Euphytica 126: 283–289, 2002.© 2002 Kluwer Academic Publishers. Printed in the Netherlands.

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Genetic gains in Nordic spring barley breeding over sixty years

Rodomiro Ortiz1,∗, Minna Nurminiemi2, Sten Madsen1, Odd Arne Rognli2 & ÅsmundBjørnstad3

1Department of Agricultural Sciences, The Royal Veterinary and Agricultural University, 40 Thorvaldsensvej, DK-1871 Frederiksberg C, Copenhagen, Denmark; 2Dept. of Chemistry and Biotechnology, Agricultural Universityof Norway, P.O.B. 5040, N-1432, Ås, Norway; 3Department of Horticulture and Crop Sciences, AgriculturalUniversity of Norway, N-1432, Ås, Norway; 4author for correspondence; New address: IITA, c/o Lambourn & Co,Carolyn House, 26 Dingwall Road, Croydon, CR9 3EE, U.K., E-mail: r.ortiz@cgiar.org

Received 19 February 2001; accepted 30 October 2001

Key words: adaptation, evolution, grain yield, Hordeum vulgare, Nordic Region, Scandinavia

Summary

Accurate assessments of genetic gains ensuing from plant breeding for the most important agronomic character-istics in Nordic spring barley (Hordeum vulgare L.) are not available. Hence this research was aimed to determinethe rate of genetic improvement in the Nordic barley breeding pool. This study included 90, 2-row spring barleycultivars released (1942–1988) and 29, 6-row spring barley cultivars released (1930–1991) adopted by Nordicfarmers that were tested in four Nordic locations for three consecutive years. Relative genetic gain owing to plantbreeding was 13% in 2-row barley and 34% in 6-row barley for grain yield. The absolute gain for this characteristicwas 13 ± 3 kg ha−1year −1 in 2-row barley, and 22 ± 3 kg ha−1year−1 in 6-row barley. Improved yield wasachieved in Nordic barley by reducing plant height (0.20 ± 0.04 cm year−1 for 2-row barley and 0.16 ± 0.06 cmyear−1 for 6-row cultivars), thereby reducing significantly lodging (0.5 ± 0.1% year−1 and 0.4 ± 0.1 year−1), andincreasing significantly the harvest index (0.0008 ± 0.0002 year−1 and 0.0018 ± 0.0002 year−1). Additionally,in 2-row spring barley cultivars resistance to powdery mildew (0.19 ± 0.08% year−1) and thousand-kernel weight(0.07 ± 0.03 g year−1) were also significantly enhanced, whereas hectoliter weight was improved (0.06 ± 0.02 kgyear−1) in 6-row barley cultivars in the period investigated.

Introduction

Barley is an important crop in the Nordic Region ofEurope (Denmark, Finland, Norway and Sweden).Denmark has the largest acreage (783 000 ha), fol-lowed by Finland (542 000 ha), Sweden (465 000 ha)and Norway (175 000 ha), and the average grain yieldranges from 3.4 t ha−1 in Finland to 5.3 t ha−1 inDenmark (FAO, 1997). The Nordic Region exhibits alarge variation in climate and soil. Nevertheless, bar-ley breeders in this region have the same objectives:to develop new cultivars with high, stable yield andoutstanding quality (Nurminiemi et al., 1996).

Two-row barley has been known to this regionsince 1638 but became important with the cultivationof spring cultivars after 1900 (Jørgen L. Christiansen,

personal communication, 2000). Growers prefer two-row barley cultivars in southern Scandinavia, and6-row barley cultivars in northern latitudes because oftheir earliness, although 6-row barley cultivars yieldless than 2-row barley cultivars bred for the NordicRegion (Nurminiemi & Rognli, 1996). The selectionenvironment could account for this relatively low yieldin 6-row Nordic barley cultivars, because they werebred in locations with low potential grain yield. Two-row barley cultivars are also more important for theNordic brewing industry owing to their malting qual-ity (Jørgen L. Christiansen, personal communication,2000).

