Linking pod-set and seed yield of faba bean across organ, phytomer, plant, and population scales

Pod-set is the conversion of flowers to pods, but its connection to crop yield of pulses must traverse scales of biological organization; here we address scaling from organ to crop in faba bean. We hypothesized that crop-level resource capture drives pod-set and yield of faba bean, whereas allocation to pods or between pods plays a minor role. We combined new field experiments and published data to test supporting hypotheses in four studies. We showed that node-level pod-set is not modular but is coordinated across the whole plant. Crop yield and pods per m2 were associated with crop growth in our data, not with plant growth or supposed competition between plants or pods. Seed number, seed size, and pod wall mass had yield-neutral trade-offs. Indeterminate shoots facilitate resource capture, and, surprisingly, fruit removal could increase yield by up to 49% when it allows continued growth and resource capture. We concluded that pod-set is mainly dependent on crop growth but could be targeted for its feedback to post-flowering phase duration. Our work provides conceptual links between plant reproductive biology and crop yield that could be relevant to other indeterminate crop species.