Cytological investigations in diploid potato (Solanum spp.) (original) (raw)

Meiotic Aberrations Underlying Pollen Sterility in Cultivated Potato (Solanum tuberosum L.)

CYTOLOGIA, 2016

Meiotic behaviour of plant chromosomes is influenced by both genetic and environmental factors. The present paper shows the effect of abnormal meiosis on pollen fertility. Meiotic restitution is considered to be a common mechanism of polyploidization in plants and hence is one of the most important processes in plant speciation. Pollen mother cells (PMCs) of cultivated potato from anthers at different stages of meiotic process were analyzed for their chromosomal behaviour and irregularities. Various meiotic irregularities; univalent and multivalent formation, chromosome bridges, lagging chromosomes, etc. were reported for the first time in India.

Meiotic behavior of pollen mother cells in relation to ploidy level of somatic hybrids between Solanum tuberosum and S. chacoense

Plant Cell Reports, 2010

Potato somatic hybrids obtained by protoplast fusion between Solanum tuberosum (4x) and Solanum chacoense (2x) were investigated for genome stability and meiotic behavior associated with the pollen viability in order to elucidate the mechanism influencing the fertility of the somatic hybrids. The ploidy level detections conducted in 2004 and 2007 demonstrated that 68 out of 108 somatic hybrids had their ploidy level changed to be uniform and euploidy after successive in vitro subcultures, which mainly occurred in octaploids, aneuploids, and mixoploids, while 74% hexaploids were still stable in their genome dosage in 2007. Different types of abnormal meiotic behavior were observed during the development of pollen mother cells (PMCs) including the formation of univalents, multivalents, laggard chromosomes, and chromosomal bridges, as well as triads and polyads. A higher proportion of abnormal meiosis seemed to be accompanied with a genome dosage higher than the hexaploids expected in this study. A significant positive correlation between defective PMCs and the number of small pollen grains and negative correlation between number of small pollen grains and pollen viability strongly suggested that abnormal meiosis could be a causal factor influencing the fertility of the somatic hybrids. The hexaploids with stable genome dosage and a certain level of fertility will have great potential in a potato breeding program.

Varietal variation and chromosome behaviour during meiosis in Solanum tuberosum

Heredity

Naturally occurring autopolyploid species, such as the autotetraploid potato Solanum tuberosum, face a variety of challenges during meiosis. These include proper pairing, recombination and correct segregation of multiple homologous chromosomes, which can form complex multivalent configurations at metaphase I, and in turn alter allelic segregation ratios through double reduction. Here, we present a reference map of meiotic stages in diploid and tetraploid S. tuberosum using fluorescence in situ hybridisation (FISH) to differentiate individual meiotic chromosomes 1 and 2. A diploid-like behaviour at metaphase I involving bivalent configurations was predominant in all three tetraploid varieties. The crossover frequency per bivalent was significantly reduced in the tetraploids compared with a diploid variety, which likely indicates meiotic adaptation to the autotetraploid state. Nevertheless, bivalents were accompanied by a substantial frequency of multivalents, which varied by variety ...

Cytological mechanisms of 2n pollen formation in the wild potato Solanum okadae and pollen-pistil relations with the cultivated potato, Solanum tuberosum

