CHAPTER XV
GRAPE-BREEDING
Chance, pure and simple, has been the greatest factor in the production of varieties of American grapes. From the millions of wild plants, an occasional grape of pre-eminent merit has caught the eye of the cultivator and has been brought into the vineyard to be the progenitor of a new variety. Or in the vineyards, more often in near-by waste lands, from the prodigious number of seedlings that spring up, pure or cross-bred, a plant of merit becomes the foundation of a new variety. An interesting fact in the domestication of the four chief species of American grapes is that none came under cultivation until forms of them, striking in value, had been found. Catawba, representing the Labrusca grapes; the Scuppernong, the Rotundifolias; Norton, from Vitis æstivalis; Delaware and Herbemont from the Bourquiniana grapes; and Clinton from Vitis vulpina, are, after a century, scarcely excelled, although in each species there are now many new varieties.
That our best grapes have come from chance is not because of a lack of human effort to produce superior varieties. Of all fruits, the grape has received most attention in America from the generation of plant-breeders just passing. Grape-breeders have produced 2000 or more varieties, a medley of the heterogeneous characters of a dozen species. That so many of this vast number are worthless is due more to a lack of knowledge of plant-breeding than to a lack of effort, for the order and system in plant-breeding that now prevail, disclosed by recent brilliant discoveries, were unknown to grape-breeders of the last century.
Grape Hybrids
As early as 1822, Nuttall, a noted botanist, then at Harvard, recommended "hybrids betwixt the European vine and those of the United States which would better answer the variable climates of North America." In 1830, William Robert Prince, [Fig. 48], fourth proprietor of the then famous Linnean Botanic Nursery at Flushing, Long Island, grew 10,000 seedling grapes "from admixture under every variety of circumstance." This was probably the first attempt on a large scale to improve the native grapes by hybridizing, although little seems to have come of it. Later, a Dr. Valk, also of Flushing, grew hybrids from which he obtained Ada, the first named hybrid, the introduction of which started hybridizers to work in all parts of the country where grapes were grown.
Fig. 48. William Robert Prince.
Soon after Valk's hybrid was sent out, E. S. Rogers, [Fig. 49], Salem, Massachusetts, and J. H. Ricketts, Newburgh, New York, began to give viticulturists hybrids of the European Vinifera and the American species which were so promising that enthusiasm and speculation in grape-growing ran riot. Never before nor since has grape-growing received the attention in America as given during the introduction of Rogers' hybrids. It was the expectation of all that we were to grow in America, in these hybrids, grapes but little inferior, if at all, to those of Europe.
Fig. 49. E. S. Rogers.
A statement of the difference between European and American grapes shows why American viticulturists have been so eager to grow either pure-breds from the foreign grape or hybrids with it.
European grapes have a higher sugar-and-solid content than the American species; they, therefore, make better wines and keep much longer after harvesting and can be made into raisins. Also, they have a greater variety of flavors, which are more delicate, yet richer, with a pleasanter aroma, seldom so acid, and are always lacking the disagreeable, rancid odor and taste, the "foxiness," of many American varieties. There is, however, an unpleasant astringency in some of the foreign grapes, and many varieties are without character of flavor. American table-grapes, on the other hand, are more refreshing, the unfermented juice makes a pleasanter drink, and lacking sweetness and richness, they do not cloy the appetite so quickly. The bunches and berries of the European grapes are larger, more attractive and are borne in greater quantities. The pulp, seeds and skins are somewhat objectionable in all of the native species and scarcely so at all in the Old World sorts. The berries of the native grapes shell from the stem so quickly that the bunches do not ship well. The vines of the Old World grapes are more compact in habit and require less pruning and training than do those of the native grapes; and, as a species, probably through long cultivation, they are adapted to more kinds of soil, to greater differences in environment and are more easily propagated than the American species.
Fig. 50. T. V. Munson.
Because of these points of superiority in the Old World grape, since Valk, Allen and Rogers showed the way, American grape-breeders have sought to unite by hybridization the good characters of the Old World grape with those of the American. Nearly half of the 2000 grapes cultivated in eastern America have more or less European blood in them. Yet, despite the efforts of the breeders, few of these hybrids have commercial value. Whether because they are naturally better fixed, or long cultivation has more firmly established them, the vine characters of Vitis vinifera more often appear in varieties arising as primary hybrids between that and the native species, and the weaknesses of the foreign grape, which prevent their cultivation in America, crop out. Hybrids in which the vinifera blood is more attenuated, as secondary or tertiary crosses, give better results.
Several secondary hybrids now rank among the best of the cultivated grapes. Examples are Brighton and Diamond. The first is a cross between Diana-Hamburg, a hybrid of a Vinifera and a Labrusca, crossed in its turn with Concord, a Labrusca; the second is a cross between Iona, also a hybrid between a Vinifera and a Labrusca, crossed with Concord. Both were grown from seed planted by Jacob Moore, Brighton, New York, in 1870. Brighton was the first secondary hybrid to attract the attention of grape-breeders, and its advent marked an important step in breeding grapes.
