COOL STORAGE OF APPLES.

New Zealand Journal of Agriculture, Volume XXV, Issue 1, 20 July 1922, Page 34

COOL STORAGE OF APPLES.

AN INVESTIGATION OF FLESH - COLLAPSE.

R. WATERS,

Biological Laboratory, Wellington.

[Paper read at the annual conference of the New Zealand Fruitgrowers’ Federation, Wellington, June, 1922.] Fruit held in cool storage is liable to deteriorate from a number of different causes, and in order to perfect our methods of preserving fruit in this manner the various defects that are met with must first be sharply distinguished one from the other. Where it is possible this can best be done by a study of the nature of the primary causes. BLACK-SPOT, “ STING,” AND SCALD. In order to form some idea of the different natures of the diseases in cool-stored apples we may first briefly consider the well-known condition of black-spot fungus (Venturia inaequalis). There is no doubt - that a certain amount of development of black-spot takes place in cool store. But further, than this, judging by the very early infection that is met with, it is clear that perfectly sound apples can be attacked in cool store — is, that black-spot can spread in such low temperatures. This is obviously a trouble that must not be attributed to the storage conditions ; the remedy is to be applied before the fruit is picked.

Secondly, one meets in the cool store with a class of disease known as “ sting/' This term appears to cover a number of different conditions. Strictly speaking, it bears reference only to such injury as succeeds the punctures of insects. Popularly, however, sting is seen to be some form of rot or decay. Blue mould (P enicillium), bitterrot (Glom&rella), or botrytis (a fungus that in the held may set up rot in the eye of the apple) may be the cause of the rot, but the real cause of sting is due primarily to some form of mechanical injury to the skin. In this case the fungi do not spread in the store like black-spot, for the skin must be injured before they can set up infection. This, then, is another trouble that is instituted in the apple prior to its arrival at the store. Thirdly, we may take another type of —scald. This disease is very striking in its appearance. It may appear as small up to very large dark sunken patches in the surface of the apple. , The fruit may be almost covered with the disease, only a small portion at the stalk and eye ends remaining undamaged. The disease does not spread through the fruit like a fungus, nor does it spread from one fruit to another. It is not caused by a fungus but by vapours. Certain American investigations have shown that these vapours, known as esters, are given off by the apple, and that if they accumulate in sufficient quantities they are liable to produce the effect known as scald. This type of disease is due more to storage conditions than any we have yet considered. It is worse among apples packed in barrels. - Satisfactory ventilation will disperse the vapours and prevent injury. The investigators, however, suggested another remedy, that of wrapping the fruit in oiled paper. This method has been tried out with success by the Biology and Horticulture branches of the Department of Agriculture. The fourth type of disease consists in those whose cause is still unknown. This brings me to a special form of injury to which I have given some attention. FLESH-COLLAPSE DISEASE. Recently cabled reports have appeared in our local papers referring to shipments of Tasmanian and Australian apples which have opened up in England in bad condition. The important feature of the trouble as. reported was that while the outside of the fruit showed no sign of injury the inside was browned. Other reports have stated that “ brown-heart ” is very prevalent in the shipments. I believe that these troubles will be found to be identical with an important disease affecting cool-stored apples in New Zealand. In the first place this local disease may be clearly distinguished from scald and all other surface injuries by the fact that the skin remains undamaged until the last stage of the disease. This, in fact, is one of its characteristic features. Beneath the skin it may appear in various degrees of severity. It may occur merely as a narrow band of pinkish-brown soft flesh running parallel with the skin. The brownish condition, however, may involve a much larger portion of the flesh ; in fact, the whole of the interior may be thus damaged, while the skin shows little or no signs of injury. Microscopic examination of the flesh shows that the cells are collapsed. We in New Zealand have therefore come to know the disease as “ flesh-collapse.” Affected apples when squeezed in the hand are not firm, but abnormally

