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A _H- .5. :'\".;1 a: ‘5 V ‘3 luv-13L k: :0 522:; 1&3 ICHI IIIIIIIIIIIIIIIIIIIIIIIII 31293 000851000 _ : THE EFFECT OF CATHODE RAY IRWXDIATIOI‘J ON SPRCIJ TIN G, WEIGiT LOSS AND OXYGEN CONSUL'TPTION OF POTATOES By RICHARD WIILIAM TAYLOR AN ABSTRACT Submitted to the School for Advanced Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Farm CI‘OpS Year 1958 Approved [6M 9% RICHARD WILLIAM TAYLOR ABSTRACT Russet Rural, Sebago, and Katahdin potatoes were irradiated with cathode rays at dosages of 0, 2,500, 5,000, and 10,000 rep both early and late in the storage season, and stored at AA degrees F. and 92 percent relative humidity for four months to detennine the effect of cathode ray irradiation on sprouting, weight loss and oxygen consumption. Irradiation inhibited sprouting of all three varieties when applied either early or late in the storage season. As the dosage increased, sprouting was correspondingly less. At a dosage of 10,000 rep sprouting was negligible with all varieties regardless of time of irradiation. The rate of weight loss and the weight loss exclusive of sprouting were dependent on the variety and the time of irradiation. In general it seemed that the highest level of irradiation caused a higher rate of loss than the control during the first month, subsequently becoming lowest durb ing the fourth.month. Irradiation affected the total weight lost due to respiration and transpiration, depending on the variety and the time of irradiation. With Russet Rural this weight loss was increased slightly with increasing irradiation in.the early experiment, but remained essen— tially the same as the control in the late experiment. Sebago reacted similarly in both experiments, weight loss increasing slightly as the dosage increased to 10,000 rep. Katahdin was not affected by increased.dosages of irradiation during the early experiment, but increased in weight loss during the late experiment. Oxygen consumption was affected materially by all dosages during the first experiment. Oxygen consumption of Russet Rural was highest at 48 hours RICHARD WILLIAM TAYLOR ABSTRACT (750 percent of control) followed by a gradual decline to essentially the same as the control at four months. Sebagos were greatest at 96 hours, followed by a similar decline to that of the control or slightly less. 'With Katahdin the rate of oxygen consumption fluctuated from.400 to 700 percent of the control between 24 hours and two months. After two months the rate declined gradually to slightly less than the control at four months. THE EFFECT OF CATHODE RAY IRRADIATION ON SPROUTING, WEIGHT LOSS AND OXYGEN OONSUNPTION 0F POTATOES By 310mm WILLIAM TAYLOR A THESIS Submitted to the School for Advanced Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Farm Crops Year 19 58 ACKNOWLEDGMENT The author wishes to express his gratitude to Dr. Donald R. Isleib without whose guidance and counsel this investigation would have been more difficult to accomplish. Appreciation is extended to Dr. Carter M. Harrison for his aid.in the preparation of the manuscript. Acknowledgment is also due to the Department of Agricultural.Engi- nearing, Michigan State University, for the use of the cathode ray facility. Finally, the author is indebted to his wife for her encouragement during the past year. TABLE OF INTRODJCTION . . . . . REVIEW OF IITERARJRE . EXPERIMENTAL . . . . . EXPERIMENTAL RESULTS . SUMMRY AND DISCUSSION CONCLUSIONS . . . . . LITERATURE CITED . . . CONTENTS Page . . . . . . . . . . . . l . . . . . . . . . . . . 3 . . . . . . . . . . . . 8 . . . . . . . . . . . . 12 INTRODUCTION Sprouting and excessive weight loss due to shrinkage in storage have long been problems in the potato industry. Generally, stored potatoes will lose from.one to six.percent of their weight per month, depending on storage conditions. Temperatures between A0 and 50 degrees F. delay sprouting for several months but unrefrigerated storage is usually not feasible beyond early spring because of the seasonal rise in temperature. Even with refrigeration it is difficult to hold untreated potatoes later than,May. Recent investigations into the use of ionizing radiation as a sprout inhibitor have been part of a large-scale attempt to utilize the waste fuels of nuclear reactors. Gamma irradiation in particular has been ex? tensively investigated with one of the main prdblems arising from.the fact that the rays pass completely through the tuber. Indications are that such complete penetration may cause mechanical.damage to inter- cellular structure, possible internal blackening, and inhibition of the wound-healing process. Gamma radiation consists of electromagnetic waves occurring in the range from lO°to 10’3 angstrom.units, while cathode rays consist