EFFECT OF TILLER TRIMMING ON PHYLLOCHRON AND TILLERING REGULATION DURING TALL FESCUE DEVELOPMENT

Tall fescue (Festuca arundinacea Schreb.) seedlings grown in controlle d-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 decr ease and to examine the interrelationship between leaf and tiller appe arance and growth. Each primary tiller from three tall fescue populati ons differing in tillering capacity was trimmed 5 d following its appe arance, then regrowth was removed twice weekly. Trimming tillers incre ased the number of tillers per plant by 29 to 134%. Plants with trimme d tillers had higher leaf appearance and elongation rates than control s after 30 to 37 DAP. Higher leaf appearance rates increased the poten tial number of tillers per plant by 185 to 273%. Tiller trimming did n ot affect the proportion of potential sites which produced tillers (si te 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. I ncreased tiller production was primarily due to increased production o f potential tiller sites. Leaf appearance rate depended on duration of leaf tip elongation within the whorl, and on the timing of leaf initi ation. Increasing the duration of leaf elongation increased the interv al between initiation of successive leaves and decreased leaf appearan ce rate. The main stem was apparently able to support initiation of al l tillers on the plant while maintaining high leaf elongation rates, s uggesting that competition with main stem leaves was not limiting till er appearance.