Estimation of potential tiller production and site usage during tall fescue canopy development

Tiller appearance in tall fescue (Festuca arundinacea Schreb.) occurs in an orderly, predictable manner with the potential for a high degree of synchronization among tillers on a given plant. Estimates of potential cumulative tiller production (Tmax) are made for synchronous (Tmax(1x) = 2(Lx +1) - 1, where Lx is the axil number of the youngest leaf on the main stem which bears an emerged tiller) and non-synchronous (Tmax(1) = 2(L - NLAT) - 1, where L is the number of leaves on the main stem and NLAT the number of leaves above the youngest primary tiller at its appearance) conditions. A method for determining the degree of synchronization and an equation for estimating site usage are also presented. Early in seedling development, site usage of a tall fescue population with high tillering capacity was near 90%, and tillering was regulated largely by rate of tiller site formation. As the canopy developed the phyllochron (time between successive leaf appearances) and NLAT increased, slowing the rate of tiller production in temporal terms and in relation to leaf appearance, respectively. Beyond 45 d after planting, site usage decreased rapidly, further reducing tiller production. High tiller production appeared to be associated with synchronized tiller appearance, with a lack of synchrony being associated with decreased site usage. Tillers formed in prophyll axils were less likely to be in synchrony with other tillers and frequently failed to appear. In contrast with branching in dicotyledons, apical dominance appears to play a minor role in regulating tillering in tall fescue. Tiller production initially appears to proceed at near maximum rates then is down-regulated during later development by longer phyllochrons, slower rate of tiller elongation and reduced site usage.