Analysis of Crystallinity Index and Hydrolysis Rates in the Bioenergy Crop Sorghum bicolor

Maximum yield from any cellulosic bioenergy crop is largely dependent upon total dry weight at harvest and process-specific bioconversion rates. Using enzymatic hydrolysis rate as a bioconversion metric, we have investigated the relationship between the biomass crystallinity index (CI) and hydrolysis yield potential (HYP) among ??20 Sorghum bicolor varieties grown in two environments. The comparison of HYP to CI revealed a significant negative correlation in both environments indicating that high cellulose crystallinity in sorghum can have an impact on conversion yield. Interestingly, no correlation was seen between CI and HYP after pretreatment. Compositional analysis revealed a significant positive correlation between lignin content and CI, as well as a significant negative correlation between lignin content and HYP. Additionally, CI and HYP were found to be significantly correlated only after 24?h of hydrolysis. These results suggest that when a sorghum cultivar is being considered for industrial scale production, the inclusion of cellulose crystallinity should be factored into the decision along with total biomass yield and lignin composition.     

Impact of agronomic uncertainty in biomass production and endogenous commodity prices on cellulosic biofuel feedstock composition

This study evaluates the effect of agronomic uncertainty on bioenergy crop production as well as endogenous commodity and biomass prices on the feedstock composition of cellulosic biofuels under a binding mandate in the United States. The county‐level simulation model focuses on both field crops (corn, soybean, and wheat) and biomass feedstocks (corn stover, wheat straw, switchgrass, and Miscanthus). In addition, pasture serves as a potential area for bioenergy crop production. The economic model is calibrated to 2022 in terms of yield, crop demand, and baseline prices and allocates land optimally among the alternative crops given the binding cellulosic biofuel mandate. The simulation scenarios differ in terms of bioenergy crop type (switchgrass and Miscanthus) and yield, biomass production inputs, and pasture availability. The cellulosic biofuel mandates range from 15 to 60 billion L. The results indicate that the 15 and 30 billion L mandates in the high production input scenarios for switchgrass and Miscanthus are covered entirely by agricultural residues. With the exception of the low production input for Miscanthus scenario, the share of agricultural residues is always over 50% for all other scenarios including the 60 billion L mandate. The largest proportion of agricultural land dedicated to either switchgrass or Miscanthus is found in the southern Plains and the southeast. Almost no bioenergy crops are grown in the Midwest across all scenarios. Changes in the prices for the three commodities are negligible for cellulosic ethanol mandates because most of the mandate is met with agricultural residues. The lessons learned are that (1) the share of agricultural residue in the feedstock mix is higher than previously estimated and (2) for a given mandate, the feedstock composition is relatively stable with the exception of one scenario.     

Maize and sorghum: genetic resources for bioenergy grasses

The highly photosynthetic-efficient C4 grasses, such as switchgrass (Panicum virgatum), Miscanthus (Miscanthusxgiganteus), sorghum (Sorghum bicolor) and maize (Zea mays), are expected to provide abundant and sustainable resources of lignocellulosic biomass for the production of biofuels. A deeper understanding of the synthesis, deposition and hydrolysis of the distinctive cell walls of grasses is crucial to gain genetic control of traits that contribute to biomass yield and quality. With a century of genetic investigations and breeding success, recently completed genome sequences, well-characterized cell wall compositions, and a close evolutionary relationship with future bioenergy perennial grasses, we propose that maize and sorghum are key model systems for gene discovery relating to biomass yield and quality in the bioenergy grasses.     

Assessment of Sugarcane Billet Harvester on Recovery of Sweet Sorghum Biomass for Ethanol Production

Sweet sorghum (Sorghum bicolor L. Moench) is a promising bioenergy crop for the production of ethanol and bio-based products. Sugarcane billet harvesters can be used to harvest sweet sorghum. Multiple extractor fan speed settings of these harvesters allow for separating the extraneous matter in the feedstock, which has been associated with increased milling throughput and better juice quality at the processing facility. This removal is not completely selective, and some stalk material is also lost. These losses can be higher for sweet sorghum than sugarcane due its lower weight. This paper presents an assessment of how the speed of the primary extractor fan of a sugarcane billet combine used for harvesting sweet sorghum affects the biomass yield, biomass losses, and quality at delivery for the production of ethanol from extracted juice and fiber. Three primary extractor fan speeds (0, 800, and 1100 rpm) were evaluated. Higher fan speeds decreased fresh biomass yields by up to 28.3 Mg ha^?1. Juice quality was not significantly different among treatments. Ethanol yield calculated from sweet sorghum harvested at 0 rpm was 6075 L ha^?1. This value decreased by about half for material harvested at 1100 rpm due to the differences in biomass yield.     

