Effect of Tiller Trimming on Phyllochron and Tillering Regulation during Tall Fescue Development

Abstract

Tall fescue (Festuca arundinacea Schreb.) seedlings grown in controlled‐environment chambers experience a rapid decrease in the rate of leaf and tiller appearance about 30 to 35 d after planting (DAP). A tiller‐trimming experiment was conducted to determine the cause of this decrease and to examine the interrelationship between leaf and tiller appearance and growth. Each primary tiller from three tall fescue populations differing in tillering capacity was trimmed 5 d following its appearance, then regrowth was removed twice weekly. Trimming tillers increased the number of tillers per plant by 29 to 134%. Plants with trimmed tillers had higher leaf appearance and elongation rates than controls after 30 to 37 DAP. Higher leaf appearance rates increased the potential number of tillers per plant by 185 to 273%. Tiller trimming did not affect the proportion of potential sites which produced tillers (site usage) in two of the three populations, but reduced site usage from 0.66 to 0.58 in the population with the highest tillering capacity. Increased tiller production was primarily due to increased production of potential tiller sites. Leaf appearance rate depended on duration of leaf tip elongation within the whorl, and on the timing of leaf initiation. Increasing the duration of leaf elongation increased the interval between initiation of successive leaves and decreased leaf appearance rate. The main stem was apparently able to support initiation of all tillers on the plant while maintaining high leaf elongation rates, suggesting that competition with main stem leaves was not limiting tiller appearance.