Basal Sterility in Wheat

Abstract

THE wheat spike is an example of the occurrence of parallel development of morphologically similar structures, namely, the spikelets and florets. The spike consists of an axis upon which are arranged two opposite rows of spikelets. Each spikelet consists of an axis upon which are arranged two rows of florets. The apical and basal spikelets are often sterile, and in each spikelet the third floret (counting from the base) is often sterile and the fourth floret usually sterile. Apart from these differences, the spikelets and florets are indistinguishable at maturity. This similarity emphasizes the interest of the action of the ‘sterile base’ genotypes¹ which condition a sterility of the basal floret of each spikelet. Three types are known: St₁, in which the basal (first) florets are sterile; St₂, in which the basal and second florets are sterile; and St₃, in which the basal, second and third florets are sterile. Only the St₁ type has been studied in any detail. The St_F (basally fertile) type when crossed with the St₁ type gives in the F₂ a range of sterility/fertility from completely basally fertile to completely basally sterile. The intermediate types, in which some spikelets are basally fertile and some basally sterile in the same spike, are termed St_i.