Crop Science 41:1737-1743 (2001)
© 2001 Crop Science Society of America
CROP BREEDING, GENETICS & CYTOLOGY
Comparisons of Two-Row and Six-Row Barley for Chemical Composition Using Doubled-Haploid Lines
Judith Frégeau-Reida,
Thin-Meiw Choo*,a,
Keh-Ming Hoa,c,
Richard A. Martinb and
Takeo Konishic
a K.M. Ho, Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Ottawa, ON, Canada K1A 0C6
b Crops and Livestock Research Centre, Agriculture and Agri-Food Canada, P.O. Box 1210, Charlottetown, PEI, Canada C1A 7M8
c Kibi-gun, Okayama 710-1311, Japan
* Corresponding author (ChooTM{at}em.agr.ca)
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ABSTRACT
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Comparative studies on chemical composition between two-row and six-row barley (Hordeum vulgare L.) and between purple and yellow barley are very limited. Therefore, a study was conducted to compare two-row and six-row barley and to compare purple and yellow barley for five chemical traits. In addition, the effects of four other marker loci—srh (short rachilla hair), Raw1 (rough awn), Est1 (esterase 1), and Est5 (esterase 5)—on the five traits were also studied. One hundred ninety doubled-haploid (DH) lines were derived from a ‘Leger’/‘CI9831’ cross by the bulbosum method. The DH lines and the two parents were evaluated for protein, starch, ß-glucan, neutral-detergent fiber (NDF), and acid-detergent fiber (ADF) content at two locations in Eastern Canada in 1993. Results showed that two-row (vrs1.t) lines contained 14 to 20% more protein, 4% less starch, and 6 to 7% more ß-glucan than six-row lines; while purple lemma (Pre2) lines contained 2 to 4% less NDF and 0 to 3% less ADF than yellow lemma lines. Differences in grain protein, starch, and ß-glucan content were associated with the Pre2 locus, but they were shown to be caused by linkage between the Pre2 and vrs1 loci. Alleles at the srh, Raw1, Est1, and Est5 loci had very little effect on the five traits. Protein content was not correlated with ß-glucan content for either two-row or six-row lines. Protein and ß-glucan content, however, were correlated with NDF and ADF content for the two-row lines. Additive x additive epistasis was detected for starch and NDF content. The results of this study suggested that selection for high protein or low ß-glucan is possible in two-row/six-row crosses.
Abbreviations: DH, doubled haploid • QTL, quantitative trait loci • NDF, neural-detergent fiber • ADF, acid-detergent fiber
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INTRODUCTION
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BARLEY CAN BE CLASSIFIED as two-row and six-row types on the basis of spike morphology. The difference in spike type is controlled primarily by a single gene vrs1 with the two-row type being dominant. This vrs1 gene has remarkable effects on many other characteristics. Recently, Jui et al. (1997) reported that six-row lines outyielded deficient two-row (vrs1.t) lines by 20 to 27% in Eastern Canada but that two-row lines had higher test and seed weight and better resistance to lodging. Two-row (vrs1.t) lines also produced larger and more circular seeds than did six-row lines (Frégeau-Reid et al., 1996). Since two-row barley produces larger seeds with higher test weight and seed weight than six-row barley, it is very likely that two-row barley produces better quality feed than six-row barley. In fact, Bouard et al. (1980) found that two-row (vrs1.b) barley had 4.6% better feed conversion than six-row barley in a swine feeding trial. Comparative studies on chemical composition between two-row and six-row barley are very limited. Two-row (vrs1.b) genotypes had higher protein content than six-row genotypes (Day and Dickson, 1957; Pomeranz et al., 1973; Hockett and Standridge, 1976; Takahashi et al., 1976; McGuire and Hockett, 1983; Marquez-Cedillo et al., 2000). Comparing 32 two-row (vrs1.b) cultivars with 43 six-row cultivars, Narasimhalu et al. (1995) found that ß-glucan content, on average, was lower for two-row than six-row barleys; and Kong et al. (1995) reported that two-row cultivars on average contained more starch and less fiber than six-row cultivars. The findings of these two studies, however, were confounded by different genetic backgrounds between the two types of barley. To our knowledge, no one has studied the effect of the deficient allele vrs1.t on protein, ß-glucan, starch, and fiber content in barley.
