&*T'*. Division of Agricultural Sciences UNIVERSITY OF CALIFORNIA 0, »J»^ CALIFORNIA AGRICULTURAL EXPERIMENT STATION BULLETIN 792 THE VALUE OF MOISTURE-RESISTANT CONTAINERS IN VEGETABLE SEED PACKAGING 1 by JAMES F. HARRINGTON Vegetable seed packaging has been undergoing major changes, among them a rapid shift toward the use of moistureproof or moisture-resistant containers. This shift has been brought about through the research of Barton (1935, 1939) , 2 Boswell et at. (1940), and the Associated Seed Growers, Inc. (1954), which repeat- edly demonstrated that sufficiently dried seeds will maintain germination and vigor much longer than seeds of higher moisture contents. However, little information has been available on the relative value of different types of containers as barriers against penetration of water vapor. This bulletin reports research findings on the value of moisture- resistant con- tainers for preserving high germination and vigor of vegetable seeds, and on several related factors that affect seed storage in moisture-resistant containers. Seven experiments are reported in this bulletin. The main findings were these: The data confirmed previous experi- ments that the higher the storage tem- perature the faster the loss in germina- tion; also the higher the seed moisture the faster the loss in germination. The findings substantiated the rule of thumb that each 1% drop in moisture doubles the life of the seed. Among various containers tested, the tin can was found moistureproof if prop- erly sealed. If tin cans are considered to be 100% resistant to moisture-vapor 1 Submitted for publication May, 1962. 2 References refer to sources listed in Litera- ture Cited, page 23. FEBRUARY, 1963 The Author: James F. Harrington is Profes- sor of Vegetable Crops and Olericulturist in the Agricultural Experiment Station, Davis. transmission, then three other types of containers can also be so regarded. These are aluminum cans (but proper sealing seemed to be more difficult) , hermetically sealed glass jars, and pouches made of aluminum foil (.0035-inch thick lami- nated to mylar or polyethylene, with or without surface paper lamination). Containers 80 to 90% resistant to moisture-vapor penetration and satis- factory as moisture-resistant seed con- tainers include aluminized polyester pouches, multiwall paper bags with inner aluminium lamination and properly sealed, and high-density polyethylene of 3 mil or more in thickness. Containers showing fair resistance to moisture-vapor transmission include asphalt-laminated multiwall paper bags, polyethylene-laminated paper bags, and friction-top tin cans. Containers showing no resistance to moisture-vapor transmission were paper and cloth bags. Polyethylene was found more resistant to moisture-vapor transmission at lower than at higher temperatures. When the oxygen and C0 2 content of [3] the atmosphere around seeds in sealed storage was analyzed, it was found that there was a drop in 2 concentration which was greater than the build-up in C0 2 concentration. This drop in 2 con- centration and build-up of C0 2 concen- tration was faster in warmer storage and with seeds of higher-moisture content, which indicated greater respiration. Yet, onion seed showed excellent germination after the storage when 2 had dropped to as low as 4% and the C0 2 concentra- tion had increased to as high as 13%. Although containers in which the seed had died always contained an atmosphere low in 2 and high in C0 2 , this change in atmosphere was not necessarily cor- related with seed deterioration. Old seeds or seeds declining in ger- mination were less resistant to adverse storage conditions than high-germinat- ing, freshly harvested seed. Onion seeds properly dried for storage, treated with the fungicide Arasan or the combination fungicide-insecticide Delsan, were not adversely affected by these treatments. If seeds dried for safe storage in sealed containers were kinds which develop hard seed coats, it was found that acid scarification to eliminate the hard seeded- ness was unsatisfactory. Abrasive scarifi- cation was satisfactory for okra, flower- ing morning glory, and garden peas. Neither method of scarification was satis- factory for sweet peas, pole beans, and lima beans. It is evident that other important quali- ties for containers include ruggedness, ease of sealing and handling, low cost, and resistance to insect and rodent pene- tration. A more detailed discussion of the seven experiments follows. ' « EXPERIMENT I INVESTIGATION OF EIGHT TYPES OF CONTAINERS FOR MOISTURE TRANSMISSION AND GERMINATION OF SEEDS STORED IN THEM v TYPE OF CONTAINERS The following containers were tested to package the seed: 1. Paper — multiwall kraft paper bags (4-ply 50 1bkraft). 2. Paper-poly — multiwall kraft paper bags, with a layer of poly-ethylene laminated to the inner surface of the inner ply (3-ply 50 lb kraft + 1- ply 1/10 lb PE on 50 lb kraft) . 3. Crepe-double poly — multiwall kraft crepe paper bags, with two layers of polyethylene (2-ply 1/10 lb PE on 70 lb crepe kraft + 2-ply 50 lb kraft). 4. Paper-poly + poly bag — same as 2, with a 3-mil high- density poly- r> ethylene liner in each bag. 5. Poly bag — polyethylene 6-mil high- density bags. *+ 6. Paper-foil — multiwall kraft paper bags, with aluminum foil laminated with polyethylene to inner ply (3- JP ply 50 lb kraft + 1-ply 1/10 lb PE, (J .0035 foil, 1/10 PE on 50 lb kraft) . 7. Foil pouch — aluminum foil pouch (paper 1/10 lb PE, .0035 foil, 1/10 lbPE). 