Volume 12, No. 1, 1988

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(pp. 1-15)
Seed Imbibition: A Critical Period For Successful Germination
L. W. Woodstock
Imbibition, the uptake of water by the dry seed, involves absorption of water by cell wall and protoplasmic macromolecules, i.e., proteins and polysaccharides, wherein water molecules are "held" by electrostatic forces such as hydrogen bonds. The movement of water into the seed is due to diffusion and capillary action with water moving from a region of higher to lower water potential. Of the three components of seed water potential, i.e., osmotic potential, matric potential, and turgor pressure, it is the matric potential of cell walls and their contents which is primarily responsible for imbibition. 

Permeability of the testa, or seed coat, is a major factor controlling the rate of water uptake. Although necessary, imbibition is a period of peril: rapid uptake of water may cause imibibitional injury, cold temperatures may cause chilling injury, anaerobic conditions may lead to accumulation of toxic chemicals, and leaching of cellular constituents into the soil may stimulate microbial attack. Low vigor legume seeds with permeable seed coats are especially susceptible to imbibitional injury. The imbibition period offers opportunity as well as hazard. Seeds may be primed for increased vigor by imbibing and then drying back. High membrane permeability during early imbibition may facilitate insertion of germination-promoting and anti-pathogen chemicals into seed tissues. This review covers: The physical process of imbibition, the seed coat as a protection against imbibitional injury, membrances during imbibition relative to seed vigor, leachates as indicators of vigor, and use of the imbibition period to improve vigor.
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(pp. 16-23)
Short Term Storage Effects on Dormancy and Germination of Chickpea (Cicer arietinum)1
C. C. Frisbee, C. W. Smith, L. E. WIiesner, and R. H. Lockerman2
Poor chickpea (Cicer arietinum L.) stand establishment often occurs when seeds are planted in cool soils. The effects of storage temperature and duration on 'Garnet' chickpea seed germination at low temperature were determined. In a storage temperature study three seedlots were stored at 5o C., 23o C., and open temperatures (16-27o C.).

In a storage duration study seeds were stored 104 weeks at 5o C., then transferred to 23o C. for periods ranging from 1 to 8 weeks before germination testing. Storage at 23o C. or open storage reduced germination percentage and germination index and increased hardseededness. Seedling growth rate at 5o C. germination temperature was not influenced by storage temperature, but was significantly lower at 27o C. germination temperature for seed from open storage. Seeds moved from cool to warm storage environments rapidly exhibited decreased germination and increased hardseededness.
Additional Index Words: Germination index, hard seed, seedling growth rate test, temperature.
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(pp. 24-36)
Factors Influencing the Tray Accelerated Aging Test for Soybean Seed1
L. J. Tomes, D. M. TeKrony and D. B. Egli2
Although the accelerated aging (AA) test has been widely used as an indicator of seed vigor, lack of standardization has resulted in variation in results. Experiments were conducted to evaluate the influence of the aging chamber and several testing variables on soybean [Glycine max (L.) Merr.] seed germination following accelerated aging when using the inner chamber (tray) procedure. The basic aging procedure involved placing 40 g of seeds on a wire mesh tray suspended over 50 ml of water in the inner chamber (plastic sample box with lid). The inner chambers were placed on trays in an outer aging chamber for 72 h at 41°C (± 0.5"C) after which the seeds were planted for standard germination. Aging time, temperature and seed moisture interacted during aging to reduce seed germination.

Temperature had the greatest effect on germination and 41°C was a threshold of sensitivity for soybean seed. An aging time of 72 h at 41°C provided excellent separation in vigor across seed lots; however, little deterioration occurred after 48 h and excessive deterioration occurred after 96 h. Relative humidity in the inner chamber reached 90% after 24 h and gradually increased to 95% by 72 h. Final seed moisture after aging ranged from 31-34% and was one of the most repeatable aspects of the test. Initial seed moisture levels ranging from 8.0 to 13.5% had little effect on final seed moisture; however, both initial and final seed moisture should be monitored during aging. Seed size influenced final seed moisture following aging, but could be controlled by determining sample size on the basis of seed weight (40 g) rather than seed number (200 seeds). Air temperature nside the inner chamber was influenced by opening the outer chamber door, the number of inner chambers per shelf ahd the location of shelves within the chamber. The effects of these factors were eliminated, however, by limiting the number of inner chambers to nine per shelf, placing shelves in the upper portions of the aging chamber and keeping the outer chamber door closed during the test. These results support the inner chamber (tray) accelerated aging system and identify methods for controlling several testing variables which improve the standardization of this test.
Additional index words: Germination, Vigor,  Glycine max (L.) Merrill, Seed Moisture.
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(pp. 37-53)
The Bulk Conductivity Test as an Indicator of Soybean Seed Quality1
T. M. Loeffler, D. M. TeKrony and D. B. Egli2
The bulk conductivity test has shown potential as a quick, nonsubjective test of seed vigor and has been suggested for use in a wide range of crop species. This research was conducted to evaluate the seed and test variables which may influence the bulk conductivity test when measuring soybean [Glycine max (L.) Merr.] seed vigor.