Barley can also be classified as black, purple, and yellow (white) on the basis of lemma and pericarp color. Syrian farmers have firmly believed that a black-seeded landrace "provides better feed for sheep than the white-seeded landrace" (Ceccarelli and Grando, 1999). The two types of landrace, however, showed no difference in protein and lysine content (Ceccarelli and Grando, 1999). On the other hand, black barley was reported to contain more protein, crude fiber, riboflavin, lysine, and calcium than white barley (Li et al. 1999). To our knowledge, no comparative studies on chemical composition between purple and yellow barley have been published in the literature.
Doubled-haploid (DH) lines are ideal for genetic analysis because they represent a random set of completely homozygous lines. Therefore, DH lines derived from a two-row/six-row cross were used in this investigation. Our objectives were to determine the effects of the vrs1.t and Pre2 alleles on five chemical traits (protein, starch, ß-glucan, NDF, and ADF contents), investigate the potential for obtaining transgressive lines for the five chemical traits, and determine if additive x additive epistasis (i.e., homozygote x homozygote interaction) and genetic correlations are present for the five chemical traits in a two-row/six-row barley cross. Data for four other marker loci—srh (short rachilla hair), Raw1 (rough awn), Est1 (esterase 1), and Est5 (esterase 5)—were also available, and thus they were used to study the effects of these four other markers on the five chemical traits.
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MATERIALS AND METHODS
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Plant Materials
One hundred ninety DH lines were derived from the F1 hybrids of a Leger/CI9831 cross of barley by the bulbosum method (Choo et al., 1992). Leger is a six-row cultivar well adapted to Eastern Canada while CI9831 is a two-row introduction resistant to net blotch, caused by Pyrenophora teres (Died.) Dreschsl. (Ho et al., 1996). Leger carries the vrs1.a, pre2, srh, raw1, Est1.Ca, and Est5.Te alleles. In contrast, CI9831 (which was obtained from the Plant Gene Resources of Canada) carries the vrs1.t, Pre2, Srh, Raw1, Est1.Pr, and Est5.Ri alleles. The 190 DH lines can be classified into 12 marker classes according to the six marker loci (Table 1). The Est5 gene segregated distortedly, but all the other genes segregated at random (Choo et al., 1992). The vrs1 and Pre2 loci were linked in this set of DH lines with a recombination value of 0.11, while the Srh and Raw1 loci were linked with a recombination value of 0.30 (Jui et al., 1997). The two parents and the 190 DH lines were seeded at Charlottetown (Prince Edward Island) and Ottawa (Ontario) in 1993, in a randomized complete block design with four replicates at each location (see Jui et al., 1997 for details). The two parents were each represented five times in each replicate. Standard cultural practices were followed at each location.
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Table 1. Classification of the 190 doubled-haploid (DH) lines derived from a Leger/CI9831 cross of barley into 12 marker classes on the basis of six marker loci.
