I94I ] MILLER AND MCGOLDRICI-I : EFFECT OF DAY LENGTH ON GROWTH 26".

tribasic copper sulfate when used at concentrations of 3 pounds to 5o gallons of water gave increased yields not significantly different than standard Bordeaux in I93 9. All plants sprayed with the fixed copper usually ripened from 4 to IO days earlier than the Bordeaux plots.

For the commercial grower of Irish Cobbler in southeastern Wis- consin 5-5-50 Bordeaux mixture is equal to or better than any of the other Bordeaux formulae or fixed copper compounds tested, in increas- ing yields. The proprietary copper compounds, however, may be used wisely by the small grower or the home gardener since they may be more convenient to make up and apply.

LITERATURE CITED

i. Bonde, R. I932. Potato spraying and dusting experiments. I929-I93I. Maine Agr. Exp. Sta. Bul. 362:I77-232.

2. Mader, E. O. and Blodgett. F. M. I935. Effects of modifications of the potato-spray program. Cornell Univ. Agr. Exp. Sta. Bul. 62L 34 P.

E F F E C T O F DAY L E N G T H U P O N T H E V E G E T A T I V E G R O W T H , M A T U R I T Y , AND T U B E R C H A R A C T E R S

O F T H E I R I S H P O T A T O

JULIAN C. MILLER

Louisiana State University, Baton Rouge, Lob, AND

FRED McGOLDRICK

Cornell University, Ithaca, N. Y.

INTRODUCTION

Since I93 5 when the breeding program was begun in Louisiana, it has been observed that all seedling plants when grown to maturity in the fall set tubers. Also it has been observed that a large percentage of these fall-grown potatoes resulting from seedling plants were smooth as compared with spring-grown potatoes from the same seedlings. With most family lines, when grown during the spring not more than 50 per cent of the potatoes were smooth and with some lines as many as 2 5 per cent of the spring-grown plants did not produce any potatoes al- though the plants were extremely vegetative.

The temperature and photoperiod of the two seasons, spring and fall, are as follows: under fall conditions the temperature advances from warm to cool and the photoperiod decreases from a I4-hour day to a Io-hour day; in the spring the temperature advances from cool to warm and the photoperiod from a I I ~ - h o u r day to a I4-hour day. Of

262 THE AMERICAN POTATO JOURNAL [Vol I8,

the two environmental factors, temperature and day length, it seemed that day length exercised the major influence.

In the spring of I939 an experiment was set up to determine what effects different length photoperiods would have upon the vegetative growth, maturity, and tuber characters of the Irish potato.

METtt0D OF PROCEDURE

In order to study the photoperiod effects, four treatments were set up as follows: Treatment I-I8 hours; treatment 2-8 hours; treat- ment 3-I2 hours; and treatment 4-normal day length. In order to arrange for photoperiod controls, cold frames were constructed. The cold frames were built to a height of about three feet in the back and two feet in the front. Partitions were made so that the frame was divided into four sections, each section measuring six by six feet.

Day length was supplemented by suspending one 3oo-watt bulb about four feet above the plants in the frame receiving extra light. In treatments 2 and 3, where the day lengths were shorter than normal, the frames were covered with two layers of black satin cloth to regulate the day length. The cloth was rolled down over the frames in the af- ternoon at the proper times to regulate day length as desired. Electric fans were set up in treatments 2 and 3 to bring in outside air and main- tain the normal outside air temperature as nearly as was possible.

In each of the four frames three varieties were planted on the Ioth of February : ( I) Mexican Seedling No. 8, which is considered a short-day plant; (2) K:-I selfed Katahdin. This variety is extremely early and is con-

sidered a long-day plant; (3) T 3-I--Selfed Triumph, a short-day plant. In planting these three varieties in the four treatments the plant- ings were made in a randomized design. All plants were given the same cultural treatments throughout the growing period. All plots were harvested on the 7th of June.

EXPERIMENTAL RESULTS

Treatment I. All plants in this treatment showed extreme vege- tative growth. The Mexican Seedling No. 8 and T 3-1 were indeter- minate in vegetative growth, making vines from five to six feet in length. The plants were still growing at harvest time and had pro- duced as many as three or more crops of blossoms. All plants pro-

1 9 4 1 1 M I L L E R A N D MCGOLDRICH : EFFECT OF DAY L E N G T H ON GROW'TH 263

duced a heavy set of seed balls. This treatment produced a higher yield than treatment 2, although the tubers were rough and irregular except those of the K-I, which although it made a heavy vegetative growth, was not indeterminate in its growth habits.

Treatment 2. Plants in this treatment which were given eight hours of day length, showed less vegetative growth than plants in any of the other treatments: K-I reached an average height of 12 inches; the T 3-1, 18 inches ; and the Mexican Seedling No. 8, 22 inches. These plants also matured first, between the 15th and the 2oth of May. The K-I reached maturity first; the T 3-1 second; and the Mexican Seed- ling No. 8 was last. The plants were considered mature when they had died to the ground level. In this treatment none of the plants of the three varieties blossomed. The tubers of all three varieties were smoother and the eyes more shallow than those in any of the other treatments, although the yield was the lowest obtained. The T 3-1 and the Mexican Seedling No. 8 were very smooth as compared with the normal appearance of these two seedlings when grown in the field in Louisiana.