of electrons which have been accelerated by electrostatic forces. Three terms are used to express the radiation dosage: roentgen (r), rad, and roentgen-equivalent-physical (rep). For the purposes of this experiment the three terms will be used synonymously. The depth of penetration of electrons depends, among other things, upon the density of the material being irradiated and the kinetic energy of the electrons expressed in million-electron volts (MEV). In this experiment a one MEV electron accelerator was used as the radiation source. The percent entrance of ionization of this machine, as shown by Nicholas (1958), decreases from 100 percent at zero depth after an initial rise to 120 percent at 0.5 millimeter depth. For potatoes the maximum.depth at which ionization occurs is approximately four millimeters. The purpose of this experiment was to observe the effects of four different dosages of cathode-ray irradiation on sprouting, weight loss, and oxygen consumption of three varieties of potatoes, in comparison to results obtained using similar dosages of gamma irradiation. The experi- ment was duplicated to include irradiation both early and late in the storage season. Experiment I was started in December, 1957, and con- tinued through April, 1958. Experiment II began in March, 1958, and ended in July, 1958. REVIEW OF LITERATJRE Little has been published concerning the use of cathode-ray irradia- tion to inhibit potato sprouting, although the use of gamma rays has been investigated rather extensively in the United States, in England, and in the U.S.S.R. The United States Army Quartermaster Corps has been parti- cularly interested in irradiation as a means of preserving potatoes as well as other fresh food products for military use. Sproutigg and weight loss. Brownell, EE.E;° (1957) reported that Idaho- grown Russet Burbank seed potatoes irradiated with gamma rays in the late spring sprouted less than those treated in the fall or early winter. A dosage of 15,000 rep appeared to be optimum regardless of storage temperature. Tubers receiving 5,000 rep developed sprouts three to five millimeters long at AS degrees F. after five months. 'Weight loss was found to decrease logarithmically with increasing dosages up to 15,000 rep when the tubers were stored lhO days at 50 degrees F. and 90 percent humidity. This behavior has lent support to a hypothesis that weight loss is proportional to the number of living cells, if the cells are inacti- vated by a random, statistical process. However, a different explanation was necessary to interpret the effect of irradiation on Sebago and Russet Rural tubers which were treated shortly after harvest. The Sebago variety increased in weight loss as the radiation dosage increased. Russet Rural was intermediate in response to irradiation, weight loss being largely independent of dosage. FTom.these observations it was clear that the physiological differences between varieties must be considered in any explanation of weight loss due to radiation treatment. .3- In England, Burton and Hannan (1957) reported that lower doses of gamma radiation than were found necessary in research done in the United States were as effective in suppressing sprout growth. Using five varie- ties, sprout inhibition was essentially complete with dosages ranging from.5,000 to 8,500 rep. Heiligman (1957) noted that, after two months' storage, weight loss of gamma irradiated tubers due to respiration and transpiration, decay, and sprouting was less than the controls. This occurred when the dosage was the minimum (10,000 rep) required for sprout inhibition. As the dosage increased above 10,000 rep weight loss also increased. Russian workers, Rakitin and Krylov (1957), found that gamma rays in doses of 10,000 rep and A0,000 rep completely stopped the sprouting of one variety of potatoes, and sharply decreased weightoloss. The tubers had been irradiated in March and stored for seven months "in the usual vegetable storage place." During this period, the control tubers lost 72-percent of their original weight while irradiated tubers lost only 9.7 to 11.8 percent. In preliminary tests with tonMEV cathode rays Hannah (1956) noted that a dosage of less than 50,000 rep may be sufficient to prevent Sprouting of potatoes. However, further testing revealed that even at low levels the irradiated tissue was damaged. The irradiated portion of cut tubers browned more rapidly than untreated tubers. Sparrow and Christensen (195h) report that although sprouting of the Katahdin variety was inhibited above 5,000 rep gamma irradiation, the treated tubers showed a greater rate of loss of weight than did the controls. After eight months storage the controls had lost a total of 9.7 percent -L,- of their original weight (including sprouts) and those