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Chemical Analysis
Seed samples from two replicates were analyzed for protein and NDF and ADF content, while seed samples from one of the two replicates were analyzed for starch and ß-glucan content. Each sample was analyzed in duplicate. Seed samples used for chemical analyses were ground to pass through a 0.5-mm screen on a Udy-mill. Moisture content was measured following the air-oven method, AACC method 44-15A (AACC, 2000). All results were expressed on a dry weight basis. Protein content (N x 6.25) was determined with a Tecator Kjeltec Auto Analyzer 10301 (Tecator AB, Höganäs, Sweden) with the macro-kjeldahl unit attachment. Starch and ß-glucan content were determined enzymatically following the barley grains procedures of the commercial kits from Megazyme (Megazyme International Ireland Ltd., Bray, County Wicklow, Ireland); the starch protocol was AACC method 76-13 (AACC, 2000) and the ß-glucan protocol was AACC method 32-23 (AACC, 2000). NDF and ADF content were measured following slightly modified protocols (incubation time for NDF = 80 min. and for ADF = 70 min.) developed by ANKOM Technology Corp. with the ANKOM 200 Fiber Analyzer (ANKOM Technology Corp., Fairport, NY). Before fiber determinations, starch was removed by overnight incubation at 40°C in a phosphate buffered solution with alpha-amylase at pH = 7.0. All chemicals and the alpha-amylase enzyme were ANKOM brand purchased through Anachemia Canada Inc.
Statistical Analysis
Data from each location were analyzed separately. The average of the duplicate samples was used for each experimental unit. The mean of the 190 DH lines was compared with the mid-parent by an F-test to detect whether or not additive x additive epistasis was present for each trait (Choo et al., 1986). In theory, the two means should be the same in the absence of additive x additive epistasis (Choo et al., 1986). The frequency distribution of the 190 DH lines was tested for normality by the W-test (Shapiro and Wilk, 1965) to determine if additive x additive epistasis was present for the chemical traits. The frequency distribution should be normal in the absence of additive x additive epistasis (Choo and Reinbergs, 1982). DH lines were compared with each parent by the t-test. The pooled mean square among the five entries for each parent was used as error mean square for starch and ß-glucan content.
Phenotypic correlation was used to detect genetic linkage and/or pleiotropy. Assuming Traits X and Y with heritabilities h2X and h2Y, respectively, Falconer (1960) showed that phenotypic correlation (rp) between X and Y is a linear combination of genetic correlation (rA) and environmental correlation (rE). Mathematically, rp = hXhYrA + eXeYrE where e2X = 1 - h2X and e2Y = 1 - h2Y (see Falconer 1960, Eq. [19.1]). When an identical set of DH lines is grown at locations as diverse as Charlottetown (C) and Ottawa (O), then the environmental correlation for X and Y becomes negligible or zero (i.e., rE = 0). Consequently, the resulting phenotypic correlation is due solely to the genetic correlation. By this method, two phenotypic correlation coefficients between X and Y were obtained, one was between X at C and Y at O and the other was between X at O and Y at C. The two correlation coefficients varied somewhat dependent upon the heritability values. Correlation analysis was conducted for the 94 two-row lines and for the 96 six-row lines to detect linkages of loci (except the vrs1 locus) affecting two chemical traits.
The effects of the six marker loci on chemical traits were studied by comparing the two marker classes for each of the six marker loci. The between classes mean square was tested against the within classes mean square by the F-test (Choo, 1983). If means of the two marker classes of DH lines were significantly different, then this would suggest the presence of either linkage between the marker locus and quantitative trait loci (QTL), or a pleiotropic effect of the marker gene. The variance component between classes and variance component within classes were estimated by equating the expected mean squares to their observed mean squares. The effect of the marker genes were further studied by determining the percentage of the variance component between classes over the total variance (i.e., sum of between classes and within classes variance components). The effects of the two chromosome segments, one flanked by the vrs1 and Pre2 loci and the other by the Srh and Raw1 loci, on the five chemical traits were studied by comparing the means and variances of the four marker classes in two by two factorials (Choo, 1983). Bartlett's and the F-tests were used to determine if the four variances were homogeneous (Snedecor and Cochran, 1967).
