INFLUENCE OF TEMPERATURE ON VEGETATIVE GR OWTH OF PTILOTUS-EXALTATUS R BR

The influence of different temperature regimes on vegetative growth of Ptilotus exaltatus was studied in growth chamber experiments (irradia tion 280 mu mol cultivated for 12 m(-2) s(-1)). The mother plants were weeks at 30/25 degrees C, 25/20 degrees C, and 20/15 degrees C (day/n ight) and 12 additional weeks at 35/17 degrees C, 23/25 degrees C, and 30/25 degrees C (day/night) and harvested weekly in both periodes, re spectively. Statistically significant differences were observed betwee n the various temperature ranges during the three harvesting months wi th respect to both yield and number of cuttings with inflorescence ind uctions/mother plant. Yields were highest at the temperature levels 25 /20 degrees C and 20/15 degrees C (day/night) with 61.1 and 54.0 cutti ngs/mother plant, respectively. However, the proportion of cuttings wi th inflorescence inductions (89.6 and 74.8 %, respectively) was large, so that the cuttings were not usable. At 30/25 degrees C (day/night) the yield of cuttings per mother plant was 42.2 from which only 2.1 % were inflorescence induced. The small proportion of inflorescence indu ced cuttings is attributed to the temperature cycle during the juvenil e phase. Subsequent variation df the temperature in the chambers indic ated that neither the daytime nor the night temperature alone, but the daytime temperature sum prevents the change to the generative phase. The induction of inflorescence can be prevented by mean daily temperat ures above 25 degrees C.