Volume 21, No. 1, 1999

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(pp. 5-14)
Effect of Large Diurnal Temperature Variation on Alfalfa Seed Germination and Hard Seed  Content
D. G. Stout*, B. Brooke and J.W. Hall
Five experiments were conducted to evaluate the effects of diurnal temperature variation on seed germination and hard seed content of three alfalfa (Medicago sativa L.) cultivars.  The germination tests were mostly of 7 days duration, after which the seeds were classified as germinated (radicle ≥ 2mm), fresh (swollen and radicle ≤ 2 mm), dead, abnormal, or  hard.

The first hypothesis tested was that germination under diurnal variations will be similar to that measured at constant 20 °C.A diurnal temperature variation with a high temperature (i.e. 20/35 °C [16-h night/8-h day]), resulted in alfalfa germination similar to that at 20 °C. However, when the range in diurnal temperature was large and the temperature was high (i.e. 5/35 °C), many seeds imbibed water but failed to germinate (fresh seed). When moved to favourable environmental conditions (i.e. 20 °C), the majority of these fresh seeds germinated normally. Thus, the combination of a large range in diurnal temperature and a high temperature inhibited seed germination. The second hypothesis tested was that hard seed content is decreased by diurnal temperature variation compared with that at 20 °C. A treatment including both a large range in diurnal temperature and high daytime temperature (i.e. 5/35 °C) decreased the hard seed content, however these formerly hard seeds germinated when moved to favourable environmental conditions (20 °C). The inhibition of seed germination and the decrease in hard seed content caused by a wide range in variable temperatures, did not depend on genotype or seed lot.However,whether or not the inhibited seeds originated from hard seeds or from rapidly (7 d) germinating seeds did depend on seed lot.
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(pp. 15-24)
Electrical Conductivity and Field Performance of Soybean Seeds
R. D. Vieira*, J. A. Paiva A. and D. Perecin
One of the most important considerations of seed users is field performance of the seed lot, because the grower expects an ideal plant population. Several laboratory and field tests were conducted to determine the relationship between electrical conductivity (EC) and soybean seed quality and seedling emergence in the field and to determine the EC range which predicts establishment.

Six cultivars representing 54 seed lots were used in 1993 and five cultivars representing 50 seed lots were used in 1994 with four cultivars in common in both years. The physiological quality of the seed lots was evaluated, and three field emergence (FE) tests were conducted each year. The evaluation of performance of the lots with specific EC values and their field emergence allowed the identification of electrical conductivity values, which may result in field emergence equal to or greater than the expected minimum. Seed lots with EC " 90 μmhos cm-1 g-1 resulted, in field emergence values that were equal to or greater than 70%, with a high degree of precision. The use of seed lots with EC up to 110 μmhos cm-1 g-1, resulted in field emergence values equal to or greater than 60%, also with a high degree of precision. The electrical conductivity test appears to be a useful tool to help soybean growers to establish their seeding rate, based on the expected field environmental conditions.
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(pp. 25-33)
Variability of Germination Tests of Corn and Soybeans
H. Liu, L. O. Copeland*, O. Schabenberger and D. Jamieson
This study was conducted to measure variability in results of germination tests, to estimate tolerances needed to cover variation in test results, and to determine the minimum number of seeds required for producing germination results within the limits of established tolerances.

Data were collected from conventional germination referee (CGR) tests on corn (Zea mays L.) and soybeans (Glycine max (L.) Merrill), conducted by up to 46 Association of Official Seed Analysts (AOSA) and Society of Commercial Seed Technologists (SCST) laboratories in the Midwest and Upper Great Lakes Region in 1994 to 1996. In 1997, a “blind germination referee (BGR) test” was conducted on the same crops by 23–25 laboratories in the same region in which the individual replicates of the same seed lots were unknown to the analysts performing the test. A positive “inter-replicate bias” in which a significant correlation existed among the results of replicate tests occurred in the CGR but not in the BGR tests. Tolerance limits calculated for germination above 90% from both CGR and BGR test results were close to International Seed Testing Association (ISTA) Rules, but lower than those in the AOSA Rules. Tolerances calculated for germination levels below 90% from both CGR and BGR test results were generally higher than both the AOSA and ISTA tolerances. The greatest decline of test variability was observed when sample sizes were increased from one 100-seed replicate to two 100-seed replicates.
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(pp. 37-40)
The Effect of Storage Conditions on Peroxidase Activity
Richard A. Vierling and Dennis M. TeKrony
Soybean [Glycine max (L.) Merr] seed coats are an abundant and inexpensive source of peroxidase. Peroxidase’s main function is to oxidize molecules using hydrogen peroxide and elemental oxygen as a donor. Therefore, soybean peroxidase could be an economical alternative to current chemical oxidation techniques.