receiving 20,000 rep had lost 7.3 percent. As stated previously, temperatures between 40 degrees and 50 degrees F. will delay sprouting while higher temperatures result in excessive sprout— ing and rotting. Sawyer and Dallyn (1955) reported that gamma irradiation of the Green Mountain variety above 10,000 rep gave complete sprout inhibi- tion at temperatures of no degrees, 50 degrees and even 70 degrees F. after six months storage. Comparing these results with those obtained by Schwimmer gt El. (1957), it was found that even under similar storage conditions there is a difference between varieties in response to irradia- tion. Russet Burbank tubers treated with 5,200 rep gamma radiation.and stored at #0 degrees F. for 35 weeks sprouted very little; at a storage temperature of 70 degrees F., sprouts were 230 millimeters long. Respiration. Nothing has yet been reported on the effect of cathode ray irradiation on potato respiration. Relatively few of the recent investi- gations concerning the effects of ionizing radiations on potatoes have dealt with measurements of respiration. One of the first respiration investigations was performed by Sussman (1953) using small Irish Cobbler tubers. It was found that the respiratory gas exchange was markedly enhanced by doses of gamma and XEirradiation. The Q02 (mm.3 oxygen/hour/mg. fresh weight) increased from two to sixefold several hours after irradiation, then decreased. A similar increase in QCOg (mm.3 carbon dioxide/hour/mg. fresh weight) was noted except that this increase occurred on the first day after irradiation, then decreased. In both cases the peaks were highest at 10,000 rep. In an attempt to explain this apparent radiation-induced increase in respiration, cytochrome -5- oxidase and tyrosinase activity were measured. The results indicated that only extremely high dosages had any effect on these systems, reduc- ing tyrosinase activity by about one-half at 3,200,000 rep. Cytochrome oxidase activity was not appreciably affected. Brownell gt 31. (1957) also studied respiration of irradiated tubers using both.whole tubers and bud tissue slices. 'With the tissue slices, gamma irradiation up to 15,000 rep had no significant effect on respira— tion. Doses from.50,000 rep to 200,000 rep resulted in continued higher respiration as compared to the controls. Whole tubers gave results similar to the tissue slices at the higher doses. Compared to the controls the lower doses respired about 30 percent less than the controls the first day, followed by an increase to 60 percent greater the second day. By the thirteenth week, respiration had declined to a point about five per- cent less than the controls. Studies by Rakitin and Erylov (1957) showed that during the 81X? 'weeks period following gamma irradiation at 10,000 rep the average rate of carbon dioxide evolution decreased from.about h50 percent of control the first week to a value approximately the same as the control at the end of six weeks. Gustafson 23 El. (1957) conducted a comprehensive study of the effects of gamma irradiation on the respiration of whole tubers and tissue slices. It was demonstrated that the carbon dioxide production of whole tubers receiving dosages of 5,000, 15,000, and 25,000 rep increased shortly after irradiation and remained at a high level for several weeks. This was followed by a decline to a level similar to that of the controls. Treatments of 50,000 rep and higher caused respiration to remain high throughout the experiment. The oxygen consumption at the lower dosages -6- exhibited two peaks, the first day after irradiation, and during the third week. It was thought that the low oxygen consumption coupled with high carbon dioxide production was due to a "temporary aerobic fermentation". Since the respiration rate returned to a normal level after a period of time, it could be assumed that no permanent physiological changes were induced. In summary, the following data have been gathered concerning the effects of ionizing radiation on potatoes: 1) Varieties differ in their response to irradiation treatment. 2) At the sprout-inhibiting levels and lower, irradiated tubers lose less weight than untreated tubers. 3) Irradiation doses higher than necessary for sprout inhibition may induce permanent physiological damage. 4) Storage temperature and irradiation dosage seem to be correlated with amount of sprouting. 5) Respiration rate of whole tubers and of potato tissue slices increases shortly after irradiation, followed by a gradual decline to that of untreated tubers. 