Factors' Influencing the Development of Soggy Break-Down in Apples ^
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FACTORS' INFLUENCING THE DEVELOPMENT OF SOGGY BREAK-DOWN IN APPLES ^ By H. H. PLAGGE, research assistant professor, and T. J. MANEY, research professor and head, Subsection of Pomology, Iowa Agricultural Experiment Station INTRODUCTION The influence of storage temperature on soggy break-down ^ in certain apple varieties is generally recognized, but the relation of other etiologic factors to this disease is not so clearly understood. For example, it has been assumed that delayed storage is essential to the development of soggy break-down, and that late picking favors its occurrence. The effect of these and other causal agencies has not been demonstrated conclusively. Among other factors which have been considered as favorable or essential to the development of soggy break-down are inadequate ventilation of containers and storage rooms, a prolonged storage period, temperatures lower than 32° F., variations in fertilizer treatments, and climatic conditions. The effect of these and certain other factors on soggy break-down is con sidered in this paper. The importance of storage temperature in the control of soggy breakdown has been emphasized in earlier pubhcations {11, 16, 17)? This paper presents further evidence to show the relation of storage temperature to the disease in the varieties that were previously listed as susceptible and in other varieties for which little or no information is on record. The relative importance of other storage and prestorage factors as judged by the results of more than 11 years' work is indicated. REVIEW OF LITERATURE Investigators have emphasized the importance of immediate storage in the control of the soft scald type of soggy break-down in the Jonathan apple (Í, S, 6, 18y 19). In an earlier paper {IS) the writers indicated that delaying storage for 1 week, as compared with immediate storage or storage after 2 and 3 weeks' delay, usually increased sus- ceptibility in this variety. It should be noted, however, that imme- diate storage did not invariably prevent the disease, and that delays of 2 and 3 weeks gave best control. On the other hand, delaying the storage of Grimes Golden and Golden Delicious has usually resulted in greater susceptibihty to soggy break-down (Í0, 15). Harding found that cold-storing Grimes Golden whue it is in an active state of respiration produces a high degree of susceptibility (4), and that it reaches its highest respiratory activity between 3 and 5 weeks at 50*^ F. Harley and Fisher {6) concluded that a high concentration of carbon dioxide in Jonathan apple tissues is not a contributory cause of soggy break-down; Brooks and Harley {2) found that short exposures to 1 Received for publication Jan. 15,1937; issued December 1937. Journal Paper No. J432 of the Iowa Agri- cultural Experiment Station; project No. 281. 2 The two types of low-temperature disease designated in the literature as "soggy break-down" and "soft scald" are considered by the writers to be the same, and in this paper will be included under the term "soggy break-down." The reasons for this classification have been given {11,17) .3 3 Reference is made by number (italic) to Literature Cited, p. 762. Journal of Agricultural Research, Vol. 55, no, 10 Washington, D. O. Nov. 15,1937 Key no. Iowa-27 (739) 740 Journal of Agricultural Research Vol. 55, no. 10 this gas and high temperature reduced the tendency toward the disease. Gerhardt and Ezell (5), working with Jonathan at Wanatchee, Wash., found that immediate storage at 32^ F., when preceded by a 24-hour exposure to carbon dioxide, gave approximately as good control as ordinary storage at 36°. With delayed storage, however, carbon dioxide exposures gave less consistent results. RELATION OF STORAGE TEMPERATURE TO SOGGY BREAK-DOWN Although results of storage experiments of a rather comprehensive nature, showing that temperature is of primary importance in the control of soggy break-down in Grimes Golden, have been published {11,15,17), information concerning the ejïects of storage temperature on other varieties is limited. Some results for Jonathan, Wealthy, and Golden Delicious are on record {9, 10, 14, 16), but so far as the writers can determine, no results have been published for North- western Greening and Winter Banana. STUDIES WITH JONATHAN TABLE 1.