title: Regulation of tillering in sorghum: environmental effects.
abstract: OBJECTIVE
  Tillering has a significant effect on canopy development and, hence, on resource capture, crop growth and grain yield in sorghum. However, the physiological basis of tillering and its regulation by environmental effects are not fully understood. The objective of this study was to understand and quantify the environmental effects on tillering in sorghum using a carbohydrate supply-demand framework.
  
  
  METHODS
  A series of five experiments with a wide range of radiation and temperature conditions was conducted and details of the tillering responses of a single representative hybrid were monitored. The concept of internal plant competition for carbohydrate was developed for analysis of these responses.
  
  
  RESULTS
  Tiller appearance was highly synchronized with main shoot leaf appearance, with a consistent hierarchy for tillering across environments. The main environmental effect was on the frequency of tiller appearance, in particular of the lower-rank tillers. This explained some of the observed environmental differences in the onset of tillering. A generalized index of internal plant competition, which took account of plant assimilate supply and demand (S/D(index)) during the critical period for tillering, explained most of the variation in maximum tiller number observed across the five experiments.
  
  
  CONCLUSIONS
  This result was consistent with the hypothesis that internal plant competition for assimilates regulates tillering in sorghum. Hence, the framework outlined has a predictive value that could provide the basis for dynamic simulation of tillering in crop growth models.
authors.affiliation: The University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Hae Koo
authors.initials: HK
authors.lastname: Kim
authors.forename: Erik
authors.initials: E
authors.lastname: van Oosterom
authors.forename: Michael
authors.initials: M
authors.lastname: Dingkuhn
authors.forename: Delphine
authors.initials: D
authors.lastname: Luquet
authors.forename: Graeme
authors.initials: G
authors.lastname: Hammer
mesh_terms: D008962:Models, Theoretical; D018515:Plant Leaves / Q000254:growth & development; D045868:Sorghum / Q000254:growth & development*; D013696:Temperature