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RESULTS AND DISCUSSION
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Potential of Lines
At Charlottetown, CI9831 contained 41% higher protein than Leger and it contained a similar amount of starch, ß-glucan, NDF, and ADF as Leger (Table 2). At Ottawa, CI9831 contained 38% higher protein than Leger but Leger contained 7% higher starch, 12% higher ß-glucan, and 11% higher ADF than CI9831. The two parents were not different in NDF content at Ottawa. Four lines contained higher protein than CI9831 at Charlottetown. Two of the four lines were two-row (191 and 198 g protein kg-1) and the other two were six-row (193 and 195 g protein kg-1). Twenty-four lines contained higher protein than CI9831 at Ottawa. Twenty-three of them were two-row (164 to 181 g protein kg-1) and only one was six-row (164 g protein kg-1). One two-row line contained the highest amount of protein at both locations. No lines contained less protein than Leger at either location. None of the 190 lines contained more starch than Leger and less ADF than CI9831. One six-row line contained the lowest ß-glucan at Charlottetown (23 g kg-1) and the second lowest at Ottawa (29 g kg-1). On the other hand, one two-row line contained more ß-glucan than Leger at Charlottetown (65 g kg-1). One two-row line contained less NDF than Leger at either location. Many of these DH lines contained more NDF than CI9831 with the majority of them being six-row lines (36 vs. 31 at Charlottetown and 60 vs. 33 at Ottawa). In this study, CI9831 contained 38 to 41% higher protein than Leger. Still, DH lines with higher protein content than CI9831 were found in this cross, indicating that the low-protein parent Leger also carried high protein genes. Previously, Marquez-Cedillo et al. (2000) reported that the largest QTL for protein content was coincident with the vrs1 locus, but there were also four minor QTL on four different chromosomes (2H, 4H, 5H, and 7H) in the ‘Harrington’ (two-row)/‘Morex’ (six-row) cross. The six-row parent Morex was found to carry minor high-protein alleles on 2H, 5H, and 7H.
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Table 2. Means and tests for normality for 190 doubled-haploid (DH) lines derived from a Leger/CI9831 cross of barley grown at two Eastern Canada locations.
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Detection of Additive x Additive Epistasis
The coefficients of variation were low for protein (4.0–4.1%), NDF (3.4–5.6%), and ADF (7.2–8.7%) content. Significant line x location interactions were detected for protein, NDF, and ADF content (P < 0.01). Variation among DH lines was significant for all five traits at both locations with the exception of starch content at Charlottetown. The mean of the DH lines was lower than the mid-parent for starch content at both locations and for ß-glucan content at Ottawa (Table 2). On the other hand, the mean of the DH lines was higher than the mid-parent for protein content at Ottawa, NDF content at both locations, and ADF content at Charlottetown. The frequency distributions of the 190 DH lines for protein content appeared to be bimodal while those for the other four traits appeared to be unimodal at both locations (data not shown). The frequency distribution was nonnormal for protein and ß-glucan content at Ottawa and for NDF and ADF content at Charlottetown (Table 2). Both the normality method (which was based on the DH lines only) and the mean comparison method (which was based on both DH lines and their parents) detected additive x additive epistasis for NDF and ADF content at Charlottetown and for protein and ß-glucan content at Ottawa. Of the two methods, the mean comparison method should be more accurate because theoretically it has a smaller standard error (Kendall and Stuart, 1967). The results indicated that additive x additive epistasis was present at least for starch and NDF content, and perhaps for protein, ß-glucan, and ADF content also. To our knowledge, additive x additive epistasis has not been reported for these chemical traits previously. If additive x additive epistasis is indeed important for these chemical traits, then selection for these chemical traits should not be too severe in early stages of a breeding program for allowing desirable epistatic combinations to come together.