Peroxidase enzyme activity declines after harvest, therefore reducing the extraction horizon or preventing the loss of enzyme activity during seed storage could generate significant cost savings. The objective of this research was to determine the effect of seed moisture content and temperature during storage on soybean seed coat peroxidase activity. Seed lots of high peroxidase cultivars were conditioned to differing seed moisture levels (9 and 13%) and stored in controlled temperature incubators (10, 20, 30, and 40 °C) or in a warehouse. Peroxidase activity was measured using the soybean seed coat peroxidase capture assay. Seed moisture did not affect the loss of peroxidase activity in stored soybean seeds but as storage temperatures increased from 10 to 40 °C the loss of peroxidase activity was accelerated.
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(pp. 41-43)
Calcium Nitrate to Control Collar Rot During Chickpea Germination.
Neal R. Foster
Hypocotyl collar rot in chickpeas (Cicer arietinum L.) may increase the variability in germination results between seed laboratories resulting in tests being out of tolerance. A study was conducted using two seed lots to evaluate the effectiveness of calcium nitrate for control of hypocotyl collar rot. Germination tests were conducted in four seed testing laboratories with and without calcium nitrate pre-treatments. The results indicate that calcium nitrate was effective in the control of hyopcotyl collar rot, which increased germination test results among laboratories.
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(pp. 44-48)
Ion Leakage as an Indicator of Vigor in Field Bean Seeds
M A. Barros, S. Ohse and J.Marcos-Filho*
This preliminary study was conducted to determine whether the physiological quality of field bean (Phaseolus vulgaris L.) seeds could be rapidly evaluated using the potassium leachate and the conductivity tests. Five seed lots of cultivar IAC-Carioca were tested for germination, accelerated aging (41 °C/72 h) and exposed to nine preconditioning periods (from 1 to 24 h) at 25 °C before conductivity readings.

The potassium leakage was determined after six imbibition periods ranging from 15 to 90 min. Results confirmed previously reported information on the usefulness of the potassium leachate test as differences of physiological quality among seed lots were identified using the combination of 25 pure seeds imbibed in 75 ml distilled water at 30 °C for 30 or 45 min. The possibility of shortening the imbibition period (up to 12h) for field bean seeds conductivity test was also determined.
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(pp. 49-52)
Tachigaren: Phytotoxic Effects on Sugarbeet Seed Germination and Emergence
Mark Anfinrud
Tachigaren 70 WP is a fungicide approved in 1995 for use as a seed treatment for pelleted sugarbeet seed that has high germination and strong vigor. At the labeled rate Tachigaren 70WP will control low levels of Aphanomyces, a fungi that causes seedling damping off, however, phytotoxicity has been reported in laboratory tests.

Six pelleted seed lots were treated with Tachigaren and laboratory and field trials were conducted to evaluate the phytotoxic effects of the fungicide on germination and field emergence. Tachigaren treated seed resulted in lower standard germination compared to the control (AOSA blotter test) and a pleated paper germination test for all seed lots. When the test was conducted in a soil/sandmixture, the results for Tachigaren treated seed germination was similar to the control. Tachigaren significantly reduced field emergence in three of the six seed lots, but not to the extent measured bythe standard germination blotter test.
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(pp. 57-65)
Volatile Compounds as Indicators of Seed Quality and Their Influence on Seed Aging
A. G. Taylor*, P. C. Lee and M. Zhang
Volatile organic compounds are chemical compounds that evaporate rapidly, and form a gaseous state. These compounds are naturally present in seeds and can be detected from seeds in storage. Certain volatiles can be sensed as aromas from an opened container of seeds. For analytical purposes, gas chromatography is used to separate a mixture of volatiles and then quantify individual compounds.

