Frequency of Polyploids of Solanum tuberosum Dihaploids in 2X × 2X Crosses

When breeding diploid potatoes, tetraploid progeny can result from the union of 2n eggs and 2n pollen in 2x-2x crosses. Thirty-three crosses were made to examine tetraploid progeny frequency in 2x-2x crosses. All crosses were between S. tuberosum dihaploids and diploid self-compatible donors, M6 and DRH S6-10-4P17. Using chloroplast counting for ploidy determination, the frequency of tetraploid progeny was as high as 45% in one of the 33 crosses. Based upon single nucleotide polymorphism (SNP) genotyping, the tetraploid progeny were attributed to bilateral sexual polyploidization (BSP), which is caused by the union of 2n egg and 2n pollen. Dihaploids were identified that produce lower frequencies of 2n eggs. The results of this study suggest that S. tuberosum dihaploids with a high frequency of 2n eggs should be avoided in 2x - 2x crosses for diploid breeding programs.

Rare instances of haploid inducer DNA in potato dihaploids and ploidy-dependent genome instability

In cultivated tetraploid potato, reduction to diploidy (dihaploidy) allows hybridization to diploid germplasm, introgression breeding, and may facilitate the production of inbreds. Pollination with haploid inducers yields maternal dihaploids, as well as triploid and tetraploid hybrids. It is not known if dihaploids result from parthenogenesis, entailing development of embryos from unfertilized eggs, or genome elimination, entailing missegregation and loss of paternal chromosomes. A sign of genome elimination is the occasional persistence of haploid inducer DNA in some of the dihaploids. We characterized the genomes of 1,001 putative dihaploids and 134 hybrids produced by pollinating tetraploid clones with three haploid inducers, IVP35, IVP101, and PL4. We detected inheritance of full or partial chromosomes from the haploid inducer parent in 0.87% of the overall dihaploid progeny, irrespective of the combination of parental genotypes. Chromosomal breaks commonly affected the paternal genome in the dihaploid and tetraploid progeny, but not in the triploid progeny. Residual haploid inducer DNA is consistent with genome elimination as the mechanism of haploid induction. Further, the fact that paternal chromosome breaks are specific to dihaploids and tetraploid progeny suggests that they may be specific to 2x sperms, and supports the hypothesis that 2x sperms facilitate genome elimination.

Sexual and Apomictic Seed Reproduction in Aronia Species with Different Ploidy Levels

The genus Aronia Medik., also known as chokeberry, is a group of deciduous shrubs in the Rosaceae family, subtribe Pyrinae. The four commonly accepted species include A. arbutifolia (L.) Pers., red chokeberry; A. melanocarpa (Michx.) Elliott, black chokeberry; A. prunifolia (Marshall) Reheder, purple chokeberry; and A. mitschurinii (A.K. Skvortsov & Maitul). Wild and domesticated Aronia species are found as diploids, triploids, and tetraploids. Genetic improvement of polyploid Aronia genotypes has been limited by suspected apomixis, which may be widespread or distinct to tetraploids. The objectives of this study were to elucidate the reproductive mechanisms of Aronia species and reveal the occurrence of apomixis within the genus and along ploidy lines. Twenty-nine Aronia accessions [five A. melanocarpa (2×), five A. melanocarpa (4×), eight A. prunifolia (3×), four A. prunifolia (4×), six A. arbutifolia (4×), and one A. mitschurinii (4×)] were used in this study. Intra-accession variability was evaluated by growing out progeny from each open-pollinated maternal accession and comparing plant phenotypes, ploidy levels, and amplified fragment length polymorphism (AFLP) marker profiles between the progeny and maternal accession. Progeny of diploid and tetraploid maternal plants had ploidy levels identical to maternal plants, except for UC009 (A. melanocarpa, 2×) which produced a mix of diploids and tetraploids. UC143 and UC149 (A. prunifolia, 3×) produced all triploid offspring, whereas all other triploid accessions produced offspring with variable ploidy levels including 2×, 3×, 4×, and 5×. Pentaploid Aronia has not been previously reported. Diploid accessions produced significant AFLP genetic variation (0.68–0.78 Jaccard’s similarity coefficient) in progeny, which is indicative of sexual reproduction. Seedlings from tetraploid accessions had very little AFLP genetic variation (0.93–0.98 Jaccard’s similarity coefficient) in comparison with their maternal accession. The very limited genetic variation suggests the occurrence of limited diplosporous apomixis with one round of meiotic division in tetraploid progeny. Triploid accessions appear to reproduce sexually or apomictically, or both, depending on the individual. These results support our understanding of Aronia reproductive mechanisms and will help guide future breeding efforts of polyploid Aronia species.