Structured barley breeding started in the Nordicregion between the end of the 19th century and early20th century, and largely depended on selections from

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Nordic landraces. After the available variation in thelandrace gene pool was fully utilized, new cultivarsresulted from crossing chosen parents. These cul-tivars often possessed one or more of the distinctcharacteristics of the chosen parents (Aikasalo, 1988).

Grain yield in barley has improved significantlyin the last 50 years due to high yielding cultivarsand enhanced crop husbandry (Naylor et al., 1998).Thirty-three to 75% of this gain in grain yield can beaccounted for by better cultivars, whose grain yieldmay be enhanced significantly by the improved pro-duction technology (Silvey, 1986; Wych & Rasmus-son, 1983), though the response pattern to inputsdiffers among barley cultivars. For example, old cul-tivars showed a smaller yield gain than newer cultivarsafter application of N fertilizer (Sandfer et al., 1965).This grain yield gain in the new cultivars was as-sociated with more spikes (or fertile tillers) per unitarea, superior lodging resistance and better adapta-tion of this germplasm to modern cultural practices.Likewise, a preliminary examination of the databaseof Nordic spring barley cultivars (Nordic Gene Bank,1992) suggested that improved yield in newer Nor-dic spring barley cultivars was achieved by shorteningplant height, thereby reducing lodging, and increasingresistance to diseases such as powdery mildew (Erysi-phe graminis DC. ex Merat hordei Marchal) (Ortiz,1999a). In Danish cultivars, resistance to powderymildew enhanced spike length, which was also cor-related with kernel weight. Using data from 851 trials(1960–1992) with seven overlapping check cultivars,Strand (1994) determined the contribution of breedingand enhanced husbandry in yield improvement of Nor-wegian barley. About 40% (28 kg ha−1 year−1) wasaccounted for by breeding.

An assessment of genetic gains due to plant breed-ing within a specific period not only shows the benefitof breeding efforts, but also provides a means to under-stand the phenotypic changes that are associated withthis improvement. There have been some attempts todetermine the genetic improvement of barley in someNordic countries. In Finland, Peltonen-Sainio & Kar-jalainen (1991) indicated no clear genetic gains, es-pecially for hectoliter weight, thousand kernel weightand lodging, though the plant height was significantlyreduced. MacKey (1994) reported a 21% genetic gainin Sweden for the period 1945 to 1988. However, theresults of Peltonen-Sainio & Karjalainen (1991) referto a small set of cultivars using data from long-termyield trials and those from MacKey (1994) were meas-ured as relative grain yield versus the standard cultivar

Table 1. Number of 2- and 6-row Nordic spring barley cul-tivars investigated according to country of origin and decadeof release

Decade Denmark Finland Norway Sweden Other Total

2-row

1940s 2 2

1950s 1 4 5

1960s 1 2 2 5

1970s 11 13 2 26

1980s 16 1 34 1 52

Total 29 3 55 3 90

Decade Denmark Finland Norway Sweden Iceland Total

6-row

1930s 2 2

1940s 2 2

1960s 1 8 9

1970s 2 2 3 7

1980s 4 4 8

1990s 1 1

Total 7 16 4 2 29

Gull. Assessment of genetic yield improvement fromlong-term yield trials may be biased, because it isdifficult to determine the influence of cultivation tech-niques on yield throughout the testing period. Hence,the objective of this research was to determine the ge-netic gains attributed to breeding Nordic spring barleyusing replicated multi-location experiments across theregion.

Materials and methods

This experiment included 90, 2-row and 29, 6-row bar-ley cultivars (Table 1). The 2-row cultivars were bredmostly in Denmark and Sweden whereas the 6-rowcultivars were mostly selected from Finland and Nor-way. All but 3, 2-row barley cultivars were developedby Nordic breeders. Nevertheless farmers in the regionadopted these non-Nordic cultivars that were tested atresearch stations in the region, and further recommen-ded and marketed by the seed sector. Nurminiemi etal. (1996) provided the names, origin, and pedigreesof these barley cultivars.

