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Crop Science 40:352-358 (2000)
© 2000 Crop Science Society of America

CROP BREEDING, GENETICS & CYTOLOGY

Enhancing Yield of Semidwarf Barley

Kendell B. Hellewella, Donald C. Rasmussonb and Maria Gallo-Meagherc

a Hybritech, 6025 West 300 South, Lafayette, IN 47905 USA
b Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108 USA
c Agronomy Department, University of Florida, Gainesville, FL 32611-0300 USA

rasmu002{at}maroon.tc.um.edu


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
Semidwarf barley (Hordeum vulgare L.) lines and cultivars with the sdw gene have not fulfilled early expectations of increased grain yield. Accordingly, both breeding and molecular mapping experiments were undertaken to enhance and evaluate performance of lines with sdw. The objectives were to examine, in sdw semidwarf barley, the effect on grain yield of enhancing yield component traits—spike number, kernel number, and kernel weight—to confirm the reported allelic relationship between sdw and denso, to identify the chromosome location of sdw, and to determine the genetic relationship between sdw, height, and heading date. Eight tall barley lines having high yield-component phenotypes or high grain yield were crossed to `Royal', an sdw semidwarf, to obtain semidwarf populations for study. Grain yield of semidwarf lines was not significantly increased by enhancing yield-component traits or by the use of high-yield parents. Allelism tests and gene mapping procedures were used to determine the relationship between sdw and denso and to map the sdw allele location. The sdw gene was allelic to denso and mapped to barley chromosome 3H in the same region as denso. The sdw allele reduced height by 10 to 20 cm and delayed maturity by {approx}3 d. We hypothesize that the sdw allele itself, not linkage drag, is the basis for mediocre yield and late maturity of this short-stature germplasm. The information obtained encourages use of alternative short-stature sources.

Abbreviations: cM, centimorgan • RFLP, restriction fragment length polymorphism


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
SHORT-STATURE CULTIVARS have been developed by cereal breeders worldwide to reduce lodging and increase grain yield. In barley, the effort to achieve short-stature genotypes has relied in part on the sdw gene in North America and the denso gene in Europe. The sdw and denso genes arose from separate mutation events, but have been reported to be allelic (Haahr and von Wettstein, 1976; Mickelson and Rasmusson, 1994). The cultivars with sdw have not gained wide acceptance in the USA and none have been used as a malting barley. This contrasts with Europe, where many currently grown malting barley cultivars are short-stature and possess denso.

Although the sdw and denso mutants arose from separate mutation events, they have similar effects on agronomic traits. The denso gene has been associated with late heading, low seed weight, high screenings, and high ß-glucan content (Powell et al., 1985; Thomas et al., 1991). Barua et al. (1993) reported that a quantitative trait locus for heading date could not be genetically separated from the denso locus. Similar effects associated with sdw were found by Foster and Thompson (1987) using paired isogenic F7 lines from two crosses. The sdw lines were 2 to 3 d later than tall isolines and had lower yield, test weight, and percentage of plump kernels than the tall isolines.

The sdw semidwarfs were inferior to their tall counterparts in grain yield in early cycles of breeding in Minnesota. However, in later cycles, grain yield of semidwarf and tall progenies were similar (Ali et al., 1978; Zahour et al., 1987). More recently, yield improvements in tall cultivars have again widened the gap between tall cultivars and sdw semidwarfs (Rasmusson and Phillips, 1997).

There is general agreement that high-yielding progeny tend to occur in crosses between high-yielding parents (Busch et al., 1974; Rasmusson, 1987). Alternatively, Woodworth (1931) advocated selecting parents on the basis of their grain yield-component phenotype (spike number per unit area, kernels per spike, and kernel weight) instead of their yield per se. This procedure is appropriate since gains in grain yield are achieved by increases in one or more of the grain yield components and heritability of these components is often higher than for grain yield (Grafius, 1964). All three yield components are associated with grain yield in barley and wheat (Triticum aestivum L.) (Rasmusson and Cannel, 1970; Puri et al., 1982; Jedel and Helm, 1994). In spite of all the research, consensus is lacking on the desired relationship among the components to maximize grain yield and on the value of component breeding.

Obtaining additional genetic information about sdw in relation to the successful denso gene appears to be worthwhile. The denso gene was recently mapped to the long arm of chromosome 3H (Barua et al., 1993; Laurie et al., 1993). Mapping sdw could confirm the genetic relationship between sdw and denso and would allow further analysis of the relationship between the sdw locus and quantitative traits with which it has been associated.

