Duration of the stem elongation period influences the number of fertile florets in wheat and barley

Yield increases in temperate cereals have been associated with increases in grain number. An experiment was conducted to investigate whether altering the duration of the stem elongation period in wheat and barley increases fl oret fertility and thereby grain number. A photoperiod- responsive spring w heat (UQ189) and spring barley (Arapiles) were grown in a naturally lit phy totron. Plants were grown at constant (9, 13 and 19 h) and reciprocally int erchanged photoperiod [at terminal spikelet (TS, wheat) or triple mound (TM , barley)] to alter the duration of the stem elongation period. An increase d duration of the late reproductive phase from TS to heading in wheat resul ted in more fertile florets per spike. A similar relationship was observed in barley but only for a limited range of duration of the stem elongation p eriod. Shorter photoperiods reduced the rate of floret development and exte nded the time to reach the fertile floret stage. The fact that the duration of the late reproductive phase during which the spike and stem competing f or assimilates was associated with the number of fertile florets per spike suggests that extending the stem elongation period in cereals could be a wa y to reduce assimilate competition and thereby increase the number of ferti le florets and grain yield.