6) The mechanism of radiation-induced effects on sprouting, weight loss, and respiration is still. largely speculative. EXPERIMENTAL Three varieties of potatoes were used in this experiment: Russet Rural, Sebago, and Katahdin. A thousand pounds of each variety were obtained on November 12, 1957, from.growers in.Monroe,County, Michigan. The tubers were washed and transferred to wooden boxes, each box.con- taining approximately 20 pounds. These were stored at AA degrees F. and 92 percent relative humidity for five weeks prior to irradiation. At the end of the five-week period 72 of the 1AA boxes of potatoes were removed from storage, weighed, and irradiated the following day with four dosages of cathode rays: 0, 2,500, 5,000, and 10,000 rep. Each treatment was replicated six times. The source of the cathode ray irradiation was the one MEV electron accelerator loCated in the Department of Agricultural Engineering at Mfichigan State University. .A special conveyor, shown in Figure l, was used which rotated the tubers as they passed beneath the electron tube. Conveyor Speed was 33 1/3 feet per minute and the distance from.the electron tube window to the conveyor rolls was A7 centimeters. Different levels of radiation were produced by varying the micro-amperage of the machine. After irradiation the tubers were returned to the storage. ‘Weight loss was determined by weighing the boxed tubers at monthly intervals. At the end of the fourbmonth period all tubers were weighed, de—sprouted, and the sprouts weighed. weight loss due to sprouts and due to shrinkage was then calculated. Observations were also made on the extent of sprouting. . Respiration.measurements were made immediately preceding irradiation, and at intervals of 24, A8, and 96 hours, and l, 2, 3, and h months after -8- Figure 1: Potato conveyor used for cathode ray irradiation. Cathode ray tube is visible at top of picture. irradiation. Six tubers were used for each determination. All measure- ments on whole tubers were made within the storage compartment to avoid errors due to temperature variation. Prior to the measurement the tubers ‘were placed in jars and left to respire for three hours. The cover of each jar was fitted with two l/8-inch copper tubes. A rubber balloon was attached to the bottom of one tube to act as an expansion chamber when a sample of air was withdrawn. The second tube was left open to the atmosphere except when a sample was being withdrawn. .All measurements 'were made with a Haldane-type Burrell gas analysis apparatus, model 39-507. 'Weight and volume measurements of the tubers within the jar were made at monthly intervals. Between determinations all tubers were stored in mesh bags within the storage compartment. ‘In an effort to obtain more accurate observations on the effect of irradiation on oxygen consumption, a preliminary study was done on the oxygen.uptake of potato tissue slices. Three tubers of the Sebago variety, approximately two inches in diamter, were used from.each treatment. The tubers had been irradiated 2h hours previous to use, and were stored at room temperature. From.each tuber five cork-borer sections six.millimeters in diameter were taken, and from each section one slice approximately one millimeter in thickness was removed. Neither the external 0.5 millimeter nor any bud tissue were used. At the same time a similar number of slices were obtained from.the center of the tubers in order to ascertain whether or not there was any indirect effect of irradiation on the internal tissue. All slices were washed in ice water for a short period, then transferred to warburg flasks containing three milliliters of phOSphate buffer, pH 5.9, and 0.25 milliliters of 20 percent potassium.hydroxide in the center well. -10- The temperature of the water bath was 26 degrees C. After a 15 minute period of equilibration, the manometer taps were closed and readings were taken at 15 minute intervals for two and one-half hours. The tissue slices were then removed and dried for dry weight determination. -11- EXPERIMENTAL RESULTS Experiment I. There was a definite indication of a difference between varieties in response to cathode ray irradiation. As was expected, 10,000 rep resulted in the least amount of Sprouting in all varieties. It appeared that the sprouts had started to grow but were inhibited after reaching about 1/8 inch in length. The amount of weight lost varied between varieties and between treatments. It may be seen in Figure 2 the extent to which sprouting occurred in Russet Rural at the end of four’months. Figure 3 illustrates the percent of original weight lost from Russet Rural due to sprouting, and due to respiration.and.transpi- ration at the end of four months. Total weight loss was least, about six percent, with a treatment of 5,000 rep. At 10,000 rep the total weight loss increased slightly to seven percent of the original weight. This may indicate some mechanical damage to the cells, facilitating moisture loss. The appearance of the Sebago variety at the end of four months is shown in Figure A. Total weight loss may be seen in Figure 5. 