Potentiality of dry matter production and overwintering ability in dwarf napiergrass [Pennisetum purpureum] introduced from Thailand

The present research was aimed to investigate the growth characteristics in relation with dry matter production and overwintering ability in the field-grown dwarf napiergrasses, as compared with the normal ones for assessing the potentiality of growing dwarf napiergrass in Miyazaki, southern Kyushu, Japan. Two normal varieties of Wruk wona (Abbreviated as Wr) and Merkeron (Me), and two dwarf ones of early heading (D-E) and late heading (D-L) were transplanted at the density of 4 plants/ m2 by one tiller per plant. Growth characteristics and dry matter production were investigated every month through to late October, 1997 and overwintering ability was inspected in March and April, 1998. At the end of the growth season, plant length, top dry weight and mean tiller weight were the highest in normal napier, Wr, followed by Me, D-E and D-L, but the difference in leaf area index was small among the varieties and thus the dry weight percentage of leaf blade to the whole top was higher in the dwarf varieties than the normal ones. Particularly, tiller number was higher in D-L than other three varieties. Dwarf varieties tended to have the comparative leaf development with the lower net assimilation rate, which resulted in the lower crop growth rate than the normal varieties. At the end of the growth season, dwarf varieties tended to have leaf blades with shorter length, slightly smaller width, smaller area and dry weight, and larger specific leaf area than the normal. As for the internode, dwarf varieties had shorter internode length especially at the lower nodal positions before its stem-elongation. The sum of internode dry weight among the elongated nodal positions was linearly related with the sum of its volume, which suggested that the stem dry weight, the major part of plant dry weight, was primarily determined by the internode volume. In the dwarf varieties, the dry matter production, associated with the enlargement in internode volume was suggested to be suppressed severely by its dwarfism. Dwarf varieties had the similar overwintering ability with the normal, reaching above 80 % of the overwintered plants, irrespective of cutting at either pre- or post-wintering. Thus, dwarf napiergrass was assessed to have some productive potentiality as the perennial plant in Miyazaki, if it should be planted at the higher planting density than the ordinary one for compensating the lower individual plant growth