Factors affecting flower abscission in field beans (Vicia faba L. minor)
A study of flower abscission in commercial varieties of faba beans grown under field conditions showed that least flower drop occurred to flowers situated on proximal flower positions and most on distal positions within every raceme. Application of stresses to plants increased flower drop, most of which occurred to flowers situated on middle and upper flower positions. Many fertilised flowers abscised and manual tripping of all flowers did not ensure a high level of pod set. Decreasing within plant competition and the application of growth regulators all reduced flower drop. An ultrastructural study showed that either abscission or pod set occurred after a series of clearly defined cellular and enzymatic changes at the pedicel/peduncle junction. Flower removal experiments demonstrated that all flowers were capable of setting a pod and that much flower drop was initiated by the presence of small proximally situated pods. Observations on plants with different floral and plant morphologies revealed two inbred lines which displayed minimal flower drop. Experiments showed that there had been no change in the gross morphology of the stem vasculature. In commercial varieties the first formed flower was, in many cases, independent of other flowers, while the second and third flowers were connected to other flowers via the vascular strands. The inbred lines possessed an independent vascular supply to all flowers within every raceme. This arrangement circumvented any communication between proximal and distal flowers, allowed for an even distribution of assimilates, so a high level of pod set was achieved. Initial experiments showed that independent vascular supply lines were more tolerant to stress. The results obtained are discussed in the thesis.