STOCKS AND RESISTANT VINES
Phylloxera, a tiny root-louse, made its appearance in France in 1861
and began multiplying with a fury unparalleled in the insect world. By
1874, the pest had become so widespread in Europe that it threatened
the very existence of the great vineyard industry of that continent.
All attempts to bring the pest under control failed, although the
French government offered a reward of 300,000 francs for a
satisfactory remedy. Numerous methods of treating the soil to check
the ravages of the insect were tried, also, but none was efficacious.
Finally, it dawned on European vineyardists that phylloxera is not a
scourge in America, its habitat, and that European vineyards might be
saved by grafting Vinifera vines on the roots of immune American
grapes. At once the reconstruction of vineyards in Europe was begun by
grafting the grapes on phylloxera-resistant roots. Meanwhile,
consternation spread to California when it was discovered that
phylloxera was running riot in some of the vineyards of the Pacific
slope; however, with the knowledge derived from viticulturists in
Europe, they too began reconstructing vineyards on immune roots,
without the same success as the Europeans, it is true, but with such
measure of success that it soon became the approved method of growing
grapes in this great region.
Through the use of resistant stocks, phylloxera is now defied in
Vinifera regions. Millions of American stocks are annually struck at
home, in Europe and wherever Vinifera grapes are grown, to be
top-worked with varieties susceptible to phylloxera. Seldom has
mastery over a pest been so complete; but, to triumph over the tiny
insect, the industry has had to be revolutionized. Resistant stocks,
in their turn, brought innumerable new problems, many of which are
still unsolved. Investigations and experiences in rehabilitating
vineyards have been carried on for forty years, the results set forth
in books and bulletins and yet there are many problems to be solved.
The grape-grower in regions infested with phylloxera is always under
the necessity of taking advantage of the latest demonstration of
practices in the use of resistant stocks. These practices are best
studied in the experiments of state experiment stations and the United
States Department of Agriculture, and in the vineyards of leading
grape-growers, since even those most needing elucidation can be but
briefly discussed in the following paragraphs.
The wild vines of a species are always seedlings and are hence
exceedingly variable. The first vineyards of resistant stocks were
vines grafted on stocks of wild vines, and the results were very
unsatisfactory; for, naturally, there was divergence in many
characters and especially in the vigor of the vines. Also, there was
difficulty in grafting, since some wild vines are stout and others
slender; some bear grafts well, while others do not. It soon became
apparent that to succeed, varieties must be selected from the
different species for vineyard work. The great task of the
experimenter and grape-grower, therefore, has been to select varieties
of the several species sufficiently resistant, vigorous and otherwise
possessed of characters fitting them to become good stocks. Out of
vast numbers tested, a few are now generally recognized as best for
the several groups of Vinifera grapes and the several distinct regions
in which these grapes are grown.
_Resistant species and varieties._
The reconstruction of phylloxera-ridden vineyards by the use of
resistant stocks is possible only because some species and varieties
are, as has been said, more resistant to the root-louse than others.
All degrees of resistance exist, as would be suspected, from immunity
to great susceptibility. It is obvious that the foundation of the art
of growing resistant vineyards is exact knowledge of the immunities
and susceptibilities of the many varieties and species of grapes. From
the first use of resistant vines, experimenters everywhere have set
themselves at work to determine not only what the most resistant vines
are, but what the causes and conditions of immunity. In spite of a
wealth of empirical discoveries as to what grapes can best resist the
root-louse, causes and most of the conditions of immunity are still
little understood. Definite, useful knowledge, so far, goes little
further than the establishment of lists of species and varieties, the
latter subject to change, that are most useful in setting resistant
vineyards.
Phylloxera does little damage to species of Vitis native to the same
general region in which the pest has its habitat, but nevertheless
there are some differences in resistance in American grapes. Munson,
one of the best American authorities on the resistance of species to
phylloxera, says:[7] "Rotundifolia is entirely immune, then Rupestris,
Vulpina, Cinerea, Berlandieri, Champini, Candicans, Doaniana,
AEstivalis and Lincecumii are so high in resistance as to be
practically uninjured, though they may be attacked, while Labrusca is
low in resistance and is much weakened in clay soils, if infested, and
Vinifera is entirely non-resistant." Some of these species are hard to
propagate and difficult to suit in soil and climate so that but two of
them are much used for resistant stocks. The two most used are
Rupestris and Vulpina (Riparia), of both of which there are varieties
which give satisfaction. Bioletti, a leading authority on resistant
stocks in California, says:[8]
"Varieties of resistant stocks which will in all probability be used
in California are Rupestris St. George (du Lot), Riparia x Rupestris
3306, Riparia x Rupestris 3309, Riparia Solonis 1616, Mourvedre x
Rupestris 1202, Aramon x Rupestris 2, Riparia gloire, and Riparia
grande glabre. These are all varieties which have given excellent
varieties for years in Europe, and have all been tested successfully
in California. Among them are varieties suitable for nearly all the
vineyard soils of California, with perhaps the exception of some of
the heavier clays.
