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With increasing environmental pressure and soil pollution, sustainable energy and food production for a steadily growing world population is a grand challenge. Globally, nearly 12 million hectares of croplands are contaminated by cadmium (Cd), and how to develop a production system for the cleaning and utilisation of such contaminated land is essential for sustainability. Herein, a diverse panel of 166 sorghum accessions was grown in typical Cd-contaminated fields in two consecutive years, and the effect of different accessions and organs on the phytoremediation potential was evaluated by analysing the Cd concentrations of stems, leaves and grains at maturity. Both the bioaccumulation factors (BCFs) and the aboveground Cd accumulation varied substantially and the differences were up to 13–24 fold. The aboveground Cd accumulation was positively associated with important bioenergy traits including biomass, stem Brix, internode numbers and plant height, as envisaged by the high Cd concentration in sweet sorghum accessions, while BCF was significantly negatively correlated with relevant agronomic traits except Brix. The genetic regulation of Cd concentration in grains is different from those in leaves and stems, which allowed us to screen for three types of sorghum resources with the potential to couple soil phytoremediation with the production of bioethanol, safe grains and forage. A sorghum farming system was further proposed, which could reduce soil Cd concentration below the safe level within 12 years and obtain economic returns of about 70.5–169.5 million Chinese Yuan (CNY) by producing bioethanol, safe grains and forage in one season in 30% of the Cd-contaminated soil in China. A sorghum farming system for phytoremediation of cadmium-contaminated soil and safe crop production. Image 1 • Large variation was found in Cd concentration and accumulation amongst diverse sorghum accessions. • Three types of sorghums were selected to couple phytoremediation with the production of bioethanol, safe grain and forage. • A sorghum farming system is proposed for remediation of Cd-polluted soil within 12 years with considerable economic benefit. [ABSTRACT FROM AUTHOR]

Key Message: Eight morphological, biomass and biofuel traits were found with high broad-sense heritability and 18 significant QTLs discovered including one locus controlling the stem juice trait for sorghum grown in Denmark and China. Sweet sorghum with tall plant, fast maturation and high stem Brix content can be bred as a biofuel crop for Northern Europe. Sweet sorghum (Sorghum bicolour), a native tropical C4 crop, has attracted interest as a bioenergy crop in northern countries due to its juice-rich stem and high biomass production. Little is known about the traits important for its adaptation to high altitude climatic conditions and their genetic controls. Recombinant inbred lines derived from a cross between a sweet and a grain kaoliang sorghum were used in five field trials in Denmark and in China to identify the stability and genetic controls of morphological, biomass and biofuel traits during three consecutive summers with short duration, cool temperatures and long days. Eight out of 15 traits were found with high broad-sense heritability. Strong positive correlations between plant height and biomass traits were observed, while Brix and juice content were under different genetic controls. Using newly developed PAV (presence and absence variant) markers, 53 QTLs were detected, of which 18 were common for both countries, including a locus controlling stem juice (LOD score = 20.5, r (2) = 37.5 %). In Denmark, the heading stage correlated significantly with biomass and morphology traits, and two significant maturity QTLs detected on chromosomes SBI01 and SBI02 co-localised with QTLs previously associated with early-stage chilling tolerance, suggesting that accelerating maturation might be a means of coping with low-temperature stress. Our results suggest that selection for tall and fast maturating sorghum plants combined with high Brix content represents a high potential for breeding bioenergy crop for Northern Europe.