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FORAGE

Performance of 15 Miscanthus Genotypes at Five Sites in Europe

^a Univ. of Hohenheim, Inst. for Crop Prod. and Grassl. Res. (340), D-70599 Stuttgart, Germany
^b Svalöf Weibull, AB-S 268 81, Sweden
^c Departamento de Fitotecnica, Universidade de Évora, Herdade da Mitra, P-7001 Evora/Codex, Portugal
^d Rothamsted Exp. Stn., Harpenden, Hertfordshire AL5 2JQ, United Kingdom
^e Danish Inst. of Agric. Sci., Dep. of Soil Sci., Res. Cent. Foulum, P.O. Box 50, 8830 Tjele, Denmark

* Corresponding author (jcbrown{at}tcd.ie)

Received for publication October 6, 2000.

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Miscanthus is a genus of high-yielding perennial rhizomatous grasses with C₄ photosynthesis. Extensive field trials of Miscanthus spp. biomass production in Europe during the past decade have shown several limitations of the most widely planted clone, M. x giganteus Greef et Deu. A 3-yr study was conducted at five sites in Europe (Sweden, Denmark, England, Germany, and Portugal) to evaluate adaptation and biomass production potential of four acquisitions of M. x giganteus (No. 1–4) and 11 other genotypes, including M. sacchariflorus (Maxim.) Benth. (No. 5), M. sinensis Andersson (No. 11–15), and hybrids (No. 6–10). At each site, three randomized blocks containing a 5- by 5-m plot of each genotype were established (except in Portugal where there were two blocks) with micropropagated plants at 2 plants m^-2. In Sweden and Denmark, only M. sinensis and its hybrids satisfactorily survived the first winter following planting. Mean annual yields across all sites for all surviving genotypes increased each year from 2 t ha^-1 dry matter following the first year of growth to 9 and 18 t ha^-1 following the second and third year, respectively. Highest autumn yields at sites in Sweden, Denmark, England, and Germany were 24.7 (M. sinensis hybrid no. 8), 18.2 (M. sinensis hybrid no. 10), 18.7 (M. x giganteus no. 3), and 29.1 t ha^-1 (M. x giganteus no. 4), respectively. In Portugal, where irrigation was used, the top-yielding genotype produced 40.9 t ha^-1 dry matter (M. sinensis hybrid no. 7). Highest-yielding genotypes in Sweden and Denmark were among the lowest yielding in Portugal and Germany, demonstrating strong genotype x environment interactions.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
MISCANTHUS x giganteus was introduced to Europe in the 1930s by Aksel Olsen and was observed to have exceptionally vigorous growth (Linde-Laursen, 1993). In the late 1980s, interest in C₄ perennial rhizomatous grasses, such as Miscanthus spp. (Nielsen, 1987), switchgrass (Panicum virgatum L.) (Christian, 1994), Cyperus spp., and Spartina spp. (Potter et al., 1995), for biofuel production increased due to their high yield potential and rising energy prices. Since 1983, extensive field trials of M. x giganteus have been carried out in northern Europe, showing the capacity of this genotype for yields >20 t dry matter ha^-1 year^-1 (Nielsen, 1987; Schwarz et al., 1994).

There are several reasons why European-wide biomass production from a single genotype within the Miscanthus genus is inadequate. First, in northern Europe, a number of sites established with M. x giganteus failed to survive during the first winter (Jones and Walsh, 2001), principally due to insufficient freeze tolerance of the overwintering rhizome. Second, it is unlikely that one single clone is sufficient to fulfil all of the quality requirements of different uses (combustion and fiber). Third, M. x giganteus, being a sterile triploid (Greef and Deuter, 1993), must be propagated vegetatively, either with rhizome cuttings or by micropropagation, making establishment expensive compared with crops established from seed. Fourth, growing large areas of a single clone increases disease risk. A broad genetic base and the provision of different Miscanthus genotypes are required to overcome these limitations.

