Analysis of the Genetic Regulation of Flower Morphogenesis in Bread Wheat

The mechanism of abnormal development of flower morphogenesis associated with the Q, locus was studied in crosses between a true breeding speltoid mutant of the variety Pb.C. 591 and eight cultivars of T. aestivum sub-sp. vulgare. Abnormalities in flower morphogenesis were studied by dissecting 10 homo-speltoid plants isolated in the F₂ generation of each cross.

The results obtained in the present study are, by and large, similar to those of Frankel and his colleagues. A detailed examination however, revealed that in a flower the different organs, namely lemma, androecium, gynaeceum and palea are affected selectively and specifically. The unit of abnormal flower morphogenesis hence appears to be a flower organ rather than a complete flower.

The hypothesis of Frankel that independent genetic units cause the sterility of the first, second and later florets does not explain the systematic development of basal sterility in two directions, i.e., base to tip in a spike and periphery to centre in a spikelet. Therefore, a new hypothesis has been proposed which assumes that abnormal flower morphogenesis is the net result of the interaction of differentiation and gene action and that the genes responsible for the induction of sterility are the same as those controlling the normal development of flowers. Four genes, L, A, R and P are proposed for the regulation of the normal development of lemma, androecium, gynaeceum and palea, respectively. When Q, is present these four genes function normally. In the absence of Q, another gene I^F starts functioning which inhibits the activity of the genes, L, A, G and P resulting in the abnormal development of flower organs. It is possible that the gene I^F is present on the long arm of chromosome-IX because in nulli-IX and iso-IX for the short arm, flower development is normal. When both Q, and I^F are absent as in nulli-IX the development of flowers will be normal. But when only Q,is absent, I^F affects the developmental genes. The systematic induction of sterility can be associated with the direction of the differentiation. The reaction between the product of the gene I^F and the developmental genes may be vigorous during the differentiation of the basal florets and may become gradually reduced during the differentiation of the central florets. As a result, the central florets develop normally. This recovery with time lapse is assumed to be brought about through a feed-back type of reaction. The product of reaction between gene I^F and the developmental genes in the basal florets may inhibit the same reaction from which it was produced. This hypothesis helps to clarify the observations made during the present study and also helps to understand the basis of the wide variation found in different speltoids in the expression of basal sterility.