8. Tin can — tin cans, enamel lined. T4 < Container 1 was sewn shut; containers 2, 3, 4, and 6 were sewn and heat-sealed with a polyethylene tape over the stitch- ing; containers 5 and 7 were heat-sealed; and container 8 was sealed in a can- closing machine. SEEDS TESTED Six kinds of seed were used: cabbage, carrot, lettuce, onion, muskmelon, and tomato. Each kind of seed was divided into three lots, and the moisture content was adjusted either by drying in a de- humidifying drier at 100°F or by mist- ing with the proper amount of water, to obtain high, medium, and low moisture levels. Table 1 gives the moisture contents and the germination percentages at the start of the experiment. STORAGE CONDITIONS Four storage conditions differing in temperature and/or relative humidity (RH) were used to test the containers: Desert 100°F 12% RH Tropic 100°F 90% RH Frigid 0°F 50% RH Temperate 50°-90°F 10%-90% RH The temperate storage was a common storage subject to the daily and seasonal fluctuations in temperature and RH. With the tin cans and the foil pouches, a different container was used for each sub-lot of seed, so that any change in seed moisture was the result of moisture penetration through the container. With the other containers the sub-lots of each kind of seed were placed in cloth bags and combined to make six sub-lots in each container, because they were too large to use as individual containers. The moisture content of the different kinds of seed in a container changed slightly as they came into equilibrium with each other. This was independent of the dif- fusion of moisture in or out of the bag. The lettuce and onion seed gained ap- proximately 0.7% moisture, the tomato seed, approximately 0.2%; the carrot and muskmelon seed lost approximately 0.4% ; and the cabbage seed, approxi- mately 0.6%. Thus, to some extent the moisture level originally intended was changed in these six containers. In the tin cans and the foil pouches each kind of seed maintained the original moisture content. TABLE 1. MOISTURE CONTENT AND GERMINATION OF EACH SEED LOT AT START OF EXPERIMENT Moisture level Cabbage Carrot Lettuce Muskmelon Onion Tomato High... Medium Low. . . . High... Medium Low. . . . 86 87 87 Per cent moisture in seed 8.57 10.37 6.87 9.04 9.98 9.84 7.50 8.01 5.93 6.80 8.73 7.60 5.20 5.73 4.04 4.42 7.06 4.48 Per cent germination 80 82 83 91 95 92 [5 84 85 87 97 98 98 TIME OF STORAGE Containers were removed 1, 3, 6, and 12 months after the start of storage. Thus the treatments consisted of 8 con- tainers x 6 kinds of seed x 3 moisture levels x 4 storages x 4 dates of removal. This equaled 2,304 individual sub-lots or treatments tested. Preliminary findings of Experiment I were published by Harrington, 1960. MOISTURE TRANSMISSION The moisture transmission was deter- mined in this experiment by measuring the change in moisture content of the seeds. In figure 1 the changes of seed moisture in four representative contain- ers are shown for each of the four storage climates. In the tropic storage of 100°F and 90% RH, there was the greatest ab- solute increase in seed moisture, with the seeds in the paper bag showing the most. On the other hand, in the desert storage of 100°F and only 12% RH, there was a rapid loss of moisture from the seed in the paper bag, intermediate loss in the paper-poly + poly bag and the paper-foil containers, and no measurable loss from the tin can or the foil pouch. Under temperate and frigid storage the paper bag was the only container that allowed an appreciable transmission of moisture vapor. Apparently the polyethylene is more resistant to moisture transmission at lower temperatures than it is at higher temperatures. To give a complete picture of the rela- tive moisture transmission, it was as- sumed that the paper bag allowed 100% Figure 1. Change in moisture content of vegetable seeds stored in jour different con- tainers under temperate, frigid, tropic, or desert storage for 1, 3, 6, and 12 months Temperate Storage Frigid Storage Desert Storage 12 I 12 ' MONTHS IN STORAGE Paper / Paper-poly + poly / •— -• Paper foil / o— o Tin can [6] TABLE 2. AVERAGE MOISTURE TRANSMISSION THROUGH EACH CONTAINER AS A PERCENTAGE OF TRANSMISSION THROUGH PAPER UNDER THE SAME CONDITIONS Container- Storage Tropic Desert Temperate Frigid Average Per cent Paper Paper-poly Crepe-double poly Paper-poly + poly bag Poly bag Paper-foil Foil pouch Tin can 100 114 99 51 33 30 1 100 99 91 57 33 38 7 4 100 47 35 7 16 18 -12 -11 100 25 21 -2 5 3 -2 -7 100 71 61 28 22 22 -2 -4 Container X storage L.S.D. 99:1 = 23.4%. Container average L.S.D. 99:1 = 11.7%. transmission. The moisture transmission through the other containers after 1, 3, 6, and 12 months was calculated as a per- centage of the moisture transmission through the paper bag, and the four figures for each container under each storage condition were averaged. The data are presented in table 2. The containers fall into four groups as to resistance to moisture penetration. Excellent. The seed in the tin can and the foil pouch show no significant change in moisture content under any climatic condition tested. Thus these two contain- ers, if properly sealed, are moistureproof. Good. The containers having high- density polyethylene of 3 mil or greater thickness (poly bag and paper-poly + poly bag) and the foil-laminated bag are resistant to moisture transmission at 100°F and seem to be almost moisture- proof at temperatures of around 70° F and lower. Fair. The very thin layer of poly- ethylene on the paper-poly and crepe- double poly has little or no resistance to moisture-vapor transmission at 100°F and only fair resistance at the lower temperatures. Poor. The paper bag showed no re- sistance to moisture-vapor transmission under any storage condition tested. GERMINATION The purpose of using moistureproof or moisture-resistant packages for seeds is to maintain their germination as long and as high as possible. The above data show a