"The only one of these varieties which has been planted extensively in
California is the Rupestris St. George. There can be little doubt,
however, that it will fail to give satisfaction in many soils, and
though we may not find something better for all our soils it is
probable that we will repeat the experience of Southern France and
find that in most soils there is some other variety that gives better
results. Without attempting to describe these varieties, but to give
some idea of their merits and defects and of the soils most suited to
each, the following indications are given, based principally on the
opinions of L. Ravaz and Prosper Gervais, and on a still limited
experience in California:
"The Rupestris St. George is remarkably vigorous and grows very large,
supporting the graft well even without stakes. It roots easily and
makes excellent unions with most vinifera varieties. It is well suited
to deep soils where its roots can penetrate. Its defects are that it
is very subject to root-rot, especially in moist soils; it suckers
badly and it suffers from drought in shallow soils. Its great vigor
produces coulure with some varieties and often necessitates long
pruning.
"In moist or wet soils 1616 or 3306 had given better results in France
and gives indications of doing equally well here. In drier soils 3309
will probably be found preferable.
"Aramon Rupestris No. 2 is suited to the same soils as Rupestris St.
George, and does particularly well in extremely gravelly soils. It
has some of the defects of the St. George and is moreover more
difficult to graft, and its only advantage in California is that it is
rather less susceptible to root-rot.
"There are no better resistant stocks than Riparia gloire and Riparia
grande glabre, wherever they are put in soils that suit them. They do
well, however, only in deep, rich, alluvial soils which are neither
too wet nor too dry. Their grafts are the most productive of all, and
ripen their grapes from one to two weeks earlier than the grafts on
St. George. Their principal defect is that they are very particular as
to the soil, and they never grow quite as large as the cion. The
gloire is the most vigorous, and the difference of diameter is less
with this variety than with any other Riparia.
"The Mourvedre x Rupestris 1202 is extremely vigorous, roots and
grafts easily, and is well adapted to rich, sandy and moist soils. In
drier and poorer soils its resistance is perhaps not sufficient.
"The most promising varieties for general use at present seem to be
the two hybrids of Riparia and Rupestris, 3306 and 3309. They have
great resistance to the phylloxera, root and graft almost as easily as
St. George, and are quite sufficiently vigorous to support any variety
of vinifera. The former is more suited to the moister soils and
wherever there is danger of root-rot, and the latter to the drier
soils. In general, they are suited to a larger variety of soils and
condition than perhaps any other varieties.
"Riparia gloire should be planted only on rich, deep alluvial soil
containing an abundance of plant food and humus, what would be called
good garden land, such as river bank soil not liable to overflow.
"In most other soils Riparia x Rupestris 3306 is to be recommended,
except those that are rather dry, where 3309 is to be preferred, or
those which are very wet, where Solonis x Riparia 1616 is surer to
give good results."
The value of a species or variety for a resistant stock may be judged
somewhat by the visible effect of the phylloxera on the roots of the
vines. On susceptible species, the punctures of the insects rapidly
produce swellings which vary in size and number in accordance with
resistance of the species. Technically, the first swelling on the
young tender rootlets of the vine is called a nodosity. The presence
of a few nodosities on the root system does not indicate that a vine
is not a valuable resistant stock. When the nodosity begins to decay
and becomes of a cancerous nature, it is called a tuberosity. These
tuberosities decay more or less rapidly and deeply, and when they rot
deeply cause enfeeblement or death to the vine. Thus, on Vinifera
varieties the tuberosities are several times larger and decay sets in
much more quickly than on American species which show these
tuberosities. Ratings as to resistance of species are usually made
from the size and number of the tuberosities, though when these are
found producing a scab-like wound which scales off, there may be high
resisting power.
In order to convey with some degree of definiteness the power of
resistance to phylloxera, an arbitrary scale has been agreed on by
viticulturists. In this scale, maximum resistance is indicated by 20
and minimum by 0. Thus, the resisting power of a good Vulpina is put
as 19.5 and that of a poor Vinifera variety as 0.