Correlations between Chemical Traits
Protein content was positively correlated with NDF and ADF content for two-row lines, but not for six-row lines (Table 3). ß-Glucan content was negatively correlated with NDF and ADF content for two-row lines, but the correlation was inconsistent for six-row lines. NDF content was positively correlated with ADF content for both six-row and two-row barley lines. The positive correlation between NDF and ADF was expected because the former estimates the cell wall components cellulose, hemicellulose, lignin, silica, and heat-damaged protein, while the latter estimates lignin and cellulose. Protein content was not correlated with ß-glucan content for either six-row or two-row lines. Therefore, QTL for protein content were not linked with those for ß-glucan content in this cross. This was in contrast with what other workers (Hayes et al. 1993; Han et al. 1995) found in the ‘Steptoe’/‘Morex’ cross. Hayes et al. (1993) identified six QTL for protein content with three on chromosome 2H and one each on chromosome 3H, 4H, and 5H. Han et al. (1995) found three QTL for barley ß-glucan, one on chromosome 1H and two on chromosome 2H. The ABG703-Chs1B interval on chromosome 2H was associated with QTL for both protein and ß-glucan content. High ß-glucan content is undesirable for feed especially for poultry and malt but desirable for human nutrition. Consequently, a lack of correlation between protein content and ß-glucan content would be a positive attribute to barley breeding programs which aim at developing barley cultivars with high protein and low ß-glucan content for livestock feeds.
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Table 3. Correlation coefficients between chemical traits within two-row and six-row doubled-haploid lines derived from a Leger/CI9831 cross of barley grown at two Eastern Canada locations.
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Effects of Marker Genes and Chromosome Segments
Two-row lines contained 14 to 20% higher protein and 6 to 7% higher ß-glucan than six-row lines (Table 4). The difference between two-row (vrs1.t) and six-row (vrs1.a) alleles accounted for 67 to 77% of the total variation for protein content. The results agree with earlier findings that two-row (vrs1.b) genotypes were associated with higher protein content compared with six-row (vrs1.a) genotypes (Day and Dickson, 1957; Pomeranz et al., 1973; Hockett and Standridge, 1976; Takahashi et al., 1976; McGuire and Hockett, 1983; Marquez-Cedillo et al., 2000). Three QTL for protein content and two QTL for ß-glucan content were reported by Hayes et al. (1993) and Han et al. (1995), respectively, on chromosome 2H in the Steptoe/Morex cross. But none of these QTL are located close to the vrs1 locus. Therefore, associations between six-row and low protein and between six-row and low ß-glucan were most likely due to a pleiotropic effect of the vrs1.a allele. In this study, six-row lines contained 4% higher starch and 0 to 4% higher NDF than two-row lines. Six-row lines, however, did not differ from two-row lines in ADF content. Narasimhalu et al. (1995) and Kong et al. (1995) reported that Canadian two-row cultivars on average contained less ß-glucan, more starch, less NDF, and less ADF than Canadian six-row cultivars. But when comparisons were made with the same average genetic background as in this study, two-row lines contained more ß-glucan, less starch, and similar concentrations of NDF and ADF as six-row lines. The results of this study showed that the vrs1.t allele had a significant effect on four of the five chemical traits. Previous studies showed that the vrs1.t allele also had an effect on grain yield, test weight, seed weight, plant height, lodging resistance, seed size, and seed shape (Frégeau-Reid et al., 1996; Jui et al., 1997). Purple lemma lines contained 10 to 16% higher protein and 5% higher ß-glucan than yellow lemma lines. In contrast, yellow lemma lines contained 3% higher starch, 2 to 4% higher NDF, and 0 to 3% higher ADF than purple lemma lines. Both the srh and Est1 loci had no effect on the five chemical traits. The raw1 allele was associated with high protein content at Ottawa, but it was not associated with starch, ß-glucan, NDF, or ADF content at both locations. Alleles at the Est5 locus had a significant effect only on starch content.
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Table 4. Means of 12 classes of the 190 barley doubled-haploid lines grown at Charlottetown (C) and Ottawa (O) in 1993.
