Stability of floral differentiation in Triticum

Abstract

The pattern of floral development in the hexaploid and tetraploid species of wheat is normally invariate. The aim of this work has been to gain an understanding of the genetics of the buffering system and of its evolution. Two series of variants were used, one with defective, the other with excessive flower development: the former with one or more basal florets missing or defective, the latter with normal florets, but with flowering organs in the normally sterile glumes. These stocks were used in genetic studies as testers in crosses with normal wheats, and in physiological studies of the developmental stability of both abnormal and normal wheats exposed to a 15 day, short-day, high temperature treatment, starting at floral initiation. Basal fertility is controlled by (1) a component associated with the vulgare factor Q;(2) the Bs gene (previously called A ); and (3) a polygenic system ( P ). Q confers complete basal fertility. In the absence of Q basal fertility is under the control of P interacting with Bs and bs . Bs has the effect on the second flower that Q has on the first (Frankel, Shineberg & Munday 1969). The evidence now presented is consistent with the interpretation that Q, P, or both, control the pattern of floral development in the hexaploid and tetraploid wheats generally. Vulgare , carrying Q , is fully buffered against basal sterility, but varieties vary widely in their content of P . Hexaploid and tetraploid subspecies without Q have high levels of fertility inducing polygenes ( P ). Glume-fertile stocks have either an excess of Q (4 Q in compactoid, Cd ), or of P (in K 9 , K 10 and K 12 , with Q derived from ssp. vulgare, P from ssp. macha ). Base-sterile vulgare types were found in the cross of Chinese Spring with the sterility-inducing stock, St 1 This is interpreted as Chinese Spring having a lower valency Q -factor, Q '. The effects of the short day-high temperature treatments were as follows: (1) basal sterility of base sterile stocks was increased; (2) glume fertility of glume fertile stocks was increased; (3) no basal sterility was induced in normal wheats; (4) glume fertility was induced in vulgare , in proportion to the content of P ; and in ssp. carthlicum , the only tetraploid with Q and, it appears, with P at the level of other tetraploid subspecies. These results confirm the conclusion from genetic evidence that P and Q impinge upon the same development process. The location of the Bs gene on chromosome 5D of vulgare suggests an evolutionary connexion with Q located on 5A. It is suggested that a Bs -type gene, associated with the spelta gene, q1 (Muramatsu 1963) on 5A, was included in the multiple repeat which gave rise to Q (Kuckuck 1959). This is consistent with the interpretation of Bs as a weaker Q .