These cultivars were tested at four locations (oneeach for Denmark, Finland, Norway and Sweden)from 1987 to 1989. Agro-meteorological characterist-

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Table 2. Agro-meteorological characteristics of Nordic environ-ments included in this experiment. Relative values based onlong-term averages are indicated in brackets

Location Sowing date Season length Rainfall Heat sum

days mm > + 5◦C

Højbakkegård (Denmark, 55◦40’N 12◦18’E, fine sandy moraine

soil,3–6% humus content, pH 6.8–7.3, 78–32–90 or

65–32–80 kg NPK ha−1, 14 h daylength at sowing)

1987 11 May 141 408 (147) 1095 (84)

1988 18 April 119 175 (80) 1110 (115)

1989 10 April 126 212 (94) 1046 (109)

Svalöv (southern Sweden, 55◦57’N 20◦16’E, fine sandy

moraine soil, 6–12% rich in humus, pH 6.7–7.3,

100–44–83 kg NPK ha−1, 14 h daylength at sowing)

1987 28 April 140 358 (115) 1198 (93)

1988 20 April 117 232 (93) 1200 (119)

1989 10 April 128 227 (86) 1133 (111)

Viikii (southern Finland, 60◦15’N 25◦3’E, clayish fine sand,

fine sandy clay or miry clay soils, 3–6% humus content or

6–12% rich in humus, respectively, pH 5.5–5.6, 90–39–73 kg

NPK ha−1, 16 h daylength at sowing)

1987 23 May 129 375 (213) 893 (78)

1988 11 May 91 145 (147) 1029 (118)

1989 7 May 113 208 (162) 1230 (116)

Ås (southeast Norway, 59◦40’N 10◦48’E, silty clay,

3–6% humus content, pH 6.3–6.8, 105–20–45, 110–21–47 or

113–22–54 kg NPK ha−1, 16 h daylength at sowing)

1987 7 May 131 428 (127) 927 (78)

1988 10 May 98 287 (118) 1068 (115)

1989 9 May 112 275 (97) 1015 (94)

ics of these Nordic environments are listed in Table 2.The experimental design involved incomplete blocks(Aastveit, 1977) with two replications at each location.The accessions were randomly grouped into blocksof 20 lines, and they were randomized within blocks,and blocks within replication every year. All blocksincluded two reference cultivars: Arra (6-row barley)and Ida (2-row barley). Plot size varied from 5 m2 to10 m2 depending on the location, and the sowing ratewas 440 seeds m−2.

The characteristics recorded were days since sow-ing to heading, plant height at ripening (cm), daysto ripening, susceptibility to powdery mildew (%),lodging (%), straw yield (g m−2), grain yield (kgha−1), hectoliter weight (kg hl−1), and thousand ker-nel weight (g). Days to ripening was recorded whenall plants of a plot lost their green color, except intheir nodes, or the moisture content of the grain was

below 38%. Lodging was determined as an average ofthree observations taken per plot during the growingseason, whereas the susceptibility to powdery mildewwas visually assessed as an average percentage of dis-eased leaf area on each plot. At Højbakkegård andViikii straw yield was measured during the harvestof the whole plot, while in other locations a sampleof each plot (0.75 m2) was bound into sheaves andthreshed later. Grain yield per plot was corrected to15% moisture content and transformed to kg ha−1.Harvest index was calculated as the ratio of grain yieldand the total harvested biomass (both straw and grainyield).

PROC GLM in SAS was used for the analyses ofvariance (Anonymous, 1987). A single degree of free-dom was used to perform a linear regression analysisto determine the annual rate of genetic improvementfor the period investigated. The independent variablewas year of release and the dependent variable was themean phenotypic variation (across 2 reps × 4 sites ×3 years) for each specific characteristic within eachset of barley cultivars. Similarly, absolute rates of ge-netic improvement were divided by the mean of eachcharacteristic to calculate the genetic gains within each2-row and 6-row set of barley cultivars.

Results

Cultivars differed significantly (p < 0.001) for allcharacteristics investigated. The environments (bothlocations and years as well as their interaction) influ-enced significantly (p < 0.001) the cultivar pheno-types, because of distinct growing conditions acrossthe four locations and among the three years withineach location. The interactions between cultivarsand environments were significant (p < 0.001) formany characteristics. Nevertheless, cultivars contrib-uted most to the total sum of squares in the analyses ofvariance (data not shown).