ADAPTATIONS OF RESISTANT STOCKS TO SOILS AND CLIMATES
Resistance, of course, counts for naught in a stock which comes from a
species unsuited to the soil and climate or other circumstances of the
locality in which the vineyard is to be planted. The several species
used for stocks differ widely in the requirements affecting growth so
that the grower must make certain that the resistant stock he selects
will find congenial surroundings. Stocks in congenial circumstances
are frequently more resistant than others inherently more resistant,
but which are not otherwise adapted to the particular conditions of
the vineyard. Species of grapes vary greatly in their root systems,
some having thick, others slender roots; the roots of some are soft,
of others hard; some have roots going down deeply, others are almost
at the surface of the ground. Manifestly these various root-forms are
but adaptations to loose and heavy, dry and moist, deep and shallow
soils, or to some circumstance of climate. A vine bruised by adversity
is in no condition to withstand phylloxera. Therefore, since the
adaptability of a variety to a soil or climate may be changed by the
stock, the adaptations of stocks to soils and climates must have
attention.
_Affinity of stock and cion._
Different varieties of grapes do not behave alike on the same stocks,
and different stocks may affect varieties differently. Even when the
kinship is close, some grapes resist all the appliances of art to make
a successful union; while, on the other hand, quite distinct species
often seem foreordained to be joined. For example, Rotundifolia, which
has the highest resistance to phylloxera of any species, is useless as
a stock because it is impossible to graft any other grape on it, while
Vulpina and Rupestris unite readily with varieties of Vinifera, the
slight decrease in the vigor of the grafted vines serving oftentimes
to increase fruitfulness. Something more is necessary, then, than
botanical kinship. Just what is necessary, no one knows, beyond: that
there must be conformity in habit between stock and cion; that the two
must start in growth at approximately the same time; and that the
tissues must be sufficiently alike that there be proper contact in the
union. Yet these facts do not sufficiently explain all of the
affinities and antipathies which species and varieties of grapes show
to each other. Unfortunately, the grape-grower has had but little to
guide him in selecting stocks and has had to learn by making repeated
trials.
PROPER PLANTING OF GRAFTED VINES
Europeans and Californians long ago learned that failures with grafted
vines often came from setting the vines too deep in the soil, the
result being that the cions struck root and became independent,
whereupon the stock dies or becomes so moribund that the beneficial
effects are lost. There are grape-growers who argue that it is
beneficial to the vine to have roots from both stock and cion, but
experience and experiments very generally teach the contrary, it being
found that in most grafts the cion roots grow more vigorously than
stock roots and eventually starve out the latter. The disastrous
effects of cion-rooting are often to be found, also, when grafting has
been done on old vines in the vineyard; and, again, when the graft is
too close to the root system.
Another cause of failure is that different stocks require that the
vineyard soil be treated differently, especially at planting time.
Vulpina stocks require that the soil be much more deeply plowed than
for Viniferas on their own roots, since Vulpinas are deep-rooted and
are exacting in the depth of root-run required. Those who have had
most experience with resistant stocks maintain that all American
grapes require rather deeper plowing than European grapes on their own
roots.
INFLUENCE OF THE STOCKS ON THE CION
Up to the present, the growing of grafted grapes has been carried on
with little thought of the mutual influence of stock and cion; grapes
have been grafted only to secure vines resistant to phylloxera. Yet
there can be no doubt that stock and cion react on one another, and
that any variety of grapes is influenced for better or worse in
characters of vine and fruit by the stock upon which it is grafted. A
plant is a delicate mechanism, easily thrown out of gear, and all
plants, the grape not the least, are more or less changed in the
adjustments of stock and cion. One could fill a large volume on the
supposed reciprocal influence of stock and cion in fruits. Space
suffices, here, however, to mention only those proved and those having
to do with the influence of the stock on the cion when the grape is
grafted.
_Influence of stocks on European grapes summarized._
Common experience in Europe and California indicates that varieties of
Vinifera grapes grafted on resistant stocks which are perfectly
adapted to soil and climate produce not only larger crops but sweeter
or sourer grapes; that the crop ripens earlier or later; that the vine
is often more vigorous; and that there are some minor differences
depending on the stock used. Wine-makers assert that the character of
their product may be affected for better or worse by the stock. Often
vines are so improved by grafting that the extra expense of the
operation and of the stock is paid for; although, to be sure, about as
often the effects are deleterious. The successes and failures of
vineyards on resistant stocks make plain that the vine-grower must
study the many problems which stocks present and exercise utmost
intelligence in the selection of the proper stock.
