Second meiotic division restitution (SDR) 2n pollen formation in diploid and hexaploid species of Asparagus

Summary Plants of two cultivars of 2x A. officinalis L. and two related ornamental species, 2x A. plumosus Baker and 6x A. densiflorus (Kunth) Jessop cv. Sprengeri were screened for production of pollen of heterogeneous size. Twenty four plants out of thirty-one studied produced this type of pollen, with frequencies of 3% or more large pollen. Some of these plants also produced giant grains. The numerically unreduced pollen arose by the lack of chromosome migration at Anaphase II in either one or both cells of a meiocyte, followed by the absence of cytokinesis in cells with abnormal chromosome behavior, a Second Meiotic Division Restitution (SDR) cytological mechanism. Double unreduced pollen resulted from a similar mechanism acting at both Anaphase I and Anaphase II stages. The high frequency of plants which produced 2n pollen in significant amounts is taken as an indication that the modified meiosis observed is under genetic control.