Abstract
AbstractSweet and biomass sorghum are expected to contribute increasingly to bioenergy production. Better understanding the impacts of the genotypic and environmental variabilities on biomass component traits and their properties is essential to optimize energy yields. This study aimed to evaluate whether traits contributing to stem biomass growth and biochemical composition at different biological scales (co)vary with the genotype and the water status in sorghum. Height genotypes were studied over two years in field conditions in southern France under two water treatments (well watered vs. 25 days’ dry down during stem elongation). Main stem internode number, size, (non)structural carbohydrate, and lignin contents were measured at the end of the stress period and/or at final harvest, together with biochemical and histological analyses of the youngest expanded internode. The tallest genotypes showed the highest stem dry weights and lignin contents. Stem (structural) biomass density was positively correlated with lignin content, particularly in internode parenchyma. Stem soluble sugar and lignin contents were inversely proportional across genotypes and water conditions. Genotypes contrasted for drought sensitivity and recovery capacity of stem growth and biochemical composition. The length and cell wall deposition of internodes expanding under water deficit were reduced and did not recover, these responses being weakly correlated. Genotypic variability was pointed out in the growth recovery of internodes expanding under re‐watered conditions. According to the observed genotypic variability and the absence of antagonistic correlations between the responses of the different traits to water availability, it is suggested that biomass sorghum varieties optimizing their responses to water availability in terms of growth and cell wall deposition can be developed for different bioenergy targets.
Highlights
The quality of biomass sorghum production relies on stem biomass lignocellulosic composition, soluble sugar content, and digestibility (Trouche et al, 2014)
The eight studied genotypes exhibited a reduction of the length, the number, and the cell wall content and an increase in soluble sugar accumulation of internodes expanded during the water deficit period
Preliminary results at internode tissue level suggested that the reduction of internode lignin content by water deficit occurred both in the inner part and in the outer part of the internode, but more strongly in Z2 (Table 5: reduction in average of 60% and 40%, respectively, for %RedZ2 and %RedZ1)
Summary
Sorghum is increasingly used as a biomass crop to meet societal expectations in terms of bioenergy [bioethanol of first (Ebrahimiaqda & Ogden, 2018) and second (Mitchell et al, 2016) generations, methane (Mahmood & Honermeier, 2012; Thomas et al, 2017), bio‐based materials (Chupin et al, 2017; Vo et al, 2017) and forage productions in many regions worldwide United States: (Rooney, Blumenthal, & Bean, 2007); Europe: (Tuck, Glendininga, Smith, Housec, & Wattenbach, 2006); China: (Fu, Meng, Molatudi, & Zhang, 2016); and West Africa: (Tovignan, Luquet, et al, 2016)]. Previous studies reported different extents of relationships between stem size (mainly height) and lignocellulosic composition and suggested they are genetically and/or physiologically linked (Trouche et al, 2014) To our knowledge, this relation was not addressed with respect to Genotype × Environment interactions (G × E) in response to drought. This suggests that, organ growth and biochemical composition are linked at cell level due to the relation between cell expansion, wall thickening, and anatomy (Le Gall et al, 2015), their respective variation with the genotype and the environment should be in part independent This has strong implications for the breeding of biomass crops commonly cultivated under resource‐limited conditions ( water deficit) such as sorghum, where the objective is to maximize stem biomass yield while ensuring a biochemical composition appropriate for a given end use. Eight sorghum genotypes differing for their biomass yield and stem lignocellulosic composition were studied in the field over 2 years
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