Hilgardia 2(5):107-124. (Nov 1926)
The influence of pruning on the germinability of pollen and the set of berries in Vitis vinifera
A. J. Winkler
[A. J. Winkler was Assistant Viticulturist in the Experiment Station.]

In the progress of an investigation at the California Experiment Station of the effect of pruning on capacity, vigor, and bearing of Vinifera grapes,12 it was observed that the type of pruning influenced the germinability of the pollen and the setting of the fruit.

So far as I have been able to find, no account of the influence of pruning on the germination of pollen has been published. This is also true with reference to the set of fruit, unless we except the many reports of larger yields resulting from the less severe or so-called “long” pruning in deciduous fruits. In this case, however, the larger yields which accrue from the development of a larger number of fruits may be the result of a larger bloom without any change in the quality of the flower parts, since the less severe pruning leaves a larger number of fruit buds on the tree.

Though there are no printed records of an increase in the set of fruits as a result of the long pruning of deciduous trees, the beneficial effect of blossom thinning on set has been indicated by Miss Bradbury.(1) She reports that during the one season of her tests, 1924, the set of fruits on sour cherry trees was increased from 24 per cent on the unthinned branches to 42 per cent on the branches on which the blossom buds of the spurs were thinned as early as practicable to one blossom to a bud.

DEFINITION OF TYPES OF PRUNING USED

* Normal is used here in the sense of "usual."

Norrnal* Pruning.—Pruning as nearly as possible in accord with the best accepted commercial practices of pruning each variety.2 All bunches allowed to develop. (Fig. 1A.)

Severe Pruning.—Pruning similar to that of the normally pruned vines, but more severe, only the base buds being retained on the spurs. All bunches allowed to develop. (Fig. 1B.)

Half-long Pruning, part crop.—Pruning similar to that of the normally pruned vines, but less severe, six to ten buds being retained on the spurs. All bunches in excess of the number of bunches on the normally pruned vines, at the time of thinning, removed before blooming. (Fig. 1C.)

Cane Pruning, part crop.—Pruning similar to the commercial practice of cane pruning as used on Sultanina, except that more wood (four to nine canes, two to three feet long) is retained. All bunches in excess of the number on the normally pruned vines, at the time of thinning, removed before blooming. (Fig. 1D.)

No Pruning, part crop.—No pruning. All bunches in excess of the number on the normally pruned vines, at the time of thinning, removed before blooming. (Fig. 1E.)

No Pruning, all crop.—No pruning. All bunches allowed to develop. (Fig. 1E.)


Fig. 1. Muscat of Alexandria vines showing the types of pruning used.
A. Normal (or usual) pruning. B. Severe pruning. C. Half-long pruning. D. Cane pruning. E. No pruning.


The samples of pollen of the Muscat of Alexandria, Black Monukka, and Alicante Bouschet were collected from the twelve vines under each type of pruning. For the other varieties the pollen was taken from five vines under each type of pruning. The pollen from all the vines of a variety under the same types of pruning was massed together, and after thorough mixing, was used as a single sample in the germination tests. The percentage of germination of the pollen of the several varieties under the different types of pruning is shown in table 2.

The data in table 2 indicate that the influence of pruning on the germinability of pollen is very marked. If we take the percentage of the germination of the pollen from the normally pruned vines as a standard, the germinability of the pollen of the half-long pruned, part crop vines was increased from 38 to 277 per cent; that of the cane pruned, part crop vines from 44 to 606 per cent; that of the non-pruned, part crop vines from 219 to 606 per cent; and that of the non-pruned, all crop vines from 117 to 576 per cent, when all of the varieties are treated as a whole.

The greatest increase was in Muscat of Alexandria and Alicante Bouschet, where the .percentage of germination of the pollen from the normally pruned vines was very low. For the Muscat of Alexandria, for which the data for three years of the non-pruned vines are available, the average increase in germinability of pollen has been 277 per cent for the half-long pruned, part crop; 342 per cent for the cane pruned, part crop; 414 per cent for the non-pruned, part crop; and 296 per cent for the non-pruned, all crop vines.

TABLE 2
THE INFLUENCE OF PRUNING ON THE GERMINABILITY OF POLLEN

In the case of such varieties as Malaga, Henab, and Emperor, where the pollen of the normally pruned vines gives a relatively high percentage of germination, the increase in germinability as a result of less severe pruning was not so great. It was, however, sufficient to be significant. The average increase in germinability of the Malaga pollen—which is typical of these varieties—was 65 per cent for the half-long pruned, part crop and 105 per cent for the cane pruned, part crop vines.

