Cell wall diversity in forage maize: genetic complexity and bioenergy potential

Genetic studies are ideal platforms for assessing the extent of genetic diversity, inferring the genetic architecture and evaluating complex trait inter-relations for cell wall compositional and bioconversion traits relevant to bioenergy applications. Through the exhaustive characterization of a forage maize doubled haploid (DH) population, we have revealed the vast degree of highly heritable (h²>~65%) diversity in cell wall composition, polymeric ultrastructure and bioconversion potential available within this model grass species. In addition to variation in lignin content, extensive genotypic diversity was found for the concentration and composition of hemicelluloses; the latter found to exert an influence on the recalcitrancy of maize cell walls. Our results also demonstrate that forage maize harbors considerable variation for the release of cell wall glucose following pretreatment and enzymatic saccharification. In fact, the extent of variability observed for bioconversion efficiency (nearly 30% between population extremes) greatly exceeded ranges reported in previous studies. In our population, genotypic diversity for cell wall composition and quality was found to be controlled by 52 quantitative trait loci (QTLs). Noteworthy, from 8 QTLs regulating bioconversion properties, 5 were previously unidentified and warrant further investigation. Ultimately, our results substantiate forage maize germplasm as a valid genetic resource for advancing cell wall degradability traits in bioenergy maize breeding programs. However, since useful variation for cell wall traits is defined by QTLs with "minor" effects (R²=~10%), cultivar development for bio-based applications will rely on advanced marker-assisted selection procedures centered on detecting and increasing the frequency of favorable QTL alleles in elite germplasm.