Journal of Heredity 23(11): 467-470 (1932)
EFFECT OF STORAGE TEMPERATURE ON DATE OF FLOWERING
In the Paperwhite Narcissus
DAVID GRIFFITHS and R. C. WRIGHT
Office of Horticultural Crops and Diseases, U. S. Department of Agriculture

INVESTIGATIONS during the past three years have been conducted into the effect of storage environment on the development of the flower in the Paperwhite narcissus. This season about two dozen lots of bulbs have been employed in various ways in both commercial storage and controlled temperatures in refrigerated storage. In these investigations with Paperwhites the point at issue is one of effect of the storage temperature on time of flowering and growth of plants. There is none of the element of keeping quality involved, for the Paperwhite bulb will keep in any storage temperature from 36° F. to the limit of the temperature conditions obtaining in the various situations in which they have been handled from South Florida to the District of Columbia. These bulbs do not rot as do the Dutch stocks.

No attempt will be made to go into details now except with reference to five flats of 35 bulbs each of Florida grown stocks. These are emphasized because they point to a method of treatment which may possibly be of commercial importance, and which is of some interest to breeders and to students of effect of environment.

It should be noted that in all cases it was information on the effect of the storage environment on the comparative (late and other flowering characteristics that was mainly sought; consequently it was not practicable to attempt to get plants in early. On the contrary, a handling was practiced which was considered to be average and such as was best calculated to meet the requirements of both early and late lots.

Planting (in flats) occurred September 22 to 25 for all but one or two of the lots mentioned here. After planting, the flats were wet down and placed outside covered with straw until the tops began to appear. On October 20 all of them were placed on the benches of the greenhouse and carried without heat until the first one came into blossom, after which a night temperature of 45° to 50° was specified. Bulbs from both North and South Carolina were also carried at various temperatures mostly for the entire storage season, but a few were taken from storage and potted for forcing August 1.

As a general principle, the effect of cold storage is a dwarfing one on the Paperwhite as on other varieties of narcissus. In all lots stored at 36°, 40°, 50°, and 55° F. for the entire season there was an intolerable amount of dwarfing. Those stored at 36° invariably made practically no growth of top and but little of root. The condition from 40° was but little better. From 50° to 55° the dwarfing was still too great to be commercially tolerable. At 60° there was still dwarfing, although without checks for comparison the plants might be considered normal. Not until a temperature of 70° was reached was the growth considered normal of the bulbs submitted to controlled temperatures for the entire storage season. from June to the end of September.

Bulbs were subjected to 55° and 60° respectively from June 12 to August 1, then potted and placed in a cellar where the temperatures ran 70° to 80° during August and slightly lower in September. In both cases the growth was erratic and unsatisfactory, and the flowering and rooting subnormal.


EFFECT OF STORAGE TEMPERATURES
Figure ll
Reaction of Florida grown Paperwhites to various constant temperatures, August 15 to September 20, following normal storage. Upper left, 60°F, blossomed November 13; right, 55°, blossomed November 8; middle left, 50°, blossomed November 17; right, check, blossomed November 25; front, 36°, blossomed December 8.

The bulbs of the main Florida stock which are of most importance were received the middle of June and put in ordinary commercial storage on. Arlington Experiment Farm, Rosslyn, Va., until August 15, then subjected to various controlled storage temperatures until September 22 to 25, when they were potted. The handling from this date on was identical with that accorded to those in cold storage the entire season.

The behavior of these bulbs was very interesting and important from the commercial point of view. A summary of their behavior follows:

In the reactions there are two points not brought out above that are particularly interesting, namely, the dwarfing of the plants at 50° and 55° was not noticeable in the size of the leaves but in the number of shoots which came out of a bulb. A most unlooked-for reaction was an apparent curtailment of shoot development in the lots stored at 50° and 55°, and a negligible if any diminution at 36° and 60°. The flat stored at 36° was very much retarded, but when it came into full flower about the middle of December the shoots were as numerous as in the checks, but the stems were shorter although not detrimentally so. It will be seen that the reaction is a complicated one.

Table I—Summary of Reactions of Florida Grown Paperwhites
to Storage Temperatures, August 15 to September 22

Temperature in
Degrees F.
Dote of
Flowering
Condition of Plants Condition of Flowers
36 12/8 slightly dwarfed slightly dwarfed
50 11/17 subnormal subnormal
55 11/8 subnormal subnormal
60 11/13 subnormal subnormal
Check 11/23 normal normal

 


EARLY BLOSSOMING OF TREATED BULBS
Figure 12
The flat shown in upper right of previous figure when in height of blossom. The bulbs were exposed to a storage temperature of 55°F. The plants blossomed two weeks before the check lot.

The defect of low temperatures on the inflorescence was more striking but it ran parallel with the effect on the plants. The greatest floral injury occurred in the bulbs stored at 50° and 55°. It was such as not to be commercially tolerable at 50°, but only slight at 55°. The diminution in the size of the flower, while evident, was not serious in either the 50° or the 55° temperatures. The diminution in the number of florets at 50°, however, was serious. It is thought that there was some injury of this kind at 55°, but it was not serious enough to attract attention when the flat was in blossom. This kind of reaction was wholly unexpected; consequently, since the inflorescence was commercially acceptable, the flowers were cut at full anthesis with satisfactory spikes of blossoms. A comparison of the number of florets from 50 and the check, however, has been made and shows a yield of 284 and 430 respectively, each having 35 bulbs. The flat stored at 36° also had 35 bulbs, but produced 416 florets.

A reading on single pots of six bulbs each, South Carolina grown but stored under controlled temperatures as designated below, throws further light on the subject.

One pot in this lot was stored at 55° and was planted September 1, placed in the rooting cellar to September 22, and then carried like the others. It produced six spikes and 30 florets from six bulbs, starting to open November 22.

It is realized that the practical man who has followed its tip to this point may think that cold storaging of Paperwhites produces very complicated results. So it does! But there appear to be a few lessons that can be learned from the data.

1. That storing the bulbs at 55° F. for six weeks before potting the latter part of September induces a precocity of flowering of over two weeks with a floral modification which is commercially tolerable. In other words, the treatment appears to be practicable if the flowers are needed earlier than they. come naturally.

2. That a temperature of 36° F. for the same length of time retards flowering beyond the point at which flowering occurs from commercial storage, with floral injury that is commercially negligible.

3. That storage of Paperwhites below 60° F. for the entire storage season from June to the end of September should not be considered.

4. All this seems to coincide in a general way (but with modifications) with the work of Blaauw1 who found that to induce precocity of flowering in the tulip it was best to submit it to a temperature of about 70° for a month and then to 50° until potting.

  1. BLAAUW, PROF. A. H. Proc. Konin. Akad. van Wetenshcappen te Amsterdam, 10: 10, p. 1342, 1926.

Table Il—Effect of Storage Temperatures on South
Carolina Grown Bulbs Stored from June 15 to September 22.

Temp. in
Degrees F
Date of
Flowering
No. of
Spikes
No. of
Florets
50     no growth
60 11/12 6 32
70 11/28 6 70
Check 11/27 6 87

EDITOR'S NOTE: The results reported above on the effects of storage temperature on narcissus bulbs evidently parallel the iarovization experiments of Lissenko, in that a temperature treatment of dormant bulbs has drastically affected their later development. Since Mr. Bruman's note called attention to Lissenko's work, American research along this same line has come to our attention. A report of this is anticipated in an early number of the JOURNAL.