There were significant (p < 0.05) yearly gains forplant height, lodging score, grain yield, and harvestindex in both 2-row and 6-row barley cultivars (Tables3 and 4). Grain yield was improved at the yearlyrate of 13 ± 3 kg ha−1 in 2-row barley cultivars and22 ± 3 kg ha−1 in 6-row barley cultivars. Gainsduring the period investigated were also signific-ant (p < 0.05) for resistance to powdery mildewand thousand-kernel weight in 2-row barley cultivars(Table 3), and hectoliter weight in 6-row barley cul-

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Table 3. Means for agronomic characteristics of 2-row Nordic spring barley cultivars by decade of release. (Number of cultivars indicatedin brackets)

Decade of Days to Plant Days to Susceptibility Lodging Straw Grain Harvest Hectoliter Thousand

release heading height ripening to mildew score yield yield index weight kernel

cm % % g m−2 kg ha−1 kg weight g

1940 (2) 66 69 105 21 30 427 4235 0.489 65.0 39.7

1950 (5) 67 69 106 23 26 399 4216 0.501 65.0 41.5

1960 (5) 66 70 103 19 23 402 4140 0.494 63.5 43.8

1970 (26) 66 65 104 15 16 389 4468 0.522 64.5 43.6

1980 (52) 67 64 105 13 11 393 4583 0.522 65.1 43.9

Gain year−1 0.039 –0.197 0.016 –0.192 –0.542 –0.470 12.74 0.0008 0.017 0.066

S.E. 0.035 0.043 0.030 0.084 0.070 0.323 2.55 0.0002 0.016 0.027

P 0.2626 0.0001 0.6009 0.0253 0.0001 0.1488 0.0001 0.0001 0.2657 0.0158

Table 4. Means for agronomic characteristics of 6-row Nordic spring barley cultivars by decade of release. (Number of cultivars indicatedin brackets)

Decade of Days to Plant Days to Susceptibility Lodging Straw Grain Harvest Hectoliter Thousand

release heading height ripening to mildew score yield yield index weight kernel

cm % % g m−2 kg ha−1 kg weight g

1930 (2) 56 75 92 38 36 304 2723 0.443 54.5 31.8

1940 (2) 58 82 93 42 29 335 3611 0.515 59.2 33.8

1960 (9) 61 73 97 37 25 332 3845 0.528 58.7 32.6

1970 (7) 59 73 93 39 19 330 3944 0.536 57.5 32.9

1980 (8) 60 69 96 36 13 312 4170 0.567 60.0 34.8

1990 (1) 60 74 94 49 10 325 4291 0.560 61.6 36.5

Gain year−1 0.053 –0.162 0.050 –0.031 –0.420 –0.015 21.64 0.0018 0.064 0.044

S.E. 0.026 0.065 0.039 0.090 0.084 0.310 3.41 0.0002 0.024 0.026

P 0.0517 0.0195 0.2082 0.7266 0.0001 0.9610 0.0001 0.0001 0.0147 0.0981

Table 5. Significant relative genetic gains (%) afterimproving agronomic characteristics in 2- and 6-rowNordic barley cultivars (1930- early 1990)

Characteristic 2-row 6-row

Plant height shortening 14 14

Resistance to powdery mildew 60 NS

Lodging resistance 172 122

Grain yield 13 34

Harvest index 7 20

Hectoliter weight NS∗ 7

Thousand kernel weight 7 NS

∗ NS indicates non significant gain as per regressionanalysis shown in Tables 3 and 4.

tivars (Table 4). No significant trend in phenotypicchange was observed for the other characteristics.

The relative genetic gains ranged from 7% to 172%during the investigated period (Table 5). The highestgenetic gains (> 100%) were observed for reducinglodging in both 2-row and 6-row barley cultivars. Therelative genetic gains for both grain yield and har-vest index were greater in 6-row than in 2-row barleycultivars, but the same among them for plant heightreduction. Plant height was shortened by about 1 cmevery 5 or 6 years in 2-row or 6-row barley cultivarsrespectively (Tables 3 and 4). This explains partiallythe improved lodging resistance observed in the newercultivars. Breeders have also been improving strawstrength in Nordic spring barley cultivars.