The signal success achieved by hybridizers of the European grape with native species quickly led to similar amalgamations among American species. Jacob Rommel, of Morrison, Missouri, beginning work about 1860, hybridized Labrusca and Vulpina grapes so successfully that a dozen or more of his varieties are still cultivated. All are characterized by great vigor and productiveness; and, although they lack the qualities which make good table-grapes, they are among the best for wine-making. Rommel has had many followers in hybridizing native species, chief of whom was the late T. V. Munson, [Fig. 50], Denison, Texas, who literally made every combination of grapes possible, grew thousands of seedlings and produced many valuable varieties.
Improvement by selection.
Selection, continued through successive generations, so important in the improvement of field and garden plants, has played but small part in the domestication of the grape. The period between planting and fruiting is so long that progress would be slow indeed were this method relied on. Moreover, selection, as a method in breeding, is possible only when plants are bred pure, and it is the experience of grape-breeders that in pure breeding this fruit loses in vigor and productiveness and that the variations are exceedingly slight and unstable. Many pure-bred grapes have been raised on the grounds of the New York Agricultural Experiment Station under the eyes of the writer, of which very few have surpassed the parent or have shown promise for the practice of selection.
New varieties from sports.
Bud-sports or mutations now and then arise in grapes. But not more than two or three of the 2000 varieties now under cultivation are suspected of having arisen in this way. It is true that mutations seem to occur rather often in grapes, but they are easily confused with variations due to environment and are usually too vague to lay hands on. Until the causes of these mutations are known and until they can be produced and controlled, but little can be hoped for in the amelioration of grapes through mutations.
Hybridizing the Grape
Hybridization has been the chief means of improving the grape. At present, from what is being accomplished by many workers, it looks as if it will long continue to be the best means of improving this fruit. Since the grape-grower must depend on new varieties for progress, as old varieties cannot be changed, it should be the ambition of growers to produce varieties better than those we now have. Many amateur and professional grape-growers in the past have found breeding grapes a pleasing and profitable hobby, so that much knowledge has accumulated in regard to manipulating the plants in hybridization, and the results that follow in the offspring of hybridization.
How to hybridize.
It is assumed that the reader is familiar with the botany of flowers and the essential principles in crossing plants. If he is not, he must carefully study the structure of flowers, especially those of the grape, so as to be able to distinguish the different organs and to discover when the pollen and stigma are ready for the work of pollination. He should, also, read any one of several current books on plant-breeding.
The first task in crossing grapes is to remove the anthers before the flower opens, a process known as emasculation. This is necessary to prevent self-pollination. This first operation having been performed, the cluster of grape-flowers must be tied securely in a bag to protect it from foreign pollen which otherwise would surely be carried to the stigma by insects. As soon as the stigma is ready to receive the pollen, the bag is removed and pollen from the male parent is applied, after which the bag is again put on the flower to remain until the grapes are well set. By examining the stigmas in the flowers of uncovered grapes, the operator can tell approximately whether the covered stigma is ready to receive pollen. The time required after covering depends, of course, on the age of the bud when emasculation takes place. It is, by the way, best to delay emasculation until just before the flowers open, but one must be certain that the anthers have not discharged their pollen before the flower has been emasculated.
Emasculation is a simple operation. The essential organs of the grape-flower are covered by a small cap; this in some grapes must be removed before the anthers can be reached. In many native grapes, however, the cap and the anthers may be removed at one stroke by the operator. The best tool for this is a small pair of forceps. Each of the blades of the forceps in working with native grapes should have a sharp cutting surface, but with Vinifera sorts, where the cap must be removed before the anthers can be reached, forcep blades with a flat surface are best. There is, of course, some danger when the buds are well developed that the pollen may be squeezed out and so reach the stigma or adhere to the instrument and thus contaminate future crosses. The first danger must be avoided carefully by the skill of the operator, while the second is easily overcome by sterilizing the forceps in alcohol. An effort should be made to fertilize as many of the flowers in the cluster as possible, but success is not always certain; when there is doubt, the uncertain flower should be removed from the cluster.
The flower from which the pollen is to be taken must be protected from wind and insects; otherwise pollen from another flower may be left on it. Protection should be given by tying the flowers in a bag while still in bud. There are various ways of obtaining pollen from ripe anthers and applying it to the stigma of the flowers to be crossed. The simplest is to crush the anthers, thus squeezing out the pollen, after which, with a brush, scalpel or other instrument, it may be placed upon the stigma. A brush is very wasteful of pollen and often becomes a source of contamination to future crosses, so that the scalpel is the better implement of the two. When pollen is plentiful, as will usually be the case when a man is working with vines in his own vineyard, by far the best method is to take the cluster from the male vine and apply the pollen directly to the stigma of the flower to be crossed, thereby making certain of fresh pollen and an abundance of it. The stigma, if pollen suffice, should be covered with pollen.