Treatment 3. Throughout the period of this experiment a constant I2-hour day was maintained. The plants in this test were the second in order of maturity, which occurred between the 2oth and the 25th of May. Again K-I was first to mature, followed by the T 3-1 and Mex- ican Seedling No. 8. No blossoming occurred on any of the plants in this treatment. All the tubers from the three varieties were smooth, approaching very closely the smoothness that resulted from treatment 2.

Treatment 4. This was considered as a check and was allowed normal day length. During this experiment the day length advanced from III~ hours in March to 14 hours in June at the time of maturity. In this controlled treatment many of the plants at harvest time still showed some vegetative growth. The plants of K-I matured about the 25th of May; however, at harvest time some plants of T 3-1 were still living, showing green stems, whereas all of the Mexican Seedling No. 8 plants were still green. The Mexican Seedling No. 8 blossomed and set seed freely and some blooming and seed setting occurred on the T 3-1. There were a few flowers but no seed set on the K-I. The tubers of the Mexican Seedling No. 8 and T 3-1 were rough and had deep eyes; however, those of the K-I remained smooth.

This experiment has borne out previous observations that photo- period has a very definite effect upon the vegetative growth, maturity, and tuber characters. In reference to tubers, the length of day influ- ences very definitely the yield and the smoothness of the potatoes, par-

264 T H E A M E R I C A N POTATO J O U R N A L [Vol 18,

ticularly with reference to depth of eyes. Both heredity and environ- ment play an important part in the smoothness or roughness of the po- tatoes. It is the modification of some of the hereditary characters by environment that the authors wish to point out in this paper. To further illustrate this the following data are presented on segregations from six different lots of seedlings for long and short-day plants. Of these lots two were selfed lines and four were lines consisting of dif- ferent crosses between T 3-1, which is a selfed Triumph, and Katahdin, Chippewa, Cobbler, and K-I. Also data on selfed lines of T 3-1 and Chippewa are presented.

TABLE I.--Short and long-day segregates from first spring-groztm crop.

Variety

T 3-1 C x T 3 - I Chx T3-I K-I x T 3-I Chippewa

N o . Plants

29 83

124 25 71

No. Segregates ior

Long Day

I I 46 94 I4 5I

Short Day

i8 37 3o I I 2O

In this experiment, Katahdin, Chippewa, Cobbler, K-I , and Chip- pewa selfed are classed as long-day plants. With the ex- ception of the Louisiana K-I these plants were selected in the North under long-day conditions. The T 3-1 is a segregate from Triumph selfed and is considered a short-day plant. When grown under short- day conditions the potatoes are satisfactorily smooth but when grown under long-day conditions the potatoes are rough and plants very veg- etative. It will be noted that when early-maturing varieties, that is, long-day varieties, are crossed with T 3-1, a short-day variety, a higher percentage of the segregates belong to the long-day, or earlier-matur- ing, class. From a selfed line of T 3-I it will be noted that more of the segregates fall into the short-day class whereas with the Chippewa, an early-maturing variety, a higher percentage of the segregates fall into the long-day, or early-maturing, class.

1941] MILLER AND MCGOLDRICH : EFFECT OF DAY LENGTH ON GROWTH 265

DISCUSSION

The results obtained with fall- and spring-grown potatoes and from the light experiments discussed in this paper might help to explain the variations noted in varieties of potatoes which have been moved from one section of the world to another where the photoperiods of the local- ities are widely different. To further illustrate this, very few Euro- pean varieties have proved satisfactory in the United States. At the same time very few varieties have proved satisfactory when moved to this country from the high altitude equatorial areas of South Amer- ica. When introducing the northern European varieties into the United States, one would expect them to show a lower yield than native varie- ties and when varieties are brought from the equatorial areas one would expect them to be excessively vegetative and produce very few potatoes. The potatoes produced would be unusually rough. The same thing would apply in this country when northern-grown varieties are shipped into the south for potato production, the result being lower yields than in the area where the original selection was made. Under the short- day conditions of the south the potatoes mature earlier resulting in lower yields, although the potatoes are probably smoother than when the same varieties are grown under long-day conditions. On the other hand, if the selection is made in the South for high yielding ability, it might be that when the potato is increased in the north, the tubers would have deeper eyes and a rougher appearance than when grown in the south.

SUMMARY

I. Studies concerning the effect of length of day were made on vegetative growth, maturity, and yield and smoothness of tubers of the Irish potato when grown under field and controlled conditions.

2. With field and controlled experiments, plantings under short days showed less vegetative growth, matured earlier, and the potatoes were generally smoother. The opposite effects were obtained under long-day conditions; the plants were very vegetative, matured later, tubers had deeper eyes, and were more irregular in shape, although, the total yields were higher.

3- Seedlings representing several farrfily lines were studied and the resulting segregations could be classified as either long or short- day plants. The parental combinations had a marked influence on whether the resulting seedlings would fall into the long or short-day group.