Crop Science 40:470-475 (2000)
© 2000 Crop Science Society of America
SEED PHYSIOLOGY, PRODUCTION & TECHNOLOGY
Relationship between Laboratory Seed Quality Tests and Field Emergence of Common Bean Seed
Krystyna Kolasinskaa,
Jerzy Szyrmera and
Stefania Dula
a Seed Quality Dep., Plant Breeding and Acclimatization Institute, Radzikow, 05-870 Blonie, Poland
k.kolasinska{at}ihar.edu.pl
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ABSTRACT
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In cool climates, early planting of bean (Phaseolis vulgaris L.) is recommended to assure a longer vegetative growth period. Early planting exposes seed to unfavorable conditions and the commonly used standard germination test cannot predict field emergence. The objective of this work was to examine the relationships between various seed quality tests and field emergence of common bean seeds. Thirty-nine strains and cultivars of bean were tested in the field and laboratory over 3 yr. Each year seed samples were tested in the laboratory and then planted in the field at very early, early, and at optimal planting dates. The viability of seeds was test by tetrazolium staining and was generally high; standard germination was above 80%, but germination in the cool test (at 10°C) varied from 0 to 99%. The percentage of seeds with broken coats varied from 0.5 to 50.3 and conductivity ranged from 7 to 45 µS cm-1 g-1. Field emergence varied from 0 to 100%. Soil temperature at sowing appeared to be not only the most important environmental factor influencing field emergence but also a factor able to be used to differentiate the field emergence potential of a seed lot. Only the conductivity test could be used to predict seedling emergence in the field irrespective of soil temperature at sowing. At temperatures ranging from 9 to 15°C, the first and the last count of the standard germination test and the broken seed coat test should be used in conjunction with the conductivity test to estimate field emergence potential.
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INTRODUCTION
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SEED QUALITY TESTS should relate to field emergence. Many researchers have reported significant correlation coefficients between field emergence and standard laboratory germination tests, but they have also reported inconsistencies and difficulties with the prediction of field emergence. Standard laboratory germination tests describe the percentage of normal seedlings under optimal conditions specified by the International Seed Testing Association (ISTA, 1993). This test, commonly used to evaluate seed quality, is able to predict field emergence provided the conditions for emergence are favorable. Many authors found laboratory germination tests to correlate well with field emergence of soybean [Glycine max (L.) Merr.] (Edje and Burris, 1971; TeKrony and Egli, 1977; Johnson and Wax, 1978; Yaklich and Kulik, 1979, Szczepanska-Kolasinska, 1982) and field bean (Vicia faba L.) (Hegarty, 1977).
The first count of the standard germination test is considered to be a measure of seed vigor. Its suitability for predicting field emergence of soybean was discussed by TeKrony and Egli (1977). Generally, vigor tests have proven to be more useful as predictors of field emergence than the standard germination test.
The cold test and the accelerated aging tests have been recommended by ISTA (1987, 1995 a,b), Edje and Burris (1971), TeKrony and Egli (1977), Johnson and Wax (1978), and Kulik and Yaklich (1982). The cool germination test was developed to provide less demanding, yet sufficiently severe test conditions to separate seeds on the basis of vigor (ISTA, 1995 b).
Some physical and biochemical tests such as counting the number of seed with broken coats, electrical conductivity of seed leakage, and tetrazolium viability tests, are also considered rapid and good measures of seed quality. Tetrazolium viability staining of seeds (Kulik and Yaklich, 1982) gave reliable estimates of potential field emergence for soybean. Also, Johnson and Wax (1978) found that the results of this test correlated with field emergence but the correlations were not as high as those with the cold test. Many authors believe imbibition damage at cool temperature is responsible for low field emergence (Powell et al., 1986 a; Bay et al., 1995). According to Luedders and Burris (1979), the number of broken seed coats correlates with field emergence but not as well as the standard germination test does. The conductivity test has been developed into a routine vigor test to predict field emergence of garden pea (Pisum sativum L.), and is also used for soybean, French bean (Phaseolis vulgaris L.), mung bean (Phaseolus aureus Roxb), and field bean (ISTA, 1995 b).
Results reported by Edje and Burris (1971), Johnson and Wax (1978), Luedders and Burris (1979), Kulik and Yaklich (1982), Duczmal and Minicka (1989), and Egli and TeKrony (1995) showed that the relationship between laboratory tests and field emergence is complex, and the ability of laboratory tests to predict field emergence is variable and strongly dependent on the field environment. The objective of this work was to examine the relationships between various seed quality tests and field emergence of common bean seeds with special consideration of soil temperature at the time of sowing.
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Materials and methods
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Seeds of the 39 strains and cultivars of bean, produced at the same location each year, were tested in a laboratory and in the field for three consecutive years (1994, 1995, 1996). The laboratory tests included standard germination, cool germination, tetrazolium, and conductivity tests, and number of seeds with broken coats.
