Leaf appearance on a tiller is estimated according to a ‘broken stick’ approach based on the phyllochron concept described by Inman- Bamber (1994a). Two phyllochron intervals (i.e., the thermal time cumulated between successive leaf tip appearance) are defined with cultivar parameters (PI1 and PI2, °C-day) applied before and after a leaf number threshold (PSWITCH, cultivar parameter), respectively. Total number of leaves per tiller (TNLF) is then obtained according to the following relationship:

where is the thermal time for leaf emission, cumulated starting from tiller appearance day and based on a ecotype parameter (TTBASELFEX, °C). The “broken-stick” shape is given in the graph below, as an example, with TTBASELFEX = 10 °C, PI1 = 69 °C-day and PI2 = 169 °C-day, and PSWITCH = 18.

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