The mechanism of 2n pollen formation in diploids of Costus speciosus (Koenig) J.E. Smith and role of sexual polyploidization in the origin of intraspecific chromosomal races.

Tyagi, B. R.

doi:10.1508/cytologia.53.763

Cited by 11 publications

(8 citation statements)

References 29 publications

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“…This phenomenon is known from other taxa and reflects the increased size of nuclei containing extra sets of chromosomes (Bretagnolle and Thompson, 1995). The size ratio of reduced and unreduced pollen in A. borealis (B1:1.42) is similar to that reported in other species (Tyagi, 1988;Orjeda et al, 1990), suggesting a general guideline for screening unreduced pollen. However, reduced and unreduced pollen sometimes lack clearcut size differences in grasses and other wind-pollinated species (Li et al, 1964;Maciera et al, 1992).…”

Section: Discussionsupporting

confidence: 77%

Unreduced gametes and neopolyploids in natural populations of Achillea borealis (Asteraceae)

2006

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Polyploidy is a major mechanism of speciation and adaptation, yet little is known about the origins of polyploids in natural species. I investigated gametic nonreduction and neopolyploid formation in natural tetraploid populations of Achillea borealis (Asteraceae), an autopolyploid complex consisting of tetraploid and hexaploid cytotypes. Cytological analyses of tetraploid populations revealed the occurrence of reduced (n ¼ 2x) as well as unreduced 'big' (2n ¼ 4x) and 'jumbo' (4n ¼ 8x) pollen grains, which were clearly distinguished by size. Production of unreduced pollen was monitored in two tetraploid populations in 1997 and 1998. Mean population-level frequencies of unreduced pollen ranged from 0.030 to 0.538%, with as few as one-third and as many as one-half of sampled plants producing unreduced grains. Eight individuals were found to produce 41% unreduced pollen, with highest observed frequencies of 7.0, 13.2 and 15.8%. Experimental crosses using high unreduced pollen producers as male parents generated viable seeds. However, the frequency of neohexaploids in the progeny of experimental crosses (0.388%) was similar to that observed in progeny of randomly selected, openpollinated control parents (0.465%). These results suggest that unreduced eggs are the most likely source of new polyploids. In spite of the inefficiency of unreduced pollen in unilateral sexual polyploidization, the overall rate of neohexaploid formation (one in 233) was several orders of magnitude greater than estimates of genic mutation rates.

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Section: Discussionsupporting

confidence: 77%

Unreduced gametes and neopolyploids in natural populations of Achillea borealis (Asteraceae)

2006

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“…There is, however, strong circumstantial evidence that 2n gametes are often involved in polyploid formation. The parents of spontaneous polyploids have, upon cytological analysis, commonly been found to produce 2n gametes (18,21,24,46,52,55,83,90,94,101,166,168,173). Conversely, plants known to produce 2n gametes can be crossed to produce new polyploids (18,37,81,136,138).…”

Section: Mechanisms Of Polyploid Formationmentioning

confidence: 99%

“…Although all the steps in this pathway have rarely been observed in their entirety, the individual mechanisms are well substantiated. Triploids have often been observed in diploid populations (41,47,69,143,168), and it is generally believed that these are produced by the union of reduced (n) and unreduced (2n) gametes. Studies of such spontaneous triploids, as well as triploids produced by crossing diploids and tetraploids, indicate that many of the gametes produced by autotriploids are not functional, because they possess aneuploid, unbalanced chromosome numbers.…”

Section: Pathways Of Polyploid Formationmentioning

confidence: 99%

“…For example, Einset (47) found a small fraction (4.39 × 10 −4 ) of tetraploid seedlings while cytotyping the progenies of open-pollinated diploid apple varieties. Tyagi (168) crossed clones of Costus speciosus that were observed to produced some 2n pollen, and recovered a small number of tetraploid seedlings. This process has been observed in several other taxa (18, 69,81,85,89,122).…”

Section: Pathways Of Polyploid Formationmentioning

confidence: 99%

“…Both 2n pollen and 2n eggs have been observed in hybrid and nonhybrid agricultural cultivars and natural plant species (11,13,24,36,37,83,101,116,136,142,147,151,163,164,177). Unreduced pollen grains can often be identified by size, as they typically have a diameter 30-40% larger than that of reduced pollen (78, 168, but see 101,105), and the distribution of pollen size in plants known to produce 2n pollen is often bimodal (131,168). Unreduced female gametophytes can sometimes be identified by size (161), but more often the frequency of 2n gametes is indirectly estimated using controlled, interploidy crosses in plants with very strong interploidy crossing barriers.…”

Section: Unreduced Gametes and The Origin Of New Polyploidsmentioning

confidence: 99%

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Pathways, Mechanisms, and Rates of Polyploid Formation in Flowering Plants

Ramsey

Schemske

1998

Annu. Rev. Ecol. Syst.

1,709

1,874

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Polyploidy is widely acknowledged as a major mechanism of adaptation and speciation in plants. The stages in polyploid evolution include frequent fertility bottlenecks and infrequent events such as gametic nonreduction and interspecific hybridization, yet little is known about how these and other factors influence overall rates of polyploid formation. Here we review the literature regarding polyploid origins, and quantify parameter values for each of the steps involved in the principal pathways. In contrast to the common claim that triploids are sterile, our results indicate that the triploid bridge pathway can contribute significantly to autopolyploid formation regardless of the mating system, and to allopolyploid formation in outcrossing taxa. We estimate that the total rate of autotetraploid formation is of the same order as the genic mutation rate (10 −5 ), and that a high frequency of interspecific hybridization (0.2% for selfing taxa, 2.7% for outcrossing taxa) is required for the rate of tetraploid formation via allopolyploidy to equal that by autopolyploidy. We conclude that the rate of autopolyploid formation may often be higher than the rate of allopolyploid formation. Further progress toward understanding polyploid origins requires studies in natural populations that quantify: (a) the frequency of unreduced gametes, (b) the effectiveness of triploid bridge pathways, and (c) the rates of interspecific hybridization.

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Evidence of the production of 2n eggs in diploid plants of the autopolyploid complex Turnera sidoides L. (Passifloraceae)

Kovalsky

Neffa

2015

Plant Syst Evol

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The mechanism of 2n pollen formation in diploids of Costus speciosus (Koenig) J.E. Smith and role of sexual polyploidization in the origin of intraspecific chromosomal races.

Cited by 11 publications

References 29 publications

Unreduced gametes and neopolyploids in natural populations of Achillea borealis (Asteraceae)

Unreduced gametes and neopolyploids in natural populations of Achillea borealis (Asteraceae)

Pathways, Mechanisms, and Rates of Polyploid Formation in Flowering Plants

Evidence of the production of 2n eggs in diploid plants of the autopolyploid complex Turnera sidoides L. (Passifloraceae)

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