Cytological and genetic investigation of abnormal pollen development in sugarbeet.

Six unique sugarbeet (Beta vulgaris L.) mutations (al, a3, a4, a5, a6, and ap) causing abnormal pollen development were investigated. Cytological examinations of al and a6 indicated that the male sterility caused by these mutations was due to degradation of microspores after initiation of pollen grain wall formation. Genetic investigations of al and a6 demonstrated that these mutations were non-allelic nuclear genes. Mutations a3 and a4 also resulted in male sterility and had monogenic inheritance. The male sterility controlled by a5 is inherited as a digenic character. Cytological observations of a3, a4, and a5 indicated that even though microspore degeneration begins during pollen wall formation for all three, the three mutations were not identical. The ap mutation (accreting pollen) was inherited as a single recessive nuclear gene causing fertile pollen grains to aggregate in the tetrads. All six mutations may be useful in molecular studies of pollen cell wall development. The ap mutation allows tetrad analysis in sugarbeet and the male sterile mutants may have utility in situations where hand emasculation is now required.