Pod-shedding habit in Medicago species, evaluated by breaking strength of pedicels

Abstract

The pod-shedding habit was evaluated as breaking strength of the pedicel in 32 populations of 11 Medicago species. Tensile strength, bending strength, and water content of pods were measured at intervals during pod maturing. Both breaking strengths increased with pod growth, and decreased with pod desiccation in all populations. The tensile strength was highly correlated with pedicel diameter 20 days after flowering, but the correlation decreased at ripening. Microscopic observation revealed that some populations developed abscission tissue at the base of pedicel during maturation. In these populations, the pod detached at low breaking strength. The breaking strength at ripening was compared between the populations with spiny and smooth pods, and no difference in pod-shedding habit was observed between the two types. Principal component analysis, however, separated 32 Medicago populations into four groups, smooth pod type with an easy-shedding habit, smooth pod type with a shedding tolerance, spiny pod type with easy-shedding habit, and spiny pod type with the shedding tolerance.