As part of the European Miscanthus Improvement Project, a Miscanthus gene pool was created by combining collections directly from Asia and material already made available in Europe by German, Danish, and Swedish breeders. M. sinensis is characterized by a tuft-forming rhizome with high shoot densities while M. sacchariflorus is characterized by a broad, creeping rhizome with thick tall stems. M. x giganteus shows an intermediate type of rhizome between M. sinensis and M. sacchariflorus and is most probably a natural hybrid of the two (Greef and Deuter, 1993; Hodkinson et al., 1997).

In this paper, we report on field trials planted with 15 Miscanthus genotypes, which can be broadly divided into four genetic groups, at five locations: Sweden, Denmark, England, Germany, and Portugal. The objective was to screen these genotypes in different soil and climatic conditions for yield performance traits, including height, stem density, flowering time, autumn senescence rate, and yield. These measurements were used to identify the most suitable genotypes for the various regions of Europe and to improve our knowledge of the genetic base for the future development of Miscanthus spp. as a biomass crop.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Genotypes
From the gene pool held by European breeders, 15 of the most promising genotypes were selected (Table 1). Four acquisitions of M. x giganteus genotypes (No. 1–4) were chosen because different crosses between M. sacchariflorus and M. sinensis were suspected to be in circulation all under the same name. Amplified fragment length polymorphism (AFLP) analysis had revealed small detectable differences between some of these acquisitions (Greef et al., 1997). One, M. sacchariflorus (No. 5), was selected from a collection described by Matumura et al. (1985). Five pure M. sinensis types were selected, four of which were collected by the Danish collector Poul Brander in 1983 on Honshu Island (No. 11–14) and one from central Hokkaido in 1990 by the Swedish collector Zandra Andersson (No. 15). Five Miscanthus spp. hybrids from crosses within M. sinensis and M. sacchariflorus (No. 6–10) were selected based on known differences in key physiological characteristics such as flowering time and autumn senescence time.

At each site, three randomized blocks containing a 5- by 5-m plot of each genotype were established (except in Portugal where there were two blocks). Plantlets were planted by hand between March and June 1997 at a density of 2 plants m^-2. Plots were irrigated after planting at all sites. In Portugal, irrigation was necessary throughout all growing seasons because of the limited rainfall during the growing season and sandy soils (Tables 2 and 3). Fertilizer was applied at rates equivalent to 60, 44, and 110 kg ha^-1 yr^-1 N, P, K, respectively, which, combined with residual nutrients, was estimated to saturate crop requirements (Lewandowski et al., 2000). Mechanical weed control was used between transplanting and September in 1997.

Each autumn, a sample of 2 m² was harvested from within the central area of the plot (avoiding border effects) to assess the total aboveground productivity of each genotype. Cutting height for yield determinations was 5 cm. Moisture content was measured by drying at 80°C until constant weight had been achieved, and dry matter yield was calculated as tonnes of dry matter per hectare.

Statistical Analyses
When data were normally distributed, analysis of variance (ANOVA) was used to determine significant differences. For comparisons of shoot density, plant height, and yield among genotypes within a country at a particular sampling time, a minimum significant difference was calculated by the Tukey procedure at P = 0.05. Interactions among genotype, year, and country, where appropriate, are shown in the tables. For shoot greenness, plot means from the five selected plants were used from the three replicate plots for each genotype at each site to produce a standard error. Regression relationships between genotype yields in the different years were calculated across all countries. Plant height and shoot density in the third growing season were regressed with yield to assess the yield predictability using these simple growth parameters. All statistics were performed within Data Desk v.6 (Data Description, Ithaca, NY).

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Climatic Conditions during the Growing Season
Mean air temperatures and rainfall sums from April to September are given in Table 3 for all 3 yr of the field trials. The long-term means (>10 yr of data) and the whole year are also shown. Growing season air temperatures in 1997, 1998, and 1999 were generally warmer than normal for the five locations. Air temperatures in Portugal were at least 5°C higher than at the other locations.