Identification of bioconversion quantitative trait loci in the interspecific cross Sorghum bicolor × Sorghum propinquum

For lignocellulosic bioenergy to be economically viable, genetic improvements must be made in feedstock quality including both biomass total yield and conversion efficiency. Toward this goal, multiple studies have considered candidate genes and discovered quantitative trait loci (QTL) associated with total biomass accumulation and/or grain production in bioenergy grass species including maize and sorghum. However, very little research has been focused on genes associated with increased biomass conversion efficiency. In this study, Trichoderma viride fungal cellulase hydrolysis activity was measured for lignocellulosic biomass (leaf and stem tissue) obtained from individuals in a F₅ recombinant inbred Sorghum bicolor × Sorghum propinquum mapping population. A total of 49 QTLs (20 leaf, 29 stem) were associated with enzymatic conversion efficiency. Interestingly, six high-density QTL regions were identified in which four or more QTLs overlapped. In addition to enzymatic conversion efficiency QTLs, two QTLs were identified for biomass crystallinity index, a trait which has been shown to be inversely correlated with conversion efficiency in bioenergy grasses. The identification of these QTLs provides an important step toward identifying specific genes relevant to increasing conversion efficiency of bioenergy feedstocks. DNA markers linked to these QTLs could be useful in marker-assisted breeding programs aimed at increasing overall bioenergy yields concomitant with selection of high total biomass genotypes.     

Genomic prediction applied to high-biomass sorghum for bioenergy production

The increasing cost of energy and finite oil and gas reserves have created a need to develop alternative fuels from renewable sources. Due to its abiotic stress tolerance and annual cultivation, high-biomass sorghum (Sorghum bicolor L. Moench) shows potential as a bioenergy crop. Genomic selection is a useful tool for accelerating genetic gains and could restructure plant breeding programs by enabling early selection and reducing breeding cycle duration. This work aimed at predicting breeding values via genomic selection models for 200 sorghum genotypes comprising landrace accessions and breeding lines from biomass and saccharine groups. These genotypes were divided into two sub-panels, according to breeding purpose. We evaluated the following phenotypic biomass traits: days to flowering, plant height, fresh and dry matter yield, and fiber, cellulose, hemicellulose, and lignin proportions. Genotyping by sequencing yielded more than 258,000 single-nucleotide polymorphism markers, which revealed population structure between subpanels. We then fitted and compared genomic selection models BayesA, BayesB, BayesCπ, BayesLasso, Bayes Ridge Regression and random regression best linear unbiased predictor. The resulting predictive abilities varied little between the different models, but substantially between traits. Different scenarios of prediction showed the potential of using genomic selection results between sub-panels and years, although the genotype by environment interaction negatively affected accuracies. Functional enrichment analyses performed with the marker-predicted effects suggested several interesting associations, with potential for revealing biological processes relevant to the studied quantitative traits. This work shows that genomic selection can be successfully applied in biomass sorghum breeding programs.     

Energy Potential of Biomass from Conservation Grasslands in Minnesota,USA

Perennial biomass from grasslands managed for conservation of soil and biodiversity can be harvested for bioenergy. Until now, the quantity and quality of harvestable biomass from conservation grasslands in Minnesota, USA, was not known, and the factors that affect bioenergy potential from these systems have not been identified. We measured biomass yield, theoretical ethanol conversion efficiency, and plant tissue nitrogen (N) as metrics of bioenergy potential from mixed-species conservation grasslands harvested with commercial-scale equipment. With three years of data, we used mixed-effects models to determine factors that influence bioenergy potential. Sixty conservation grassland plots, each about 8 ha in size, were distributed among three locations in Minnesota. Harvest treatments were applied annually in autumn as a completely randomized block design. Biomass yield ranged from 0.5 to 5.7 Mg ha⁻¹. May precipitation increased biomass yield while precipitation in all other growing season months showed no affect. Averaged across all locations and years, theoretical ethanol conversion efficiency was 450 l Mg⁻¹ and the concentration of plant N was 7.1 g kg⁻¹, both similar to dedicated herbaceous bioenergy crops such as switchgrass. Biomass yield did not decline in the second or third year of harvest. Across years, biomass yields fluctuated 23% around the average. Surprisingly, forb cover was a better predictor of biomass yield than warm-season grass with a positive correlation with biomass yield in the south and a negative correlation at other locations. Variation in land ethanol yield was almost exclusively due to variation in biomass yield rather than biomass quality; therefore, efforts to increase biomass yield might be more economical than altering biomass composition when managing conservation grasslands for ethanol production. Our measurements of bioenergy potential, and the factors that control it, can serve as parameters for assessing the economic viability of harvesting conservation grasslands for bioenergy.     

