Faba-bean (Vicia faba L.) - Physiology and Genetics

"When compared with a trim, modern cereal field, a bean field at harvest is spectacularly untidy, with a dense canopy, often badly lodged and prone to pests and diseases. When individual plants are examined their yield of pods and seeds seems meagre from such a profusion of leaves". In a functional sense, yield formation is the result of 1. dry matter production and 2. partitioning dry matter into grains and other organs. As outlined in the preceding article, dry matter production may be regarded as the product of light interception and light use efficiency. Light-use efficiency is influenced by physiological traits such as stomatal conductance, stomatal density, osmotic adjustment to drought, by the efficiency of N-fixation or nutrient uptake, by the efficiency of the photosynthetic pathway etc. Information on genetic variability of light use efficiency is sparse but apart from mutants like the st- and ti-it is questionable whether there are useful differences. Even the prospects for the st- and the ti-result only from their improved lodging resistance and their reduced height, not from specific physiological advantages. Light interception is likely to be much more variable since it is the result of a genotype's partitioning strategy: A long vegetative phase will lead to a large amount of intercepted light. Dry matter partitioning into reproductive structures depends on their number, their individual size and the time, strength and duration of their activity as sinks. So, accelerated flowering and the formation of an increased number of seeds at the lower nodes are likely to divert more assimilates into reproductive organs. On the other band, canopy development may remain incomplete and consequently light interception and dry matter production will be suboptimal.