springy. As a result of the damage thus sustained fungus rots may subsequently set in and discoloration of the skin finally .make its appearance. This disease has already accounted for . extensive losses in. apples cool-stored in New Zealand, also for losses to our fruit after shipment to London. In my opinion, outside of orchard practice, the question of paramount importance to the success of our apple export trade is how to. prevent the development of flesh-collapse. In November, 1920, I was instructed to take up the study of flesh-collapse. Many reasons were at that time suggested as the cause of the disease, and there was very little agreement in the opinions of different individuals. Only in two particulars was there any concurrence of opinion. Those persons, for instance, who were interested in the various cool stores inclined to the view that the trouble arose from certain conditions in the orchard. The or char dists, on the other hand,' showed a strong tendency to claim that the cause of the trouble should be sought in the cool store. The real cause of the disease has not yet been demonstrated in any part of the world. We in New Zealand have certainly made some advance, inasmuch as we have shown that certain opinions as to the cause are wrong. My present purpose is not to dogmatize as to Tie cause of flesh-collapse, but rather to relate briefly the results of the work that has'been done, and to show what I believe to be the most promising direction in which to seek a solution of this most difficult problem. The various conditions that have been suggested as the cause of flesh-collapse will next be considered. Weather : Drought followed by much rain was believed to result in a rush of sap that rendered the developing fruit susceptible to fleshcollapse. The trouble, however, was just as abundant in 1921 as in 1922, and the seasonal peculiarities must have been similar in both years if they were the cause ; but this was not the case. Lack of cultivation : It is quite clear that if the weather condition had exerted a bad influence on the fruit, then a sufficiency of cultivation might certainly have done much to equalize any excess or deficiency in soil-moisture. Apples, however, were shown to develop fleshcollapse despite liberal cultivation. Maturity of the fruit : The varying stages of maturity at which the apples were picked were held to be the cause. Under this heading size of fruit comes in, and also the difference between fruit gathered at the first picking as compared with that gathered at the later pickings. . Age of trees : It is widely accepted that the fruit from older trees stores better than that from younger trees. . It was shown, however, that the fruit of certain growers stored well in 1919, whereas in 1920 their stored fruit failed. Thus the trees when a year younger gave better results. Time elapsing between packing and delivery : In this matter there was little definite evidence available. I was dependent mainly upon the word of the grower. But if it is held that delayed delivery was the. cause of the trouble, one has to assume that a number of successful growers who are thoroughly aware of the necessity of prompt delivery failed to carry this out in two successive years. This by no means exhausts the evidence that was collected to show that none of the field conditions referred to were in themselves the cause of flesh-collapse. But I will now pass on to the experiences of several

growers who happened to have stored part of their fruit in one firm’s cool store and part in that of another firm. There were several instances in which fruit - stored perfectly in one store and developed flesh-collapse in another, and these examples are of immense value in showing that certain of the suspected field conditions were not in themselves capable of inducing the disease. If, for instance, an orchardist picks the fruit of a single variety in his orchard, that crop as it is picked has certainly experienced the same weather and soil conditions. The cultivation will have been the same, the age of the trees is the same, and it matters not how inefficient the pickers were ; they were the same throughout, and the maturity will be similar throughout. Further, if that orchardist puts, say, 2| in. to 3 J in. fruit in one store and the same size in another store, one would certainly, expect, such fruit to keep a similar time if the storage conditions were alike. In several cases, however, it was found that such apples stored well in one store but developed flesh-collapse in the other. The evidence went strongly to show that neither the weather, the cultivation, the maturity, the size of apple, nor the age of the tree was in itself the cause. Now comes what may on the surface appear to be a contradiction of what has just been said. Despite the foregoing remarks, I firmly believe that apples as they reach the cool store differ markedly in their resistance to cool-storage conditions. My reasons are as follows : — Regarding the susceptibility of apples to flesh-collapse —firstly, the flesh of one variety admittedly differs from that of another : Sturmers are well known to keep longer, than Jonathans. , Next there are differences in the fruit from different localities : the Sturmers from one locality developed no flesh-collapse, while those from another developed it abundantly even in the same store. Thirdly, there are differences among individual apples in the same package ; some develop fleshcollapse and others do not. Lastly, in the same apple one side seems more susceptible than the other ; the uncoloured side commonly showed more damage. Actually this is not contradictory. The whole of these arguments are governed by the next statement : One would certainly regard the fruit from the orchardist who had experienced the most trouble with flesh - collapse as being the most susceptible, but despite this such susceptible fruit was' affected in one store yet kept well in another. The conclusion I draw from this is as follows : One is bound to admit that the quality of the flesh of some varieties, lines, or individual apples as they reach the cool store is such as to render them more liable than others to flesh-collapse ; but by no means can one admit that this inherent susceptibility in such apples is sufficient to prevent them from being satisfactorily cool-stored. • Cool-storage Conditions: Temperahire. We now arrive at a consideration of cool-storage conditions in connection with the investigation. It was very commonly held that fleshcollapse was brought about by freezing, the suggestion being that inadvertently or through negligence the temperature of a store was allowed to drop below 32 0 F., and thus result in injury. Firstly, fleshcollapse was found to occur in a number of stores, and it is somewhat unlikely that negligence in the matter of temperatures would be a common occurrence. This argument, however, is inconclusive, and can be dismissed. Secondly, it was decided to make a test of the effects

