Rushing, T. T.

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Mississippi State University Scholars Junction Proceedings of the Short Course for Seedsmen MAFES (Mississippi Agricultural and Foresty Experiment Station) 4-1-1968 Use of Stress Tests To Determine the Storage and Field Stand Potential of Seeds T. T. Rushing Follow this and additional works at: https://scholarsjunction.msstate.edu/seedsmen-short-course Recommended Citation Rushing, T. T., "Use of Stress Tests To Determine the Storage and Field Stand Potential of Seeds" (1968). Proceedings of the Short Course for Seedsmen. 199. https://scholarsjunction.msstate.edu/seedsmen-short-course/199 This Article is brought to you for free and open access by the MAFES (Mississippi Agricultural and Foresty Experiment Station) at Scholars Junction. It has been accepted for inclusion in Proceedings of the Short Course for Seedsmen by an authorized administrator of Scholars Junction. For more information, please contact scholcomm@msstate.libanswers.com. 75 USE OF STRESS TESTS TO DETERMINE THE STORAGE AND FIELD STAND POTENTIAL OF SEEDS Travis T. Rushingl/ A stress test may be defined as the application of unfavor-able environmental conditions to the seed in order to determine a specific performance characteristic. For example, the two stress tests we will consider here are the accelerated aging test and the cold test. In the accelerated aging test high temperatures and relative humidities are used to accelerate deterioration processes and this then enables us to predict the storage potential of several lots of a given seed kind with a few days. In the cold test, on the other hand, cool temperatures and moist soil are used to determine the ability of the seed to emerge under unfavorable field conditions. Now with your permission let us think in t erms of measuring storage potential with the accelerated aging test and measuring storage potential with the accelerated aging test and measuring the field stand potential with the cold test. First 1 let us consider storage potential and the accelerated aging test. Accelerated Aging After production and processing, a primary concern of the seedsman is maintenance of the seed in a good viable condition until they are purchased by the farmer . S ~edsmen frequently have the unhappy experience that some lots of seed of apparently good via·bility rapidly decline in germination during storage, while other lots of equal viability hold up well. Similar differential responses in field emergence among lots of equal viability are also frequently encountered. In other words 1 a high germination percentage does not necessarily indicate that a seed lot will store safely or that it will produce a satisfactory field stand . 1/ Mr. Rushing is Assistant Agronomist I Seed Technology Labora-tory I M ississippi State University. 76 Those of you associated with quality control programs have probably been faced with the difficult task of determining which lots from among many available should be marketed first and which lots should be held for possible carry-over if the market is not strong, or as a hedge against shortages the next year . Germination per-centages of the lots provide some useful information for making this decision if there is a considerable range in germination among the lots. This is seldom the case, so the seedsman randomly selects for possible carry-over, and he often finds the next season that several of them did not carry-over very well. The failure of a seed lot of apparent good germination to maintain that germination in storage at a retail outlet or at the wholesaler constitutes a serious problem - one that can be most damaging to the seedsman ' s profits and reputation . The solution to problems related to storability of seed lots lies in the development of a test - other than the standard germina'-tion test - which will differentiate among seed lots with respect to storage potential. A test that is attracting attention in the seed industry is the accelerated aging test developed here at the Seed Technology Laboratory . This technique is based on the hypothesis that the degree of deterioration is variable among seed lots within a given seed kind, even though deterioration has not progressed to the point where it has affected germination. Therefore, by sub-jecting small samples of various lots of the same seed kmd and approximately the same current germination to an extreme environ-menta 1 condition, i.e. , high temperature and relative humidity, the process of deterioration can be accelerated to the extent that w1thin a few days low vigor lots are drastically reduced in germmative capacity while high vigor lots are relatively unaffected . Thus, accelerating the physwlogical agmg processes perm1ts evaluation or prediction of the long term storage potential of seed lots w1thin a few days. Environemental conditions and period of exposure requ1red to obtain maximum differences in res ponse among seed lots vary with the kind of seed. In general, the most satisfactory conditions are 100% relative humidity, temperatures of 35° to 45°C. , and exposure periods of 2 to 8 days. The effectiveness of accelerated aging as an assay of the storage potential of seed lots 1 s evaluated by comparison of the germination percentages after accelerated aging with those of the same lots after intervals of storage. 