wide range of moisture resistance from the moistureproof tin can and foil pouch to the moisture-permeable paper bag. The data in figure 2 show the effect of storage up to 12 months in these con- tainers. Moreover, the loss in germina- tion is a function of the moisture content of the seed and the length of storage. A particular container was effective in maintaining high germination only so long as it maintained low seed moisture. Figure 2 shows the curve of deteriora- tion in germination ability with increase in moisture of each kind of seed follow- ing 1, 3, 6, and 12 months of storage. The area below the crosshatching on each [7] PS w o 100 H 80 (J w 60 Oh 3 4 5 6 7 8 9 10 II 12 Months : I / 3 / 5 6 7 8 9 10 II 12 13 14 PER CENT MOISTURE — 6 / 12 4 5 6 7 8 9 10 II 12 13 14 Figure 2. Germination percentages of vegetable seed as a function of their moisture content when stored at 100° F for 1, 3, 6, and 12 months graph represents the region where a sig- nificant drop in germination has oc- curred. The chi-square test by analysis of variance shows that there is no significant change in germination in any of the seeds stored in the frigid storage even after 12 months of storage. The average germina- tion and the standard error for each kind of seed are as follows : Cabbage . 87.8 ± 4.57 Carrot . 81.9 ±3.94 Lettuce . 88.8 ±4.97 Muskmelon .... . 93.8 ±2.77 Onion . 85.5 ±3.95 Tomato . 97.8 ±1.56 Therefore, the straight line below the crosshatching of the chart for each kind of seed is the line of the mean germina- tion in frigid storage less the standard error of that mean. Lettuce declined in germination at lower moisture contents than the other kinds of seeds, and tomato at higher moisture contents. However, if the mois- ture content was 10% or higher, the seeds of all kinds tested were dead or very low in vitality after 12 months. Data in figure 2 show that carrot seed of lower moisture content declined in germina- tion more rapidly at six months than at 12 months. This cannot be explained. Table 3 gives the moisture contents at which a significant decline in germina- tion was apparent after 1, 3, 6, or 12 months for each kind of seed. The 12- month value for cabbage was inter- polated. Lettuce was anomalous: by three months of storage it had dropped to a plateau in the lower moisture range that was significantly below the germination of the seed from the frigid storage. Yet [8 TABLE 3. SEED-MOISTURE CONTENT AT WHICH A SIGNIFICANT DROP IN GERMINATION OCCURRED AFTER 1, 3, 6, AND 12 MONTHS OF STORAGE AT 100°F Seed Months of storage 1 3 6 12 Cabbage Per cent seed moisture 5.4 5.0 3.9 3.4 Carrot 8.8 8.3 6.4 5.8 Lettuce 7.3 6.1 5.6 4.7 Muskmelon 7.0 6.5 5.6 4.2 Onion 9.2 8.1 6.9 6.6 Tomato 9.2 7.5 7.4 5.9 Average 7.8 6.9 6.0 5.1 1 there was still a sharp break where ger- mination declines seriously for each stor- age time. The moisture content at this sharp breaking point is used in table 3 for lettuce. At 100°F, the rule of thumb that a 1% drop in moisture doubles the life of the seed was reasonably substantiated by the average moisture content at which the six kinds of seed showed a significant decline in germination. At 3 months this average was 6.9% ; at 6 months it was 6.0%, or a drop of 0.9% ; and at 12 months it was 5.1%, another drop of 0.9%. EXPERIMENT n THREE TYPES OF MOISTURE- RESISTANT CONTAINERS TESTED FOR LOW-MOISTURE SEED IN HIGH-HUMIDITY STORAGE TYPES OF CONTAINERS Since Experiment I had established the hermetically sealed can (tin can) as acceptable standard for judging the de- sirability of other containers for pack- aging low-moisture seed, two other con- tainers were studied for comparison under conditions of high-humidity stor- age. They were a heat-sealable alumi- nized polyester pouch, and a triple-seal, friction-top can such as is used for paints. The cloth bag was used as a check. Onion seed, variety Excel, moisture content, 7.2% (dried at 90°F in a de- humidifying drier), germination 82%, [9 was packaged in the following containers on July 14, 1960: 1. Tin can — baby-food size. 2. Paint can — pint-size with triple- friction seal lid. 3. Pouch — aluminized polyester. 4. Cloth bags. Approximately one ounce of seed was put in each container. Two lidded alu- minum buckets were used to hold the containers. Five containers of each kind were placed in each lidded bucket. The containers were set on a wire screen over water in the bottom of the bucket. Wetted blotting paper was placed under the lid. The blotting paper was rewet as needed to keep the humidity in the buckets as near saturation as possible. The buckets were transferred daily except Saturdays and Sundays between 77°F for 16 hours and 32°F for 8 hours. VAPOR-PENETRATION STUDIES Water vapor can penetrate a container in two ways: by diffusion through the container walls if they allow vapor trans- mission; through cracks or poor seals, even through minute holes if there is an expansion and contraction of the internal atmosphere because of temperature changes. To test for both methods of vapor penetration, the above four kinds of containers filled with seed were placed under high-humidity conditions and the temperature was alternated between 77°F and 32°F daily. SAMPLING One of each kind of container was re- moved from each bucket 2, 4, 8, 16, and 32 weeks after the beginning of the ex- periment. Carbon dioxide, oxygen, and nitrogen content of the atmosphere in each con- tainer was determined by gas chromatog- raphy of a sample obtained by punctur- ing the container through a rubber gasket sealed on the side and immediately withdrawing the sample in a hypodermic syringe. A sample of the seed in each container was taken immediately on opening the container and was tested in duplicate