Standard Germination Test
Seed germination was measured by placing four replicates of 50 seeds each in sand at 25°C for 5 (first count) and 9 d (final count). Germination was assessed as the percentage of seeds producing normal seedlings as defined by ISTA Rules (ISTA, 1993).
Tetrazolium Test
Two replicates of 50 seeds each were stained with a 10 g kg-1 solution of tetrazolium chloride according to ISTA method (ISTA, 1993). Seeds were evaluated and classified as viable or nonviable.
Cool Germination Test and Germination Speed Coefficient
The percentage of normal seedlings was determined by placing four replicates of 50 seeds in sand at 10°C in darkness. The speed germination coefficient as defined by Kotowski (1926) was also calculated. It is a measure of the number of seeds germinating daily, over the period that it takes the seed in a seed lot to germinate. Cool test and speed of germination were expected to describe the seed response to low temperature in two ways: as a percentage of total germinated seeds and as the speed of germination of successfully germinating seed.
Conductivity Test
The electrolyte leakage from seeds was measured with two replicates of 50 weighed seeds incubated for 24 h in 250 mL flasks containing 200 mL of deionized water at 20 ± 2°C. The electrical conductivity was measured with conductivity meter and expressed as ìS cm-1 g-1 (ISTA, 1995 a).
Broken Seed Coats
Four replicates of 50 seeds were visually scored for the presence or absence of cracks in the testa prior to germination testing.
Environmental Conditions of Field Experiment
Seeds from each sample were sown 5 cm deep by hand in three replicated plots. All samples were sown at three planting dates (very early: 11–19 April, early: 26–30 April and optimal: 11–14 May) annually in Typic Hapludolls soil at Sandomierz in southeastern Poland. Soil temperatures 5 cm beneath the surface, and rainfall were recorded daily.
Field Emergence
The number of emerged seedlings at the first leaves stage was counted daily until no further seedlings appeared. The average emergence of three replicates of 50 seeds for each sample was used for further analysis.
Statistical Analysis
Systat Ver. 5.03 (SYSTAT, Inc. Evanston, IL) was used to calculate regression and correlation coefficients to determine the relationship between field emergence and laboratory test results.
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Results and discussion
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Most of the 39 seed samples had standard germination percentages above 80%, but some samples had lower germination and a high percentage of abnormal seedlings (Table 1)
. The tetrazolium viability of seeds was above 90%, although there were a few samples with a high percentage of nonviable seeds. Germination at 10°C was below 60% and variable and the speed coefficient ranged from 0 to 19 (Table 1). In 1995, the seed in the cool test germinated well (59%) better than in 1994 (27%) and 1996 (45%). Standard germination and the first count were the lowest in 1995 and mean conductivity (26 µS cm-1g-1) and percentage of seeds with broken coats (13%) were the highest (Table 1).
Soil temperature on the day of sowing was very low for the very early sowing date, especially in 1995 (2.3°C) (Table 2)
. Average temperature after sowing, expressed as a mean for the 2-wk period after sowing, ranged from 10.0 to 16.5°C. Average rainfall per day during the period before and after sowing was between 0.2 and 5.8 mm.
Average field emergence varied from 17% for the very early planting date in 1995 to 91% under better conditions during the very early planting date in 1996. All measured environmental factors influenced significantly field emergence (Table 2), with soil temperature on the day of sowing most evident. This last relationship is illustrated as a logarithmic function in Fig. 1
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Fig. 1 Field emergence in relation to soil temperature on the day of sowing. Each point is the mean of 39 seed samples. ** Significant at P = 0.01
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The most consistent correlations (Table 3)
between field emergence and individual laboratory tests was with the conductivity test. The conductivity test correlated well with field emergence of dwarf French bean (Powell et al., 1986 a,b), and pea (Duczmal and Minicka, 1989). Correlations between conductivity and field emergence of soybean seeds were observed by Yaklich et al. (1979) at some but not all locations. Also, conductivity test results correlated with field emergence of lupine (Lupinus luteus L.) and maple pea (Pisum sativum L.); however, the author (Tulo, 1987) concluded that the loss of germination ability may not always be detected by this test. Also, Kulik and Yaklich (1982) reported that field emergence and conductivity test results were not consistently correlated, the calculated linear regression coefficients (slopes) were variable.
To analyze further the relationship between field emergence and the conductivity test, linear regression parameters (slope and intercept) were calculated for year and planting date (Table 4) . Coefficients of detemination calculated to compare with other authors results varied from 0.116 to 0.483, and the regression slope ranged from -0.27 to -1.69. A similar large range of differences in correlation coefficients and slopes for two different environments were obtained by Hegarty (1977) for field beans. These results suggested that environmental factors may affect the field emergence-conductivity relationship. To check this hypothesis, the calculated coefficients of determination and slopes were compared with soil temperature at sowing (Fig. 2)
, and also with average field emergence (Fig. 3) , which may be considered to represent total environmental impact on emerging seeds (Egli and TeKrony, 1995).