77 Equipment The accelerated aging chamber we are using was made from an old, water cooled germinator with 2 1/2 11 insulated walls and door. It has inside dimensions of 2 6 11 width, 24 11 height , and 20 11 depth . All water tubing and other internal eq mpment - except tray racks - were removed from the germinator . All gaskets, holes, etc . I were resealed with' 3M weather strip adhesive {black) . A water reservoir approximately 1 l/2 11 deep is maintained in the bottom of the chamber . In the water reservoir is a flexible 1 immersion heating rod. Temperature is controlled by a thermister temperature controller equipped with a general purpose thermister probe. A plexiglass chamber was designed as an insert or liner for the chamber to maintain a more constant temperature and relative humidity . The plexiglass liner fits on a rack about 5 inches from the bottom of the chamber and 2-4 inches from the side, walls I back and ceiling. The liner has a water reservoir I glides for 2 trays , and a removable access panel in the front. The top rack of the plexiglass liner is covered with blotters to collect any condensation dripping from the top (actually 1 very llttle condensation forms on the top or walls of the liner) . The bottom rack is used for holding the samples of seed as a set distance of 3 inches from the surface of the water. A long stem dial thermometer is inserted through the front access panel of the liner, and a sensitive glass mercury thermometer is attached to the sample tray placed in the liner . In operation, water is placed in the bottom of the chamber and p lexiglass liner . The temperature controller is energ ized and adjusted to the desired temperature setting w1th the gla s s thermo-meter inside the liner. After the desired temperature is achieved, the tray is removed and samples to be tes ted are prepared and placed in small wire screen baskets on the tray . The tray is placed in the liner and accelerated aging begun . After accelerated aging for the desired number of hours or days the samples are removed and standard germination tests are made on tha samples. Typical data are given in Table 1. 78 Table 1 . Germination percentages of corn 1 tall fescue I garden bean I crimson clover and - onion s.eed lots after accelerat ed aging and intervals in open storage . Lot !nit. Accelerated Oeen Storage {Months} No. Germ. Aging 4 ' 6 12 Corn 1 100 94<y 100 98 2 100 92 99 98 3 92 44 90 74 4 84 22 94 78 5 96 19 96 22 y Accelerated aging at 42S'c. - 100% r.h./144 hrs. Tall Fe:scue 1 95 94 'g/ 96 93 2 92 83 92 52 3 87 80 90 48 4 88 56 73 24 ~Accelerated aging at 40° C . - 100% r . h . /84 hrs. Garden Beans 1 97 95~ 97 94 2 97 35 97 93 3 77 51 77 71 4 87 7 85 35 c/Accelerated aging at 42°C. - 100% r.h./7 2 hrs . Crimson Clover 1 94 90~ 96 92 2 94 74 93 86 3 78 52 81 60 4 88 80 92 86 r!fAccelerated aging at 40° C. - 100% r . h./72 hrs . 79 Table 1 continued. Lot !nit. Accelerated Oeen Storage ~Months) No. Germ. Aging 4 6 12 Onion 1 93 93 91 2 93 46 31 3 88 76 72 4 95 67 49 e Accelerated aging at 40°C. - 100% r . h./120 hrs. Cold Test Favorable environmental conditions are used 1n conducting germination tests I with conditions of temperature and mo1sture as near optimum as possible . The use of these conditions gives a measure of the maximum germination of a seed lot but does not give a measure of its germination under adverse conditions which often occur in the field. In cold tests, seeds are subjected to cool., wet conditions in order to obtain some measure of the ability of seed lots to emerge under unfavorable conditions encoun-tered during a cool I wet spring. For example, corn may be planted and immediately followed by a "cold front" that causes cod , wet conditions to prevail for several days or weeks. The emergence period may be 2 or 3 weeks . Under these conditions I only vigorous 1 sound, we'll treated, seeds are capable of emergence while the weak (but still germinable m germ1nat1on test) and unsound seeds often decay due to soil orgamsms before more favorable conditions are again established. Cool I wet soil 1s unfavorable for both seedling emergence and sml pathogens , but these conditions are relatively less favorable for germination than for the soil pathogens . Generally fy!hium species are the most Important soil orga-nisms in cold tests . These species are usually the first invaders of seed planted in moist field soil . Probably the most frequent _ _ species identified is Pythium debaryanum. In seed with perica.rp injuries, Pythium invasion occurs immediately after plantmg . Other organisms that cause stand reduction are Penicillium 1 Rhizoctonia I 80 and Fusarium . Uses of the Cold Test Most of the larger corn seed companies are usmg the cold test to: l. Determine the quality of carry-over seed 2 . Evaluate seed treatments 3 . Test the effects of processing methods on the seed. 4 . Evaluate vigor in parent stocks. 