_Influence of stocks on American grapes._
No doubt American species of grapes may be as profoundly modified by
stocks as the European species, but there is but little evidence on
this phase of grape-growing to be drawn from the experience of
vineyardists. One rather conclusive experiment, however, shows that
American grapes may be improved by growing them on stocks which give
them better adaptations to their environment. The experiment was tried
in the Chautauqua grape-belt in western New York by the New York
Agricultural Experiment Station. The test was carried on for eleven
years, during which time many interesting possibilities in grafting
grapes in this region came to light. It was proved that the stock
materially affects the vigor and productiveness of the vine and the
quality of the grapes. The following brief account is taken from
Bulletin No. 355 of the New York Station:
In this experiment a number of varieties were grafted on St. George,
Riparia Gloire and Clevener stocks, and a fourth group on their own
roots. The varieties grafted were: Agawam, Barry, Brighton, Brilliant,
Campbell Early, Catawba, Concord, Delaware, Goff, Herbert, Iona,
Jefferson, Lindley, Mills, Niagara, Regal, Vergennes, Winchell and
Worden. The planting plan and all of the vineyard operations were
those common in commercial vineyards.
Yearly accounts of the vineyard show that the vines passed through
many vicissitudes. The experiment was started in 1902 when St. George
and Riparia Gloire stocks from California were set and grafted in the
field. Many of these died the first year. The winter of 1903-04 was
unusually severe, and many more vines were either killed or so
severely injured that they died during the next two years. The vines
on St. George, a very deep-rooting grape, withstood the cold best.
Fidia, the grape root-worm, was found in the vineyards early in the
life of the vines and did much damage in some years. In the years of
1907 and 1909 the crops were ruined by hail.
But despite these serious setbacks it was evident throughout the
experiment that the grafted grapes made better vines and were more
productive than those on their own roots. As an example of the
differences in yield, a summary of the data for 1911 may be given. In
this year, an average of all the varieties on own roots yielded at the
rate of 4.39 tons to the acre; on St. George, 5.36 tons; on Gloire,
5.32 tons; on Clevener, 5.62 tons. The crops on the grafted vines
were increased through the setting of more bunches and the development
of larger bunches and berries.
The grapes on the vines grafted on Gloire and Clevener ripened a few
days earlier than those on their own roots, while with St. George a
few varieties were retarded in ripening. Changing the time of maturity
may be very important in grape regions where there is danger of early
frost to late-ripening sorts, and where it is often desirable to
retard the harvest time of early grapes.
In the behavior of the vines, the results correspond closely with
those given for yields. In the growth ratings of varieties on
different stocks, the varieties on their own roots were rated in vigor
at 40; on St. George, at 63.2; on Gloire, at 65.2; on Clevener, at
67.9. There is no way of deciding how much the thrift of the vines
depends on adaptability to soil, and how much on other factors. Since
all of the varieties were more productive and vigorous on grafted
vines than on their own roots it may be said that a high degree of
congeniality exists between the stocks and varieties under test.
The experiment suggests that it would be profitable to grow fancy
grapes of American species on grafted vines, and that it is well
within the bounds of possibility that main-crop grapes can be grafted
profitably. In the general tuning-up of agriculture now in progress,
it may be expected that soon American as well as European varieties of
grapes will be grown under some conditions and for some purposes on
roots other than their own.
DIRECT PRODUCERS
Attempts innumerable have been and are still being made to secure, by
hybridizing _V. vinifera_ and American species of grapes, varieties
that will resist phylloxera, the mildew and black-rot. The grapes of
this continent are relatively immune to all of these troubles, and if
hybrids could be obtained to produce directly, without grafting,
grapes with the good qualities of the Viniferas--in short, European
grapes on American vines--the cultivated grape flora of the whole
world might be changed. So far, a "direct producer" that is wholly
satisfactory in either Europe or California has not been found for the
wine or raisin industries, although a number of varieties are rated as
very good table grapes, and a few are used in wine-making. The best of
the direct producers are Lenoir, Taylor, Noah, Norton's Virginia,
Autuchon, Othello, Catawba, and Delaware.
[Illustration: PLATE V.--Vinifera grapes grown out of doors in New
York. _Top_, Malvasia; _bottom_, Chasselas Golden.]