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Discussion

The results of this multi-location experiment indic-ate that genetic improvement of Nordic barley cul-tivars involved higher grain yield, shorter plant height,thereby improving lodging resistance, as well as util-ization and partitioning of assimilates for grain filling,i.e., newer cultivars show improved harvest index.These findings agree with early reports in other breed-ing pools from North America and Europe (Boukerrou& Rasmusson, 1990; Jedel & Helm 1994a,b; Lekes,1988a,b; Martiniello et al., 1987; Riggs et al. 1981;Wych & Rasmusson, 1983). Higher fertilizer inputs,especially N, and mechanized harvesting could alsoexplain some of the observed changes brought by plantbreeding in this Nordic spring barley germplasm, e.g.short and stiff straw cultivars were developed espe-cially in Finland (Aikasalo, 1988), but also by Nordicbreeders in other locations. Strand (1994) reported thata 1% increase in lodging resistance resulted in a grainyield gain of 0.3 kg ha−1 in Norwegian barley.

The newer 2-row barley cultivars also exhibiteda high yield potential owing to their resistance topowdery mildew as well as large grains, as determ-ined by thousand-kernel weight. In 2-row barley, ker-nel weight appears to be one of the most importantyield components (Gymer, 1981; Wych & Rasmus-son, 1983). The gains in hectoliter weight in recent6-row barley cultivars can be partially explained byan increased, though non-significant, thousand kernelweight; i.e., more grains were included in hectoliterweight.

The yearly gains for grain yield in Nordic barleycultivars are within the range of those reported earlierfor spring barley breeding in Canada (12 to 41 kgha−1), USA (15 kg ha−1) or Great Britain (19 kg ha−1)(Boukerrou & Rasmusson 1990; Jedel & Helm 1994a;Riggs et al. 1981); but considerably lower than thoseobtained for winter barley in Italy (52 to 74 kg ha−1)(Martiniello et al., 1987). The relative genetic gainsfor grain yield in Nordic spring barley cultivars werelower (13%) in 2-row Nordic spring barley cultivars orgreater (36%) in 6-row Nordic spring barley cultivarsthan those reported for British barley cultivars (0.39%yearly) (Riggs et al., 1981), but both were lower thanthose obtained for winter barley in Italy (1.1% peryear) (Martiniello et al., 1987). The significant re-duction of plant height was also within the range ofreduction reported for spring barley in Canada (0.14to 0.29 cm year−1) (Jedel & Helm, 1994b), whereasthe gain in kernel weight in 2-row Nordic spring

barley cultivars (0.066 mg + 0.027 kernel−1 year−1)was the same as reported for North American barleys(Boukerrou & Rasmusson, 1990).

Emphasis on breeding for malting quality in 2-rowspring barley cultivars depends on elite germplasm,which could have narrowed the germplasm sources(Aikasalo, 1988). Promising genotypes that may be-come new cultivars are often derived from crossesbetween high quality parents (Rasmusson, 1992).However, the results from this multi-location experi-ment show that genetic gains still occur in this highlyselected germplasm. Therefore, significant variationstill exists for further breeding in this gene pool. Thisexplains why no leveling-off in grain yield improve-ment has been reported for this Nordic spring barleygermplasm.

The Mlo-resistance to powdery mildew, conferredby the recessive mlo allele, became widespread sincethe 1980s, and spring barley cultivars with this genewere grown on about 700,000 ha in Europe at the be-ginning of the 1990s (Jørgensen, 1992). Plant breedershave also incorporated other specific genes for resist-ance to powdery mildew while developing new 2-rowspring barley cultivars for Northwest Europe, espe-cially since the 1970s (Jensen et al., 1992). Thesegenes originate from about 20 distinct sources (Brown& Jørgensen, 1991; Wiberg, 1974), and each sourcemay contain one or more genes. Hence, cultivars withthe same parentage may have more than one resistancegene, which provides better resistance to this disease.However, the levels of resistance to powdery mildewin Nordic 6-row spring barley cultivars still remain lowand should be a top priority for Nordic barley breedersif these cultivars are to be grown in southern Scand-inavian latitudes. Resistance to this disease enhanceskernel weight, thereby improves grain yield (Ortiz,1999a). Powdery mildew, however, does not rankhigh for improving barley cultivars grown at 62◦N orabove, because scald or net blotch are more importantdiseases at these locations.