'Weight loss through respiration and transpiration increased nearly one percent with each dosage increment of 2,500 and 5,000 rep. At 10,000 rep, Sprouting was reduced still further while other losses remained essentially the same. Here, also, it seems that irradiation may have damaged the cells, although the lack of change at 10,000 rep is unexplained. It is possible, however, the irradiation at this level caused a decrease in the permeability of the cell‘walls. Katahdin was the most sensitive to irradiation in regard to sprouting. This is apparent in Figure 6. Sprouts on the irradiated tubers were -12- -13.. Control 2, 500 rep b7- —— - _ 5,000 rep 10,000 rep Figure 2: Effect of increasing dosages of cathode ray irradiation on sprouting of Russet Rural after four months of storage at 1:1; degrees F. and 92 percent relative humidity. Irradiated December, 1957. JpPOX ‘9 S neopirat'on and Transplrat;on 9+ larcent L14 V 2" «\ Dosafc In re: Figure 3: total we:g.t lost of irradiatcl ausset fiural tubers, expresscl as percent of original weight. -15- Control 5,000 rep 10,000 rep Figure 1;: Effect of increasing dosages of cathode ray irradiation on sprouting of Sebago after four months of storage at 1114 degrees F. and 92 percent relative humidity. Irradiated December, 1957. -16.. ll. ’ Sprar; ‘s l L, - 10" fmspiraiion and lranSjirai Com ()1 r 2‘ d N 7-: t c o 0 a: >« (L. h 1 H 31 3-4 14 O f _- “’40? ), O f),r\n0 Dosage in rep Figure 5: Total weight lost of irradiated Sebago tubers, expressed as percent of original Joight. -17.. Control 2, 500 rep 5,000 rep 10,000 rep Figure 6: Effect of increasing dosages of cathode ray irradiation on sprouting of KatahdLn after four months storage at M4 degrees F. and 92 percent relative humidity. Irradiated December, 1957. 1/8 inch or less in length. Figure 7 shows that irradiation had very little if any effect on reSpiration and transpiration losses. Figures 8, 9, and 10 illustrate the effect of irradiation on the monthly weight loss of the three varieties. Russet Rural showed its sensitivity to increasing dosages at one month when weight lOSS‘WaS greatest, 2.6 percent at 10,000 rep. Thereafter, however, the rate of loss declined with time in the irradiated.tubers. During the fourth month the rate of loss for untreated tubers rose to 2.6 percent. At 10,000 rep during this same period the rate was 1.6 percent. 'With the Sebago variety the rate of weight loss was fairly steady regardless of treatment up to the third month. Between the third and fourth months a dosage of 10,000 rep substantially reduced the loss rate, which was 2.4 percent while the control was 3.7 percent. The rate of weight loss of the Katahdin variety was essentially unaffected by irradiation, as shown by Figure 10. The data on oxygen consumption of whole tubers showed a pattern similar to the results of Gustafson.§t.§l. (1957). Carbon dioxide pro- duction was also measured, but due to the amount of rubber tubing used and the high rate of diffusion of carbon dioxide through rubber, the reliability of the 002 data was in question and they have been omitted. With Russet Rural all irradiation treatments resulted in a sharp increase in oxygen consumption, up to 750 percent of the controls A8 hours after irradiation. This is illustrated in Figure 11. By 96 hours the rate had declined to approximately 400 percent of the controls. After a slight increase at one month the rate gradually declined until at the third and 'fourth.month it was the same or slightly below that of the controls. -18— -19- ll Sprouts 10 f-‘r 3o {rat ion and Wfira‘. Lon 9 q 8 d '74 6 1 E): :3 s « uh 3 2 4 l d 0 V V V , on ’00. ,0 Dosage in rep Figure 7: Total weight lost of irradiated Katahdin tubers, expressed as percent of original weight. -20.. 2“ x Control 0 2.500 rep 0 5,000 res . 10,030 rep .1 3.. .. X X +3 C 8 2-4 L. Q) 8 1I I D O\. ’. I «I ‘3 i 0g: r: J ,m._L 3 I; Llonths Figure 8: Rate of weight loss per month m affected by cathode raw irradiation. EXprcssed in percentage. Russet Ehu‘al var. -21... b X Control / 0 2,500 rep 1 9 5,000 rep . 10,000 rap 3 + Percent N J /. \__/O Figure 9: Rate of weight loss per month as affected by cathode ray irradiation. Dcpreeeed as percentage. Sebago var. -22- P I; X Control 0 2,500 rep 9 5,000 rep ‘4 . 10,000 rep 3 4 4 +3 :2 8 2 < E: I. Q 4 u 1 d O 0 .1 0 L: ‘ J— _. 3:4» 1 2 3 Heaths figure 10: Rate of weight loss as affected by cathode m irradiation, Expressed as percent per mmth. Fatehdin var. -23.. 800 x 2,500 rep k C) 5,000 rep 5 . 