Relations of Tiller Dynamics and Herbage Mass Production in Nordic Varieties of Timothy and Tall Fescue.

Herbage mass yield of grasses is a function of the density and size of vegetative (VEG), generative (GEN), and elongated vegetative (ELONG) tillers. We determined the contribution of these tiller types to dry matter (DM) yield along with their main morphological characteristics in field-grown timothy (cv. Tammisto II) and tall fescue (cv. Retu) during primary growth (PG) and regrowth (RG). In addition, we studied the mother effect of these tiller types on the development of individual tillers and leaf appearance in RG.

Timothy contributed to DM yield mainly with stem-producing tillers (ELONG and GEN) in both cuts. GEN were dominant in PG while in RG the balance between VEG and ELONG changed with time in favour of ELONG. In tall fescue, VEG were the main contributors to DM yield in both cuts. Nevertheless, total rates of DM accumulation were similar for both species. Inside species, GEN were large and contained low proportions of leaf, whereas VEG were small and had high proportions of living and senescent leaf. ELONG were intermediate in size and contained small amounts of senesced tissue.

The developmental stage of tillers in PG (i.e. mother tiller type) did affect the success of RG tillers, albeit adversely in timothy and tall fescue. In timothy, the appearance of new RG tillers and the number of living leaves per tiller in RG were enhanced by stem-containing, especially GEN mothers. For RG in timothy, VEG mothers caused higher tiller mortality, but high number of living leaves in the survived progeny tillers. In RG of timothy, phyllochron was affected more by environmental conditions than the type of mother tiller. In contrast to timothy, VEG mothers of tall fescue promoted the post-cut survival rate and subsequent growth of tillers in RG, prominently leading to better yield formation for RG.