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Fig. 2 Relationship between soil temperature at sowing and coefficient of determination, slope. Each point represents coefficient of determination or slope of the conductivity test versus field emergence relationship calculated for one planting date. * Significant at P = 0.05
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Fig. 3 Relationship between average field emergence and coefficient of determination, slope. Each point represents coefficient of determination or slope of the conductivity test versus field emergence relationship calculated for one planting date. ** Significant at P = 0.01
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The significant relationships shown in Fig. 2 indicate that at lower temperature compared with a higher temperature of soil at sowing (i) the conductivity test is a more reliable predictor of field emergence because values of the coefficient of determination of field emergence versus conductivity are higher, and (ii) differences in seed quality determined by the conductivity test cause greater differences in field emergence since absolute values of slope are higher. These results (Fig. 2 and 3) suggested that (i) in different environmental conditions other laboratory tests can be differently related to field emergence, and (ii) the data from planting dates of similar soil temperature during sowing should be grouped. In establishing the temperature groupings, the results of other authors were considered. Kooistra (1971) found differences in bean varieties by germinating them at 10°C; these differences disappeared at temperatures above 15°C. Temperatures of 8 to10°C are considered to be a lower limit of seedling development of bean (Holubowicz and Duczmal, 1987). In our experiment, the average field emergence (Fig. 1) ceased to be dependent on soil temperature at temperatures exceeding 15°C, whereas the average field emergence rapidly dropped at temperatures below 9°C. For further analysis, the planting dates were divided into three groups according to soil temperature: low (below 9°C), intermediate (between 9°C and 15°C), and favorable (above 15°C). Data for each group were pooled and the correlation coefficients between field emergence and laboratory tests were recalculated (Table 5)
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Only temperatures below 9°C followed the very early planting in 1995. Apparently, under such low temperatures, seed survival depends mainly on seed coat permeability, which is related to conductivity test results.
At temperatures above 15°C, the conductivity test was also the only reliable indicator of seedling emergence; but, it was less indicative than at low temperature conditions. Under these favorable emergence conditions, the relationship between other laboratory tests and field emergence was not evidenced either because of a low dependence of field emergence on seed quality at these temperatures or other unidentified factors.
The range of soil temperatures with the best relationship with for laboratory tests evaluation seems to be between 9 and 15°C where field emergence correlated with all laboratory tests except tetrazolium viability (Table 5). At this intermediate temperature, the correlation between field emergence and standard germination was low (r = 0.35**) but significant. The corresponding relationship for dwarf French bean, reported by Powell et al., (1986 a, b), was r = 0.80 and 0.56 for the first and second dates of planting, respectively. For field bean, Hegarty (1977) obtained correlations of 0.42 and 0.63 in 1975 and 1976, respectively. For soybean, Kulik and Yaklich (1982) reported correlations of 0.81 and 0.65 in 1975 and 1976 respectively, while Johnson and Wax (1978) observed smaller differences (r = 0.66 and 0.69) between years. The predicted accuracy of this test calculated by TeKrony and Egli (1977) ranged from 0 to 42% depending on environmental conditions. Therefore, our results generally support the opinion that standard germination is a rather poor predictor of field emergence, but it still may be important at a defined range of temperatures.
At the intermediate temperatures, the relationship between field emergence and the first count shows that for the samples with a first count below 25%, field emergence generally is low and unpredictable, while when the first count is above 25%, field emergence is higher and more consistent (Fig. 4)
. The first count is better correlated with field emergence than the final count (standard germination). TeKrony and Egli (1977) found that the prediction accuracy of the first count test changed with environments, and that the first count was a better predictor of field emergence than the standard germination test.
In the intermediate temperature range, the population of the seeds with broken seed coat test was significantly correlated with field emergence (Table 5). The ease of conducting the seed coat test is attractive and this simple test provides an additional tool to determine seed field emergence. Also, the speed coefficient and the results of the cool test were significantly correlated with field emergence over this temperature range.
In summary, (i) soil temperature at sowing appeared to be not only the most important environmental factor influencing field emergence but also a factor able to differentiate the field emergence potential of a seed lot; and (ii) the conductivity test could predict seed emergence in the field irrespective of soil temperature at sowing while at the intermediate temperatures range of 9 to 15°C, the first and the last count of standard germination test as well as the broken seed coat test can be useful for predicting field emergence.International Seed Testing Association 1987
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ACKNOWLEDGMENTS
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The authors express their thankfulness to Pawel Kolasinski for mathematical elaboration of the results.
Received for publication November 17, 1998.
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ABSTRACT
INTRODUCTION