10,000 rep 700 600 “ 500- 1 Percent of control 3004 Hours months Figure 1.1: Effect of cathode ray irradiation on rate of anger: canmmpticn of whole Mt Mal tubers. Expressed as percent of cmtrol. -21;— 800 X 2,500 rep 0 5,000 rep 0 1.0 000 re 7004 3 1" 600 0 r1 5m *3 E: . O U kc O W U x. fl” 0 300 O O 200 lm -_-_— -___—— O 2 a n 1 2 3 0. Hour- Heath: Figure 12: Effect of cathode rq irradiatim on rate of men con-wan of whole Sebago tubers. Expressed as percent of control. 800 X 2,500 rep 0 5,000 rcp 7m 0 10,030 rep X 600 x H Sms O O 8 \ .3 C 8 cH O .3 1:00. C. Q) 8 3 300-4 200 lm —-—————d—-——-——- -———————-—--—-————a—-. ”m 0% ‘ ‘ Hours Months Figure 13: Effect of cathode ray irradiation on rate of men consumption of whole Katahdin tubers. mamaeei as percent of control. The rate of oxygen consumption by Sebagos (Figure 12) was greatest at 96 hours with a dosage of 5,000 and 10,000 rep. The tubers treated with 2,500 rep did not reach their peak until one month after irradiation. The rates then steadily declined until at the third and fourth months when oxygen consumption was between 25 and 50 percent less than that of the controls. The oxygen consumption of Katahdin (Figure 13) was somewhat erratic. A treatment of 2,500 rep resulted in two peaks, one at 2A hours, and one at one month. Two peaks again resulted from a treatment with 5,000 rep, one at 2h hours and one at 96 hours. The 10,000 rep treatment resulted in one pak of 675 percent of control at 2A hours, followed by a gradual decline until two months. Between two months and four months the rates of all the treated tubers had leveled off to 50 to 80 percent of the control. .Experiment II. The results obtained in this experiment were somewhat dif- ferent from.those in Experiment I. Figure 14 illustrates the effect of the different radiation treatments on sprouting of Russet Rural after four months. It will be noted that 10,000 rep was not as effective in inhibit- ing sprouting as was the case in the previous experiment. After four months sprouts made up 4.5 percent of the original weight of the control tubers while with a dosage of 10,000 rep sprouts represented only 0.6 percent of the original weight. The majority of the long sprouts appeared at the apical end of the tubers. In Figure 15 it will be noted that weight loss due to respiration and tranSpiration is essentially unaffected. Sebago sprouted to nearly the same extent as Russet Rural. Again the majority of the sprouts on irradiated tubers appeared at the apical end. At the end of four'months sprouting represented a loss of 8.h percent in the controls, and only 0.2 percent of those irradiated at 10,000 rep. -26- -27.. 5,000 rep 10,000 rep Figure 1h: Effect of increasing dosages of cathode ray irradiation on sprouting of Russet Ihzral after four months storage at 11).; degrees F. and 92 percent relative humidity. Irradiated March, 1958. -28... ll sprouts _ 10 deep irat '.on and .‘ransp irat ion 7.. a 6-4 +3 LL 33 t: 5+ is. .‘ .4 3-1 “-4 l-i 0.. 0 2,00 ,mo 10,000 Dosage in rep Figure 15: Total weight lost of irradiate- Russ” Rural tubers, expressed as percent of original weight. Irradiation seemed to be the cause of a rise of two percent in weight loss due to respiration and transpiration. See Figures 16 and 17. Katahdins reacted essentially the same to increasing irradiation doses. This is illustrated in Figures 18 and 19. A dosage of 10,000 rep tended to increase the loss due to respiration and transpiration over a four month period, but the actual decrease in weight was only 0.2 percent. The rates at which weight was lost in the three varieties may be seen in Figures 20, 21 and 22. Imeasurements\of the oxygen consumption during this experiment resulted in considerably different data from that obtained in experiment I. The results are given in Figures 23, 24 and 25. ‘With Russet Rural all irradia- tion treatments consumed oxygen at a higher rate than the controls until the third month, when the rate dropped slightly below the control. Sebagos reacted in essentially the same manner except that at the highest dosage the tubers stayed with or slightly below the controls. The same decrease was noted at three months. ‘With Katahdins the lowest rate occurred with the two lowest dosages. The 10,000 rep level caused a slight increase dur- ing the first 96 hours. At two, three, and feur months the rate of oxygen consumption was the same as the controls. The results of the preliminary work on oxygen consumption of potato slices are shown in Figures 26 and 27. Although it is possible that the initial high rate in Figure 26, was due to a short period of equilibration, there is nevertheless an indication that irradiation at successively higher dosages caused a corresponding increase in oxygen consumption of tissue in the epidermal layer. The tissue from.the interior of the tuber did not seem to be materially affected by cathode ray irradiation up to 10,000 rep. -29- The absolute figures for the oxygen consumption of whole tubers, treated and untreated, are given in Table 1. The effect of irradiation on reSpiration may be seen in the figures for Experiment I. The oxygen consumption was consistently higher with irradiated tubers up to the second month. After this time the rate was nearly the same as that of the controls. The data for Experiment II showed that there was essen- tially no difference in oxygen consumption between the controls and the irradiated tubers. -293- —3o.. Control 2, 500 rep L... _ ,_.