Tillering & Vegatative Growth
Branching in small grains is called tillering or stooling. Individual branches are called tillers, and the mass of tillers is the stool. Two to four primary tillers develop from buds in the crown area of the main stem. Secondary tillers develop from buds in the axils of leaves at the base of the primary tillers. Tertiary tillers may develop from buds in the axils of leaves at the base of the secondary tillers. Each plant has the potential to produce more than 50 tillers. Usually only two to four tillers survive to produce fertile spikes at normal seeding rates and growing conditions. The number of tillers that form is influenced by plant density (more with low plant density), soil moisture and nutrient supply (more with high supply), sowing date (more with early sowing), temperature (more under cooler temperatures), and cultivar. Water stress, nutrient deficiency, low temperatures, weed competition, and pest damage during early devel- opment reduce the number of tillers.
The emergence of primary tillers is synchronous with the emergence of leaves
on the main stem of the plant. The first primary tiller begins developing as leaf 4 of the main stem emerges; the second primary tiller begins developing as leaf 5 emerg- es. Subsequent primary tillers begin developing when subsequent leaves emerge. Successive tillers develop fewer leaves; flowering and grain development is only slight- ly delayed on later-developing tillers. Before the main stem and tillers begin to elon- gate, the spikes (panicles in oat) differentiate. The precursors (primordia) of all florets (flowers with lemma and palea, the outer bracts) or spikelets (units consisting of sev- eral florets on a thin axis, subtended at the base by two bracts, or glumes) develop at this time. In wheat and oat, formation of new spikelets ends with the formation of the terminal spikelet, which usually occurs when leaf 6 appears. A terminal spikelet is not formed in barley.
Wheat, barley, and oat appear very similar in the vegetative stage. However, they can usually be easily distinguished based on auricle (a pair of clawlike projections at the junction of the leaf sheath and blade) characteristics. On barley, the auricles are long and clasping; on wheat, the auricles are short; on oat, auricles are absent.