Eco-Morphological Investigations on Tiller Development and Rhizome Formation in Kentucky Bluegrass (Poa pratensis L.) for the Higher Yielding and Better Grazing Performance in Japan.

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Sward growth and tiller population dynamics of simulated Kentucky bluegrass (KBG) swards which were grown in plastic containers with vermiculite culture and defoliated in 2-week- and 4-week-interval were studied in 1995 and 1996. Developmental morphology of tillers and rhizomes of sampled KBG plants was also observed.(1) KBG plants began to tiller aboundantly soon after the establishment of simulated swards (KBG seedlings were transplanted in July 1995) and continued to generate new tillers until the first defoliation of swards made in early September, when tiller density reached ca.7,000/m^2. Then, the tillering stopped almost completely, probably because of attained dense population and warmer temperatures causing active top growth. Coming into the dormant state in November with lowered temperature and shortened day-length, KBG plants again began to tiller, continued to increase tiller number during the winter, and finally got nearly 30,000 tillers/m^2 at the first harvest in next sp … More ring. However, this dense tiller population gradually declined during the growing period from spring to early summer, and then, they abruptly decreased in hot summer periods which lasted about 50 days. Decreased tiller number was recovered very quickly in autumn of 1996 by active tillering of tops and crown formations which were derived from the anti-geotropic turn of creeping rhizomes.(2) In spite of the heavy growth depression in summer and its infection in autumn growth, the total dry matter yield in 1996 both in 4-week- and 2-week-cut sward was rather rich, each accumulated ca.2400 g.DM/m^2 and 1600 g.DM/m^2 herbage, respectively. This higher yielding level of frequently defoliated KBG swards should be mainly derived from the dense tiller population and the quicker leaf formation (about 7 days/leaf) on each existent tiller.(3) There was a distinct regularity that the appearance of each 'n'th leaf (as numbered acropetally) on growing tiller clearly synchronized with the appearance of first leaf of each successive tiller subtended by the leaf 'n-2' of mother shoot. The tiller bud which failed to elongate as a regular tiller stayd in dormant state, and some of them turned to form rhizomatous shoot apex and sprouted with a horizontal growth, mainly at the base of aerial tillers. These rhizomes changed the elongating direction upwards after the development of 15 to 20 phytomers with 15 to 20 cm rhizome length, and turned into an aerial crown at the soil surface and began to tiller regularly as preceding aerial tillers. With this morphological character, KBG plants might easily form a dense, stable tiller population throughout the seasons. Less