Responses of Orchardgrass Plant to Photoperiod and Air-Temperature

Abstract

Growth responses of three clones (NL: narrow leaf with abundant tillers, no head after a spring sowing, BL: Broad leaf with less tillers, no head after a spring sowing; ML: Intermediate leaf width, with head after a spring sowing) selected from a cultivar "Frode", were studied under the compinations of 3 photo-period and 4 air temperature treatments. Eight hours of natural daylight (SD) were supplemented with a 40 Watt incandescent lamp in each cabinet to supply 12 (MD) and 16 hours (LD) photoperiods, respectively. Within the limits of the experiment, 20°C day-15°C night temperature was most favorable for tillering under short-day condition. Under long-day, tillering was markedly deppressed. In general, the ratio of dormant buds to total tiller buds increased as the temperature raised. Tillering capacity (fig. 11) was progressively larger as the temperature declined and it was smaller under long-day than under short-day condition, while the eloegation of each tiller was greater under long-day and higher temperatures (fig. 5). Tillering capacity has a close relationship with the storage of available carbohydrate and nitrogen compounds in the tops, especially with the concentration of non-protein soluble nitrogen in the leaf-sheath and stem. When the growth of the shoot was checked under lower temperatures and shorter day-lengths, carbohydrate reserves and nitrogenous labile structural compounds were accumulated more in the tissues resulting in the greater tillering capacity and in the less T/R ratio (fig. 6, 8, 11). Dry matter production was greatest at 25°C day-20°C night and declined at higher or lower temperatures under short-day condition. Under long-day codition, a little lower temperatures such as 20°C day-15°C night or 25-20°C (when stem elongation occurred) were most favorable for the growth. The plant induced into reproductive stage with culm elongation under long-day condition was more productive in the shoot growth as compared with the vegetative plant under short-day condition. The exsistence of a clone such as ML which headed and flowered after a spring sowing was contrary to the general view that orchardgrass has an obligatory winter requirement for floral induction.