CYTOLOGY OF 2n POLLEN FORMATION IN DIPLOID ALFALFA, MEDICAGO SATIVA

Abstract

Four diploid (2x) clones of alfalfa, Medicago sativa L., which produced good seed set when used as male parents in 4x-2x crosses were selected for study. The 2x clones descended from 2x haploids of cultivated 4x alfalfa. Fertility in the 4x-2x cross was due to the production of pollen with the unreduced chromosome number (2n pollen) from the 2x parent. The cytological mechanism of 2n pollen formation was found to be disorientation of spindles at metaphase II in up to 38% of the pollen mother cells. Thus, both n and 2n pollen were produced by all four diploids examined. Normal spindles at metaphase II were oriented such that they defined the poles of a tetrahedron and resulted in normal tetrads in a tetrahedral arrangement. Disoriented spindles were basically parallel to each other and resulted in formation of dyads and occasionally a triad. Dyads developed into two 2n pollen grains; triads developed into one 2n and two n pollen grains. Since both n and 2n pollen grains are produced by the diploids, they can be maintained as diploids or they can be used as male parents in crosses to tetraploids. The genetic constitution of 2n pollen resulting from parallel spindles is similar to that expected after first division restitution of meiosis and much of the heterozygosity of the diploid parent is conserved in the gametes. The 2n gamete mechanism has potential application in germplasm transfer and in maximizing heterozygosity in tetraploid hybrids.

Cytogenetics of Four Species of Genus <i>Berberis</i> L. (Berberidaceae Juss.) from the Western Himalayas

“…The production of hypo-and hyperploid PMCs due to cytomixis (Falistocco et al 1995, Sheidai and Bagheri-Shabestarei 2007, Fadaei et al 2010 accompanied by other meiotic abnormalities lead to anomalous microsporogenesis, resulting in the formation of variable-sized pollen grains, possibly with an aneuploid condition and low pollen fertility (Villeux 1985, Nirmala and Rao 1996, Sheidai and Fadael 2005, Sheidai et al 2003. The formation of large-sized pollen grains as seen at present is in accordance with previous information about the possibility of such pollen grains resulting from unreduced 2n pollen grains as has been observed in several angiosperms by Vorsa and Bingham (1979), Bertagnolle and Thomson (1995), Sheidai et al (2008), Fadaei et al (2010) and Jeelani et al (2011). The occurrence of limited variation of chromosome numbers but diversity in meiotic behavior at the intraspecific level of the presently studied species demands the need for extensive cytological exploration on a population basis in the genus Berberis from different geographical areas.…”

Meiotic Studies in Some Members of Caryophyllaceae Juss. From the Western Himalayas

“…All these meiotic abnormalities may lead to anomalous microsporogenesis and in turn to variable-size pollen grains and the occurrence of aneuploidy (Villeux, 1985;Nirmala and Rao, 1996). Giant pollen grains, possibly unreduced 2n pollen grains, have been reported in several species (Vorsa and Bingham, 1979;Bertagnolle and Thomson, 1995;Sheidai et al, 2008;Fadaei et al, 2010). Pollen grain fertility in these meiotically abnormal populations/species is reduced with the formation of pollen grains varying in size.…”

Cytogenetic study of diploid and spontaneous triploid oaks, Quercus robur L

“…The meiotic irregularities caused diversity in pollen chromosome number and disturbances in male gametophyte development (fig 3d-g (fig 4a). The 2n pollen was found to be formed by parallel spindles (sensu, Mok and Peloquin, 1975) Other triploid Q robur have been observed in studies of twin seedlings by Johnsson (1946) and Burda and Schepotiev (1973 (Mok and Peloquin, 1975) and Medicago (Vorsa and Bingham, 1979). In these 2 crop species, the triploids formed in this manner expressed heterosis due to the high heterozygous 2n gametes.…”