Manual of American Grape-Growing. U. P. Hedrick
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, Æstivalis 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 × Rupestris 3306, Riparia × Rupestris 3309, Riparia Solonis 1616, Mourvèdre × Rupestris 1202, Aramon × 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 Mourvèdre × 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 × 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 × 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