Biomass Engineering in Field Crops Using Genetic Tools: A Critical Appraisal of Targets, Trade-offs and Translational Evidence

Abstract

Biomass is simultaneously the substrate of grain yield, the raw material of forage and bioenergy systems, and the largest reservoir of harvestable carbon in arable landscapes. Genetic tools now permit unprecedented precision in altering how much biomass a crop accumulates and what that biomass is made of, yet the translation of such precision into field-validated agronomic gain remains uneven. This review critically evaluates the evidence base for genetic biomass engineering in field crops, defined here as annual and short-cycle cereals, legumes, oilseeds, forages and cane crops grown at agronomic scale, together with the perennial grasses that supply the conceptual models for grass cell wall manipulation. Literature was identified through a structured search of bibliographic and full-text scholarly sources and through backward and forward citation tracing, and was appraised for methodological adequacy, replication and ecological relevance rather than citation count alone. Four analytical themes emerge. First, interventions on biomass quantity through photosynthetic, architectural and nitrogen-economy targets produce the most robust field evidence when they relieve a demonstrated limitation, and the weakest when a source limitation is assumed rather than established. Second, interventions on biomass quality, principally lignin content and composition, hydroxycinnamate acylation and matrix polysaccharide structure, deliver consistent and mechanistically well-understood improvements in digestibility and saccharification, yet the magnitude is frequently modest once pretreatment and processing context are considered. Third, a recurring trade-off architecture links cell wall modification to lodging, pathogen and insect susceptibility, and altered water relations, and these costs are systematically underdetected in controlled environments. Fourth, the greenhouse-to-field gap, rather than editing efficiency, is now the rate-limiting step. Confidence in current conclusions is constrained by the scarcity of multi-environment field evaluation, the geographical concentration of evidence, and the dominance of model species. Priorities include multi-season field validation of edited alleles in elite backgrounds, explicit quantification of defence and mechanical penalties, and integration of biomass targets into breeding pipelines rather than their pursuit as isolated transgenic demonstrations.