Development Rate in Wheat as Affected by Duration and Rate of Change of Photoperiod

A field study was conducted to test the hypothesis that wheatdevelopment rate responds to the rate of change of photoperiod.Two wheat cultivars (Condor and Thatcher) were sown on 18 Aug.1992 at Melbourne (38° S). Photoperiod was extended artificiallyto give five treatments up to terminal spikelet initiation (TS)viz.: natural photoperiod (rate of change of photoperiod, 2·3mind d^-1), two faster rates of change (9·8 and 13·1min d^-1) and two constant photoperiods of 14·0 and 15·5h. After TS, the two constant photoperiods were extended to15·0 and 16·5 h, respectively and treatments wererandomly re-allocated, i.e. some plots received different photoperiodregimes before and after TS. There were no significant differences among treatments in thelength of the period from sowing (S) to seedling emergence (E)phase, ranging from 15 to 16·3 d. The rate of developmentfrom E to TS responded to increases in photoperiod in both cultivars,increasing with average photoperiod across all treatments butthere was no effect of rate of change of photoperiod independentof its average photoperiod. The rate of development from TSto anthesis (A) did not show any trend with average photoperiod.This lack of effect of photoperiod on the period from TS toA contrasts with other results from the literature and possiblereasons for this conflicting result are discussed. Rate of changeof photoperiod did not affect the duration of the phase fromTS to A either. Therefore, the effect of photoperiod on theduration of the S-A period was strongly and positively correlatedto that of the length of the E-TS phase.Copyright 1994, 1999Academic Press Triticum aestivum L., wheat, phasic development, photoperiod, rate of change