October-December 2000 Investigntion of Abnormnl Pollen Development 143 Cytological and Genetic Investigation of Abnormal Pollen Development in

Six unique sugarbeet (Beta vulgaris L.) mutations (aI, a3, a4, as, a6, and ap) causing abnormal pollen development were investigated. Cytological examinations of al and a6 indicated that the male sterility caused by these muta tions was due to degradation of microspores after initia tion of pollen grain wall formation. Genetic investigations ofal 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 as is inherited as a digenic charac ter. Cytological observations of a3, a4, and as 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) wa