BARLEY DEVELOPMENT AS AFFECTED BY RATE OF CHANGE OF PHOTOPERIOD

The rate of leaf appearance of barley varies substantially with time o f sowing. This variation has been related to both the length and the r ate of change of photoperiod at the time of plant emergence. An outdoo r pot experiment was conducted to test if rate of change of photoperio d directly affects phasic development and rate of leaf emergence of sp ring barley. Two photoperiod-sensitive cultivars (Bandulla and Galleon ) were subjected to five photoperiod regimes: two constant photoperiod s, of 14 and 15.5 h, and three different rates of change of photoperio d of c. 2, 9 and 13 min/day from seedling emergence to awn initiation. Photoperiod treatments significantly affected the duration from seedl ing emergence to awn initiation in both cultivars. Rate of change of p hotoperiod did not affect the rate of development towards awn initiati on independently of the absolute daylength it produced. Although Bandu lla had a longer duration than Galleon at any photoperiod regime, the cultivars did not vary in their sensitivity to photoperiod. When this phase was divided into the leaf initiation (LI) and spikelet initiatio n (SI) phases, it was evident that the sensitivity to photoperiod was not constant, being in general higher during the SI than during the LI phase. However, the magnitude of the change in sensitivity was cultiv ar-dependent, indicating that sensitivity to photoperiod during the di fferent phases could be under independent genetic control. Final numbe rs of primordia (leaves together with maximum spikelet number) were ne gatively affected by increasing photoperiods, but once again, there wa s no evidence of any effect of the fate of change of photoperiod which was independent of the average photoperiod. Both cultivars showed sim ilar sensitivities for final leaf number but maximum spikelet number w as more sensitive to photoperiod in Galleon than in Bandulla. Highly s ignificant linear relationships between leaf number and thermal time w ere found for all combinations of cultivars and photoperiod regimes (r (2) > 0.98). The rate of leaf appearance (RLA) was similar for both cu ltivars (c. 0.0185 leaves/degrees Cd) and did not alter during plant d evelopment or in response to the change in photoperiod at awn initiati on. The range in RLA was greater for Galleon (0.0170-0.0205 leaves/deg rees Cd) than for Bandulla (0.0173-0.0186 leaves/degrees Cd). Neither of these cultivars exhibited a significant relationship between rate o f leaf emergence and photoperiod or rate of change of photoperiod. The lack of significant relationships between RLA and length or rate of c hange of photoperiod is in contrast with previous reports using time o f sowing as a main treatment.