FLORAL INITIATION, LEAF INITIATION AND LEAF APPEARANCE IN SUNFLOWER

This paper examines the hypothesis that leaf number visible at floral initiation (LN(fi)) and final leaf number (FLN) are correlated in sunf lower (Helianthus annuus L.). The relationship between these variables is described by a model that takes into account the rate of leaf prim ordium initiation (RPI), the rate of leaf appearance (RLA) and time fr om emergence to floral initiation (FI). Data from glasshouse and field experiments were used to test the model. Combination of eight hybrids and four inbred lines and a wide range of growing conditions yielded values from 4 to 20 for LN(fi) and from 12 to 42 for FLN. The observed relationship between LN(fi) and FLN was in good agreement with the th eoretical model. A constant RLA:RPI ratio underlies the association be tween LN(fi) and FLN, and suggests that leaf initiation and appearance are co-ordinated processes. The relationship between LN(fi) and FLN i s proposed as a non-destructive method to estimate the time of FI.