for moisture content. Another sample of seed was taken for germination tests made according to offi- cial methods (Justice, 1952). MOISTURE CONTENT AND GERMINATION As shown in table 4, under the short time (32 weeks) and relatively cool tem- perature average of this experiment (77°F for 16 hours and 32°F for 8 hours for an average of 62°F), seed germina- tion did not decline in any of the mois- ture-resistant containers. In the cloth bags the moisture content of the seed rose to 59% and the germination dropped to 0%. There was no change in moisture con- tent of the seed in the tin cans. The average moisture content was 7.09 ± 0.03. Seed moisture in aluminized pouches had risen significantly in 16 weeks, and after 32 weeks was 0.6%-0.7% higher than at the start. In paint cans moisture con- tent increased significantly in 4 weeks. The apparent decrease in moisture from the 16- to the 32-week averages was most likely caused by variations in the tight- ness of the seals between the lids and the cans. RESPIRATION The respiration of the seed in the tin cans, measured by C0 2 increase, was low but constant, approximately doubling each time storage time doubled. Seed res- piration in the pouches, measured by C0 2 increased, was more rapid. This can be explained by the fact that the moisture content of the seeds increased with stor- age time. The C0 2 content of the atmos- phere in the paint cans increased to about 1% and then remained roughly constant, presumably because C0 2 diffused out through the same cracks by which the [10] TABLE 4. COMPOSITION OF ATMOSPHERE, MOISTURE CONTENT OF SEED, AND GERMINATION OF ONION SEED STORED IN FOUR TYPES OF CONTAINERS FOR 2, 4, 8, 16, AND 32 WEEKS UNDER CONDITIONS OF HIGH RH AND 77°-32° F DAILY ALTERNATING TEMPERATURE Container Tin can Pouch Paint can Cloth bag 2 Weeks Per cent CO2 0.1 0.2 0.3 0.1 0.3 0.1 0.2 1.4 4 8 16 0.6 1.0 1.3 32 1.2 2.1 1.0 2 Per cent O2 20.6 20.9 4 19.9 19.8 20.4 8 21.0 21.4 21.0 16 20.0 18.4 19.2 15.9 19.4 18.6 32 Per cent moisture in seed 7.2 7.2 7.2 7.2 2 7.0 7.0 7.2 16.5 4 7.0 7.1 7.4 22.9 8 7.1 7.2 7.6 30.3 16 7.2 7.5 12.4 40.3 32 7.1 7.8 9.4 59.0 Per cent germination 82 82 82 82 2 83 84 80 81 4 80 82 80 72 8 83 80 81 65 16 80 80 7!) 43 32 81 83 86 moisture vapor entered. The daily al- ternation of temperatures caused con- densation of moisture on the different containers, and two of the paint cans rusted completely through. The data from these cans are not included. COMPARISON OF PERFORMANCE This experiment again confirmed that the hermetically sealed tin con allows no moisture transmission and is still the standard by which to judge other con- tainers as a means for storing seed. cm The paint can did not provide a com- pletely desirable barrier, as the seed moisture content rose from 7.2% to 12.4% in 16 weeks and C0 2 diffused from the can. However, even after 32 weeks at the relatively cool average tem- perature of 62°F, the germination of the seed had not declined. The aluminized polyester pouch was nearly as effective as the tin can, even though there was an increase of about 0.6% moisture in the seed under these high-humidity conditions. If onion seed of 6.5% moisture is packaged in this con- tainer, properly sealed, there should be no decline in germination in three years under natural climatic conditions even in the southeastern United States. EXPERIMENT m EFFECT OF SCARIFICATION ON HARD-COATED SEED STORED IN MOISTUREPROOF CONTAINERS THE PROBLEM OF HARD SEED Many seeds develop hard seeds if dried to moisture contents satisfactory for safe storage in sealed containers. Hard seeds are not dead but do not germinate immediately when planted in moist soil; where rapid germination is essential for good crop yield, hard seeds must be avoided. This can be done by scarification of the seeds, either by abra- sion or acid treatment. Both of these methods, however, may reduce the stor- age life of the seeds. Drying seeds below natural dryness and storing them in moisture-proof con- tainers will prolong the storage life of the seeds but may counteract the effect of scarification. This experiment was de- signed to investigate this problem. PREPARATION OF SEEDS Seven kinds of seeds were used to com- pare the effect of scarification on the germination and hard-seed percentage at three moisture contents after storage for a year. The original germination, hard- seed percentage, and moisture content of the seeds tested are shown in table 5. Abrasive scarification was done by nicking the seedcoat of each seed with a file. Acid scarification of the seeds was accomplished by dipping them in concen- trated sulfuric acid, rinsing thoroughly with water and drying them quickly. The duration of the acid treatment was determined in a preliminary experiment, using 2-, 5-, 15-, and 60-minute treat- ments. Fifteen minutes appeared to be most satisfactory for every kind except morning glory. The seeds did not appear pitted and germination immediately after treatment was normal; hard seeds were completely or almost completely elimi- nated. In the case of morning glory, one- minute treatments of acid were given; treatment even as short as two minutes caused all seeds to rot. All seeds were individually inspected, and those showing a visible crack were eliminated. One-third of each kind of seed was scarified, one-third acid treated, and one-third was not treated. The lots were further subdivided and stored in two-quart Mason jars. One set of jars contained no desiccant; another, freshly [12] TABLE 5. ORIGINAL GERMINATION, HARD-SEED PERCENTAGE, AND MOISTURE CONTENT OF SEEDS USED IN THE SCARIFICATION EXPERIMENT Seed Variety At start of experiment Germination Hard seed Moisture content U.C. Breeding Line . . . Lazy