Genetic Resources and Crop Evolution, 2008

Solanum okadae Hawkes et Hjert is a wild diploid potato species endemic to Argentina and Bolivia, of potential breeding value. However, no genetic studies have been carried out with this species and its crossability relations with the common tetraploid potato, S. tuberosum L. ssp. tuberosum, are unknown. Furthermore, accessions from both countries differed in their morphological phenotypes. To ascertain the feasibility of incorporating this wild germplasm into cultivated potato, 2n pollen screening was carried out in 10 accessions and families derived from crosses between accessions; also, pollen-pistil compatibility relations were studied in reciprocal interspecific crosses. Plants of four of the 10 accessions produced 2n pollen (0.1 to 5.0%) and 4n pollen (0.0 to 3.0%). Parallel and tripolar spindles at Anaphase II were the cytological mechanisms involved in 2n pollen formation; lack of chromosome migration in both meiotic divisions originated the 4n pollen. Both full compatibility and incompatibility at various sites along the pistil were observed in the S. tuberosum · S. okadae combinations; most reciprocal combinations were incompatible. Compatible genotypes produced 2n pollen. However, only a few seeds were obtained and chromosome counts could not be carried out in the hybrid progeny because seedlings died at an early stage. The pollen-pistil barriers are incomplete and can be circumvented by the appropiate choice of parents. The identification of the postzygotic barriers will be the focus of further studies. Accession 1 Geographic location Argentina OKA 7618 B Jujuy, Tilcara, Piscuno, 23°36 0 S 65°11 0 W OL 4908 Salta, Chicoana, Quebrada de los Yastos 25°09 0 S 65°50 0 W OKA 7584 A Jujuy, Capital, Falda de Sombra 24°07 0 S 65°38 0 W OKA 4388 · OKA 4404 Jujuy, Tilcara, Piscuno, 23°38 0 S 65°06 0 W; Jujuy, Tilcara, Encrucijada OKA 4392 B · OKA 4407 Jujuy, Tilcara, Piscuno, 23°34 0 S 65°17 0 W; Jujuy, Tilcara, Encrucijada CLE 1583 Salta, Chicoana, San Martín, 25°10 0 S 65°49 0 W Bolivia HPS 2 Bolivia, Larecaja, La Paz , Ilabaya, 17°02 0 S 67°15 0 W HPS 4 Bolivia, Inquisivi, La Paz, 17°02 0 S 67°15 0 W HPS 6 Bolivia, Inquisivi, La Paz, 17°02 0 S 67°15 0 W HHA 6585 · HPS 6 Bolivia, Ayopaya, Cochabamba, Independencia, 17°06 0 S 66°55 0 W; Bolivia, Inquisivi, La Paz, 17°02 0 S 67°15 0 W

Female reproductive development and pollen tube growth in diploid genotypes of Solanum cardiophyllum Lindl

Sexual Plant Reproduction, 2004

We have characterized female gametophyte (megagametophyte) development and the kinetics of pollen tube growth in self-pollinated diploid genotypes (2n=2x=24) of Solanum cardiophyllum Lindl. that show normal seed formation. In this species megasporogenesis and megagametogenesis give rise to a female gametophyte of the Polygonum type composed of two synergids, an egg cell, a binucleated central cell and three antipodals; however, asynchronous abnormalities resembling mechanisms that prevail during the formation of second division restitution gametes were observed. In self-pollinated pistils at least 1-2% of germinating pollen tubes were able to reach the megagametophyte 60-84 hours after pollination (hap). Although the egg cell acquired a zygote-like morphology 60-84 hap, division of the primary endosperm nucleus was only observed 84 hap. The analysis of genetic variability in full-sib progeny confirmed that seeds are derived from sexual reproduction. These observations suggest that diploid genotypes of S. cardiophyllum can serve as an ideal system to genetically investigate true seed formation in a tuber-bearing Solanum species.

Chromosome doubling in monohaploid and dihaploid potatoes by regeneration from cultured leaf explants

Plant Cell, Tissue and Organ Culture, 1984

Plants were regenerated from cultured excised leaf segments of monohaploid (2n = x = 12) and diphaloid (2n = 2x = 24) potato (Solanum tuberosum L.) and a sample has been studied cytologically. In the case of monohaploids, a single leaf regeneration cycle resulted in almost total recovery of doubled monohaploid plants (2n = 2x = 24), whilst 50% of the plants regenerated from doubled monohaploid leaves had doubled again to the doubled double monohaploid (or homozygous tetraploid, 2n = 4x --48) level. Regeneration from dihaploid leaf pieces also gave a good proportion (60%) of doubled genotypes. Very few mixoploids and very few aneuploids were found. These results, together with the general applicability of the method to a large number of potato eultivars, suggest that it can be used as a simple and reliable method of obtaining homozygous tetraploid potatoes.