Nordic barley breeders, as well as those in otherEuropean locations and North America, have been ma-nipulating the partitioning of total biomass, as clearlydemonstrated by the results of this experiment. Morecarbohydrates were translocated into grain rather thanretained in the straw, as indicated by the harvest indexof the newer cultivars. However, no significant trendswere observed for straw yield in this Nordic springbarley germplasm. Likewise, total biomass weight (orbiological yield) was almost the same in old and recent2-row spring barley cultivars (8.2–8.5 t ha−1), while

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a slight increase was observed in 6-row barley cul-tivars (excluding the two 1930 barley cultivars fromIceland): from 7 t ha−1 in the 1940s to 7.5 t ha−1 inthe early 1990s. Thus, the challenge for increasingtotal biomass accumulation still remains for Nordicplant breeders. After improving total biomass, furthergains may be achieved by again manipulating harvestindex, as the results of this experiment have shown.Wild Hordeum species or other exotic germplasm mayprovide the source of genes needed to improve bio-logical yield in Nordic spring barley. Methods forintrogression or incorporation of non-adapted geneticmaterial are available in barley (Ortiz, 1999b). Ex-perimental breeding populations, which were obtainedby these methods, exist for further utilization by Nor-dic barley breeders (Lehmann et al., 1998; Veteläinen,1996a,b), and this germplasm will also help to broadenthe genetic base of this crop.

Acknowledgements

We are grateful to the Nordic plant breeding com-panies, research stations, and agricultural universitiesfor providing plant materials, experimental sites, andtechnical assistance. This research was supported bygrants from the Nordic Plant Breeding (SNP-project87:1) under the Nordic Council of Ministers and theNorwegian Research Council (NFR). The senior au-thor also thanks the Nordic Council of Ministers forproviding funding for his Nordic Professorship inPlant Genetic Resources at the Royal Veterinary andAgricultural University of Denmark.

References

Aastveit, A.H., 1977. Statistisk analyse av markforsøk med et stortantall forsøksledd. Hovedoppgave I matematisk stastistikk vedUniversiteit i Oslo, Norway.

Aikasalo, R., 1988. The results of six-row barley breeding and thegenetic origin of varieties released. J Agric Sci (Finland) 60:293–305.

Anonymous, 1987. SAS/STAT guide for personal computers, 6thed. SAS Institute, Cary, North Carolina.

Boukerrou, L. & D.C. Rasmusson, 1990. Breeding for high biomassyield in spring barley. Crop Sci 30: 31–35.

Brown, J.K.M. & J.H. Jørgensen, 1991. A catalogue of mildewresistance genes in European barley varieties. In: J.H. Jørgensen(Ed.), Integrated Control of Cereal Mildew: Virulence Patternsand Their Change, pp. 263–286. Risø Nat. Lab., Roskilde,Denmark.

FAO (Food and Agriculture Organization – United Nations), 1997.Production yearbook. FAO, Rome, Italy.

Gymer, P.T., 1981. The achievements of 100 years of barley breed-ing. In: Proc 4th Int Barley Genetics Symp, pp. 112–117.Edinburgh, Scotland.

Jedel, P.E. & J.H. Helm, 1994a. Assessment of western Canadianbarleys of historical interest: I. Yield and agronomic traits. CropSci 34: 922–927.

Jedel, P.E. & J.H. Helm, 1994b. Assessment of western Canadianbarleys of historical interest: II. Morphology and phenology.Crop Sci 34: 927–932.

Jensen, H.P., E. Christensen & J.H. Jørgensen, 1992. Powdery mil-dew resistance genes in 127 northwest European spring barleyvarieties. Plant Breed 108: 210–228.

Jørgensen, J.H., 1992. Discovery, characterization and exploitationof Mlo powdery mildew resistance in barley. Euphytica 63: 141–152.

