Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop Exploiting pre- and post-harvest metabolism in sweet sorghum genotypes to promote sustainable bioenergy production Christos E. Vlachos a,1 , Ourania I. Pavli b,1, *, Emmanouil Flemetakis c , George N. Skaracis a a Agricultural University of Athens, Department of Crop Science, Iera Odos 75, 11855 Athens, Greece b University of Thessaly, Department of Agriculture Crop Production and Rural Environment, Fytokou, 38446, Volos, Greece c Agricultural University of Athens, Department of Biotechnology, Iera Odos 75, 11855 Athens, Greece ARTICLE INFO Keywords: Sweet sorghum Sugars metabolism Metabolomics Transcriptomics Biofuel conversion Harvesting window ABSTRACT Sweet sorghum's high yielding ability, low-input demands and tolerance to stresses, render it highly suitable for syrup and bioenergy production. Exploiting its biomass, however is hampered by the seasonality of its pro- duction and the rapid post-harvest sugar catabolism degrading biomass quality. We aimed at elucidating aspects of sweet sorghum’s metabolism at different developmental and post-harvest stages, to investigate possibilities of expanding the harvesting window. GC–MS-mediated metabolic profiling was employed to monitor changes across growth stages and targeted transcriptomic analysis was used to determine the expression of genes in- volved in sucrose metabolism. Changes were studied both in the leaves and stems before, during and after the stage considered as optimum for harvest, whereas harvested stems were analyzed to determine post-harvest changes. Significant alterations in the levels of sugars, amino acids and organic acids were found, sugar levels attaining a maximum at soft dough stage. Overall data suggest that sugar metabolic content is regulated at transcriptional level, while temporal regulation of development and sucrose metabolism is under strong geno- typic dependency. Although total sucrose levels were relatively lower at stems harvested one month past the optimum stage or harvested on time and piled for one month, compared to the optimum stage, losses en- countered are adequately compensated by the prolonged period of biomass supply to the processing plants. It becomes evident that fine tuning of crop's harvesting and delivery time could significantly contribute to relaxing seasonality-related bottlenecks, thus upgrading the economic operation of plants utilizing sweet sorghum as a bioenergy crop. 1. Introduction In recent years, sweet sorghum [Sorghum bicolor (L.) Moench.] is increasingly gaining interest for the production of new age biofuels, mainly bioethanol and biogas (Hansen and Ferraris, 1985; Rooney et al., 2007; Antonopoulou et al., 2008; Regassa and Wortmann, 2014; Salimbeni, 2013; Mathur et al., 2017). Features that placed sweet sor- ghum well among the most promising candidates for biofuel feedstock include its short life cycle, its high biomass yield, its low input re- quirements and wide adaptation which renders it capable of growing on marginal lands (Rooney et al., 2007; Mathur et al., 2017). More im- portantly, the crop is characterized by a high cumulative potential for sugars, in the form of juice, which can be directly fermented to ethanol. Accumulation of juice may reach up to 78 % of its total biomass, while soluble sugars, measured in Brix units, range from 14 to 23 % (Almodares and Sepahi, 1996; Vinutha et al., 2014). In this context, the trait of stem sugar concentration in elite sweet sorghum cultivars has reached a high plateau, therefore setting the improvement of stem juice yield, and specifically its two determining components i.e. stem juici- ness and stem fresh weight, as the main breeding target for increased sugar yield (Murray et al., 2008). The abovementioned features, cou- pled with the fact that sweet sorghum is not competitive with food crops for arable land, underline the possibility for its sustainable ex- ploitation as biofuel feedstock and simultaneously strengthen the need to further improve the suitability of its candidacy in order to meet current and future challenges. Despite its advantages over starch based feedstocks, as it provides directly exploitable sugars, the economic viability and sustainability of sweet sorghum’s biofuel value chain is strongly influenced by the crop’s high seasonality. The limited period of raw material availability https://doi.org/10.1016/j.indcrop.2020.112758 Received 20 January 2020; Received in revised form 24 June 2020; Accepted 3 July 2020 ⁎ Corresponding author. E-mail addresses: vlachoschrist@yahoo.gr (C.E. Vlachos), ouraniapavli@uth.gr (O.I. Pavli), mflem@aua.gr (E. Flemetakis), gskaracis@aua.gr (G.N. Skaracis). 1 These authors contributed equally to this work. Industrial Crops & Products 155 (2020) 112758 0926-6690/ © 2020 Elsevier B.V. All rights reserved. T