In this study, both breeding and molecular mapping experiments were undertaken with the goal of evaluating and enhancing the use of sdw in North American six-row barley germplasm. The first objective was to evaluate, in sdw semidwarf barley, the effect on grain yield of using parents high in one of the yield-component traits: spike number, kernel number, or kernel weight. A second set of objectives was to confirm the reported allelic relationship between sdw and denso, to identify the chromosome location of the sdw locus, and to determine the genetic relationship of sdw with height and heading date.


   Materials and methods
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
Results and discussion
 Conclusions
 REFERENCES
 
Yield Component Selection
Eight tall barley lines having high yield-component phenotypes or high grain yield were crossed to Royal, a sdw semidwarf recently released by the University of Minnesota barley breeding program (Rasmusson et al., 1994). The eight parents were `149-23' and `149-31' with high spike number, `Manker' and `M88-598' with high kernel number, `M86-117' and `M57' with high kernel weight, and high-yielding lines `Excel' and `M66'. The six yield-component parents were developed in breeding programs in Minnesota to obtain high levels of the respective components and were selected for this study on the basis of their component level and acceptable grain yield performance. Excel and M66 were chosen based on their high grain yield.

Approximately 130 F3.4 progeny lines from each of the eight populations were grown at St. Paul in 1993, and sixteen semidwarf lines were randomly chosen from each population for yield evaluation after eliminating lines with poor emergence of the spike from the boot and lines that headed three or more days later than Royal. The 16 semidwarf lines representing each of the eight populations were grown in a sets-in-replication design (Schutz and Cockerham, 1966) with four sets per replication and three replications at St. Paul and Crookston, MN in 1994 and 1995. Each set consisted of four lines from each population and Royal or `Robust' as a check. In 1995 two of the eight tall parents were included in each set. Plots consisted of two rows 3 m long with rows spaced 30 cm apart. Seeding rate was 108 kg ha-1. In the analysis of variance, all sources of variation were considered random except type of cross and populations within type of cross.

In each plot, spike number was counted in 1 m of row at maturity, kernel number was counted on six spikes, kernel weight was determined on a 200-kernel sample, and two 2.44-m rows were harvested to measure grain yield. Growing conditions were favorable at St. Paul in 1993, 1994, and 1995 and in Crookston in 1994. At Crookston in 1995, heavy rains and crusting caused poor stands; hence, the nursery was abandoned. The eight tall parents and Royal were grown in a separate yield trial at St. Paul and Crookston, MN in 1994; in 1995, they were included in the semidwarf trial.

Mapping the sdw Gene
Allelism Test
The allelic relationship between sdw and denso was investigated in a Royal (sdw) x `Triumph' (denso) cross. Three Royal x Triumph populations were evaluated at St. Paul, MN. The first population consisting of 200 F2.3 lines was grown in 1995; the second population consisting of 225 F4.5 lines was grown in 1996. The third population consisting of 100 F1 plants was space-planted in 1996. Height and heading date were measured in all populations. `Morex' was grown as a tall check.

Mapping Populations
Royal was crossed to Morex, and the resulting population was advanced by single seed descent through the F4 generation. In summer 1995, 286 F4.5 lines were grown at St. Paul in single 2.1-m rows. Seedling leaf tissue was sampled from several plants in the row. Heading date was recorded when 50% of the spikes emerged from the sheath. Plant height was measured on typical plants in the row; lines that were 80 cm or shorter were classified as semidwarf and were presumed to possess the sdw allele. The remaining lines exceeded 85 cm and were classified as tall and were presumed to have the Morex allele or to be segregating for it (Fig. 1) .



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  		Fig. 1 Distribution of plant height in the Royal x Morex F4.5 population, St. Paul, MN in 1995. Lines 80 cm or shorter were classified as semidwarf and are presumed to carry the sdw allele and those 86 cm or taller were classified as tall and are presumed to carry the Morex allele or to be segregating for it

 
Because of limited marker polymorphism in the Royal x Morex population, a second population, Royal x `Steptoe', was included in the study. In 1996, 194 F3.4 lines were grown in two separate trials at St. Paul. In the first trial the lines were space-planted in single 3.0-m rows to permit detection of segregation for height. In the second trial, which was densely seeded, the same F3.4 lines were grown. Seedling leaf tissue was sampled from several plants in the dense-seeded trial to obtain DNA and height and heading data. Lines 85 cm or shorter were classified as semidwarf and were assumed to be homozygous for the sdw gene (Fig. 2) .



