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temperature and the greater the proportion of air, the longer would the injury be averted or the less serious would it be; but unless allowed nearly twenty times their volume of air the tubers thus hermetically sealed would not sprout normally in the jars and were liable to show typical blackheart.
With equal volumes of tubers and air, confinement for ten or twelve days at a temperature of 70° caused the tubers in the jars to become moist over some or all of their surfaces. When the potatoes are removed from the jars, these moist areas turn brown, and the flesh at the center of the tuber changes to pink and then to black-blackheart. Reduction of the temperature at which the jars were held to 55° or 60° F. delayed the appearance of the moist areas and the accompanying development of blackheart to 20 days; and tubers held at 40° remain uninjured for from 23 to 40 days. When the jars are only one-half or one-quarter full of potatoes, thus increasing the proportion of air, the development of the injury is delayed; but it appears before the normal length of time for storing potatoes is reached.
Until ten times as great a volume of air as of tubers was enclosed in the jars, little or no sprouting of the potatoes took place; but with about nineteen times as much air the tubers sprouted normally and showed no other signs of injury.
As these jar tests indicate that lack of air soon Tubers results in injury to tubers or their death, it was
stored evident that improper storage conditions might in tanks. lead to the same trouble. Accordingly, many tests
were made with potatoes stored in tall, slender, upright metal tanks, closed at the bottom but usually open at the top. Each of the tanks was nine inches in diameter, but they were made of various heights, ranging from 61 to 101 feet, and wire-netting separators were placed in the tanks as they were filled with tubers thus dividing them into sections so that the effect of the various conditions imposed could be easily determined for the potatoes at different depths. Altho these tanks, with sides impervious to air, do not imitate exactly the conditions in piles or bins of potatoes of different depth, it is believed that they approximate them so closely that the results are a good guide to proper storage conditions.
Seven experiments were carried thru, using from one to four tanks, and in some cases sealed or unsealed jars were also used as checks or guides. In all the tests the conditions outside the tanks were quite like those actually surrounding stored potatoes, and in one case the tanks were placed in a cellar used for storage of apples, potatoes and roots. Careful records were kept of temperatures and only slight differences in readings were found between thermometers surrounded by the potatoes and others placed at corresponding heights outside the tanks.
The results secured in the different tanks and different tests do not show strict uniformity and there were noticeable differences between individual tubers under the same conditions in each tank; yet the very plain teaching from the tests is that it is not safe to pile potatoes more than six feet deep, if they are to be held for some months, even if the temperature remains below 40° F. If to be stored more than three or four weeks where temperatures rise above 50° the tubers should not be piled more than three feet deep.
The injury to the potatoes in the tanks is very similar to that of the tubers in the sealed jars, often with the addition of rotten spots due to the action of fungi and bacteria. In general, tho, they show the same collection of moisture on the surface, external discoloration when exposed to the air and frequent occurrence of typical blackheart. Like the potatoes in jars those in tanks failed to sprout normally when held long at any considerable depth even if the temperature favored germination.
After these studies were begun it was learned that Potatoes potatoes stored in "pits" (i. e., piled in conical in “ pits." heaps on the ground and covered with coarse
manure, stalks, straw, etc., and soil), sometimes showed blackheart; so a study was made of three such pits. No injury to the potatoes resulted altho conditions were apparently quite favorable to occurrence of the trouble. This would indicate that ventilation in " pits” is better than would be supposed from the conditions.
There is no doubt that blackheart may be caused, Cause and as Bartholomew states, by overheating potatoes, appearance of especially if poorly ventilated, but it is equally blackheart. clear that lack of air alone produces an almost
identical condition at quite low temperatures. That it is to lack of air, or oxygen, not to the accumulation of carbonic acid gas which the potatoes exhale, that the trouble is due is proved by two tests. In these tests the potatoes were enclosed in sealed receptacles and chemicals were placed below the tubers, but not in contact with them, to absorb this gas as it was produced. In spite of the withdrawal of this possibly harmful gas the tubers developed blackheart as markedly as those under similar conditions but with the gas present.
Blackheart produced by heating and that caused by lack of oxygen are very similar, so far as the flesh of the tuber is concerned; but the skin of heat-blackhearted potatoes shows no signs of injury, while those affected with blackheart from the lack of oxygen are more or less browned or discolored.
In both types of the injury the flesh first turns pink, then brown and finally black, and in extreme cases the discolored portion may become tough and leathery and so shrink that considerable cavities are formed.
