Trends of population density of standing tillers, and developmental morphology of stolons and aerial-tillers in Japanese Iawn grass (Zoysia japonica Steud.) growing in sward conditions.

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Standing tiller densities in frequently defoliated Japanese lawn grass (Zoysia japonica Steud.) populations were generally kept at very high level around 15,000/m^2, and revealed quite excellent contrast to those of Festucoid grasslands cultivated in Japan where initial plant densities tend to decrease quickly during actively growing periods after the establishment. Besides, Zoysia swards examined often showed their ability to realize relatively prominent yield even under frequent defoliations.Principal part of aerial-tillers that constructed the above mentioned dense population of Zoysia was composed of so-called Ta tillers which vigorously generated from the lower nodes of every multiple-node of stolons. In contrast with this, regular emergence of Tb tillers which located one node above the Ta tillers seemed to be rare, as a larger part (nearly 80%) of Tb buds stayed dormant for a longer period during the seasons. Under highly frequent defoliations as conducted in the present study, secondary and tertiary tillers appeared rather freely from the leaf axils of aged and senescing Ta and Tb tillers, and so they supplemented 20 to 30% of total existing tillers.The formation of multiple-node and extension growth in each stolon growing under a sward condition was suppressed strongly as compared with those of single-plants ; average number of multiple-nodes formed per year was ca. 20 and total stolon elongation was around 30 cm. In anatomical investigation in this study, a distinct difference of development was clearly observed between Ta and Tb buds near the apex of each stolon. The differential tiller bud initiation commenced in Ta and Tb tiller buds, both attaching to the same multiple-node, seems to be one reason to result the following diverse development of Ta and Tb tillers.