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  		Fig. 2 Distribution of plant height in the Royal x Steptoe F3.4 population, St. Paul, MN in 1996. Lines 85 cm or shorter were classified as semidwarf and are presumed to carry the sdw allele and those 86 cm or taller were classified as tall and are presumed to carry the Steptoe allele or be segregating for it

 
Restriction Fragment Length Polymorphism (RFLP) Analysis
Plant DNA was extracted from the two mapping populations by a modified method of Tai and Tanksley (1990). Parental DNA was individually digested with 16 restriction enzymes: BamHI, BglII, DraI, EcoRI, EcoRV, KpnI, HinfI, HindIII, PsaI, RsaI, SalI, ScaI, SstI, SstII, XbaI, and XhoI (Gibco/BRL, Gaithersburg, MD) and electrophoresed in a 0.8% (w/v) agarose gel. DNA was transferred to a nylon membrane (Immobilon-N; Millipore, Marlborough, MA) by pressure blotting according to manufacturer's instructions (Posiblotter 30-30; Stratagene, La Jolla, CA).

Parental DNA was screened for polymorphism using clone sequences identifying markers previously associated with the denso gene (Laurie et al., 1993) and clone sequences for markers previously located on the long arm of chromosome 3H in the Steptoe x Morex linkage map (Kleinhofs et al., 1993) and in a consensus linkage map of barley (Langridge et al., 1995). Clone sequence–enzyme combinations that produced polymorphic patterns between the parents were used to screen the two mapping populations. Ninety-six lines were randomly selected from each population and were screened with the polymorphic markers by the same procedures used to screen the parents. The linkage relationships between sdw and polymorphic markers in the Royal x Morex population were analyzed using Map Manager Classic version 2.6.5 (Manly, 1993) and in the Royal x Steptoe population using MapMaker version 3.0 (Whitehead Institute for Biomedical Research, Cambridge, MA). The Royal x Morex population was analyzed as recombinant inbred F4.5 lines, and the Royal x Steptoe population as an F3 intercross (by self mating). The amount of variation in height and heading date explained by the sdw gene and linked markers was estimated by regression analysis (Statistix 4.1, Tallahassee, FL).


   Results and discussion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
Conclusions
 REFERENCES
 
Yield Component Breeding
Parent Performance
The six component parents performed as expected, and in each case they ranked highest for their respective yield component with only one exception (Table 1) . The high-yield parents, Excel and M66, ranked first and third for yield and were intermediate for the three yield components.


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  		Table 1 Mean performance of eight tall barley parents and Royal, the semidwarf parent, for specific grain yield components and grain yield evaluated in three Minnesota environments

 
Royal, the sdw semidwarf, ranged from 13 to 22 cm shorter than the eight tall parents. Similarly, the eight tall parents differed from Royal for the three yield components. The mean of the high spike-number parents (149-23 and 149-31), high kernel-number parents (Manker and M88-598) and high kernel-weight parents (M86-117 and M57) exceeded Royal by 27, 10, and 13%, respectively. Grain yield of Royal was higher than expected and only 3% below the average of the high-yield parents (Excel and M66). This result contrasts with local and regional yield data where Royal has routinely yielded lower than tall cultivars including Excel and M66.

Well-known component compensation relationships were observed among the parents. This was most striking for the high spike-number parents (149-23, 149-31), which were low in both kernel number and kernel weight (Table 1). The high kernel-number and high kernel-weight parents were especially low in spike number.

Progeny Performance
The objective of obtaining sets of semidwarf lines with relatively high levels of each yield-component trait was achieved in part (Table 2) . Each pair of populations was high for their respective yield component selected. The spike-number type was the most distinctive among the four cross types, averaging 472 spikes m-2 compared with the second-ranking type, high yield, with 430 spikes m-2. The spike-number cross-type progeny had the fewest kernels per spike and the lowest kernel weight. The two kernel-number populations averaged three more kernels per spike than the next highest ranking population. The Manker x Royal population was particularly low in spike number, averaging 105 fewer spikes m-2 than the spike-number population, 149-31 x Royal. The two kernel-weight populations averaged only 1% higher in kernel weight than the kernel-number populations but were 7% higher than the spike-number populations. In relation to the amount of diversity for the yield components, recall that there was no selection for the component traits in identifying the semidwarf lines for testing.