Long-term annual rainfall at all sites was similar (626–696 mm), but rainfall distribution varied markedly with location. On average, the German site had relatively wet summers (425 mm) while Portugal had wet winters (509 mm). Consequently, in Portugal, natural water availability for crop growth was very limited, and irrigation was necessary.

Plant Survival
Established Miscanthus spp. stands grow from overwintering rhizomes in spring. At the more northern sites of Denmark and Sweden, nearly 100% and >50% of the plants of M. x giganteus and M. sacchariflorus, respectively, died during the first winter following planting, but losses of M. sinensis plants were only 1 to 16% (Table 4). In Denmark and Sweden, plant losses of M. sinensis hybrids (No. 6–10) varied from only 1% in Genotype no. 10 to 60% in Genotype no. 9. In these countries, winter soil temperatures in the first year following planting fell below -4.5°C. In England, Germany, and Portugal, where winter soil temperatures were warmer (> -2.8°C), all genotypes survived. These observations are consistent with artificial freezing tests, which showed that rhizomes of M. sinensis hybrids could survive temperatures below -4.5°C, but rhizomes of M. x giganteus and M. sacchariflorus are killed at approximately -3°C (Clifton-Brown and Lewandowski, 2000). It appears, therefore, that temperatures in Sweden and Denmark were too cold for M. x giganteus and M. sacchariflorus. Consequently, M. sinensis and M. sinensis hybrids can be recommended for the regions where soil temperatures at 5-cm depth are likely to fall below -3°C.

In the third year, the highest-yielding genotypes in Germany and England were of M. x giganteus. In Portugal, the highest yield was obtained from M. sinensis hybrid no. 7, with autumn yield of 40.9 t ha^-1. M. sinensis genotypes (No. 11–15) produced a consistently lower yield than the highest-yielding genotype at any given location. Interestingly, at the higher latitudes in Sweden and Denmark, the yield gap between the M. sinensis genotype group (No. 11–15) and the other genotypes was smaller than at lower latitudes. This can be explained through lower overall yields at higher latitudes due to the shorter growing season.

Biomass yield interactions between year and genotype in any given country were significant at P < 0.001. Interactions among country, year, and genotype were also significant at P < 0.001. This shows that stand maturity increases yield significantly for all surviving genotypes. Equally, the different environmental conditions, particularly climate and soil, influence genotype yield performance (Table 5).

Comparisons between yields obtained in these field trials and other trials in Europe can only be made for the widely grown M. x giganteus. Trials in northern regions tend to mature slower than at southern latitudes, and ceiling yields of 15 t ha^-1 are reached after only the fourth or fifth year (Lewandowski et al., 2000). Yields with irrigation in excess of 25 t ha^-1 in southern Europe are often achieved in the second year with M. x giganteus (Clifton-Brown et al., 2001). Therefore, in warm climates, yields after the second growing season are a good indication of the potential ceiling yield from a genotype, but in cooler climates, it takes at least 3 yr to reach a ceiling. As expected, regression coefficients with third-year yield against first- and second-year yields were better for the second year than for the first year (Table 6).

Genotypic differences in shoot emergence time in the spring were not observed within these field trials. Evidently, monthly measurements of plant height were insufficient to identify emergence differences at a site (data not shown). However, the monthly measurements did show the earlier start to the growing season in Portugal (data not shown). By the end of the third growing season, plants were tallest in Portugal (223 cm) and shortest in Denmark (120 cm) (Table 7).