Grape pollen does not keep well and an effort should be made to have it as fresh as possible. The work of pollination is best performed in bright, sunny weather when the pollen is very dry. As may be seen from the foregoing statements, tools and methods are of less importance than care in doing the work. The only tool absolutely necessary is a pair of forceps, although a hand-lens is often helpful. Bags for covering the flowers should be just large enough and no larger. A bag to cover the pollen-producing flower may well be an ordinary manilla bag sufficiently large to amply cover the flower-cluster. It is helpful, however, to have a light transparent oiled bag through which one can see the condition of the anthers. It is desirable that the bag for the female flower be permitted to remain until the fruits ripen as a protection against birds and fungi. It must, therefore, be of larger size. While the bags are still flat, a hole is made near the opening through which a string is passed which can be tied when the upper end of the bag is squeezed about the cluster.
Choosing the parents.
Very much depends on the immediate parentage in hybridizing grapes. Some varieties when crossed produce much higher averages of worthy offspring than others. There is so much difference in varieties in this respect that to discover parents so endowed should be the first task of the grape-breeder. Fortunately, considerable work has been done by several experiment stations in breeding grapes, and their accumulated knowledge, together with that from such workers as Rogers, Ricketts, Campbell and Munson, furnishes beginners with good starting points. There is no way possible of discovering what the best progenitors are except by records of performance. Very often varieties of high cultural value are worthless in breeding because their characters seem not to be transmitted to their progeny and, to the contrary, a good-for-nothing variety in the vineyard is often valuable in breeding.
From present knowledge it does not appear that new characters are introduced in plants by hybridizing. A new variety originating from hybridization is but a recombination of the characters of the parents; the combination is new but the characters are not. Thus, one parent of a hybridized grape may contribute color, size, flavor and practically all the characters of the fruit, while the other parent may contribute vigor, hardiness, resistance to disease and the characters of the vine. Or these and other characters in the make-up of a new grape may be intermingled in any mathematical way possible. The grape-breeder must make certain that one or the other of the parents possesses the particular characters he desires in his new grape.
It is now known that the characters of the grape, in common with those of other plants, are inherited in accordance with certain laws discovered by Mendel. The early workers in grape-breeding did not know of these laws and could not take aim in the work they were doing. Consequently, hybridization was a maze in which these breeders often lost themselves. Mendel's discoveries, however, assure a regularity of averages and give a definiteness and constancy of action which enable the grape-breeder to attain with fair certainty what he wants if he keeps patiently at his task. The grape-breeder should inform himself as to what Mendel's laws are, and on the work that has been done on the inheritance of characters of the grape. A technical bulletin published by the State Experiment Station at Geneva, New York, and another from the North Carolina Station at Raleigh give much information on the inheritance of characters in certain grapes, and further information can be secured by applying to the United States Department of Agriculture at Washington for literature on the subject.
The grape-breeder can hope to progress only by making many combinations between different varieties and growing large numbers of seedlings. He should extend his work to all varieties which show promise in the breeding of grapes for the particular purpose he has in mind. The seed may be saved and planted as directed in the [chapter on propagation]. Unless he desires to make scientific interpretations of his results, weak seedlings should be discarded the first year, and a second discard may be made before the young plants go in the vineyard. The breeder will soon discover that he can tell fairly well from the character of the seedlings whether they are of sufficient promise to keep. Thus, if the number of leaves is small or if the leaves themselves are small, the vine is of doubtful value; if the internodes are exceedingly long, the prospect is poor; slenderness of cane, if accentuated, does not promise well; on the other hand, great stoutness and very short internodes are not desirable indications. Through these and other signs, the breeder will come quickly to know which vines should eventually go to the vineyard.
Results of Grape-breeding
There are now 2000 or more varieties of grapes of American origin, all produced within approximately a century. It is doubtful whether any other cultivated plant at any time in the history of the world has attained such importance in so short a time from the wild state as American grapes. It would seem that almost every possible combination between species worth considering has been made. Through hybridization, species and varieties have become so mixed that the grape-breeder cannot now work intelligently with these gross forms and must work with characters rather than with species and varieties which are but combinations of characters. Great progress, it is true, has been made in the past in breeding grapes in America, but the work has been wholly empirical and extremely wasteful. Many varieties have been called, but few have been chosen. With the new knowledge of breeding and with the experience of past workers, progress should be made with greater certainty. From what has been done and from work now under way, it is not too much to say that we shall soon be growing grapes everywhere in America, and kinds so diverse that they will meet not only all purposes to which grapes are now put, but also the demand for better grapes made by more critical consumers.
Plate XXI.—Jefferson (×3/5).