Manual of American grape-growing

by U. P. Hedrick

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.