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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

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.

Next: Results Of Grape-breeding

Previous: Grape Hybrids

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