ROLE OF LEAF APPEARANCE RATE AND THE COLEOPTILE TILLER IN REGULATING TILLER PRODUCTION

Forage production in tall fescue (Festuca arundinacea Schreb.) depends on elongation of existing leaves and production of new leaves and tillers. Genetic selection for high leaf elongation rate (LER), however, results in plants with limited tillering capacity. Our objective was to examine how the development of individual leaves and tillers affects total tiller production in populations of tall fescue selected for high or low LER. Seedlings were grown for 32 to 70 d in controlled environment chambers (500 mu mol m(-2) s(-1) PPFD, 14-h photoperiod). The low LER (high tillering) population produced twice as many coleoptile tillers as the high LER population, and coleoptile tillers and their progeny accounted for 80% of the difference between populations in tillers per plant after four tiller production cycles. With the exception of the coleoptile tiller, no difference in site usage (number of tillers appearing per axillary bud produced) was observed between populations. Site usage was greater than 0.80 in both populations during the first 30 to 35 days after planting (DAP), but decreased to approximate to 0.20 by 70 DAP. Both populations had similar leaf and tiller phyllochrons until 30 to 35 DAP. Thereafter, rate of leaf and tiller appearance slowed significantly, beginning first in the high LER population. Thus, tillering differences between populations were initially due to differences in coleoptile tiller production, but after 30 to 35 DAP differences in leaf appearance rate also contributed to differences in potential number of tillers per plant.