The production of blackheart by lack of air is Blackheart accompanied by a loss of vitality of the eyes, so
potatoes that such blackhearted potatoes will not sprout for seed. normally, putting out very small, short stems or
none at all. These sprouts, however, are not like those in “spindling sprout ” — long, and very slender — but are merely dwarfed or miniature sprouts. Unless the trouble is so serious that the surface of the tubers is discolored, the sprouting ability of the potatoes is not greatly affected. Sprouting may be delayed by the small supply of oxygen while the tubers are in storage, but on free access of air normal sprouting occurs unless the internal injury has gone so far that evidence of it shows on the surface.
With heat-blackhearted tubers, decay usually follows severe injury, and germination is not greatly affected unless the internal injury is severe; so the same rule applies: If potatoes in the same lot with those showing blackheart do not present some external evidence of the trouble, either discoloration or decay, they may probably be safely used for seed. In cutting the seed it may be well to reject those tubers showing very extensive areas of blackened flesh.
The results of this investigation emphasize the Application importance of providing ventilation for potatoes of results in storage. The need of ventilation depends very to potato
largely upon the temperature. As the temperature storage. rises the volume of air required increases rapidly.
At low temperatures, potatoes may be stored in deep piles for long periods of time. At high temperatures, it is necessary to avoid deep piling or else provide special means of ventilation. If the temperature is kept below 40° F. potatoes may be piled in bins and cellars to a depth of six feet without any ventilation except that provided thru free access to the air overhead. Under such conditions, potatoes may be stored with safety for at least six months and perhaps longer. It is probable that no harm will result if the temperature goes up to 45° F. for a few days. But a long period of storage followed by a two weeks' exposure to a temperature of 50° F. or higher is liable to result in the ruin of most of the tubers below a depth of about three feet. Potatoes stored in deep piles should be carefully watched in the spring as the temperature rises. A few days of high temperature may cause much loss.
It is not in the province of this bulletin to discuss the means by which the ventilation of potatoes may be secured. The methods to be employed will vary according to circumstances. The principles to be kept in mind are as follows:
(1) Potatoes stored at high temperatures require more ventilation than those stored at low temperatures.
(2) Better ventilation is required for potatoes which are to be stored for a long period than for those which are to be stored for only a short time.
(3) Until more accurate determinations are made, six feet should be regarded as the maximum depth to which potatoes may be piled without special provision for ventilation when stored for six months at temperatures below 45° F. If greater depths than six feet are employed ventilators should be provided and so arranged that none of the tubers will be more than six feet distant from an abundant supply of air.
(4) At temperatures of 50–70° F. potatoes should not be piled over three feet deep if they are to be kept longer than about three weeks.
(5) No kind of ventilation is sufficient to prevent the occurrence of blackheart in potatoes kept for even a few days continuously at a temperature above 100° F.
(6) Complete exclusion of the air will ruin potatoes at any temperature.
(7) Small potato pits do not need ventilation; but some provision should be made for the ventilation of large pits.
ONION NECK-ROT IN STORAGE HOUSES. *
F. H. HALL.
In the fall of 1913 word was received at the Station Old, but not of an outbreak of disease in an onion-storage house well-studied in western New York. The disease was said to disease. threaten the entire stock of onions in the house.
Examination proved the trouble a serious one, of which the exact cause was unknown, but which had previously been reported from many places under various names, as mold, gray mold, storage rot, onion rot, onion bulb rot, dry rot, black-neck dry neck-rot, stem rot and neck-rot. As neck-rot is simple and appropriate it has been chosen as the common name for the disease.
Only casual study was needed to prove the trouble Trouble of due to a fungus, and to identify the organism fungus causing it as one of a large group of disease-proorigin. ducing fungi. The disease, or others similar to it
in some respects, had been ascribed by plant pathologists to different members of the genus Botrytis, or to species of allied genera; but careful study of the fungus and comparison of it, point by point, with more than a dozen other species reported as causing onion rots of this type or known to affect other species of the onion family, proved it a new species and resulted in giving it the name of Botrytis allii.
The disease is most common on stored onions, on Nature and which it usually appears, externally, as large black
extent of bodies or crusts, generally on the bulb near or the disease. surrounding the neck, less commonly on the sides,
and occasionally at the base. Beneath these bodies or crusts one or more of the scales, or the thickened leaf bases that make up the bulb, are rotted -- but without the production of much moisture, thus leading to the name "dry rot." On the onions the disease may also show as a dense ring or band of closely interwoven threads covered with smoke-gray fruit-bodies of the fungus, hence the name "gray mold.” Occasionally, an onion attacked by this
* Reprint of Popular Edition of Bulletin No. 437, July, 1917; for Builetin see p. 319. [Plates XXIII and XXIV illustrated this text.]