5 . Compare the resistance of inbreds and single crosses . 6. Evaluate the adequacy of storage conditions with respect to seed deterioration. 7 . Determine the extent of frost injury and immaturity and its effect on seed vigor . Factors that Affect CoJsi Test Results Many inte rrelated factors are known to influence the results obtained with the cold test . The test IS sometimes difficult to standardize between laboratories . Some of the factors that contn-bute to lack of standardization are : l. Different soils used m cold test. Sml used m vauous laboratones give d1fferent results due to variatJOn in population and acti vlTy of soil-borne orgam sms . 2 . Different species or strajns of orgamsms exh1bit vanous degrees of vuulence. 3 . Type of storage of soils used in cold tests may be a source of error . 4 . Difference m cold test methods. Extremes in mojsture content, length of cold period and temperature during cold period may cause vary1 ng results . 81 The lack of standardization, however, need not limit the usefulness of the co l·~ test as a q uality control tool. As long as one method is consistantly followed comparisons can be made between lots, varieties, and yecurs. If one test method is used on one lot and another method on another lot, however, the results c ould be mis leading . Thus, each laboratory or company must employ the test method that provides the most information about the quality of their seed. This may often require a more vigorous type cold test for early season varieties while a progressively less severe test may be more realistic for varieties planted Later in the season . The severity of the cold test cou ld be regulated simply by varying the temperature and test period , a re: The methods employed in the Seed Technology Laboratory 1 . The soil (top soil) Is obtained from a field where the seed kind to be planted has been grown the previous year. 2. Next we bring ~he soil in and screen it through round hole screen to remove crop residue, gravel, 1 umps of soil, etc . 3. The screened soil is then mixed with builders sand in a 1 part sand to a l part soil ratio m a small concrete mixer . 4 . 1500 grams of the sand-soil mixture are placed 1n plastic crispers , The soil is leveled, then rP s eed are placed uniformly over the soil . The Sbed are then covered With an addit10nal l 000 grams of the sand-soil mixture . The soil 1 s then packed lightly by pressing wlth a flat board and adjusted ru 60% saturation . 5. The containers are then placed at 50°F. for a specifiC period of time depending on the crop . We have found that 7 days for corn and 5 days for cotton soybeans, and sorghum give satisfactory results . 6. After the chilling period the conta1n ers are transferred to 86°F. till seedlings are evaluated (usually 3-4 days after chilling) . 82 7 . The emerged seedlings are then class1hed as normal or abnormal. W hen considering the cold test as a tool in q uahty control , some important factors that effect cold test results shou ld be known: Seed Maturity - Generally , the difference between germmation p.ercent and cold test results is greatest for the most immature seed lots . Maturity of seed has onl y a minor i nfluence on seedhng emergence under regular germination test and fails to indicate the abillty of seed to germinate in cold , wet soil. Also , the greater mechanical inj ury associated with 1mmaturity contributes to low seedling e mergence in cold test. Se ed Permeability - This is associated w1th seed coat injury and deterioration of seed . The possible explanations for the low germination as seed permeab11lty increases are (1) matenals tha t diffuse out of seed serve as food for the organisms respons1ble for reducuon in cold test and (2) (2} pathogens can more easily mvade the permeable seed . Artificial drying - Corn seeds artificially dned at 110°F are more susceptible to invasion by s01l pathogens than ears dried in an open room . Artif1c1al dry1ng causes an increase i n the amount of bhstering of the seed coat , th1s is especially true of i mmature seed . In add1t10n to seed coat i n jury , a p hysiologi cal differ ence ex ists between ani-flcially and naturally dned seed that affects their suscepti-bility t o soil pathogens So a combination of se t.!d c oat injury and physiological effects seems to be the main factors contribunng to seedhng reduction in cold test Mecha mcal damage {pencarp inJury) - InJury of the seed coat 1s