The occurrence of plants producing 2n pollen was ascertained in nine diploid (2n = 2x = 14) subspecies of the polyploid grass complex Dactylis glomerata by determining the ploidy level of the progeny in 100 tetraploid (4X) × diploìd (2X) crosses. The possibility of using pollen size to screen for plants which produce large quantities of 2n pollen was tested by comparing the frequency distributions of pollen diameter in plants which did and did not produce 4X progeny in an interploidy cross. The ploidy level of the progeny was determined by chromosome counts or nuclear DNA quantification using flow cytometry. Parental genotypes of known constitution at different loci coding for enzymes were crossed and the offspring genotypes determined by electrophoresis to identify progeny produced by cross and self-fertilization. Depending on the subspecies, from 20 to 75% of the tested plants produced 4X cross progeny. The average 2n pollen frequency was 0·98% for all crosses, and 3·02% for crosses where 2n pollen was detected. Variability among individuals was greater than that among subspecies. Six genotypes produced exceptionally high frequencies of 2n pollen, ranging from 8.04 to 14·35%. Pollen diameter varied significantly among subspecies. Within subspecies of similar pollen size, the pollen diameter of plants which did or did not produce 4X cross-progeny were not statistically different, although the frequency distribution was biased towards the highest classes of 2n pollen producers. By fixing an arbitrary threshold to normal pollen diameter in each group of subspecies with similar pollen size distribution, 73% of 2n pollen producers could be detected.
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MACEIRA et al. (1992) studied this question.