____._____ __ .,__ 5,000 rep 10,000 rep Figure 16: Effect of increasing dosages of cathode ray irradiation on sprouting of Sebago after four months storage at M4 degrees F. and 92 gercent relative hmnifity. Irradiated March, 195 . -31- Sprouts [ ,__J 10‘ Respirat ion and [—— hanspiratim 94 Percent V s" 3’ 0,000 Dosageinrep Figure 17: Total weight lost of irradiatei Sebago tubers, expressed as percent of original weight. -32.. Control 2,500 rep a. -- i::-IIIIII ‘— - *— ——” 5,000 rep 10,000 rep Figure 18: Effect of increasing dosages of cathode ray irradiation on sprouting of Katahdin.after four'months storage at hh degrees F; and 92 percent relative humidity. Irradiated March, 1958. _33- ll , - Lhwcuts l - ] lO Respirat ion and 'Lranspiration 9 8 7 6 ‘— I +3 C Q) 8 e S h , e'e e‘e'e Doeege in rep Figure 19: Total weight lost of irradiated Katehdin tubers, eaqareseed as percent of original weight. -3h- Control 2,500 rep 5:000 "p 10,000 rep OOOX iercent O O/ Mm“ Figure 20: Rate of weight loss per month as affected by cathode re: irradiating. Ebcpressed as percentage. lamest Pun-a1 var. -35.. X Gmtrol 0 5:000 mp 0 10,000 rep /’\x a /<> 3; 2 \o 0/ 2%. 9 1‘ Months Figure 21: Rate of weight loss per month as affected by cathode rw irradiation. Ibqaressed as percentage. Sebago Var. -36.. b: x Control 0 2,5CD rep 0 5,000 rep “ 0 10,000 rep *9. E; ii 2 x :53 O /\ 1 N 9 .4 1 3 IJonths Figure 32: Rate of weight loss per month as affected by cathode ray irradiation. hhqiressed as percentage. Hatshdin var. -37.. H 8 O 5,000rep ‘3 0 10,000 rep 8 ‘a ‘— ———- a §O é Ham-e lathe Figure 23: Effect of cathode re: irradiatim a: rate of ongen cmtim of whole Faucet Rural tubere. Ebcpressed as percent of control. 2%! H 8 .3 C O 0 L a \“ O 8 a? Rowe Mmthe Figure 24: Effect of cathode ray irradiation on rate of oxygen corruption of whole Sebago tubers. bcprossed as percent of control. Percent of control 21. he 96 1 2 3 4 Hours Mmthe Figure 25: Effect of cathode raw irradiation «1 rate of men consuuption of whole Katahdin tubers. kpressed as percent of control. -33.. 33> omeoem we need”. esp-3 Hear-3H0 ac cognizance go no 83133.: hen eve—33 we aoeuuu RN 939: ooafludx on an on so 8 a. 8 3 on A a o JII'IIEHFEIIJHIIIIIII I 8a 3,0,0! 4? O! 10' 1". Di RN . 8m 84 [0.]. 8m . 8‘. g 80 at 08.2 0 and 8o.“ 0 a8 oR.~ x 8.: toaauoo JO guessed -39.. .am> cannon mo moowde Commas Hasnoeca mo coaadfisncoo :omhxo so coaasfiemana hen avocado mo aoouum “om shaman monzhfix OmH and ONH mOH 00 ms 00 ad on «A J 4 C -meummemw ujn‘. .. .. ........... pa 0 § § §§ toaauoo Jo quooaog use ooo.oH e8 08$ dot com.“- X0. Table l: Respiration rates (mg. 02/100 g. fresh weight/hour) of three varieties of'whole potatoes irradiated with cathode rays early and late in the storage season. Measurements made with Haldane gas analysis apparatus. variety and 24 48 96 1 2 ‘ 3 4 Treatment hours hours hours month month month month (rgpg 1y EXP. I) Russet Rural Control 0.77 0e37 0e62 0031 lei-l9 3080 11.114 2,500 0.97 2.78 2.18 1.32 2.99 3.70 3.85 5,000 1.13 2.71 2.48 1.46 2.91 3.06 3.29 10,000 1.20 3.00 2.76 1.49 3.00 3.29 3.26 sebago Control 1.28 0.90 0.51 0.62 1.37 4.40 5.34 2,500 2.96 2.85 2.61 3.84 2.96 3.14 3.28 5,000 3.39 2.93 3.18 3.67 2.64 3.23 3.20 109000 3e61 3e61 3e21 0096 3e ' 3e2h Bel-17 mean 2.81 2.57 2.38 2.27 2.60 3.50 3.82 Katahdin CODtI‘Ol 00,43 OeS? OeS7 0e58 1.55 3e68 3e9h 2,500 2.66 2.53 2.66 3.44 1.40 3.12 3.32 5,000 2.14 2.48 2.93 2.85 0.90 2.80 2.98 10,000 2.90 3.51 2.66 0.73 1.27 2.92 3.28 Mean 2.03 2.27 2.21 1.90 1.31 3.13 3.38 LateCEXP. II) Russet Rural Control 3.29 3.16 3.16 3.10 3.66 3.71 2,500 3.86 3.71 3.96 3.52 4.02 3.98 5,000 3.66 3.66 3.56 3.52 3.62 3.64 10.000 3.55 3.70 3.41 3.52 3.62 3.71 M6811 3e59 3e55 3e52 3.141 3e73 3076 Sebago contrOl 3.06 3e32 3.06 3e00 Bel-$8 3.52 2,500 3.64 3.64 3.50 3.58 3.70 3.69 5,000 3.67 3.52 3.52 3.24 3.42 3.47 10:000 2.98 3.23 3.11 2.90 2.96 3.00 mean 3.33 3.42 3.29 3.18 3.39 3.42 Katahdin Cantrol 3.09 3.22 3.48 3.48 3.87 3.90 2,500 2.89 3.37 3.13 2.68 3.20 3.25 5.000 3.03 3.05 3.16 2.56 3.07 3.04 10,000 3.91 3.91 3.77 3.50 3.86 3.82 mean 3.23 3.38 3.38 3.05 3.50 3.50 -39a~ SUMMARY AND DISCU SSION It has been shown that cathode ray irradiation up to 10,000 rep considerably decreased the Sprouting of three varieties of potatoes. The mechanism of this inhibition is not