Optimizing harvest timing in rapeseed (Brassica napus L.): Balancing oil yield, metabolic quality, and field efficiency

Harvest timing critically influences the oil content and nutritional value of Brassica napus L., a globally vital oilseed crop. This study examines the trade-offs between combined harvesting (direct harvest at maturity) and two-stage harvesting (early cutting followed by field ripening) on seed oil metabolism and secondary metabolites. Three two-stage treatments—cutting plants at 23, 29, or 35 days after final flowering (DAFF) followed by 3–12 days of field ripening—were evaluated. Late two-stage harvesting (35 DAFF) preserved oil content at levels equivalent to combined harvesting, whereas early cutting (23 and 29 DAFF) reduced oil yield by 5.0 % and 2.3 %, respectively, in the ZS11 variety. Mechanistic analyses revealed that early harvesting disrupted photosynthesis through downregulation of key genes (PsbO, PsbP, PsbQ, and antenna proteins) and suppressed fatty acid biosynthesis, while accelerating fatty acid degradation. Early two-stage harvesting impaired flavonoid biosynthesis by markedly suppressing the expression of critical genes (e.g., TT18 and BAN), leading to reduced levels of key flavonoid metabolites such as epicatechin. Interestingly, while this led to lower DPPH radical-scavenging activity, early harvesting triggered a compensatory antioxidant response, boosting peroxisome activity and vitamin content, suggesting a shift in antioxidant strategies. Crucially, late two-stage harvesting (35 DAFF with 6–9 days ripening) achieved optimal outcomes: oil and metabolite profiles comparable to combined harvesting, coupled with earlier field clearance that facilitates crop rotation. These results provide actionable insights for farmers and processors aiming to maximize both oil yield and metabolic quality in rapeseed production.