Frequency Of Unreduced Gametes Research Articles

Meiotic behavior and fertility of Capsicum interspecific hybrids

ABSTRACT This study was performed to evaluate the meiotic behavior and fertility of four hybrids obtained from the crossing of Capsicum baccatum and its botanical forms with Capsicum chinense and Capsicum frutescens. We aimed to identify the causes of the low fertility in interspecific hybrids involving species from different gene pools of Capsicum. Hybrid flower buds were fixed in fixative solution and the slides were prepared using 1%-acetic carmine solution. Meiosis was observed in all phases and the main meiotic abnormality observed was the complete or partial lack of chromosome pairing, indicating that the species are either genetically distant or that some asynaptic gene was present in the hybrids. Meiotic index (MI), the frequency of unreduced gametes (type 2n), and pollen viability were estimated. MI and pollen viability of the hybrids were low. We concluded that due to the complete or partial lack of chromosome pairing, the species used in the hybrid combinations are genetically distant. We also noticed that the low-fertility hybrids are a consequence of the lack of chromosome homology between the two genomes involved. The hybrids were considered partially sterile since their pollen viability percentage was lower than 50%.

Unreduced gamete formation in wheat×Aegilops spp. hybrids is genotype specific and prevented by shared homologous subgenomes.

The presence of homologous subgenomes inhibited unreduced gamete formation in wheat×Aegilops interspecific hybrids. Unreduced gamete rates were under the control of the wheat nuclear genome. Production of unreduced gametes is common among interspecific hybrids, and may be affected by parental genotypes and genomic similarity. In the present study, five cultivars of Triticum aestivum and two tetraploid Aegilops species (i.e. Ae. triuncialis and Ae. cylindrica) were reciprocally crossed to produce 20 interspecific hybrid combinations. These hybrids comprised two different types: T. aestivum×Aegilops triuncialis; 2n=ABDU(t)C(t) (which lack a common subgenome) and T. aestivum×Ae. cylindrica; 2n=ABDD(c)C(c) (which share a common subgenome). The frequency of unreduced gametes in F1 hybrids was estimated in sporads from the frequency of dyads, and the frequency of viable pollen, germinated pollen and seed set were recorded. Different meiotic abnormalities recorded in the hybrids included precocious chromosome migration to the poles at metaphase I and II, laggards in anaphase I and II, micronuclei and chromosome stickiness, failure in cell wall formation, premature cytokinesis and microspore fusion. The mean frequency of restitution meiosis was 10.1%, and the mean frequency of unreduced viable pollen was 4.84% in T. aestivum×Ae. triuncialis hybrids. By contrast, in T. aestivum×Ae. cylindrica hybrids no meiotic restitution was observed, and a low rate of viable gametes (0.3%) was recorded. This study present evidence that high levels of homologous pairing between the D and D(c) subgenomes may interfere with meiotic restitution and the formation of unreduced gametes. Variation in unreduced gamete production was also observed between T. aestivum×Ae. triuncialis hybrid plants, suggesting genetic control of this trait.

Meiosis in Solanum phureja

Meiosis and pollen mitosis were studied in a clone of Solanum phureja in order to elucidate the generally high frequency (about 90 %) of tetraploid progeny in tetraploid X diploid crosses involving S. phureja. The first meiotic division was normal with 12 bivalents in metaphase and apparently normal chromosome disjunction. The second meiotic division showed normal metaphases with 12 chromosomes in each of the two spindles, along with cells showing a bi- or tripolar spindle (cell wall formation was simultaneous). At the end of the second division those disturbances resulted in unreduced cells either with two diploid nuclei or with one diploid and two haploid nuclei along with the normal tetrads with four haploid nuclei. The frequency of unreduced gametes was about 50 %. First and second pollen mitoses were also represented by normal haploid as well as unreduced diploid cells. Hence, the high frequency of tetraploid offspring in Solanum tuberosum X S. phureja crosses could be caused by selective fertilization with unreduced diploid pollen grains.

PATHWAYS, MECHANISMS, AND RATES OF POLYPLOID FORMATION IN FLOWERING PLANTS

▪ Abstract 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.