known, although there is evi- dence to show that it is a delay rather than complete inhibition. At the end of Experiment I, the de-sprouted tubers were further stored at 62 degrees F. for twelve weeks. A perfunctory examination at that time revealed that a large percentage of the tubers, regardless of variety or irradiation dose, had sprouts up to 15 inches in length. The data on weight loss indicate that doses at or near the minimum for sprout inhibition caused a decrease in the total weight lost. How- ever, although the response to weight loss exclusive of sprouts depended upon the time between harvest and irradiation, and upon variety. In general the monthly rate of weight loss was less with the treated tubers than with the controls. During EXperiment I the irradicated tubers lost a greater percentage of their weigit the first month than the con- trols. However, during the ensuing three months the rate was less than that of the control. In Experiment II the rate of weight loss was less than the controls during the four month period. In comparing the rate of oaqrgen consumption with the rate of weight loss it would seem that during the first two months the majority of the weight lost was due to accelerated respiration, as measured by oxygen consumption. Heiligman (1957) noted that a similar rise caused by gamma irradiation may be associated with a rise in sugar content. As the surplus sugar is used up the rate of respiration returns to normal. -40- It is possible that a similar explanation may be valid for the results obtained in this experiment. The data on oxygen consumption of the potatoes in Experiment II is difficult to explain, although the results of Brownell 23.91, are similar and of the same magnitude. Two possible explanations of the lower oxygen consumption at the later date are that the respiration mechanism was less susceptible to radiation stimulation late in the storage season; or that the cell walls offered greater resistance to the penetration of electrons at this time. (DNCLU SION S l) Cathode-ray irradiation affects sprouting, weight loss, and oxygen consumption of potatoes much the same as gamma irradiation. Irradiation inhibited sprouting of all three varieties when applied either early or late in the storage season. Weight loss exclusive of sprouting was dependent on variety and time of irradiation. Oxygen consumption increased shortly after irradiation followed by aggradual decline until at the third and fourth month the rate was the same or slightly less than the control. 2) The Optimum sprout-inhibiting dose is between 5 ,OOO rep and 10,000 rep, varying with the variety and time of time of irradiation. 3) Cathode-ray irradiation produces no permanent physiological changes between 2,500 rep and 10,000 rep, as measured by orqrgen consumption. 4) It would appear that cathode-ray irradiation delays rather than completely inhibits sprouting. -42- LITERATURE CITED 1. Brownell, L. E., C. H. Burns, F. G. Gustafson, W. J. Hooker, D. R. Isleib, J. V. Nehemias, R. A. Martens, A. Pendill, and F. Heiligman. 1957. Gamma-ray sprout inhibition of potatoes. Ibrminal report, project 2386. Univ. of Mich. Eng. Res. Inst. 2. Burton, W. G. and R. S. Hannah. 1957. Use of gamma radiation for preventing the sprouting of potatoes. Jour. of the Sci. of Food and Agr. 8:707-715. 3. Gustafson, F. G., L. E. Brownell, and R. A. Martens. 1957. In- fluence of gamma irradiation of potato tubers on the rate of respiration. Amer. Potato Jour. 34:177-182. 4. Hannan, R. S. 1956. Research on the Science and Technology of Food Preservation by Ionizing Radiations. Chemical Pub. Co., New York 5. Heiligman, F. 1957. Effects of ionizing radiation on white potatoes. Amer. Potato Jour. 34:153-157. 6. Nicholas, R. C. 1958. The application of high-energy electrons to some grain-infesting pests. Unpublished thesis for Ph.D. Michigan State University. 154 numbered leaves. 7. Rakitin, Yu. V. and A. V. Krylov. 1957. Physiological changes in plants with growth inhibition induced by gamma rays. Fizologia Rasteny (Plant Physiology) Vol. 4, No. 1. Trans. from.Russian by Amer. Inst. Biol. Sci. 8. Sawyer, R. L. and S. L. Dallyn. 1955. The effect of gamma irradia- tion on storage life of potatoes. Amer. Potato Jour. 32:141-143. 9. Schwimmer, S., H. K. Burr, W. O. Harrington, and W. J. Heston. 1957. Gamma radiation of potatoes: effects on sugar Content, chip color, germination, greening and susceptibility to mold. Amer. Potato Jour. 34:31-41. 10. Sparrow, A. H. and E. Christensen. 1954. ggproved storage quality of potato tubers after exposure to Co gammas. Nucleonics l2(8):l6-l7. ll. Sussman, A. S. 1953. The effect of ionizing radiations upon the respiration and oxidases of potato tubers. J. Cellular and Comp. Physiol. 42:273-283. -43- m. P; '1t10n dept. ’4‘