Bushy, a dominant pea mutant characterised by short, thin stems, tiny leaves and a major reduction in apical dominance

Abstract

The spontaneous, single-gene dominant, pea (Pisum sativum L.) mutant bushy is characterised by short, thin stems, tiny leaves and a proliferation of basal lateral branches. We symbolised the dominant mutant allele bsh and the recessive wild-type allele BSH. Some effects were very large, e.g. the reduction in internode length was around 10-fold in pure mutant plants. The effect on branching was qualitative under our conditions as the wild-type did not branch and the mutant branched extensively. Analysis of epidermal cells indicated the reduction in internode length arose principally from a reduction in cell length. The bushy mutation also altered root morphology with a reduction in the number and length of lateral roots. Time to first open flower was increased but node of flower initiation was not affected. In a few cases, bushy plants died before producing an open flower even though tiny abortive flower buds were produced in the upper leaf axils. In pure mutant plants, individual seed weight was reduced by 30%, number of seeds per pod was reduced 3-fold, and seed number per plant was reduced 4-fold. However, pod size was essentially normal for a given seed content, and the flowers were fertile and of normal structure. Grafting studies showed the primary action of the bushy mutation occurred in the shoot. In summary, the reduced cell and shoot elongation, loss of apical dominance and a primary action in the shoot, all point toward auxin deficiency (or perceived deficiency) as a possible cause of the bushy phenotype. The overall characteristics of bushy make it a useful mutant for research on plant development.