Wife Per cent Lima Bean Pole Bean 83 91 100 75 78 79 60.5 3 4 10 34 9.3 12.8 Runner Bean Garden Pea Scarlet Runner Little Marvel 9.4 8.6 Sweet Pea Okra Morning Glory. . . Floribunda Mixed Clemson Spineless Heavenly Blue 9.9 8.8 8.8 dried silica gel ; and a third, phosphorous pentoxide. Some jars were stored at 95°F and others at room temperature, 68° to 77°F. Enough seed of each kind to pro- vide two 100-seed germination tests and two 2-gram samples for moisture tests were wrapped in cheesecloth and placed in each jar. Only 50 seeds each were used for the two germination tests of runner beans. Germination and moisture tests on each lot of seed were made after one year of storage. MOISTURE CONTENT The moisture content of the seeds in the sealed containers without a desiccant was essentially unchanged by the end of the experiment except for the pole beans. These, with a higher initial moisture con- tent of 12.8%, declined as the different kinds of seeds came into equilibrium with each other in each container. The quan- tity of P 2 5 placed in the containers did not bring the moisture content of the seeds down quite as low as in the con- tainers with silica gel. EFFECT ON BEANS Table 6 summarizes the principal re- sults of this experiment. At moisture con- tents below 5.0% there were no hard seeds in the Scarlet Runner variety of runner beans. Thus, it would appear that hard seeds are not a problem with this variety and no scarification seems to be necessary. However, a white-seeded variety such as White Dutch Runner might show hard seeds, since white- seeded snap and lima-bean varieties show a greater tendency toward hard- seededness than colored-seeded varieties. The germination data indicate that the HoS0 4 treatment was injurious to runner beans. In contrast to the pole and lima beans, drying to below 5.0% moisture did not affect germination of runner beans. The pole bean was the only kind tested that showed a drop in germination in the undesiccated treatments. This was prob- ably due to the high original moisture in these seeds, too high for safe storage. Drying to 6% moisture and below seri- ously reduced the germination of lima- [13] TABLE 6. MOISTURE CONTENT, GERMINATION, AND HARD-SEED PERCENTAGE OF SEVEN KINDS OF SEED STORED FOR ONE YEAR AT ROOM TEMPERATURE OR 95°F IN SEALED CONTAINERS OVER NO DESICCANT, P 2 0„ OR SILICA GEL Seed Desiccant None P2O5 Sil. gel None P 2 6 Sil. gel None P2O5 Sil. gel Moisture content Germination Hard seeds Per cent Lima Bean Room temp., untreated 95°F, untreated 95°F, H0SO4 95°F, filed Pole Bean Room temp., untreated 95°F, untreated 95°F, H,S0 4 95°F, filed Runner Bean Room temp., untreated 95°F, untreated 95°F, H2SO4 95°F, filed Garden Pea Room temp., untreated 95°F, untreated 95°F, H2SO4 95°F, filed Sweet Pea Room temp., untreated 95°F, untreated 95°F, H 2 S() 4 95°F, filed Okra Room temp., untreated 95°F, untreated 95°F, H 2 S0 4 95°F, filed Morning Glory Room temp., untreated 95°F, untreated 95°F, H,S(), 95°F, filed 9.9 9.8 10.0 9.7 9.8 9.7 9.9 9.4 10.3 9.6 10.0 9.5 9.1 9.0 9.0 8.5 10.3 10.1 9.9 9.6 9.5 8.8 9.0 8.8 8.8 8.6 8.8 8.5 6.3 6.0 6.0 5.5 6.2 6.1 5.6 5.4 6.1 6.1 5.8 5.5 5.4 5.4 5.2 4.7 6.1 6.2 5.8 5.4 5.4 5.4 5.0 5.0 5.5 5.5 5.2 5.0 5.0 4.8 4.6 4.6 5.0 4.7 4.5 4.5 5.0 4.7 4.6 4.6 4.3 4.3 4.2 4.2 4.9 4.7 4.6 4.6 4.4 4.1 4.2 4.0 4.5 4.3 3.9 3.9 87 88 91 85 61 69 60 31 93 85 98 81 93 96 90 78 77 60 74 63 90 87 77 93 95 98 39 30 37 12 17 13 39 29 99 96 98 95 92 89 90 90 72 69 54 44 80 74 78 70 71 74 97 26 12 29 12 4 9 25 95 91 70 96 88 84 93 82 62 48 55 15 60 54 56 60 69 68 74 96 21 4 5 12 43 1 57 76 1 29 25 24 1 bean seeds even when the hard seed con- tent was included. The scarification by either H 2 S0 4 or filing eliminated the hard-seededness, but also caused a serious decline in germination of both lima and pole-bean seeds at moisture contents of 6% or lower. Therefore, it is not safe to dry these seeds to 6% for long-time stor- age. From the data it appears that a range of 9 to 10% moisture is safe. PEAS On the other hand, drying to 4% mois- ture did not affect the germination of garden-pea seeds, and neither did scarifi- cation by either H 2 S0 4 or filing. Scarifi- cation eliminated the hard seeds, al- though the percentage was not high at the beginning. Little Marvel, however, is not one of the pea varieties most subject to hard-seededness. Scarification by either method seri- ously reduced sweet-pea germination at all moisture contents and, therefore, does not appear to be a desirable practice with this kind of seed. OKRA AND MORNING GLORY Filing, or abrasive scarification, suc- cessfully eliminated hard seeds of both okra and morning glory without loss in germination. Acid scarification was not successful with either of these kinds of seed — as, in fact, it was unsatisfactory for all seeds tested. It is possible that high-temperature storage alone de- creased the hard-seed content of morn- ing-glory seed of about 8% moisture content without any decline in germina- tion. EXPERIMENT IV MOISTUREPROOF STORAGE OF SEED TREATED WITH FUNGICIDE AND INSECTICIDE, AND OF LOW-GERMINATING OR OLD SEED TESTS ON ONION SEED Seedmen who plan to store seeds in moistureproof or moisture-resistant pack- ages need to know the effects of fungi- cides and insecticides on longevity and the role of temperature and moisture on maintaining longevity of low-germinating or old seed. Onion seed, among the vegetable seeds, loses its viability most quickly and, for this reason, lends itself to a study of viability deterioration. The following three lots of onion seed were obtained: Excel Lot 22607, 1956 crop, germi- nating 92% in November, 1956. Excel Lot 22217, 1956 crop, germi- nating 83% in August, 1956. Sweet Spanish "A" Lot 15730, 1953 crop, germinating 90% in November, 1954; 90% in August, 1954; 90S in January, 1955; 82% in February, 1956; and 75% in August, 1956. DIVISION INTO LOTS Part of the first lot was slurry-treated with Arasan, an organic fungicide, and another part was slurry-treated with Delsan, which is Arasan plus the insecti- cide Dieldrin. Thus there were five lots of seed in all, as shown on the next page. [15] TABLE 7. AVERAGE MOISTURE CONTENT OF ONION SEED IN SEALED CONTAINERS AT THE START OF EXPERIMENT AND AFTER 3 YEARS Seed condition Seed moisture High Medium Low Start End Start End Start End High germination Low germination Old seed Per cent seed moisture 7.6 7.8 8.2 8.4 8.4 7.5 7.9 8.2 8.3 8.4 7.2 7.2 7.0 6.8 6.9 7.3 7.3 7.0 6.9 7.2 6.2 6.6 6.1 5.9 6.1 6.2 6.5 6.1 5.9 6.1 Arasan treated Delsan treated Average 8.1 8.1 7.0 7.1 6.2 6.2 1. High-germinating new crop seed, untreated. 2. Low-germinating new crop seed, un- treated. 3. Old seed breaking over from high to low germination, untreated. 4. High-germinating new crop seed, Arasan treated. 5. High-germinating new crop seed, Delsan treated. Each lot was dried to three moisture levels. The high-moisture level was ap- proximately 8% ; the medium, 7% ; and the low, 6%. Other workers, including Boswell et at. (1940), have found that 6% is proper for long-time storage, with 7% and 8% adequate for storage for shorter periods. During the three years of the experiment there was no change in moisture content of the seed in the cans at any temperature or with any treat- ment, as can be seen in table 7. The seeds of the 15 lots were canned in baby-food cans and stored in water- jacketed incubators at 32°, 59°, 68°, 77°, 86°, and 95°F. The incubators had a variation of ± 1.0°F, depending on posi- tion of the sample in the incubator, and ± 2.0°F fluctuation in temperature when properly adjusted. There were 10 cans for each of the five treatments, at each of the three moisture contents, at each of the six temperatures, or a total of 900 cans. Cans were removed after 1, 2, 3, 5, 8, 12, 18, 24, 30, and 36 months. GERMINATION RESULTS The germination results are shown in tables 8 and 9. In table 8 the germination figures are presented for the original high-germinating seed, untreated, treated with Arasan, and treated with Delsan. There was no deterioration of high-vigor onion seed of 8% moisture or lower when stored at 86°F or lower for a period of three years, nor of onion seed of 6% moisture or lower when stored at 95°F or lower. Treatment of the seed with Arasan or Delsan had no effect under these conditions. However, the seed of 7% or 8% moisture stored for three years at 95°F significantly declined in germination, and the treated seed de- clined in germination faster under these [16 conditions than did the untreated seed. Practically speaking, there was almost no difference between the untreated and treated seed. In table 9 the germination figures are presented for the untreated, originally high-germinating seed (these figures are also in table 8), the originally lower- germinating seed, and the seed that was old at the beginning of the experiment. At 32°F, regardless of the original quality of the seed, there was no decline in germination during the three years of storage of seed of 8% moisture or lower. At 77°F only one condition had caused a significant decline in germination: the old seed of 8% moisture stored for three years. At 86°F only the old seed had significantly declined in germination, but even the old seed of 6% moisture de- clined significantly in only one year. At 95°F the decline of germination in the old seed was much more rapid, to 0% germination at the higher-moistures and the longer-storage times. At this high- storage temperature there were signifi- cant drops in germination after three years of both the high- and lower-germi- nating lots if the moisture content was 7% or 8%. It appears, then, that old onion seed that is beginning to decline rapidly in TABLE 8. GERMINATION AFTER 0, 1, 2, AND 3 YEARS OF THE ORIGINALLY HIGH-GERMINATING ONION SEED, UNTREATED, TREATED WITH ARASAN, OR TREATED WITH DELSAN Time in years Untreated Arasan-treated Delsan-treated Storage temp. Seed moisture 6% 7% 8% 6% 7% 8% 6% 7% 8% Per cent germination 94 94 94 94 94 94 92 92 92 32°F 1 91 91 88 93 93 92 92 89 92 2 86 93 94 94 96 88 94 93 98 3 90 90 91 90 90 90 91 89 90 77°F 1 89 94 96 88 92 92 88 92 94 2 95 93 89 97 94 93 91 89 90 3 90 88 88 94 92 90 93 92 91 86°F 1 91 92 92 94 92 91 98 95 92 2 90 79 93 90 92 93 83 98 91 3 86 85 90 92 91 88 88 92 82 95°F 1 85 94 87 92 91 87 92 90 86 2 93 89 86 93 92 78 94 92 82 3 90 71* 40* 88 60* 0* 90 60* 0* LSD 99:1 - 17.72 LSD 99:1 - 26.21 * Germinations significantly less than at the start. LSD 99:1 - 26.18 [17] TABLE 9. GERMINATION AFTER 0, 1, 2, AND 3 YEARS OF NEW ONION SEED OF HIGH GERMINATION, LOWER GERMINATION, AND OLD SEED AT THE START OF THE EXPERIMENT Storage temp. Time in years High original germination Lower original germination Old seed Seed moisture 6% 7% 8% 6% 7% 8% 6% 7% 8% 32°F. 77°F 5°F. 95°F. Per cent germination 94 91 86 90 89 95 90 91 90 86 85 93 90 94 94 82 82 82 69 69 91 88 80 82 84 60 59 93 94 66 82 84 64 73 90 91 78 70 81 63 53 94 96 76 74 82 59 58 93 89 81 76 78 53 56 88 88 83 72 80 66 55 92 92 82 80 84 51* 56 79 93 69 62 69 35* 47* 85 90 70 70 62 38* 38* 94 87 77 72 70 58 41* 89 86 80 66 52* 49* 30f 71* 40* 71 36* Of 14* ot 69 62 73 65 57 67 42* ',{)* 26* 5t 17f Of 0t LSD 99:1 - 17.72 LSD 99:1 - 23.29 LSD 99:1 - 17.53 * Germinations significantly less than at the start. | Germinations of 0% or not significantly different from 0%. germination in open storage is much more affected by adverse temperature or seed moisture than new seed. Further, the