Sorghum insect problems and management

Sorghum (Sorghum bicolor) has high levels of starch, sugar, and fiber and is one of the most important energy crops in the world. Insect damage is one of the challenges that impacts sorghum biomass production. There are at least 150 insect species that can infest sorghum varieties worldwide. These insects can complete several generations within a growing season, they target various parts of sorghum plants at developmental stages, and they cause significant biomass losses. Genetic research has revealed the existence of resistant genetics in sorghum and insect tolerant sorghum varieties have been identified. Various control methods have been developed, yet more effective management is needed for increasing sorghum biomass production. Although there are no transgenic sorghum products on the market yet, biotechnology has been recognized as an important tool for controlling insect pests and increasing sorghum production.     

Sorghum Insect Problems and Management

Sorghum (Sorghum bicolor) has high levels of starch,sugar,and fiber and is one of the most important energy crops in the world.Insect damage is one of the challenges that impacts sorghum biomass production.There are at least 150 insect species that can infest sorghum varieties worldwide.These insects can complete several generations within a growing season,they target various parts of sorghum plants at developmental stages,and they cause significant biomass losses.Genetic research has revealed the existence...     

The Physiology of Heterosis in Sorghum with Respect to Environmental Stress

The hypothesis that heterosis in biomass production of sorghum(Sorghum bicolor L. Moench) may be ascribed to stability incarbon exchange rate (CER) over a wide range of environmentalconditions was evaluated. This hypothesis was based on previousresults from detached leaves that hybrids sustained greaterCER over a wider temperture range than their parents. Two grain sorghum hybrids (ATx378/RTx430 and ATx378/RTx434)and their parental lines were grown in the greenhouse in a gradientof ambient temperatures under two water regimes (well-irrigatedand drought up to heading). Plant water-use (estimated by weighingpots), leaf area, leaf gas exchange, grain yield, and above-groundbiomass were determined. Significant heterosis was found for biomass, grain yield perplant, and grain number per panicle. No heterosis occurred forharvest index, indicating that heterosis in grain yield wasdue to heterosis in biomass. Neither growth duration nor leafarea could explain heterosis in biomass. CER and stomatal conductancefor hybrid ATx378/RTx430 in the controls were greater than forboth its parents at leaf temperatures above 38 °C. This,however, was not observed in the other hybrid which was lessheterotic for biomass and grain yield in the controls. WhenCER data were subjected to a stability analysis by joint linearregression, the two hybrids had greater CER than their respectiveparents especially under conditions favouring high CER. Whenextreme stress conditions developed, the hybrid's performancedepended on its genetic background more than on heterosis. Sorghum, Sorghum bicolor L. Moench., heterosis, hybrids, photosynthesis, transpiration, stomata, drought, heat, temperature     

Simulation of Biomass Yield and Soil Organic Carbon under Bioenergy Sorghum Production

Developing sustainable management practices including appropriate residue removal and nitrogen (N) fertilization for bioenergy sorghum is critical. However, the effects of residue removal and N fertilization associated with bioenergy sorghum production on soil organic carbon (SOC) are less studied compared to other crops. The objective of our research was to assess the impacts of residue removal and N fertilization on biomass yield and SOC under biomass sorghum production. Field measurements were used to calibrate the DNDC model, then verified the model by comparing simulated results with measured results using the field management practices as agronomic inputs. Both residue removal and N fertilization affected bioenergy sorghum yields in some years. The average measured SOC at 0–50 cm across the treatments and the time-frame ranged from 47.5 to 78.7 Mg C ha⁻¹, while the simulated SOC was from 56.3 to 67.3 Mg C ha⁻¹. The high correlation coefficients (0.65 to 0.99) and low root mean square error (3 to 18) between measured and simulated values indicate the DNDC model accurately simulated the effects of residue removal with N fertilization on bioenergy sorghum production and SOC. The model predictions revealed that there is, in the long term, a trend for higher SOC under bioenergy sorghum production regardless of residue management.     

