Origin and Causes

Abstract

The fertility of an organism is controlled by three major gene groups (st, mm, and mst), the majority of which are in the dominant state. The mutation of any of these to the recessive state leads to anomalies in sex organ development, differentiation and sporo- or gameto-genesis. Of these, the most common are the sterility (st) genes which cause absence, abortion, deformation, malformation or transformation of sporophylls or inhibit pollination or fertilisation, leading to total or partial male-female sterility. In another group, the meiotic mutant (mm) genes do not influence sex organ differentiation or development, but affect male-female meiosis almost equally and impair gametic fertility partially to completely. In the third group, the male sterility (mst) genes suppress male sexuality, rendering the organism female fertile-male sterile. The mst genes impair androecial or PMC’s differentiation and development, microsporogenesis and/or anther dehiscence. This produces an array of mst’s classified on a phenotypic basis into structural, sporogenous and functional types (Table 1.1). Control of all these anomalies is either exclusively by nuclear or by the interaction of nuclear and cytoplasmic genes (Fig. 1.1). Both these mst types arise through mutations at either the genie or cytoplasmic or at both these levels.