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  		Table 2 Mean performance of pairs of barley populations in which tall parents high in yield or a yield component were crossed with the semidwarf Royal and evaluated in three Minnesota environments{ddagger}

 
Grain yield means of the six yield-component populations and the two high-yield populations were disappointing, with population mean yield below the midparent value and the semidwarf parent Royal value in most cases (Tables 1 and 2). Of the 128 semidwarf lines tested, only 16 had mean grain yield higher than that of the semidwarf parent, Royal, and the tall check, Robust. The two highest-yielding lines in each cross type exceeded Royal and Robust by 5 to 10% (Table 3) , a relatively small amount considering the effect of random variation for yield in a population of 128 semidwarf lines. In each cross type, the two highest-yielding lines tended to be high for the yield component that characterized the tall parent. This was most pronounced for the high spike-number and high kernel-weight populations. Unlike the situation for the yield-component traits, the two highest-yielding lines from the high-yield cross type were not particularly high yielding.


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  		Table 3 Mean performance of the two highest yielding barley lines from four cross types in three Minnesota environments

 
The poor yield performance of the high-yield cross type population was unexpected since the two parents Excel and M66 are known to yield well and M66 ranked first and Excel ranked third among the eight tall parents (Table 1). We have no explanation for the very low yield of the Excel x Royal population. In this population, only three lines were in the top 50% of all lines tested. Excel is a high-yielding cultivar and has been used successfully in many crosses. All populations were treated the same, with selection only for inadequate emergence of the spike from the boot and late maturity. The Excel population was similar in heading date to the other populations.

The yield obtained for the semidwarf lines in this study is disappointing. After more than 30 yr of breeding to develop an sdw semidwarf malting barley for the upper Midwest, the best semidwarf lines are still inferior in grain yield and malting quality to their tall counterparts. Royal, the semidwarf parent in this study, is the only cultivar to come from this long-term breeding effort and it is not competitive for grain yield with contemporary tall cultivars. The failure to obtain high-yielding semidwarf lines in this study is consistent with our experience, that is, the semidwarf progeny are generally later maturing and lower yielding than their tall counterparts.

The sdw semidwarf gene has been used to develop feed barley cultivars for the western USA, western Canada, and Australia, but to our knowledge no successful malting cultivars possess the sdw gene. This contrasts sharply with the success of the denso gene. Most malting barley cultivars in Europe are semidwarf and trace to Triumph, which carries denso (Fischbeck, 1991). Semidwarf germplasm tracing to Triumph is also a major component of the Coors (Denver, CO) malting barley breeding program in the western USA (Treat, 1998).

Allelism Testing and Mapping the sdw Gene
Allelic Relationship between sdw and denso
Height of the F1 progeny of Royal x Triumph indicated sdw and denso are allelic. The F1 plants were semidwarf with a mean height of 70 cm, slightly taller than Royal (63 cm) and Triumph (68 cm). Morex, the tall check, had a mean height of 80 cm. Furthermore, in the Royal x Triumph F2.3 (n = 200) and F4.5 (n = 225) populations, all the progeny were semidwarf.

Mapping sdw
The frequency distribution for height in the Royal x Morex and Royal x Steptoe populations was bimodal, corresponding with the presence or absence of the sdw allele (Fig. 1 and 2). In these populations, height differences were sufficient to score the presence or absence of sdw. As shown in the distributions, there was considerable variation for height within each allelic class (the short and tall classes).

Royal and Morex were initially screened for polymorphism with 21 markers that had been previously mapped in other populations to the 54-centimorgan (cM) interval between markers ABG 315 and ABC 174 on chromosome 3H (Fig. 3A) . Of these 21 markers, only MWG 847 was polymorphic. The low level of polymorphism observed within the Minnesota germplasm is consistent with other reports (Dahleen, 1997; McElroy et al., 1996). In the Royal x Morex population of 96 F4.5 lines, sdw cosegregated with MWG 847 (Fig. 3A). Two other markers, ABG 315 and ABC 174, were linked to sdw, which mapped 21.7 cM proximal to ABG 315 and 32.7 cM distal to ABC 174 in this population (Fig. 3A).