treatment of high-germinating seed with Arasan or Delsan has little or no adverse effect on onion seed of 8% mois- ture or lower stored in sealed containers. GAS ANALYSIS The onion seeds were canned in Febru- ary, 1957 in baby food cans, each holding slightly over two ounces of seed (about 71 grams per can) . Each can contained a volume of 140 cc, of which the seeds oc- cupied approximately 67 cc (onion seed sp. gr. = 1.17) and the atmosphere 73 cc. The cans were sampled by gluing a piece of gum rubber on the side, driving a small nail through the rubber and can side, and quickly taking out a sample of the internal atmosphere with a hypo- dermic needle. The Aerograph gas chromatograph method was used. Cans from all treat- ments were analyzed for 2 , C0 2 , and N 2 . The results shown in table 10 are the averages of all five treatments. The results show the sharp decline in [18 2 percentage, even at 32°F. However, the C0 2 percentage did not increase as fast as the 2 percentage decreased, re- sulting in a negative pressure in the can. It is possible that some of the oxygen was used up in oxidation of the tin or iron of the can itself, but this is unlikely, as the can and lid were both enameled. How- ever, the enamel may have oxidized to some extent and the seed coats of the onion seeds which were dead may have oxidized, or there may have been adsorp- tion of oxygen by the seed. It is also pos- sible that there was considerable an- aerobic respiration. The higher the temperature, as long as there was no decline in germination, the greater the amount of oxygen used and the greater the release of C0 2 . This is, no doubt, due to the greater rate of respira- tion at the higher temperatures. But at 95°F, where there was a sharp decline in germination after three years of stor- age, the oxygen used was not as great as at 86°F and the C0 2 produced was greater. In fact, with the 8% moisture seed at 95°F, the 2 plus C0 2 percentage of 23.8% exceeded the total of these two gases in the original atmosphere. Perhaps on death of the cells the C0 2 and 2 are released from the cells of the seed to the atmosphere of the container. TABLE 10. GAS ANALYSIS OF ATMOSPHERE AROUND ONION SEED STORED IN SEALED CONTAINERS FOR THREE YEARS AS COMPARED TO THE SEED MOISTURE AND SEED GERMINATION Storage temp. Seed moisture 02 C0 2 N 2 Seed germination Per cent 32°F 6 7 8 6 7 8 6 7 8 6 7 8 14.4 14.5 10.0 7.2 7.9 5.3 4.9 4.6 3.6 3.8 6.3 10.8 0.8 0.7 0.8 3.8 4.9 7.6 13.6 11.2 7.8 14.2 15.6 13.0 84.8 84.8 89.2 89.0 88.2 87.1 82.5 84.2 88.6 82.0 78.1 76.2 83 77°F 78 84 85 86°F . . . 80 78 75 95°F 75 66 71 45 8 [19 EXPERIMENT V ALUMINUM CAN INVESTIGATED AS SEED CONTAINER ONION SEED TESTED The aluminum can, a container not included in the previous experiments has the advantage of not rusting. To test it as a seed container, onion seed of two moisture contents (7.3% and 9.3%) ger- minating 75.5% was sealed in aluminum cans on February 17, 1957, and stored at 86°F or 95°F until November 21, 1960, a period of 3 years and 9 months. Gas samples of the atmosphere in the sealed cans were analyzed by gas chroma- tography at the end of the experiment. The moisture content of the seed and its germination were also determined. There were originally three cans for each mois- ture level at each temperature, but gas analysis and careful examination of the cans revealed that the one can in each temperature containing the low-moisture seed had been poorly sealed. The data for these cans are reported separately. GERMINATION AND MOISTURE CONTENT The results (see table 11) indicate that 9.3% moisture in the onion seed was too high for 3% years' storage at 86°F or 95°F, and that a moisture content of 7.3% was too high for storage at 95°F for the same period, but was satisfactory at 86°F. The results also indicate that it may be more difficult to obtain a good seal with an aluminum can than with a tin can. As germination goes down, 2 is depleted; but germination does not always decline when the atmospheric 2 declines. Also, 95°F appears to be in- jurious to onion seed of moisture contents of 7% or higher. TABLE 11. GERMINATION AND MOISTURE CONTENT OF ONION SEEDS STORED 3% YEARS IN ALUMINUM CANS, AND THE C0 2 AND 2 CONTENT OF THE ATMOSPHERE IN THE CANS Original seed moisture Can seal After 3% years' storage Storage temperature Germination Seed moisture Can atmosphere C02 C-2 Per cent Good Poor Good Good Poor Good Per cent 86°F 95°F 7.3 7.3 9.3 7.3 7.3 9.3 76 64 1 3 3 7.3 7.2 9.3 7.3 7.0 9.4 5.5 0.1 13.3 3.0 1.0 18.7 8.1 21.0 2.8 6.4 19.4 1.8 [20 EXPERIMENT VI RELATIONSHIP BETWEEN CO* PRODUCED AND GERMINATION OF SEEDS SEALED IN TIN CANS TEST WITH EGGPLANT SEED Eggplant seed was dried to several moisture levels, sealed in tin cans, and stored from July, 1958 to July, 1960 at 77°F, common storage, or 32°F. At the conclusion of the expermient the gas at- mosphere was analyzed for C0 2 , and the seed germination and seed moisture were determined. The results are presented in table 12. The results are the averages from two or three cans. There appears to be a relationship be- tween the C0 2 produced and the loss in germination, with an amount of 0.1 mg C0 2 per gram dry weight of seed in two years being related to a decline in ger- mination and an amount of around 1.0 mg C0 2 being related to death of all the seed. As the temperature increased, the rate of C0 2 produced and the decline in germination are both hastened, but the relationship between C0 2 produced and loss in germination is the same at each temperature. TABLE 12. C0 2 PRODUCED (EXPRESSED AS MG C0 2 PER GM DRY WEIGHT OF SEED), GERMINATION, AND MOISTURE CONTENT OF EGGPLANT SEED STORED FOR TWO YEARS IN A SEALED CONTAINER AT THREE DIFFERENT TEMPERATURES 