Productivity of a Dwarf Type Soybean Induced by Mechanical Stimulation Applied during Vegetative Stage

Abstract

As an attempt for better understanding the relationship between canopy architecture and seed production, the upper portions of the canopy, cv. Kitahomare, were mechanically stimulated during the period from the fifth trifoliolate leaf stage to the young pod stage, and its effect and after effect on morphology, canopy structure, light penetration, growth and yield was investigated. Mechanical stimulation inhibited growth of the main stem, but promoted that of the lateral branches ; the main stem-branch ratio of dry matter in each part was 1:1 in unstimulated control plants, but 1:2 or more in stimulated plants at the end of the treatment. Morphologically, stimulated plants had 1) shorter, thicker and sturdier stems, 2) smaller and thicker leaves with shorter petioles, and 3) greater a number of branches when compared with the controls ; thus modified to a typical dwarf type form. After the treatment has finished, stimulated plants showed a typical table type canopy throughout the pod filling period, but their light extinction coefficients were smaller than those of controls. The pod development was retarded by the treatment during the flowering stage. Stimulated plants, however, showed higher net assimilation rates and pod filling rates, and produced more pods than controls, resulted in 38% greater seed production at maturity, because of a greater increase in branch quantity. A plant form such as dwarf type with smaller sized leaves may be advantageous for high yielding under high population densities that cause a severe mutual shading and risks of lodging.