Several experiments were conducted using seed lots which had a wide range in seed vigor but acceptable standard germination. Low initial seed moisture (<11%) significantly increased conductivity, however, there was little difference when seed moisture ranged  from 11 to 18%. Water temperature must be maintained at 25o C. following the 24 h soak period, since a 5o C. change prior to evaluation significantly influenced conductivity results. Visual identification of mechanically injured and diseased seeds prior to testing was found to be subjective and inaccurate. Thus, the seeds used for the conductivity test should be randomly selected from the pure seed portion of the seed lot. Increasing the number of seeds tested from 25 to 50 seeds per replication reduced the coefficients of variation for the test from 19.0 to 9.8% when averaged over 20 seed lots.
There was no increase in conductivity for intact seed infected with high levels of Phomopsis sp. or Cercospora kikuchii, however, moderately or severely fissured (diseased) seed showed high rates of electrolyte leakage. Fungicide seed treatment with Captan-80, Arasan-50 and Vitavax 200 had little effect on conductivity results, however, precautions must be taken when other fungicides or seed treatments are used. A bulk conductivity procedure is recommended which reduces the variability caused by testing variables and should assist in standardizing the vigor test across routine seed testing laboratories.
Additional index words: Germination, Vigor, Glycine max: (L.) Merr.
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(pp. 54-58)
Effects of Mechanically Sizing Soybean Seed on Seed Quality1
John E. Armstrong, Charles C. Baskin and J. C. Delouche2
The distribution of soybean seed size is presented and one method of dividing soybean seed lots into sizes is discussed and evaluated. Number of soybean seed per pound (kg) ranged from slightly over 3,000 per pound (7,000 per kg) to slightly over 4,000 per pound (9,000 per kg) both within cultivars and among cultivars. Seed were sized with a precision grader. Damaged caused by sizing was negligible.
Additional Word Index: seed conditioning, precision grading, mechanical damage, Glycine max L. merrill.
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(pp. 59-65)
Sizing Soybean Seed to Improve Plantability1
John E. Armstrong, Charles C. Baskin and J. C. Delouche2
The effects of mechanical sizing on soybean seed planter metering accuracy were investigated. Seven lots of four cultivars were sized into seven thickness size categories ranging from 10164 in. (3.97 mm) to 16/64 in. (6.35 mm). Metering accuracy of three plates, B24-28, BSOY2 and BSOY, manufactured by Lincoln Ag. Products, Lincoln, Nebraska was determined with 28 seed sizes and size combinations using a John Deere Planter Plate Test Stand. A planter plate cell metering accuracy percentage (CMA%) was calculated on the basis of the most frequent number of seed discharged per cell.

The B24-28 plate (widely used to plant large, round corn seed) gave CMA values of 90% or higher for 23 of the 28  seed size categories and combinations. The BSOY2 plate gave CMA values of 90% or higher when seed were uniform in size (to 1/64 inch) (0.397 mm) or when seed smaller than 13/64 in. (5.16 mm) thick were removed from the seed lot. The BSOY plate gave CMA values of 90% or higher only when seed smaller than 13/64 in. thick were removed from the seed lot. Results were confirmed in large hopper box tests simulating field planting.
Additional Index Words: planting accuracy, seed conditioning, Glycine
max L. Merrill.
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(pp. 66-75)
Effects of Temperature on Seed Germination in Pterocarpus macorcarpus1
C. Liengsiri and A. K. Hellum2
Seeds of Pterocarpus macrocarpus Kurz collected in Thailand in December 1984 from six different provinces were investigated for germination in response to variable temperatures. Different germination patterns were observed among the six stands. The sensitivity and tolerance to temperatures during germination, which were determined by the area within 80% germination isolines, appeared under the influence of ecological climate rather than geographic location.