Lehmann, L.C., R. Jönsson & M. Gustafsson, 1998. Identificationof resistance genes to powdery mildew isolated from Hordeumvulgare spp. spontaneum and land races of barley. SverigesUtsädesförenings Tidskrift 108: 94–101.

Lekes, J., 1988a. Development of important traits of spring barleyfrom the beginning of selection and the detection of suitablegenetic resources – Part I. Scientia Agric Bohem 20: 81–90.

Lekes, J., 1988b. Development of important traits of spring barleyfrom the beginning of selection and the detection of suitablegenetic resources – Part II. Scientia Agric Bohem 20: 91–100.

MacKey, J., 1994. The history of cereal yield increase. Melhora-mento 33: 37–53.

Martiniello, P., G. Delogu, M. Odoardi, G. Boggini & A.M. Stanca,1987. Breeding programs in grain yield and selected agronomiccharacters of winter barley (Hordeum vulgare L.) over the lastquarter of a century. Plant Breed 99: 289–294.

Naylor, R.E.L., D.T. Stokes & S. Matthews, 1998. Biomass, shootuniformity and yield of winter barley. J Agric Sci (Cambridge)131: 13–21.

Nordic Gene Bank, 1992. The Nordic barley catalogue. NGB,Alnarp, Sweden.

Nurminiemi, M., Å. Bjørnstad & O.A. Rognli, 1996. Yield stabilityand adaptation of Nordic barleys. Euphytica 92: 191–202.

Nurminiemi, M. & O.A. Rognli, 1996. Regression analysis of yieldstability is strongly affected by companion test varieties and loca-tions – examples from a study of Nordic barley lines. Theor ApplGenet 93: 468–476.

Ortiz, R., 1999a. Genetic diversity of cultivated crops and in situconservation of genetic resources. Bot Lithuanica Suppl 2: 15–30.

Ortiz, R., 1999b. Genetic enhancement and base broadening efforts.In: T. Gass, L. Frese, F. Begemann & E. Lipman (Eds.), Con-servation and Sustainable Utilization of Plant Genetic Resourcesfor Food and Agriculture – Implementation of the Global Planof Action in Europe, pp. 191–203. International Plant GeneticResources Institute (IPGRI), Rome, Italy.

Peltonen-Sainio, P. & R. Karjalainen, 1991. Genetic yield improve-ment of cereal varieties in northern agriculture since 1920. ActaAgric Scand 41: 267–273.

Rasmusson, D.C., 1992. Barley breeding at present and in the future.In: L. Munck (Ed.), Barley Genetics VI. Vol. II, pp. 865–877.Munksgaard Int Publ Ltd Copenhagen, Denmark.

Riggs, T.J., P.R. Hanson, N.D. Start, D.M. Miles, C.L. Morgan &M.A. Ford, 1981. Comparison of spring barley varieties grownin England and Wales between 1880 and 1980. J Agric Sci(Cambridge) 97: 599–610.

Sandfer, J., J.H. Jørgensen & V. Haahr, 1965. The effect of nitrogenfertilization on old and new barley varieties. Royal Veterinaryand Agric Univ Yearbook 1965: 153–180.

289

Silvey, V., 1986. The contribution of new varieties to cereal yieldsin England and Wales between 1947 and 1983. J Nat Inst AgricBot 17: 155–168.

Strand, E., 1994. [Yield progress and sources of yield progress inNorwegian small grain production 1960–92]. Norsk Landbrugs-forsking 8: 111–126. (In Norwegian but English Abstract).

Veteläinen, M., E. Nissila, P.M.A. Tigerstedt & R. von Bothmer,1996a. Utilization of exotic germplasm in Nordic barley breedingand its consequences for adaptation. Euphytica 92: 267–273.

Veteläinen, M., M. Suominen & E. Nissila, 1996b. Agronomicperformance of crosses between Nordic and exotic barleys.Euphytica 93: 239–248.

Wiberg, A., 1974. Sources of resistance to powdery mildew inbarley. Hereditas 78: 1–40.

Wych, R.D. & D.C. Rasmusson, 1983. Genetic improvement inmalting barley cultivars since 1920. Crop Sci 23: 1037–1040.