Plant genetic engineering to improve biomass characteristics for biofuels

Currently, most ethanol produced in the United States is derived from maize kernel, at levels in excess of four billion gallons per year. Plant lignocellulosic biomass is renewable, cheap and globally available at 10-50 billion tons per year. At present, plant biomass is converted to fermentable sugars for the production of biofuels using pretreatment processes that disrupt the lignocellulose and remove the lignin, thus allowing the access of microbial enzymes for cellulose deconstruction. Both the pretreatments and the production of enzymes in microbial tanks are expensive. Recent advances in plant genetic engineering could reduce biomass conversion costs by developing crop varieties with less lignin, crops that self-produce cellulase enzymes for cellulose degradation and ligninase enzymes for lignin degradation, or plants that have increased cellulose or an overall biomass yield.     

Evaluation of Public Sweet Sorghum A-Lines for Use in Hybrid Production

A fundamental need for commercialization of sweet sorghum [Sorghum bicolor (L.) Moench] as a bioenergy crop is an adequate seed supply, which will require development of hybrid varieties using dwarf seed-parent lines. A set of six public sweet sorghum A-lines (Dwarf Kansas Sourless, KS9, N36, N38, N39, and N4692) were crossed with a set of six public sweet sorghum cultivars (Brawley, Kansas Collier, Dale, Sugar Drip, Waconia, and Wray). Grain, fiber, and sugar yields were determined, and conversion formulas were applied to estimate ethanol yields. Hybrids were grown in fields at Ithaca, NE, USA, in 1983–1984 fertilized with 112 kg ha^?1 N. In terms of yield components and overall ethanol yields, one A-line, N38, was inferior. Average total ethanol yields from hybrids made on the other A-lines were not significantly different, suggesting that any of those five A-lines could be useful seed-parents. With the exception of grain yield, cultivars used as pollen parents were among the highest-performing entries for all traits. For all traits directly contributing to total ethanol yield (grain yield, juice yield, % soluble solids, sugar yield, fiber yield), hybrids were also among the highest-performing entries. Results of this study demonstrate that hybrid sweet sorghum with performance criteria equivalent to existing sweet sorghum cultivars can be produced on the sweet sorghum seed-parent lines A-Dwarf Kansas Sourless, A-KS9, A-N36, A-N39, and A-N4692. Identification of specific seed-parent × pollen parent lines with characteristics best suited for particular growing regions and end-user needs will be critical for commercial hybrid development.     

Hydrological responses of land use change from cotton (Gossypium hirsutum L.) to cellulosic bioenergy crops in the Southern High Plains of Texas,USA

The Southern High Plains (SHP) region of Texas in the United States, where cotton is grown in a vast acreage, has the potential to grow cellulosic bioenergy crops such as perennial grasses and biomass sorghum (Sorghum bicolor). Evaluation of hydrological responses and biofuel production potential of hypothetical land use change from cotton (Gossypium hirsutum L.) to cellulosic bioenergy crops enables better understanding of the associated key agroecosystem processes and provides for the feasibility assessment of the targeted land use change in the SHP. The Soil and Water Assessment Tool (SWAT) was used to assess the impacts of replacing cotton with perennial Alamo switchgrass (Panicum virgatum L.), Miscanthus × giganteus (Miscanthus sinensis Anderss. [Poaceae]), big bluestem (Andropogon gerardii) and annual biomass sorghum on water balances, water use efficiency and biofuel production potential in the Double Mountain Fork Brazos watershed. Under perennial grass scenarios, the average (1994–2009) annual surface runoff from the entire watershed decreased by 6–8% relative to the baseline cotton scenario. In contrast, surface runoff increased by about 5% under the biomass sorghum scenario. Perennial grass land use change scenarios suggested an increase in average annual percolation within a range of 3–22% and maintenance of a higher soil water content during August to April compared to the baseline cotton scenario. About 19.1, 11.1, 3.2 and 8.8 Mg ha^?1 of biomass could potentially be produced if cotton area in the watershed would hypothetically be replaced by Miscanthus, switchgrass, big bluestem and biomass sorghum, respectively. Finally, Miscanthus and switchgrass were found to be ideal bioenergy crops for the dryland and irrigated systems, respectively, in the study watershed due to their higher water use efficiency, better water conservation effects, greater biomass and biofuel production potential, and minimum crop management requirements.     

