USDA Experiment Station Record 40: 836-837 (1919)

Some factors favoring or opposing fruitfulness in apples.
The effect of certain conditions and practices on the development and performance of the individual fruit spur,
(Missouri Sta. Research Bul. 32 (1918. pp. 3-60, pls. 4, fig. 1)

The results of a number of experiments dealing with fruitfulness in apples are reported. These include performance records of fruit spurs; sap concentration studies, both by the freezing method and by actual chemical analyses; fertilizer experiments, and experiments in girdling. tillage, pruning, and etherization. A review of the literature bearing upon the favor lug or opposing fruitfulness in apples to included.

Various performance records of individual fruit spurs on trees of different varieties of apples were started in 1913 and continued for a 5-year period in order to determine whether an individual spur or branch blossoms two or more years in succession, In alternate years, or only once in its life history as a fruit bearer. The data from these records are here tabulated in summarized form and discussed.

Jonathan, Grimes, and Winesap were able to develop a fairly high percentage of blossoms each year while Rome, York, and Gano produced an exceedingly high percentage of blossoms one season and a very low one the next. The varieties used show remarkable uniformity with respect to the percentage of the individual fruit spurs which alternate, that is, bloom only once in two years. Jonathan and Winesap were able to develop blossoms in successive seasons on the same spur in a much greater proportion than the other varieties observed.

The work indicates that the soil in which the tree is growing has little effect upon the performance of the individual spurs with respect to alternation. Contrary to the results of some investigators, however, it appears that the fruitful year of certain alternating sorts may be changed by the removal of the blossoms through either accident or design. The age of the spur systems of the various varieties is practically the same, ranging usually from 2 to 8 years, 3 to 6 or 7 years being apparently the most effective fruiting age.

In order to determine whether there to a correlation between the concentration of plant sap and stored reserves in bearing and nonbearing parts and the observed bearing or nonbearing condition, determinations were made by freezing point method and also by making an actual chemical analysis of the parts under consideration. Results as here presented indicate that sap bearing spurs has a slightly higher concentration (lower freezing point) during a considerable portion of the year than sap from nonbearing spurs. A marked decrease in the sap concentration of both bearing and nonbearing spurs occurs in late June or early July. Leaf sap from bearing and nonbearing spurs Shown considerable variation in concentration. The number of fruits on a spur affects the concentration of neither spur nor leaf sap. Sugar and starch were found to be present in slightly greater amounts in the bearing spur than in the nonbearing one.

Counts and measurement, were made of the leaves on fruit spurs during three seasons. They indicate that bearing spurs have a smaller total leaf area than nonbearing spurs, the difference being due to the number of leaves developed rather than to the size of the individual leaves.

To determine the effects of girdling upon the concentration of plant sap a number of nursery trees ranging from 3 to 5 years old were girdled in the two season 1915 and 1916. Girdling, regardless of the season, caused an increased concentration of sap in the part, above the girdle and a decreased concentration of sap in the parts nearest the girdle, the effect being lessened as the distance from the girdle increased.

Fertilizer experiments were conducted with dwarf Rome apple trees planted in boxes of sand or soil. Nitrogen, potash, and phosphorus were used both alone and in combination. The results showed that effects upon the size of the tree, the development of its fruiting wood, and the production of blossoms could be attributed only to the use of nitrogen, which was a very decisive factor in both the formation of fruiting parts and the development of blossom buds.

Tillage experiments have been conducted at the station for a number of years. Some data are given showing the effect of the tillage method upon depression of twig sap in several varieties. The results, as a whole, show that trees growing in a permanent sod of either grass or a legume had a higher concentration of twig sap than trees growing in plats planted with either annual or biennial cultivated crops.

A pruning experiment was begun in 1914 with 1-year-old Delicious apple trees to determine the relative influence of different pruning systems upon the size, character of growth, and fruiting age of apple trees. The results thus far secured show that trees headed at 5 or 6 ft. did not produce so many short branches (potential fruiting wood) during the first three years in the orchard, as trees headed at 2 ft.

In view of the fact that etherization has proved to be a very effective stimulant upon the enzym activity of detached parts of woody tissues 12 Jonathan apple trees were etherized, one each month, beginning December, 1914, and continuing until November, 1915. The data given show that etherization has little effect upon the concentration of either twig or leaf sap, and the small differences observed seemed to be only temporary.