Population regulation of Rhodesgrass cultivars in sward conditions. II. Tiller density.
Chloris gayana cv. Katambora, Fords Katambora, Kyushu 1, Kyushu 2 and Kyushu 3 (diploid cultivars) and Boma and Callide (tetraploid) were sown at 350, 700, 1400 or 2500 seeds/m2 on 18 May in field trials at Kumamoto, Japan in 1984. Swards were cut to a height of 5 cm on 21 June, 16 July, 17 Aug. or 26 Sep. Genet density was recorded in each plot on 7 June. In general, mean tiller number per surviving genet increased during the experiment. Relative tiller appearance rate (rTAR) or surviving genets depended on sowing density in the early stage of sward establishment but was independent of genet density after sward establishment. There were some differences among cultivars in rTAR. As a result of two density-dependent processes during sward establishment, i.e. mortality of genets and tillering of surviving genets, tiller density converged toward a value which was characteristic of the cultivar but independent of the initial sowing density. Despite conspicuous differences among cultivars in individual tiller weight at the end of the year as well as in tiller density, there was no significant difference among cultivars in stand yield. This was because of a close negative relationship between the two component characters of stand yield. It is concluded that although the tiller density of a heterogeneous population is not qualified as a phenotypic character in genetics, in practice its application for heterogeneous cultivars could be of value in describing cultivar performance in sward conditions.