INFLUENCE OF PHOTOPERIOD ON CULM LENGTH IN WHEAT

The effects of photoperiod on culm length (CL) were examined in a semi -dwarf (Condor) and a standard-height (Thatcher) wheat cultivar under five photoperiod regimes (natural photoperiod, two constant photoperio ds, and two under which photoperiod was artificially increased over na tural photoperiod by 9.8 and 13.1 min/d). The five photoperiod treatme nts were randomly assigned at sowing and re-randomised at terminal spi kelet initiation (TS) to give five different photoperiod treatment com binations before and after TS. The cultivars differed significantly in final CL, Thatcher being taller than Condor. Culm length was related to the average photoperiod during the period between seedling emergenc e (SE) and double ridge (DR). There appeared to be an indirect effect of photoperiod during the vegetative phase on subsequent culm elongati on, which was much stronger in Thatcher than in Condor, but the differ ences in CL between the two cultivars were smaller under long compared with short photoperiods. The effect of photoperiod on CL appeared to be closely related to the final number of leaf primordia on the main c ulm and to the number of elongated internodes, both increasing with sh ort photoperiods. In contrast, differences in CL between cultivars wer e mainly due to the lengths of the internodes.