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  		Fig. 3 Restriction fragment length polymorphism map of chromosome 3H obtained with (A) a Royal x Morex population and (B) a Royal x Steptoe population. The distance in centimorgans between each interval is shown together with the recombination fraction for each interval in brackets

 
Three markers were identified as being closely linked to the sdw gene in the Royal x Steptoe population of 96 F3.4 lines (Fig. 3B). ABG 004 was 8.8 cM distal to sdw, whereas sdw was 7.9 and 0.6 cM distal to PSR 170 and MWG 847, respectively. This places sdw at or near the site of denso, which was mapped 7.8 cM distal to PSR 170 in a Magnum x Goldmarker cross (Laurie et al., 1993). Thus, the mapping data from both populations support previous reports that suggested that sdw and denso are allelic (Haahr and von Wettstein, 1976; Mickelson and Rasmusson, 1994).

Most of the variation in plant height in the two populations was accounted for by allelic variation at the sdw locus, with r2 = 0.90 and 0.80 in the Royal x Morex and Royal x Steptoe populations, respectively. Individual regressions of height with markers linked to sdw were also significant; however, multiple regression indicated that the linked markers were associated with height only because of their linkage to sdw.

There was a strong relationship between sdw and heading date. In the Royal x Morex population, all but three of the semidwarf lines were later heading than tall lines, and in the Royal x Steptoe population the earliest semidwarf lines were similar in heading date to the latest tall lines. The allelic variation at the sdw locus explained 82 and 47% of the variation in heading date in the Royal x Morex and Royal x Steptoe populations, respectively. In both populations, RFLP markers linked to sdw were also associated with heading date; however, multiple regression indicated that the linked markers were associated with heading date only because of their linkage to sdw. The difference between the two populations in the amount of variation in height and heading date explained by sdw is probably due to the relative genetic relatedness of the parents. Royal and Steptoe are not related and hence are more likely than the related lines Morex and Royal to have genes with different alleles in addition to sdw that affect height and heading date.

Results of this study and the failure to break the association between the sdw locus and heading date with more than three decades of breeding effort suggest that the association is due to pleiotropy rather than linkage. Therefore, we propose that efforts to modify maturity of sdw semidwarfs concentrate on accumulation of modifying genes.

Future Use of sdw
Other researchers have reported low yield for sdw semidwarf barley (Foster and Thompson, 1987) so the results obtained were not unexpected. It was disappointing that none of the yield-component traits, with the possible exception of spike number, showed promise for increasing yield. Progeny selected for spike number had the highest mean grain yield, and this cross type had the largest number of individual lines exceeding Royal in yield. Increasing spike number to improve grain yield in barley is supported by the observation that modern cultivars have a relatively high spike number (Ekman, 1981; Gymer, 1981). However, this component has limitations in malting barley breeding since high spike number is often associated with low kernel weight (Benbelkacem et al., 1984). In this study, the lines highest in spike number were consistently too low in kernel weight to be acceptable as a malting barley.

A major obstacle in using sdw is its association with late maturity. In this investigation, heading notes were taken in the eight segregating populations. In these populations, the semidwarf lines averaged 3 d later heading than their tall counterparts and 2 d later than Royal, the semidwarf parent. In each population {approx}10% of the latest-maturing semidwarf lines were omitted from the follow-up investigation because of late maturity. Lines greater than 3 d later maturing than Royal are too late to be agronomically acceptable in the upper Midwest. We hypothesize that the relative earliness of Royal, the semidwarf parent, is due to minor genes favoring early maturity that have been accumulated in the course of breeding for earlier-maturing sdw semidwarfs for more than 30 yr (Mickelson and Rasmusson, 1994).


   Conclusions
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
REFERENCES
 
Grain yield of semidwarf lines was not significantly increased by use of parents high in the yield-component traits: spike number, kernel number, and kernel weight. Use of high-yield parents also was unrewarding. This result is consistent with other published research (Foster and Thompson, 1987; Mickelson and Rasmusson, 1994). We hypothesize that the sdw gene itself, not linkage drag, is the basis for the disappointing performance of this short-stature phenotype. It might be added that several years of evaluation of semidwarf lines for malting quality have revealed less-favorable malting quality in sdw semidwarfs compared with taller counterparts. The sdw gene reduced height by 10 to 20 cm, depending on the tall parent, but also delayed maturity by an average of {approx}3 d. The information obtained here encourages use of alternate short-stature sources. Why the denso gene in Europe is successfully used in breeding, while sdw has limitations in the U.S. Midwest, remains unknown.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
Paper no. 99-1-13-0110, Scientific Journal Series, Minnesota Agric. Exp. Stn.

Received for publication March 22, 1999.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 




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