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

Abstract

Pod-set is the conversion of flowers to pods but its connection to crop yield of pulses must traverse scales of biological organisation; here we address scaling from organ to crop in faba bean. Our main hypothesis was that resources drive pod-set and crop 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 organised in four studies. We found that pod-set is organised at the whole plant scale, not individual node scale, and associates with crop growth, not supposed competition between pods. Indeterminacy facilitates resource capture and yield, and, surprisingly, fruit removal could increase yield by up to 49 % when it allows continued growth and resource capture. Seed number, seed size and pod wall mass had yield-neutral trade-offs in our data. Crop yield and pods per m2 are associated with growth at the population, not plant, scale. We concluded that pod-set is dependent on crop growth but could be targeted for its feedback to post-flowering phenology and growth of plants. Our work provides conceptual links between plant reproductive biology and crop yield that could be relevant to other indeterminate crop species.