China's bioenergy potential

Despite great enthusiasm about developing renewable energy in China, the country's bioenergy potential remains unclear. Traditional utilization of bioenergy through primarily household combustion of crop residue and fuelwood is still a predominant energy source for rural China. More efficient utilization of ～300 million tons of crop residues for bioelectricity generation could add a couple of percent of renewable energy to China's total energy production. With <9% of the world's arable land supporting ～20% of the world's population, China is already a net grain importer and has little extra farmland for producing a significantly additional amount of biofuels from first‐generation energy crops, such as maize, sugarcane, and soybean. Second‐generation energy crops hold the greatest potential for bioenergy development worldwide. Miscanthus, a native perennial C4 grass that produces high biomass across almost the entire climatic zone of China, is the most promising second‐generation energy crop to domesticate and cultivate. A reasonable near‐term goal is to produce 1 billion tons of Miscanthus biomass annually from ～100 million hectares of marginal and degraded land concentrated in northern and northwestern China. This can generate ～1458 TW h electricity and mitigate ～1.7 billion tons of CO₂ emission from power coal, which account for ～45% of China's electricity output and ～28% of CO₂ emission in 2007. Furthermore, growing perennial grasses on marginal and degraded land will contribute to the ongoing efforts in China to restore vast areas of land under serious threat of desertification. With this potential taken into account, bioenergy can play a major role in meeting China's rapidly growing energy demand while substantially reducing greenhouse gas emission.     

高粱穗部主要性状的配合力分析

以4个高粱不育系13163A、1358A、128A和407A,以及6个恢复系9.1R、213R、272R、381R、矮182R和早21R为试验材料,按照不完全双列杂交设计(NCII),对其F1的穗部主要性状进行配合力分析。结果表明:亲本穗部主要性状存在显著的遗传差异,主要表现为加性基因效应遗传的性状有:穗长、一级枝梗数、二级枝梗数、穗粒数;狭义遗传力大小顺序分别为:二级枝梗数一级枝梗数穗长穗粒数穗粒重千粒重。不同亲本的一般配合力(GCA)和特殊配合力(SCA)在不同穗部性状间存在较大差异。不育系407A和恢复系早21R、9.1R是综合性状较好的亲本材料,利用它们可组配出产量较高的杂交组合。恢复系272R组配的杂交种具有穗粒数较多、千粒重较小的特点,能满足市场上对小粒高粱的需求。深入分析高粱杂交亲本穗部主要性状表现,有利于对亲本材料的进一步了解和利用。     

Genotype × environment interaction analysis of North American shrub willow yield trials confirms superior performance of triploid hybrids

Development of dedicated bioenergy crop production systems will require accurate yield estimates, which will be important for determining many of the associated environmental and economic impacts of their production. Shrub willow (Salix spp) is being promoted in areas of the USA and Canada due to its adaption to cool climates and wide genetic diversity available for breeding improvement. Willow breeding in North America is in an early stage, and selection of elite genotypes for commercialization will require testing across broad geographic regions to gain an understanding of how shrub willow interacts with the environment. We analyzed a dataset of first‐rotation shrub willow yields of 16 genotypes across 10 trial environments in the USA and Canada for genotype‐by‐environment interactions using the additive main effects and multiplicative interactions (AMMI) model. Mean genotype yields ranged from 5.22 to 8.58 oven‐dry Mg ha^?1 yr^?1. Analysis of the main effect of genotype showed that one round of breeding improved yields by as much as 20% over check cultivars and that triploid hybrids, most notably Salix viminalis × S. miyabeana, exhibited superior yields. We also found important variability in genotypic response to environments, which suggests specific adaptability could be exploited among 16 genotypes for yield gains. Strong positive correlations were found between environment main effects and AMMI parameters and growing environment temperatures. These findings demonstrate yield improvements are possible in one generation and will be important for developing cultivar recommendations and for future breeding efforts.     