Research on volatile compounds from seeds can yield fundamental and practical information. A greater understanding can be achieved concerning biochemical reactions that occur at low moisture levels. Certain   volatiles are detrimental to seed viability resulting in reduced longevity, while many volatiles have little or no effect on storage life. Volatile compounds may serve as a biochemical marker of seed quality, and the concentration of volatiles may be related to seed aging.
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(pp. 66-71)
Increasing Chilling Tolerance of Seeds During Imbibition and Early Stages of Germination
Paul H. Jennings
Low temperatures during imbibition, germination and/or early stages of seedling development are considered a major contributing factor to poor stand establishment in cold soils, and to reduced plant vigor, particularly in crops such as corn (Zea mays L.), soybean [Glycine max (L.)Merrill], cotton (Gossypium hirsutum L.), and other crops of tropical and subtropical origin (Bennett, et al., 1992). This damage is commonly referred to as chilling injury and may result in significant yield decreases (Lyons, et al., 1979).

Some plant species may be susceptible to chilling injury during imbibition but more tolerant of chilling temperatures at later stages of germination (soybean), while other species are resistant to chilling injury during imbibition but become increasingly susceptible at the time of radicle emergence [cucumber (Cucumis sativus L.)]. These differences suggest that developmental stage influences chilling sensitivity and is under genetic control. For example, what metabolic changes might be taking place during germination which leads to greater chilling sensitivity?
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(pp. 72-76)
Somatic Embryogensis Using Cucumis sativus L. Cotyledons
N.M.P. Guedes and Paul H. Jennings
General problems with in vitro culture of cucumber (Cucumis sativus L.) include abnormal embryo development, poor differentiation of callus into shoots, poor survival of regenerated plants in soil, and undesirable changes in ploidy level of regenerated plants (Punja et al., 1990; Chee, 1990). Cucumber somatic embryos have been derived using different explant sources, cultivars, growth regulator combinations, gelling agents and carbohydrates (Kim et al., 1988; Kim and Janick, 1989; Cade et al., 1990; Chee, 1990; Punja et al., 1990; Ladyman and Girard, 1992; Lou and Kako, 1994), and somatic embryos have been induced from various explants, such as cotyledons, leaves, hypocotyls and stem internodes.

A high frequency of abnormal embryogenesis, such as disordered bipolarity, embryo death, arrested growth, re-callus, and vitrification of embryos has been reported for cucumber (Chee, 1990; Ladyman and Girard, 1992; Lou and Kako, 1994). With these problems, the average frequencies of regeneration of whole cucumber plants with normal morphogenesis have been small. The objective of this studywas to investigate the influence of explant source on embryogenic callus formation, somatic embryogenesis, and plant regeneration.
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(pp. 77-86)
Predicting Changes in Corn Seed Germination During Storage
Dennis M. TeKrony, Dennis B. Egli, and Shande Tang
The survival characteristics of hybrid corn (Zea mays L.) seed during storage are important  since seeds are frequently stored for several years. Predicting corn seed deterioration would be extremely beneficial to corn seed producers to be assured of maximum seed quality at planting. Such prediction is dependent on the quantitative effects of storage temperature, seed moisture, initial quality and the crop species. Attempts to quantify loss of seed germination during storage have given rise to prediction equations for seed viability.
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(pp. 87-97)
Characterization of a Vivipary 1 Homologue in Wheat
M.E. Sorrells*, D. Benscher, W.A.Wilson, J. Zhu, S. Graznak, and D.S. Lupold
The historical association of white kernel color in wheat with susceptibility to preharvest sprouting and the comparative mapping information suggesting the possible involvement of maize (Zea mays L.) vivipary 1 were used as the basis for isolation and characterization of the wheat homologue. Consensus primers were designed based on conserved regions of the gene in rice (Oryza sativa L.), maize, and Arabidopsis.

These primers were used to amplify a portion of the wheat vivipary 1 gene for sequencing and analysis.  A comparison of sequence similarity between maize, rice, wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) revealed that exons 1 and 6 are highly diverged among all the species. Sequence divergence for rice/maize/ barley comparisons are similar across all exons. Comparisons with wheat indicate a trend for exons 2 and 5 to be slightly less conserved leading to lower sequence similarity overall for wheat. Barley sequences were all closely related to wheat, even for exon 6. If additional mapping data support a recent report that Vp1 is not responsible for red kernel color in wheat, this could facilitate enhancement of grain dormancy in white wheat by allowing manipulation of vivipary 1 without affecting kernel color.
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