of varying temperatures upon apples. A number of Sturmers of different lines were placed in the duct of a cool room. The temperature of the duct was rapidly reduced from 50° to 20° F. The fruit was kept at this for six or seven hours, and was examined at intervals. Some of the fruit was then brought out into a temperature of 60° and allowed to warm up. The temperature of the duct was allowed to rise gradually overnight to about 40°, and next day was again subjected to 20 0 for some hours. The power was then turned off and the temperature again rose. The fruit was left in the duct for a week, when it was examined. No signs of flesh-collapse developed in any of the apples. A number of attempts were made to artificially produce fleshcollapse by fluctuating temperatures and other means, but without success. It therefore seems unlikely that the dropping of the temperature for a short time would have sufficient effect to cause the trouble. I could find no quick means of producing this condition, and consequently began to think of effects that would be more gradual. It is a significant fact that both in 1920 and 1921 flesh-collapse made its appearance about the same timeSeptember. Thus for three or four months the fruit successfully withstood the storage conditions. After that flesh-collapse made its appearance. With this in mind, inquiries were made as to what temperatures were employed in different stores. The stores in general adopted the 32 0 standard. ’ Later on, however, it was found that there was very great differences in the time during which different stores kept their machinery running. Some stores reduced their temperatures to 32 0 in the morning, ran for eight hours, then shut off and trusted to their insulation to maintain a sufficiently 'low temperature. Other stores were running much longer, even up to twenty-four hours in the day. Thus there is a very considerable difference in practice. This brings me to the theory upon which I am working at present, which is as hollows : The flesh of the apple cools more Jowly and warms up more slowly than the atmosphere of the store. Hence the apple may be said to average out the varying temperature of the chamber. If one store is running twenty-four hours at 32 0 , while another is kept at that temperature for only eight hours, then it is certain that the average temperature of the apples in the eight-hour store will be higher than 32 0 . Prolonged exposure to a temperature - of 32 0 ' might possibly exert some strain upon the flesh and consequent injury. (There are certain peculiar physical happenings to water at 32 0 In a few months this might possibly manifest itself in fleshcollapse. Certainly it seemed that those stores that were running for shorter hours had less flesh-collapse than others. On board ship, where it may be presumed the machinery is running for long periods, one certainly seems to find abundant flesh-collapse. : This,is, of course, only theory; but I have an experiment going to ascertain the effects of storing Sturmers at a slightly higher temperaturenamely, 34 0 to 36°. I should like to try higher temperatures still, but this would entail either special apparatus or else some risk to a large, quantity of fruit. . ' LINES OF INVESTIGATION. - In conclusion, I may say that in New. Zealand we have practically no: first-hand knowledge as to the best storage temperature, for fruit, and one cannot say for certain, that .the temperatures used in other.

countries will suit our apples. There are therefore two lines of investigation that suggest themselves to me as important: Firstly, the investigation of the optimum temperatures for the storage of New Zealand apples; and, secondly, the means by which certain New Zealand apples can be rendered more resistant to cool-storage conditions.