Pollen production and spontaneous polyploidization in diploid populations of Anthoxanthum alpinum

Abstract

The most common form of polyploidization is that which occurs via the fertilization of unreduced 2n gametes, i.e. gametes that possess the somatic chromosome number of the species. However, very few data are available concerning the frequency of spontaneous polyploidization in diploid plant populations. In this study we have quantified both the frequency of 2n pollen production and the frequency of polyploid seed production in diploid populations of the grass Anthoxanthum alpinum. More than 6000 seeds from four different populations collected during two years of study were screened for ploidy using a flow cytometer. In parallel, the frequency both of plants with large pollen (LP) and of LP production on these plants was quantified in two populations. No tetraploid seeds were detected, although in each population a few triploid seeds were regularly produced at a frequency of two triploid seeds per thousand. The frequency of LP producers was similar in the four populations, as was the frequency of LP production. The frequency of LP was ten times that of triploid seeds. These finding suggest that the 'triploid block' is not enough to prevent the regular occurrence of triploids in diploid populations of this species. The role played by the hypothesized 'triploid bridge' in the genesis of autotetraploids is discussed in the light of these results. 0 2001 The Linnean Society of London ADDITIONAL KEYWORDS: triploid bridgepolyploidy, triploid -2n pollen -Anthomnthum alpinum.

Occurrence of viable unreduced pollen in a Begonia collection

“…It is well known that 2n pollen grains are generally larger than normal grains. The presence of giant grains frequently is an indication for the production of 2n pollen (Sala et al 1989;Van Tuyl et al 1989;Bretagnolle 2001;Becerra Lopez-Lavalle and Orjeda 2002) and our results proved that this is also the case in Begonia. However, a larger pollen diameter is no unequivocal proof for a doubled DNA content.…”

Cytogenetics, geographical distribution, and pollen fertility of diploid and tetraploid cytotypes of Santolina pectinata Lag. (Asteraceae: Anthemideae)

“…Although no unreduced gametes were found in the two diploid populations studied, the sexual mechanism of tetraploid formation through bilateral fusion of unreduced gametes (Harlan & deWet, 1975;Bretagnolle, 2001) is plausible. However, nonreduction is very rare, and so the chance that a nonreduced pollen grain will fertilize a nonreduced egg cell falls almost to zero, particularly in view of the large numbers of fertile haploid gametes that are produced by diploids (P. E. Brandham, Royal Botanic Garden, Kew, pers.…”

Hybridization between diploidCentaurea pseudophrygiaand tetraploidC. jacea(Asteraceae): the role of mixed pollination, unreduced gametes, and mentor effects

“…The presence of aberrant individuals that produce a high proportion of unreduced gametes, enabling them to overcome the barriers and produce viable polyploid offspring, would thus have great evolutionary significance. Such unreduced-gamete producers have been found in the majority of quantitative studies Maceira et al, 1992;Bretagnolle, 2001;Ramsey, 2007). Second, however, once polyploids form, mixed pollination may strengthen their reproductive isolation, and the negative effect of heteroploid hybridization may be less pronounced than expected.…”

“…These results are consistent with those of previous studies. Limited performance of unreduced pollen in natural populations has already been documented (Ramsey & Schemske, 1998;Ramsey, 2007), and most quantitative analyses and reviews have reported unequal production of unreduced gametes within individuals Maceira et al, 1992;Bretagnolle & Thompson, 1995;Ramsey & Schemske, 1998;Bretagnolle, 2001;Ramsey, 2007; and references therein).…”