CONSTANT AND INTERCHANGED PHOTOPERIOD EFFECTS ON THE RATE OF DEVELOPMENT IN BARLEY (HORDEUM-VULGARE)

Indirect and direct influences of changes in photoperiod on the rate o f development in barley (Hordeum vulgare L.) were examined using three Australian cultivars, Clipper, Galleon and Finlay. Each possessed lit tle or no vernalisation response, and were grown at a constant tempera ture of 18 degrees C with two treatments, one of each of two constant photoperiod regimes (10 and 18 h) while other treatments involved reci procal transfer between them at either or both the double ridge (DR) a nd awn primordium (AP) stages of development. Under constant 18 h phot operiod, the lengths of all three development phases were shorter comp ared to the constant 10 h regime for Galleon and Clipper, while Finlay was relatively insensitive. The final number of leaves on the main cu lm was reduced by the constant 18 h photoperiod in Clipper and Galleon but Finlay was unaffected. The rate of development from DR to AP unde r 10 h photoperiod was increased by exposure to 18 h photoperiod from sowing (S) to DR, compared with plants exposed to 10 h photoperiod fro m S to DR. A similar response was noted for plants transferred at the AP stage, indicating that rate of development was determined both by i ts influence on prior as well as current photoperiod conditions. This 'memorised' response appears to be interactive, rather than additive, with the response of the plant to the current photoperiod. Direct and indirect effects of photoperiod on leaf and spikelet number, acting th rough their influences on the duration from S to DR and from DR to AP, were also discussed.