Annals of Botany 90: 99-110, 2002
© 2002 Annals of Botany Company
Tillering in Grain Sorghum over a Wide Range of Population Densities: Modelling Dynamics of Tiller Fertility
1 CIRAD-CA, Programme cultures alimentaires, TA 70/01, avenue Agropolis, 34398 Montpellier Cedex 5, France, 2 Agricultural Production Systems Research Unit, Queensland Dept. Primary Industries, Toowoomba, Qld 4350, Australia and 3 School of Land and Food Sciences, University of Queensland, Brisbane, Qld 4072, Australia
* For correspondence. Fax + 33 4 67 61 56 93, e-mail tanguy.lafarge{at}cirad.fr
Received: 17 September 2001; Returned for revision: 22 November 2001; Accepted: 28 March 2002
The prediction of tillering is poor or absent in existing sorghum crop models even though fertile tillers contribute significantly to grain yield. The objective of this study was to identify general quantitative relationships underpinning tiller dynamics of sorghum for a broad range of assimilate availabilities. Emergence, phenology, leaf area development and fertility of individual main culms and tillers were quantified weekly in plants grown at one of four plant densities ranging from two to 16 plants m–2. On any given day, a tiller was considered potentially fertile (a posteriori) if its number of leaves continued to increase thereafter. The dynamics of potentially fertile tiller number per plant varied greatly with plant density, but could generally be described by three determinants, stable across plant densities: tiller emergence rate aligned with leaf ligule appearance rate; cessation of tiller emergence occurred at a stable leaf area index; and rate of decrease in potentially fertile tillers was linearly related to the ratio of realized to potential leaf area growth. Realized leaf area growth is the measured increase in leaf area, whereas potential leaf area growth is the estimated increase in leaf area if all potentially fertile tillers were to continue to develop. Procedures to predict this ratio, by estimating realized leaf area per plant from intercepted radiation and potential leaf area per plant from the number and type of developing axes, are presented. While it is suitable for modelling tiller dynamics in grain sorghum, this general framework needs to be validated by testing it in different environments and for other cultivars.
Key words: Sorghum bicolor L. Moench, plant density, thermal time, tiller emergence, cessation of tiller emergence, tiller fertility, leaf area index, source–sink relationships.
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