one of the greatest contnbutors to r educed e mergence in cold test It should be remembered that a s ound intact seed coat is one of the most effective barriers to s01l patho-gen . Any broken area in the seed coat IS an excellent location for _entrance by soil pathogens. Expenments with corn have shown that severe crown injury causes the greatest reduction m cold test . Seed with pericarp InJUry at the crown or over the plumule ( ~mbryo shoot) are more susceptible to soil pathogens than seed with injury over the radicle (embryo root) . Crpwn inj ury also tends to increase with the size of the kernels and more freq uently 83 in "flats than "rounds". However, injury over the embryo (germ) occurs more frequently in "rounds". Other crops receiving mechanical injury, such as soybeans , will also tend to give low emergence in cold test, but unlike corn, injury in soybeans is often of sufficient magnitude to cause fracturing of embryo parts that cause poor emergence in germination tests as well as cold test. Therefore, soybeans with appreciable injury often give equal emergence under both germination and cold test methods. However, if the sample has also been deteriorated due to inadequate storage or other causes, then one could expect the germination test to give higher emergence than the cold test . Age of seed (physiological deterioration) - In general one can expect a reduction in cold test as th·e period of storage or carry-over increases . The rate of decline in cold test will depend on the history 6f the seed (maturation I harvest method 1 processing) prior to storage as well as actual conditions during storage . It should be emphasized that seeds at maturation are at their peak in quality I after which the seeds take only one path -- toward lower quality and death. Seedsmen can only hope to slow down this process. likewise I it should be remembered that appreciable deterio-ration can occur and yet not be evident in the germination test and this is one of the factors that contributes to the usefulness of the cold test. To detect physiological deterioration with the cold test 1 seeds should be untreated . Genetic resistance - Certain corn inbreds and s1ngle crosses show different resistance to adverse planting conditions. Likewise I some inbreds and smgle crosses consistently give higher emergence in cold tests . In the production of crosses I the degree of seedling reduction in cold test or adverse field conditions depends largely on the resi s tance of the female parent . Therefore I in single crosses an inbred with known resistance to seedling decay should be used as the female parent. To a degree I the pollinator parent also has some influence on the resistance of its progency; however I it is difficult to make any prediction from its resistance rating as an inbred . Due t o difference in com-bining ability I the actual comparative resistance of hybrid seed of any genetic composition must be determined by cold test. It should be pointed out that differences among seed 84 lots may be due to environmenta 1 conditions during the growing season . Also inbreds grown by different seed pro-ducers give wide differences in cold test results, due largely to differences in seed coat injury. Fungicide treatment - Since the cold test measures the extent of interaction of the seed with soil pathogens, any protective barner around the seed from these decay organisms have a sigmficant influerce on cold test results . For this reason , the cold test ho.s been widely used to determine the effectivenes s of various seed treatment materials . In · . general , fungicide treatment greatly increases emergence over similar untreated samples under cold test conditions The degree of increase in seedling emergence by treatment will depend on the crop , the amount of mechanical injury and deterioration. The effects of harvesting and processi ng injuries can be minimized with a good seed treatment. Any open breaks in the pericarp in which treatment prevents or delays entrance of orga nisms will certainly result in higher seedling emergence under adverse planting conditions High q uality, sound seed exhibns little or no increase m seedling emergence for treatment, while low quality seed usually shows considerable e mergence increase . Matura-tion studies have shown that treated seeds gave better emergence than untreated seeds of comparable maturities, however, seed treatment does not compensate for lack of mdturity . Severely damaged soybeans show less response to seed treatment. Obviously if t he embryo parts are frac-tured or brok.en , no amount of treatment can increase seedlmg emergence. 

Use of Stress Tests To Determine the Storage and Field Stand Potential of Seeds

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Use of Stress Tests To Determine the Storage and Field Stand Potential of Seeds

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