ABSTRACT
The early growth stages of wheat are important foundations for the crop’s establishment in the field. These include the development and growth of the root system, the production of leaves and tillering, all of which have significant effects on the eventual yield. Emergence is the first visible sign of establishment and comprises the progressive stages of germination (appearance of a root radicle), subcrown internode elongation and coleoptile elongation (Jame and Cutforth, 2004). Germination is stimulated by the process of imbibition, which raises the water content of the seed to about 40% of grain dry weight (Bouaziz and Bruckler, 1989) and allows dissolved gibberellic acid to activate the aleurone layer to secrete amylase. In the endosperm, amylase hydrolyses starch into sugars, which permits respiration, and the radicle then emerges and grows downwards to anchor the seed in the soil (Blake et al., 2003). Following radicle emergence, the coleoptile elongates from the second or third node to form a subcrown internode between the coleoptile node and the node bearing the first leaf. This internode can grow to 8 cm in length and positions the crown 2-3 cm below the soil surface ensuring that the coleoptile and the tip of the first leaf emerge through the soil surface (Blake et al., 2003; Jame and Cutforth, 2004).
