Sowing date affect spikelet number and grain yield of durum wheat

Shifts in sowing date change the combination of temperature and photoperiod to which durum wheat is exposed, affecting crop phenology and grain yield. Three durum wheat (Triticum turgidum L. var. durum) varieties were field sown at month intervals over a whole year. The number of spikelets on the main culm and the duration of the period of spikelet initiation were recorded. Grain yield, spike number, and mean kernel weight were determined, too. With all sowing dates, plants formed a spike within the main culm and reached the stage of first node detectable. Physiological maturity was achieved only for sowings performed between October and May. Grain yield was highest in November and both yield and yield components were strongly affected by sowing date. The number of spikelets ranged from 11 to 24, according to sowing date and variety. It decreased from November to May in consequence of the shorter initiation period, and we hypothesize that a 12-h-daylength or longer interrupts spikelet initiation. The decrease of spikelet number was the main determinant of yield reduction with the delay of sowing from November to March.