CYTOLOGICAL MECHANISM OF 2N MICROSPORE FORMATION IN GARDEN ASPARAGUS

Microsporogenesis was studied in 42 randomly chosen F2 plants of garden asparagus (Asparagus officinalis L. cv. UC 157) (2n = 2x = 20) that had been previously screened for production of pollen of heterogeneous size. At the tetrad stage, the average frequencies of tetrads, triads, and dyads were 58.9%, 15.4%, and 25.9%, respectively. Dyads and triads originated from the lack of chromosome migration toward opposite poles at anaphase II in either one or both cells of a microsporocyte, followed by the absence of cytokinesis in telophase II. The resulting 2n microspores were, therefore, genetically equivalent to second melotic division restitution products. The observation that all plants examined produced 2n microspores in high frequencies is taken as an indication that the modified meiosis in these plants is under genetic control.