Genetic strategies to determine the mode of 2n egg formation in diploid potatoes

Euphytica, 1988

In this study, nineteen diploid potato clones (Solanum spp. 2n=2x=24) were identified as 2n egg producers on the basis of fruit set in 2x–4x crosses. The segregation of three genes mapped close to the centromere, Got-1 (1.1 cM), Pgm-2 (2.0 cM), and Sdh-1 (8.3 cM), were analyzed in the tetraploid offspring in these 2x–4x crosses to discriminate between First Division Restitution (FDR) and Second Division Restitution (SDR) modes of 2n egg formation. The co-dominant nature of these markers lead to more precise estimates of the recombinational frequencies as a result of completely classifying the segregating progenies. 2x–4x data revealed a predominance of SDR mechanisms occurring in 20 of the 21 families analyzed. With a SDR mode established, half-tetrad analysis (HTA) of four distal loci, 6-Pgdh-3, Mdh-1, Pgi-1, and Aps-1, revealed two SDR segregation patterns in some of the families. One pattern fit the expectations for the distal arm position. The gene-centromere map distances based upon SDR modes in the families following this pattern, were generally close to 4x−2x (FDR) estimates suggesting similar recombination rates between micro- and mega-sporogenesis. Heterozygosity transmission, on average, was 39.1%. In the other segregation pattern, in which the diploid parents were derived from S. chacoense PI 230580, higher than expected homozygosity levels were found in the female 2n gametophyte populations. A post-meiotic doubling of the reduced megaspore, which generates homozygous 2n eggs, is suggested to operate in three families. The common genetic background of the diploid clones suggested a heritable nature of this mechanism. Pooled data from these three deviant families calculated that 1.8% of the heterozygosity was transmitted to the tetraploid progeny. It is concluded that utilization of seven enzyme-coding loci, with previously established gene-centromere map distances, in 2x–4x crosses improved half-tetrad analysis (HTA) as a means to determine the mode of 2n gamete formation in megasporogenesis and megagametogenesis of diploid Solanum species.

Postmeiotic restitution in 2n-egg formation of diploid potato

Heredity, 1998

Four diploid (2n = 2x = 24) interspecific F 1 hybrids of tuberous Solanum species were tested for the modes of origin of 2n-eggs. The four hybrids were heterozygous for the genetic marker amylose-free starch (Amf/amf) on chromosome 8. By crossing these hybrids with tetraploid S. tuberosum parents (2n = 4x = 48) that were nulliplex for this marker, i.e. Amf/amf amf/ amf/amf/amf crosses, tetraploid progenies were generated and classified for starch phenotypes of microspores. Based on the segregation of the amf marker gene, the tetraploid progenies were classified into nulliplex, simplex and duplex genotypes. In the progenies of three F 1 hybrids, the simplex genotypes predominated and the origin of 2n-eggs could be explained as the result of second division restitution (SDR). But in the progeny of one F 1 hybrid (a S. microdontum S. tuberosum hybrid), there were only nulliplex and duplex genotypes, indicating complete homozygosity of the 2n-eggs (Amf/Amf or amf/amf) for this locus. In order to genotype the 2n-eggs also for other loci on the same chromosome, a tetraploid progeny was generated from a cross between this hybrid and a tetraploid S. tuberosum parent (Tetra 4) and analysed for four RFLP loci on chromosome 8. This analysis showed that all 2n-eggs of the S. microdontum S. tuberosum hybrid were homozygous for all four loci, as was observed for the amf locus. From the same analysis it was evident that crossovers had occurred between the two genomes of this F 1 hybrid. These homozygous and recombinant genotypes indicated that the 2n-eggs had originated from the doubling of the chromosome number in the normal haploid products of meiosis. Following the terminology of first and second division restitution (FDR and SDR), this new mode of origin of 2n-eggs in diploid potato is called post-meiotic restitution (PMR).