Influence of Vernalization and Photoperiod on Supernumerary Spikelet Expression in Wheat

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Abstract
Two tetraploid (Triticum turgidum L.emend gr. turgidum and gr. durum) and five hexaploid wheats (Triticum × aestivum L. emend gr. aestivum) with reported tendencies for ‘branched heads’ (supernurnerary spikelets) exhibited variation in its expression under different vernalization photoperiod and temperature regimes. Two main types of supernumerary spikelets were identified, multiple sessile spikelets (MSS) with two or more complete spikelets at a rachis node and indeterminate rachilla spikelets (IRS) with two to 13 spikelets on an extended rachilla. The degree of supernumerary spikelet expression in wheats with vernalization response differed from those without. Short photoperiods (9–14 h) both outdoors and in a glasshouse environment, were more conducive to supernumerary spikelet expression than 24 h photoperiod in both environments. The 24 h photoperiod glasshouse environment (higher mean temperatures) was least conducive to its expression except in lines with a strong vernalization response. The high stability of supernumerary spikelet expression in certain genotypes in the different environments indicated the feasibility of incorporating this character in breeding and selecting commercial wheats to increase grain number per head.