16th Annual Report of the Agricultural Experiment Station of the Univ. of Wisconsin (1899)
THE INFLUENCE OF HEREDITY UPON VIGOR IN THE POTATO

E. S. GOFF

The importance of the quality commonly known as "vigor" as a factor in crop production is probably too often underestimated. It is quite possible that the difference in the yield of two varieties is often due chiefly to a difference in vigor, for it is well known that varieties often lose their vigor or "run out" after a few years of culture. This has been the history of nearly all potato varieties.

1 For detailed reports of these experiments see Rep.
N. Y. Exp. Sta. (Geneva) 1884, 1885, 1886, and 1887.
2 l. c. 1887, p. 85.

Beginning in the spring of 1884, the writer, then connected with the Experiment Station at Geneva, N. Y., conducted an experiment1 through four consecutive seasons with seed potatoes selected with reference to the prolificacy of the hills that produced them. That is, the tubers of the most productive hill and of the least productive bill, respectively, in a given area, were preserved in separate sacks, and planted side by side the next spring. The larger tubers were always cut to single eyes just before planting, in order to eliminate, to a large degree, the inequality of size in the two lots of tubers. In the fall the two lots were dug and weighed separately. From the summary of these trials the following sentence is quoted: "When we consider the results of all the trials that have been made at the Station in the use of seed tubers from productive and unproductive hills, reaching through the past four seasons, the evidence has been so uniformly in favor of the former that there can be no longer any doubt of the importance of this method of selecting seed."2

On removing to Wisconsin in 1889, the writer desired to carry this work still further. The "Old Long Mercer," a variety of potato that was well known in this country about fifty years ago, and which was so badly "run out" as to yield but 20 to 30 bushels per acre in the average season, and a then modern variety,—the Rose Seedling—were selected as suitable sorts for further experiments. It was proposed to grow these varieties for a term of years, selecting the seed tubers from the most productive and least productive hills each year, to ascertain what would be the cumulative result of this method. A small plat of each of these varieties was planted in the spring of 1889, and in the fall of that year the seed selection was commenced. The experiment was carried on according to the plan until the fall of 1892, when by mistake the tubers from the most productive hill of the Rose Seedling variety were mixed with the remainder of the crop. The selection was therefore made from a plat of the Snowflake variety instead, and this variety has since been used instead of the Rose Seedling.

Up to the spring of 1898 the method described in the second paragraph of this article was strictly followed. But as the tubers from the most productive hill almost always averaged larger than those from the least productive hill, it is evident that cutting the larger tubers of both lots to single eyes did not give the least productive hill quite an equal chance with the other hill, because single eyes from a large tuber are larger, on the average, than single eyes from a small tuber. In order to entirely eliminate this inequality a slightly different method was followed in 1898 and 1899. After cutting all of the larger tubers of each lot and of each variety to single eyes, as many of the uncut timbers and cuttings from the least productive hill of each variety as were regarded of sufficient size for planting were selected and weighed on a torsion balance. The same number of tubers or cuttings from the most productive hill was then placed on the other pan of the balance. If the weight exceeded that of the weighed lot from the least productive hill the larger tubers or cuttings were exchanged for smaller ones, until the two lots balanced on the scale. Thus the amount of seed planted was the same for the two selections of seed. The number of hills planted of each of the two varieties, the weight of the same and the yield of the crop for 1898 and 1899, respectively, appear in the following table:

Table showing yields of potatoes from most productive and least productive hills.

OLD LONG MERCER

  1898 1899 Total yield
for the 2 years
in ounces
Number of
hills planted
Weight of seed
in grammes
Yield Number of
hills planted
Weight
of seed
in grammes
Yield
No. of
tubers
Weight of
same in oz.
No. of
tubers
Weight of
same in oz.
Most productive hill 14 95.5 36 21 15/16 14 118 68 41 63 15/16
Least productive bill 14 95.5 26 6 11/16 14 118 42 31 1/2 41 3/16

SNOWFLAKE

  1898 1899 Total yield
for the 2 years
in ounces
Number of
hills planted
Weight of seed
in grammes
Yield Number of
hills planted
Weight
of seed
in grammes
Yield
No. of
tubers
Weight of
same in oz.
No. of
tubers
Weight of
same in oz.
Most productive hill 13 111 42 41 10/16 32 323 190 290 1/2 323 1/8
Least productive bill 13 111 36 12 4/16 32 323 159 88 100 1/4

Adding the total yields of the most productive hill of the varieties together, and subtracting from this sum the same total for the least productive hill, it appears that the actual excess in yield of the seed from the most productive hills was a trifle over 180 per cent. It is difficult, to explain this difference in yield on any other hypothesis than the difference in the inherent vigor of the samples of seed planted. It must be remembered that the weight of the seed planted was the same, that the conditions of growth were the same and that the method of selection was rather against the most productive hills, because while the largest tubers from the least productive hills were used for seed, the majority of the largest tubers from the most productive hills were rejected. Fig. 78 shows the yield from the most productive and least productive bill of the Snowflake variety, gathered in the fall of 1898 as grown in 1899. The small groups above show the largest bill, and the smallest bill respectively as selected this season.

This experiment has not tended to increase the yield of the varieties used, because the most productive hills were continually hampered by having the seed tubers cut up fine to keep them comparable to the least productive hills. It demonstrates the increased vigor of the most productive hills and nothing more.

FIG. 78.—Yield of potatoes from seed from most productive, (left), and from least productive hill (right).

How far the yield of a variety may be increased by planting only the seed from the most productive hills will, it is hoped, form the basis for a future experiment.

It is believed that these experiments, reaching as they do through fourteen years, are sufficient to demonstrate the principle that vigor in the potato plant, as in other plants, may be maintained and increased by selection. The potato grower must decide how far he can benefit by this principle. Heretofore he has attained the end by purchasing, as often as his varieties fail, new varieties, in which vigor has been enhanced by careful breeding. But, he may doubtless prevent the failure of his varieties by the method of seed selection indicated in this article. Where time digging machine is employed, the best way to carry out the plan would be to grow a plat of potatoes each year on the best soil, to be used expressly for seed selection, and to dig this plat by hand. The selected tubers from this plat could be used the next season to produce the seed for the main crop the following year. This is substantially the method practiced by seed growers in maintaining the vigor and purity of their seeds.