As might be expected, since the difference in the severity of pruning is relatively small, there has been no great difference between the germinability of the pollen of the severely and normally pruned vines.


SUMMARY

Less severe pruning increases germinability of pollen:

When the pollen of the normally pruned vines is taken as a standard, the germinability of the pollen of the half-long pruned, part crop vines ,vas increased from 38 to 277 per cent, that of the cane pruned, part crop vines, from 44 to 606 per cent; that of the non-pruned, part crop vines, 219 to 606 per cent; and that of the non-pruned, all crop vines, 117 to 576 per cent.

Severe pruning resulted in decreased germinability of the pollen in most of the tests.

Less severe pruning increases set of normal berries:

In Muscat of Alexandria, Muscat gigas, and Hunisa which are very subject to coulure, the increase in the set of normal berries to a bunch over that of the normally pruned vines was 114, 220, and 407 per cent for the half-long pruned, part crop and 238, 320, and 728 for the cane pruned, part crop vines, respectively. The increase in Muscat of Alexandria for the non-pruned, part crop vines was 266 per cent and for the non-pruned, all crop vines was 62 per cent.

In the other varietiesMolinera, Henab, Emperor, Malaga and Ohanezwhich are little affected by coulure, the increase in the set of normal berries to a bunch ranged from 19 to 112 per cent for the half-long pruned, part crop and from 20 to 115 per cent for the cane pruned, part crop vines.

The set of normal berries on the severely pruned has been less than that on the normally pruned vines in six of the eight varieties tested.

Less severe pruning increases percentage of normal berries to a bunch:

In Muscat of Alexandria and Hunisa varieties, which are very subject to millerandage, the percentage of normal berries to a bunch was increased 36 and 230 per cent, respectively, on the half-long pruned, part crop vines, and 36 and 590 per cent, respectively, on the cane pruned, part crop vines. Similar increases were obtained under the types of no pruning With the Muscat of Alexandria.

In the other varieties, which usually set very few small seedless berries, the increase in the percentage of normal berries to a bunch ranged from 3.4 to 17 per cent for the half-long and cane pruned, part crop vines over that of the normally pruned vines.

Severe pruning has reduced the percentage of normal berries below that of the normally pruned vines in six of the eight varieties tested.

Flower parts are probably improved under less severe types of pruning:

The increased germinability of pollen, the set of normal berries, and the percentage of normal berries to a bunch, together with the pollination tests, indicate that both the male and female parts of the flowers are improved by the less severe pruning.

The improvement in the flower parts appears to follow as a result of an earlier development of the foliage and an increase in its area with less severe pruning.

Literature Cited
  1. Bradbury D. Notes on the dropping of immature sour cherry fruits. Proc. Amer. Soc. Hort. Sci. 1925. 22:105-110.
  2. Bioletti F. T., Jacob H. E. Head, cane and cordon pruning of vines. California Agr. Exp. Sta. Cir. 1924. 277:1-32.
  3. Bioletti F. T., Flossfeder F. C. H. Topping and pinching vines. California Agr. Exp. Sta. Bul. 1918. 296:371-384.
  4. Dorsey M. J., Knowlton H. E. The relation of growth to fruitfulness in some varieties of apple. Proc. Amer. Soc. Hort. Sci. 1925. 22:161-172.
  5. Haller J. H., Magness J. R. The relation of leaf area to the growth and composition of apples. Proc. Amer. Soc. Hort. Sci. 1925. 22:189-196.
  6. Hilgard E. W. The Muscat on the southern mesas. California Agr. Exp. Sta. Bul. 1884. 17:1
  7. Merjanian A. S. De la coulure et du millerandage (Russian with French summary). Bul. Sta. Oenolog., Odessa. 1919. 1:1-55.
  8. Müller-Thurgau H. Über das abfallen der Rebenblüten und die entstehung kernloser Traubenbeeren 1883. Der Weinbau no. 22.
  9. Sartorius Otto. Zur Entwicklung und Physiologie der Rebblüte. Angew. Botanik. 1926. 8:29-62.
  10. Sartorius Otto. Zur Entwicklung und Physiologie der Rebblüte. Angew. Botanik. 1926. 8:65-89.
  11. Sorauer Paul. Handbuch der Pflanzenkrankheiten. 1924. 1:5th Ed.396-398. DOI: 10.1007/BF02041127
  12. Winkler A. J. Some responses of Vitis vinifera to pruning. Hilgardia. 1926. 1:526-543. DOI: 10.3733/hilg.v01n20p525