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The pairwise analysis showed that the vrs1 locus had a significant effect on protein, starch, and ß-glucan content while the Pre2 locus had a significant effect on NDF and ADF content (Tables 5 and 6). There were no interactions between the vrs1 and Pre2 loci for these chemical traits with the exception of ADF content at Charlottetown. In single-locus analysis, differences in protein, starch, and ß-glucan content were found to be associated with the Pre2 locus (Table 4). These associations must be caused by linkage between the Pre2 and vrs1 loci, because the pairwise analysis showed little effect of the Pre2 locus on these three chemical traits (Table 5). Choo (1983) showed that in theory the variances of the four marker classes are heterogeneous in the presence of interactions between QTL and marker genes, but become homogeneous when both gene interactions and the additive effect of QTL are absent. In this study, the four variances among lines for ß-glucan content were homogeneous at both locations, indicating either the absence of QTL or the presence of the same QTL allele in the vrs1-Pre2 segment (Table 5). The four variances among lines for the four other chemical traits were homogeneous at Ottawa, but not so at Charlottetown (Table 5). These could be due to the presence of line x location interactions. Why purple lemma was associated with low NDF and low ADF is not known. Purple lemma lines contain anthocyanin pigments (Mullick et al., 1958). The biosynthesis of anthocyanin is linked to that of lignin in the shikimic acid pathway by that both require p-coumaric acid (Goodwin and Mercer, 1983). Therefore, competitions for p-coumaric acid for biosynthesis could lead to reduction of lignin production, which, in turn, could lead to low concentrations of NDF and ADF in the purple lemma lines. If so, then purple lemma could be used as a selectable marker for low fiber content in barley. Another pairwise analysis showed that the Srh locus, Raw1 locus, and their interactions had no effect on the five chemical traits (Tables 6 and 7). In most cases, the four variances among lines within the four marker classes were homogeneous for these five chemical traits. Therefore, the results suggested that alleles at both the Srh and Raw1 loci had no effect on these traits, and that either no QTL or the same QTL allele for these chemical traits were located on the chromosome 5H segment flanked by these two marker loci. Hayes et al. (1993) and Han et al. (1995) did not find QTL for protein content and ß-glucan content, respectively, on this chromosome segment in the Steptoe/Morex cross.
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Table 5. Mean squares for chemical traits of two marker loci on chromosome 2H as identified from 190 barley doubled-haploid lines grown at Charlottetown and Ottawa in 1993.
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Table 6. Means of eight genotypes found in the 190 barley doubled-haploid lines grown at Charlottetown (C) and Ottawa (O) in 1993.
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Table 7. Mean squares for chemical traits of two marker loci on chromosome 5H as identified from 190 barley doubled-haploid lines grown at Charlottetown and Ottawa in 1993.**
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This study substantiates that DH lines are very useful for genetic analysis. The effects of four morphological and two isozyme markers on five chemical traits were quantified in this study. Gene interactions and genetic correlations were detected for some of the chemical traits. No QTL affecting the five chemical traits were detected on two chromosome segments.
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CONCLUSIONS
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In conclusion, two-row lines from the Leger/CI9831 cross grown in Eastern Canada contained more protein, less starch, and more ß-glucan than six-row lines; while purple lemma lines contained less NDF and ADF than yellow lemma lines. The srh, Raw1, Est1, and Est5 loci had very little effect on these five chemical traits. Protein content was not correlated with ß-glucan content for either two-row or six-row lines. Protein and ß-glucan content, however, were correlated with NDF and ADF content for the two-row lines. Additive x additive epistasis was detected for starch and NDF content. The results of this study also suggested that selection for high protein or low ß-glucan is possible in two-row/six-row crosses.
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ACKNOWLEDGMENTS
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The authors were grateful to Moe Kuc for producing the DH lines, Sharon ter Beek and Gary Cooper for their technical assistance in conducting the field trials, E. Imbeault for conducting the chemical analyses, and L. Langille for conducting statistical analyses.
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NOTES
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1 Mention of product and equipment names is for identification purposes only and does not imply a warranty or endorsement to the exclusion of other products that may be similar. 
Received for publication October 30, 2000.
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ABSTRACT
INTRODUCTION