Genotypic variation in plant height appears to be associated with flowering time. The tallest genotypes at a site (e.g., M. sacchariflorus or M. x giganteus) tended to flower later than the earliest-flowering M. sinensis genotypes (No. 11–15). Indeed, it was only in Portugal where all of the genotypes reached flowering before autumn (Table 8). Thermal time required from emergence in spring to flowering of M. x giganteus in Portugal was >1800 degree days above a threshold of 10°C. In contrast, the M. sinensis genotypes (No. 11–15) only needed 400 to 600 degree days in Portugal. This effectively halves the length of the available growing season, approximately halving the yield (Tables 5 and 8). In Sweden and Denmark, where temperatures are lower, M. sinensis flowers later in the growing season so that less radiation is lost than at warmer sites. As with yield (Table 5), flowering time was most variable for the M. sinensis hybrid (No. 6–10) group within a site. For example, in Portugal, Genotype no. 7 was late flowering, and this coincided with the highest yield recorded throughout (Table 5).

When genotypes that failed to overwinter in Sweden and Denmark are omitted (Table 4), plant height was the growing season performance characteristic most highly correlated with yield (Table 6). Greater height implies later flowering, and therefore, longer periods for which radiation is converted to biomass. Shoot densities were not found to be significantly related to yield (Table 6) for the genotypes tested. Exceptions to these general relationships included M. sacchariflorus (No. 5), which despite being the tallest genotype, had a low shoot density that lowered its yields below the highest-yielding genotypes (Table 7). M. sinensis hybrid genotypes (No. 6–10) showed the potential for breeding genotypes with appropriate characteristics for a wide range of environmental conditions. For future breeding, M. sacchariflorus will be an invaluable parent to create new taller, and therefore, higher yielding M. sinensis hybrid genotypes with rhizome freezing tolerance and late flowering time.

Practical Issues in Relation to Miscanthus spp. Production for Biomass
Without irrigation, Miscanthus spp. would not be productive in Portugal because of the combination of a low water-retentive sandy soil type, high evaporative demand, and low rainfall during the growing season. At the other four sites, no irrigation was used in 1999. Yields were highest at the German site, which had not only the most rainfall in 1999, but also a heavy clay soil. Because biomass production must be low cost and low input, it is unlikely that irrigation will be economic, and a combination of site and genotype selection will be important to ensure survival and adequate yields.

It is important to point out that biomass quality for combustion improves if the crop is harvested in early spring rather than in the previous autumn. Yields can, however, be as much as 30% less in the following spring due to death and detachment of leaves and stem tops (Clifton-Brown et al., 2000; Jørgensen, 1997).

There is a potential weed risk from the diploid Miscanthus genotypes in Europe because fertile seeds were produced at all sites where flowering occurred. To date, seedlings have not been found to spread far from the plots, which have had frequently mown paths. Current breeding programs for Miscanthus spp. are attempting to produce infertile hybrids (K.K. Petersen, personal communication, 2000).

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
New plantations with M. x giganteus and M. sacchariflorus are unlikely to be viable where winter soil temperatures fall below -3°C at a depth of 5 cm. In England and Germany, M. x giganteus genotypes were among the top performers. These genotypes yielded well in Portugal, >34 t ha^-1, but the highest-yielding genotype in Portugal was the stay-green M. sinensis hybrid no. 7 (41 t ha^-1 dry matter). The highest-yielding genotypes in Sweden and Denmark were the M. sinensis hybrids no. 6, 8, and 10. These results demonstrate that different M. sinensis hybrids can be found for a wide range of climatic conditions in Europe. In mid-Europe, M. x giganteus is still the genotype of preference. Plant height, which is largely controlled by flowering time, was a more important selection characteristic than shoot density.

	ACKNOWLEDGMENTS

 
The authors thank Sabine Schneider, Birgit Beierl, and the team at the Ihinger Hof field station for technical assistance in the field in Germany. Kaj Eskesen is thanked for technical assistance in the field in Denmark. Michael Sommer and Søren B. Torp are thanked for their work on the soil taxonomy. Thanks also to Mike Jones for reading the manuscript. The EMI project was funded by EU contract FAIR3 CT-96-1392.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Current address of J.C. Clifton-Brown: Bot. Dep., Univ. of Dublin, Trinity College, Dublin 2, Ireland. This work was funded by the EU Contract no. FAIR3 CT-96-1392.

	REFERENCES

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