—Percentage of soggy break-down occurring in Jonathan apples during storage at different temperatures for three and for five seasons RESULTS DURING 3 SEASONS i Break-down in— 2 Temperature (° F.) Delay be- fore storing 1924-25 1926-27 1928-29 Weeks Percent Percent Percent 42.3 14.1 8.2 18.9 6.9 67.6 30.. 10.3 2.9 21.7 0 1.0 15.2 6.9 0 1.8 .6 0 19.1 32.. .6 0 16.2 0 0 .7 0 0 0 0 0 1,9 34.. 0 0 5.1 0 0 0 0 0 0 0 0 .8 0 0 .9 0 0 0 0 0 0 0 0 0 Common storage.. 0 0 0 0 0 0 RESULTS DURING 5 SEASONS s Delay Break-down in— * Temperature (° P.) before storing 1929-30 1930-31 1931-32 1932-33 1933-34 JDays Percent Percent Percent Percent Percent Í 0 76.2 8.7 0.0 11.2 0.7 30 28.2 0 12.2 3.5 16.0 I 20 1.4 0 0 0 0 1 0 0 0 0 0 0 36 __ - — 0 0 0 0 0 I 20 0 0 0 0 0 Î Fruit examined the latter part of January. 2 Picking dates: 1924. October 7; 1926 and 1928, October 2. Source of Fruit: 1924, State orchard, western Iowa; 1926 and 1928, Apple Grove orchards, central Iowa. Number of boxes per test: l to 4. The same investigation was carried out in the seasons of 1925 and 1927. No soggy break-down occurred in these 2 years. 3 Fruit examined in February 1929-30 and 1931-32 and in March 1930-31,1932-33, and 1933-34. * Picking dates: 1929 and 1931, October 2; 1930, Oct. 6; 1932, September 30. Source of fruit: 1929, 1930, and 1931, Apple Grove orchards, central Iowa; 1932 and 1933, Worth orchard, western Iowa. Number of boxes per test: 1 to 4. In 1934 there was no crop because of severe drought. Nov. 16,1937 Factors in Development oj Soggy Break-Down in Apples 741 The effect of various storage temperatures on the development of soggy break-down in Jonathan is shown in table 1. These results show that break-down developed more severely at 30° F. than at 32°, 34°, or 36°, that it was a factor at 32°, and that it was not entirely absent at 34°. At 36° only traces of the disease appeared, and in common storage there was none. Experiments similar to those report- ed for three seasons in table 1 were also carried out in the seasons of 1925-26 and 1927-28, but no soggy break-down occurred. In FIGURE 1.—Section.^ of Jonathan apples severely aflected with the soft scald or surface type of soggy break-down. In most of the specimens shown the disease extends deeper into the cortex of the apple than is usual. (See fig. 8 for typical external appearance of soggy break-down in Jonathan.) earlier work (13) the writers found extensive development of soggy break-down at 32° in each of three other seasons. The difference in the susceptibility of .Jonathan in various years is thus very marked. The tendency to break-down in different lots of fruit given various delayed treatments also varied in different years. This factor is considered later. The results of storing Jonathan at the two temperatures 30° and 36° F. for five additional storage seasons are shown in table 1. These studies also show complete control of the disease at 36°. Variation in the susceptibility of Jonathan in different years was again apparent, and dissimilar break-down tendencies between lots of fruit given different delayed treatments were also marked. The results as a whole show that at a temperature of 36° soggy break-down (fig. 1) was 742 Journal of Agricultural Research Vol. 55, no. 10 completely eliminated in each of seven seasons and that it was kept under 1 percent in each of eight. STUDIES WITH NORTHWESTERN GREENING Storage experiments in which boxes of Extra Fancy Northwestern Greening apples were stored at various temperatures for each of two seasons are shown in table 2. In both seasons the fruit tested came from trees approximately 25 years old, and was picked at the peak of the picking season. The number of fruits per box ranged from 125 to 72, but the majority of the boxes contained between 113 and S^, No color distinction between green and yellow fruit was made. The study also includes 2 years of observations of this variety under common storage. Delay before storing took place in an open packing shed. TABLE 2.—Percentage of soggy break-down occurring in Extra Fancy Northwestern Greening apples ^ at different temperatures ^ Slight break-down Severe break-down Delay Storage temperature (° F.) before storing 1924-25 1927-28 1924-25 1927-28 Days Percent Percent Percent Percent ( 2 12.5 12.7 66.4 8.7 7 12.5 16.8 17.3 8.4 30- 1 14 1.9 0 0 0 21 13.4 41.3 2 12.2 28.4 41.4 43.2 21.8 29.6 0 32 - - J 7 13.6 1 14 0 2.6 0 .9 21 14.9 4.4 Í 2 1.5 42.7 1.0 17.3 0 4.2 34 —. __ J 7 4.8 15.3 1 14 0 0 0 0 21 2.4 2.4 3 2 6.8 56.3 2.6 11.3 J 7 1.6 5.1 .8 0 36 - 1 14 0 1.7 0 0 I 21 0 0 1 4.4 2.7 40 \ 7 3.8 1.9 14 1.0 1.0 1 0 0 29-60* (common storage) 1 7 0 0 I 14 0 0 1 Picking date, October 13 in both seasons.