Sterile base florets in Triticum

Abstract

The morphology of the florets in three base-sterile speltoid mutants of Triticum aestivum L. is described. In two of the three mutants the basal floret only is affected. In one of these (St1) There is a high degree of sterility in the basal floret of all spikkelets except those on the distal part of the inflorescence; in the other (St1A) the basal floret of the basal and the distal spikelets is nearly always fertile, the highest degree of sterility being developed in the spikelets towards the middle of the ear. In the third mutant (St2) two florets are usually concerned. The basal floret of all spikelets except the apical one is practically always sterile. The second floret in the distal spikelets is mostly fertile, but in the lower spikelets it too is sterile and there is a gradient in fertility form distal to basal spikelets. The minimal effect of the sterility factor is the abortion or complete suppression of the anterior Stamen. This is accompanied by fusion and increased growth of the lodicule rudiments; all other floral parts develop normally. Greater incidence of the sterility results in the suppression of the lateral stamens with increased development of the lodioular structure and reduced growth of the palea. Fusion of the reduced palea and lodicular structure is usually followed by the abortion of the gynaeceum. In its extreme expression the sterility factor suppresses entirely the initiation of the flower primordium. Failure of florets in higher positions on the spikelets to form grain is due to immaturity and is different from basal sterility. When the basal florets are sterile, florets in higher positions than usual set grain. The mechanism by which the St genes operate and the evolutionary significance of basal sterility is discussed.