A wide range of temperature tolerance was observed among stands from cool and warm climates. Seeds originating in the warmer climate tolerated high germination temperatures better. However, all seed lots were identical in their optimum temperature regime (30/25°C day-night alternation) for maximum total germination with the overall mean of 91%. They also shared a wide common range of temperature preference for ≥80% total germination. High total germination (≥80%) was obtained over a wide range of alternating temperatures, but was restricted to a narrower range under constant temperatures.
Additional index words: Seed germination, Temperature, Tropical species.
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(pp. 76-89)
Development of Oven and Karl Fisher Techniques for Moisture Testing of Grass Seeds1
Ethan Benjamin and Don F. Grabe2
The Association of Official Seed Analysts' Rules for Testing Seeds do not contain methods for moisture testing. The oven methods in use by seed testing laboratories in the U.S. are diverse and may produce erroneous results when compared to the Karl Fischer method. The International Seed Testing Association Rules for Seed Testing contain oven testing methods for 95 kinds of seeds, but many of the methods are empirical in nature and lacking in accuracy. This research was initiated to develop more accurate oven methods for testing moisture content of seeds of temperate-climate grass species.

The test variables investigated were oven temperature, time of drying, seed grinding, and original moisture level of the seed. The species included were perennial ryegrass (Lolium perenne L.), orchardgrass (Dactylis glomerata L.), colonial bentgrass (Agrostis tenuis L.), Kentucky bluegrass (Poa pratensis Huds.), tall fescue (Festuca arundinacea Schreb.),and red fescue  (Festuca rubra L.).
Drying to constant weight at temperatures of 90, 100, 105° C. gave moisture percentages lower than the Karl Fischer value. Drying periods of 6 h or less at 130° C. gave moisture percentages in agreement with Karl Fischer results. Ground and whole seed gave similar moisture percentages after drying to constant weight, but moisture was removed more rapidly from ground seeds. The required drying time for greatest accuracy depended on the original moisture content of the seed. Moisture was removed most rapidly from the highest moisture seed; thus, it is not possible to select one drying period that will provide the same degree of accuracy on seed with different moisture levels.
Seed moisture tests on these six temperate-climate grass species should be conducted on whole seed at 130° C. The best compromise for drying periods are 3 h for perennial ryegrass, Kentucky bluegrass, tall fescue and red fescue; 1.5 h for orchardgrass; and 1 h for colonial bentgrass.
Additional Index Words: Lolium perenne L., Dactylis glomerata L., Agrostis tenuis L., Poa patensis Huds., Festuca arundinacea Schreb., Festuca rubra L.
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(pp. 90-98)
The Effect of Moist Chilling on the Subsequent Germination of Some Temperate Conifer Seeds Over a Range of Temperatures
Peter G. Gosling1
Prechilled and unchilled seeds of three conifer species (douglas fir, DF; scotch pine, SP; and sitka spruce, SS) were incubated over a range of constant temperatures (10 to 40°C). Three weeks prechilling broadened the range of temperatures over which DF seeds could germinate, and for all three species improved the maximum percentage germination at some, if not most temperatures. None of the seeds ever germinated at 40°C. Prechilled seeds were always quicker to germinate than unchilled seeds. The results are discussed in relation to various authors' concepts of 'relative dormancy'; and their practical significance to seed physiologists, plant producers, and geneticists is considered.
Additional index words: Seed, Relative dormancy, Germination.
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(pp. 99-106)
Effects of Soil Moisture Content and Crop Rotation on Cold Test Germination of Corn (Zea mays L.)
J. H. Nijëenstein1
Effects of crop rotation on cold test germination of corn were studied using soils from one origin. Absolute germination percentages were only slightly influenced by crop rotation. Previously cropped soils did not give lower germination percentages than did soils that were never cropped with corn before.
Soil moisture content influenced germination percentages of corn in the cold test to a great extent. Resuhs obtained in the present study showed reduced germination in soil above 34% waterholding capacity.
Additional index words: cold period.
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