Optimizing Sweet Sorghum Production for Biofuel in the Southeastern USA Through Nitrogen Fertilization and Top Removal

Sustainable bioenergy cropping systems require not only high yields but also efficient use of inputs. Management practices optimizing production of sweet sorghum [Sorghum bicolor (L.) Moench] for bioenergy use are needed. The effects of N rate (45, 90, 135, and 180?kg N?ha^?1) and top removal (at boot stage, anthesis, and none) on biomass, brix, estimated sugar yield, and N and P recovery of sweet sorghum cv. M-81E were investigated in Florida at two sites differing in soil type. Across all data, dry biomass yields averaged 17.7 Mg?ha^?1 and were not affected by N fertilization rate at either site (P?>?0.10). Mean brix values ranged from 131 to 151?mg?g^?1 and were negatively related to N rate. Top removal, either at boot stage or anthesis, resulted in greater brix values and 13% greater sugar yields at both locations. Whole plant N recovery was positively and linearly related to N rate and ranged from 78 to 166?kg N?ha^?1, approximately two thirds of which was in leaf and grain tissues. Based on yield and nutrient recovery responses, optimal nutrient requirements were 90 to 110?kg N?ha^?1 and 15 to 20?kg P?ha^?1. Higher N fertilization led to greater N recovery, but little to modest gain in sugar yield. Thus, proper nutrient and harvest management will be needed to optimize sugar yields of sweet sorghum for production of biofuels and bio-based products. Further research is needed to refine management practices of sweet sorghum for bioenergy production, especially with regard to the use of leaf and grain tissues.     

Accumulation of Biomass and Compositional Change Over the Growth Season for Six Photoperiod Sorghum Lines

Biomass sorghums [Sorghum bicolor (L.) Moench] are short-day photoperiod sensitive (PS) types, meaning that the crop will grow vegetatively late into the fall season in subtropical and temperate environments. This feature results in high biomass yield potential and mitigates drought susceptibility. The objective of this study is to assess biomass growth patterns and associated changes in composition over a growing season for PS sorghum. The experiment had a split-plot design with two replications, six PS sorghum genotypes, and 13 harvest dates. Harvest started at 60 days after planting (DAP) and continued every 15 days thereafter in both College Station (CS) and Corpus Christi (CC) in Texas, 2010. At each harvest, dry biomass yield, plant height and biomass composition (percent lignin and cellulose) were measured. For all genotypes, biomass accumulation followed a standard growth pattern which included an early lag phase, followed by a log phase of growth and finally, a general reduction in the rate of accumulation. The early lag phase ended at approximately 70 DAP, the log phase of growth ended at approximately 125 DAP, and biomass yields maximized between 180 and 225 DAP. The highest yielding genotype produced 24 Mg ha^?1. Plant heights up to 400 cm were also measured between 180 and 225 DAP. Plant height and biomass yield patterns were similar, indicating that height is important to increase yield. Lignin and cellulose concentrations increased with time; at the highest yields (between 180 and 225 DAP), maximum lignin content were 14.5 to 15.5 % and maximum cellulose content was 31 to 32 %. As with yield potential, significant differences were detected for composition as well. The growth curves indicate that PS biomass sorghum yields sufficiently and can be harvested as early as 130 DAP with maximum sorghum biomass accumulation occurring between 180 and 225 days. Thus, with careful selection and deployment of biomass sorghum hybrids, the harvest season of biomass sorghum can be extended over a 3-month period in southern regions of the US     

Biomass yield and heterosis of crosses within and between European winter cultivars of turnip rape (<Emphasis Type="Italic">Brassica rapa</Emphasis> L.)

Because of its high growth rate at low temperatures in early spring, there is renewed interest in Brassica rapa as a winter crop for biomass production in Europe. The available cultivars are not developed for this purpose however. An approach for breeding bioenergy cultivars of B. rapa could be to establish populations from two or more different cultivars with high combining ability. The objective of this study was to evaluate the heterosis for biomass yield in the European winter B. rapa genepool. The genetic variation and heterosis of the biomass parameters: dry matter content, fresh and dry biomass yields were investigated in three cultivars representing different eras of breeding by comparing full-sibs-within and full-sibs-between the cultivars. Field trials were performed at two locations in Germany in 2005–2006. Mean mid-parent heterosis was low with 2.5% in fresh and 3.0% in dry biomass yield in full-sibs-between cultivars. Mean values of individual crosses revealed a higher variation in mid-parent heterosis ranging from 14.6% to −7.5% in fresh biomass yield and from 19.7% to −12.7% in dry biomass yield. The low heterosis observed in hybrids between European winter cultivars can be explained by the low genetic variation between these cultivars as shown earlier with molecular markers. In conclusion, a B. rapa breeding program for biomass production in Europe should not only use European genetic resources, but should also utilize the much wider worldwide variation in this species.