77 °F storage Common storage 32 °F storage Seed moisture range CO2 prod. Germi- nation Seed moisture CO2 prod. Germi- nation Seed moisture CO2 prod. Germi- nation Seed moisture Per cent 11.0-11.2 8.5- 9.1 6.9- 7.3 4.2- 4.3 4.0- 4.2 3.32 .15 .11 .06 .01 38 65 75 78 11.2 8.8 7.1 4.3 4.1 .51 .10 .06 .03 .01 6 52 61 69 78 11.0 8.8 7.1 4.2 4.1 .01 .01 .01 .01 .01 76 75 78 73 76 11.1 9.0 7.2 4.2 4.2 [21 EXPERIMENT VII ADDITIONAL INVESTIGATIONS OF CONTAINERS FOR MOISTURE TRANSMISSION AND GERMINATION OF STORED SEED TYPES OF CONTAINERS This experiment, similar to Experi- ment I, tested five types of containers for the storage of onion seed. The storage climates were the same as in Experiment I: temperate, tropic, desert, and frigid. The onion seed lots were placed in cloth bags, and each cloth bag was placed into the following types of containers : 1. Cotton bags. 2. Multiwall paper bags. 3. Asphalt laminated multiwall paper bags. 4. Polyethylene laminated multiwall paper bags. 5. Aluminum foil laminated multiwall paper bags. Thus, numbers 2, 4, and 5 were the same as bags 1, 2, and 6 of Experiment I. The onion seed was the same as in Experiment V. At the start it contained 7.3% moisture and germinated 75.5%. The experiment lasted two years, and lots were removed 6, 12, 18, and 24 months after the start, except that no lots were received for the 24-month period from the desert and frigid stor- ages. Results are summarized in table 13. GERMINATION Under the desert storage conditions (100°F - 12% RH) the moisture dif- fused out of all containers except the foil- laminated container, so the onion seed- moisture content reached a sufficiently low level that storage was reasonably satisfactory. However, the moisture con- tent of the seed in the foil-laminated bag remained too high, causing a rapid loss TABLE 13. GERMINATION OF ONION SEED (ORIGINAL GERMINATION 75.5%) STORED FOR TWO YEARS IN VARIOUS CONTAINERS AND UNDER DIFFERENT CLIMATIC CONDITIONS Container Temperate Tropic Desert Frigid Months 12 18 24 12 18 24 12 18 12 18 Per cent germination Cotton Paper Asphalt Polyethylene Foii 65 64 64 63 72 70 71 4 78 70 64 28 66 65 67 77 70 59 38 68 84 79 76 68 66 72 52 67 72 71 65 64 60 74 70 68 69 70 45 6 6 75 74 71 73 80 [22] of germination. Thus, with high-moisture if the container was not a moisture bar- seed stored in a moisture-resistant con- rier. Thus, the seed in the cotton and tainer in the desert, the barrier to mois- paper bags rapidly lost viability. In this ture movement was a detriment, again experiment the foil-laminated multiwall emphasizing the need for properly dry- paper bag was best for resistance to mois- ing the seed before placing it in a ture penetration, the polyethylene and moisture-resistant container. asphalt laminated multiwall paper bags Under frigid storage 0°F - 50 RH) were both good, and the cotton and paper the differences among containers are bags were poor. most clearly shown. At this temperature Under tropic conditions none of the 7.3% moisture is safe for long-time bags were useful in preventing complete storage of onions, but with 50% RH the deterioration of the seed of 7% moisture seed gained moisture to 9% or greater content within six months. LITERATURE CITED Associated Seed Growers, Inc. 1954. The preservation of viability and vigor in vegetable seed. Asgrow Monograph No. 2. Barton, Lela V. 1935. Storage of vegetable seeds. Contributions from Boyce Thompson Institute 7:323-332. Barton, Lela V. 1939. A further report on the storage of vegetable seeds. Contributions from Boyce Thompson Institute 10:205-220. Boswell, V. R., E. H. Toole, V. K. Toole, and D. F. Fisher 1940. A study of rapid deterioration of vegetable seeds and methods for its prevention. USDA Tech. Bui. 708:1-47. Harrington, J. F. 1960. Preliminary report on the relative desirability of different containers for storage of several kinds of vegetable seeds. Univ. of Calif., Davis, Vegetable Crops Series Mimeo 104:1-7. Justice, O. L. (ed.) 1952. Manual for testing agricultural and vegetable seeds. USDA Agr. Handbook No. 30. ACKNOWLEDGMENTS In Experiment I the containers used were supplied by the Crown Zellerbach Corporation and the American Can Company. The seed was supplied by Asgrow Seed Company, Dessert Seed Company, Ferry-Morse Seed Company, Peto Seed Company, Lawrence Robinson Seed Company, and the Waldo Rohnert Com- pany. Storage of the seed was at the Crown Zellerbach Corporation, San Leandro, and the Department of Vegetable Crops, Davis. The seed in Experiment II was supplied by the Asgrow Seed Company, in Experi- ment IV by the Ferry-Morse Seed Company. In Experiment III the okra, runner bean, morning glory, and sweet pea seeds were furnished by the Fredonia Seed Company, the pea seed by the Ferry-Morse Seed Company, the snap bean seed bv the Kellogg Seed Company, and the lima bean seed by Dr. R. W. Allard of the Agronomy Department of the University of California, Davis. Experiment VII was done in cooperation with Luther Jones, Department of Agronomy, Davis, and the Crown Zellerbach Corporation. The author wishes especially to thank Mitzi Aguirre, laboratory technician, for running the hundreds of germination and gas-analysis tests needed in the seven ex- periments described. [23] In order that the information in our publications may be more intelligible it is sometimes necessary to use trade names of products or equipment rather than complicated descriptive or chemical identifications. In so doing it is unavoidable in some cases that similar products which are on the market under other trade names may not be cited. No endorsement of named products in intended nor is criticism implied of similar products which are not mentioned. 7y 2 m-2,'63(D3290) J. P.