Production of 2n Pollen in Red Clover¹

Abstract

The success of tetraploid red clover (Trifolium pratense L.) in Europe has stimulated interest in developing tetraploid red clover adapted to the United States. The use of 2n gametes to produce tetraploid alfalfa (Medicago sativa L.) and potato (Solanum tuberosum L.) from diploid germplasm suggests that 2n gametes may be an alternative to chemical treatment. Diploid plants that produce 2n eggs are known to occur in red clover, and plants that produce 2n pollen have been reported. The objectives of this study were to search for red clover plants producing 2n pollen, and to determine the cytological origin of such pollen. Six hundred plants, belonging to six different diploid (2n = 2x = 14) cultivars, were screened for 2n pollen production by examining dry pollen samples with the aid of a microscope. Eighteen plants (3%) produced at least 1% 2n pollen and were classifted as 2n pollen producers. Individual plants ranged from 1 to 84% in frequency of 2n pollen production. Pollen mother cell analyses revealed that 2n pollen resulted from parallel or tripolar spindles during anaphase II of microsporogenesis. This mechanism is genetically equivalent to a first division restitution (FDR) mode of gamete formation. One 2n pollen producer proved to be a synaptic mutant. Normally, synaptic mutants are male sterile, but fertility is restored by parallel spindles in this plant. Because the lack of homologous pairing limits genetic recombination, this plant can produce gametes with the same genetic constitution as the sporophyte. It is apparent from the results that 2n gametes may be useful in red clover polyploidization programs.

Sexual polyploidization in red clover

“…Other authors also reported variable GP production, ranging from 4 to 37% in alfalfa (McCoy, 1982), and from 1 to 11% in Lotus tenuis (Negri, 1992). In this study, the range of variation in GP production in the initial population (0 to 9.07%) was lower than those values cited above, but the percentage of individuals producing more than 1% GP (19.91%) was remarkably higher in comparison to the red clover population studied by Parrott & Smith (1984). In this species, 2n pollen is formed due to the occurrence of parallel or tripolar spindles during anaphase II (Parrot & Smith, 1984).…”

“…Frequency of unreduced gametes production in non-hybrid plants is generally less than 1%, and may vary among individuals (Veilleux, 1985;Ramsey & Schemske, 1998, Lyrene et al, 2003. In the work of Parrott & Smith (1984) for instance, 3% of the diploid red clover plants analyzed produced more than 1% GP (reaching up to 84% GP). Other authors also reported variable GP production, ranging from 4 to 37% in alfalfa (McCoy, 1982), and from 1 to 11% in Lotus tenuis (Negri, 1992).…”

“…According to the literature, pollen grains this size are assumed to be unreduced (Hermsen, 1984;Ramanna, 1992). Pollen grain size is considered to be a reliable method to estimate unreduced gametes production in red clover (Parrott & Smith, 1984;Simioni et al, 2004). Additionally, pollen grain size was measured in 30 grains from each of the tetraploid plants, and these measurements used as standard to classify the pollen grains of the Quiñiqueli plants.…”

“…In nature, most if not all polyploids have arisen by sexual polyploidization through unreduced (2n) gametes (De Wet, 1982;Ramanna, 1992;Ramsey & Schemske, 1998), which production is genetically controlled (Bretagnolle & Thompson, 1995) and have been reported in cultivated plants such as Alstroemeria , potato (Peloquin et al, 1992;Ramanna & Jacobsen, 1992), sweet potato (LopezLavalle & Orjeda, 2002), alfalfa (Vorsa & Bingham, 1979;McCoy & Smith, 1983;Mariani et al, 1992;Barcaccia et al, 2003), ryegrass (Wagenvoort & Den Nijs, 1992), white clover (Hussain & Williams, 1997), red clover (Parrott & Smith, 1984;Parrott et al, 1985;Mousset-Déclas et al, 1992, Simioni et al, 2004, Rosa hybrida (Crespel & Gudin, 2003), among others.…”

Reproductive Versatility and the Epigenetic Control of Female Gametogenesis

“…Numerous mutants result in the formation of unreduced gametes in flowering plants (2n gametes ;Hermsen 1984;Veilleux 1985;Parrott and Smith 1986;D'Amato 1989;Bretagnolle and Thompson 1995). Many exhibit high sex specificity, suggesting genetic divergence between mechanisms controlling unreduced pollen and unreduced egg cell formation (Veronesi et al 1986;Werner and Peloquin 1989;De Haan et al 1992).…”