridizing of the wild wheat with cultivated wheats. But on the other hand, it will probably be desirable to eliminate this propensity from the new varieties after they are fixed for commercial use. For, as already pointed out, there are advantages in the self-fertilization of a grain like wheat, to prevent deterioration of the type by undesired crossing. But the entire question of the hybridizing of the domesticated wheat with the wild type remains for future investigation. There is perhaps no single field of plant development that offers greater possibilities of usefulness. Fortunately several experimenters are alive to the importance of the subject, and it may be expected that their investigation will reveal its full possibilities in the near future. As I have already pointed out, this work is preeminently one that should go forward under government auspices. My own experiments in this line with the wild wheat are necessarily limited, as I received specimens only last season. A work that involves matters of such vast economic significance, having direct connection with the cost of living as applied to every member of the community, should not be hampered by any financial restrictions, and should have the co-operation of investigators in many parts of the world; such co-operation as a government bureau alone can command. During the past thirty years I have been experimenting in a desultory way with various grains and grasses, both of the best cultivated varieties and numerous wild species. But I have not as yet carried out serious experiments in crossing the cereals. I have selected and perfected, and some definite results are expected from work now in hand. The interest already shown by the authorities of the Department of Agriculture gives sufficient assurance that the work will be carried forward energetically and efficiently. That it will lead to developments of vast importance, having direct bearing on the improvement of all the small grains, can scarcely be doubted.

-The little company of grasses, represented by Wheat, Barley, Rye and Oats, have, since prehistoric times, occupied a preeminent position in supplying man and his domesticated animals with suitable foods.

This text is from: Luther Burbank: his methods and discoveries and their practical application. Volume 8 Chapter 2