Influence of Photoperiod on Culm Elongation and Apical Development in Semi-dwarf and Standard-height Wheats

Flower initiation (FI) coincided with the commencement of culmelongation under both long (18 h) and normal (104–144h) photoperiod in eight spring wheats, including both gibberellicacid-sensitive and -insensitive types, which differed widelyin photoperiod sensitivity At FI the apex was significantly (P = 005) higher (above ground)in three of the wheats under long, compared with normal photoperiod;with no difference between the remaining five. Differences inresponse were not related to photoperiod response or gibberellicacid-sensitivity/insensitivity differences between the wheats. Long photoperiod prolonged the phase from terminal spikeletinitiation (TSI) to anthesis (A) in all the wheats, except Sunset(with the greatest photoperiod insensitivity), with no cleardifferences in response between semi-dwarf and standard-heightwheats. Respective rates of culm elongation from FI to TSI were lowerunder normal, compared with long, photoperiod in all varieties.That from TSI to A was unaffected by photoperiod, except inSunset when it was significantly (P = 001) slower under long,compared with normal photoperiod. Rate of culm elongation from FI to TSI across cultivars andphotoperiods was inversely related to spikelet number per head(r = –053, P = 005) but not to rate of spikelet initiation(r = –014 n.s.). Gibberellin-sensitivity, spikelet number, flower initiation, terminal spikelet initiation