Production of New Cotton Interspecific Hybrids with Enhanced Fiber Fineness

<p>To improve cotton fiber fineness, the (<em>Gossypium hirsutum</em> L. × <em>Gossypium longicalyx </em>Hutch. &amp; Lee)² allohexaploid and the [(<em>Gossypium hirsutum</em> L. × <em>Gossypium thurberi </em>Tod.)² × <em>G. longicalyx</em>] allotetraploid were backcrossed to <em>G. hirsutum</em> to produce introgressed genetic stocks. The ribbon width (RW) of 600 swelled fibers produced by the hybrids, their parents, and their backcross progeny were analyzed for each compared genotype using an optical microscope. The RWs varied between 6.41±2.15 µm for <em>G. longicalyx</em> to 17.45±2.98 µm for the <em>G. hirsutum</em> parent cultivar C2. Fibers produced by the trispecific hybrids and their progeny were finer than the bispecific hybrid material. For the introgressed stocks, the lowest RWs were observed for the trispecific hybrid (10.79±2.14 µm) and certain backcross progenies (between 11.98±1.27 µm to 12.71±1.61 µm). The allohexaploid RW was 13.58±1.41 µm. One of its tetraploid progeny produced approximately the same value (13.94±2.48 µm). These results show that <em>G. longicalyx </em>is a potential genetic stock for cotton fiber fineness improvement. The genetic stocks produced are valuable materials for improve the fineness of cotton fiber.</p>

Induction and viability of tetraploids in brook trout (Salvelinus fontinalis)

Brook trout (Salvelinus fontinalis) populations are threatened by introduction of invasive species, habitat loss, and habitat degradation in their native range and are a problem invasive species in western Unites States and Canada and in Europe. Stocking sterile triploids has been promoted as an approach to reduce negative effects of stocking of brook trout for recreational fishing on native fish populations. Crossing a tetraploid with a diploid is a method of triploid production that may help hatcheries meet demand. We induced tetraploidy in brook trout by application of 633 kg·cm−2 of hydrostatic pressure for 8 min at 70%–72.5% of the first cleavage interval. Yields of above 50% tetraploid progeny at hatching were readily achieved, although few animals reached 1 year of age. We crossed a male tetraploid with female diploid fish and produced interploid-triploids with eyeing rates in excess of 50%, demonstrating male tetraploids are fertile and capable of siring triploid progeny. Female tetraploid fish were reared to 16 months posthatching and possessed follicles in secondary vitellogenesis, suggesting tetraploid females are also fertile. Tetraploid induction rates in excess of 96% were achieved applying the same hydrostatic pressure treatment to zygotes of tetraploid × diploid crosses at 30 min postfertilization.

Transmission Genetics of Chromatin From a Synthetic Amphidiploid to Cultivated Peanut (Arachis hypogaea L.): Broadening the Gene Pool of a Monophyletic Polyploid Species

Polyploidy creates severe genetic bottlenecks, contributing to the genetic vulnerability of leading crops. Cultivated peanut is thought to be of monophyletic origin, harboring relatively little genetic diversity. To introduce variability from diploid wild species into tetraploid cultivated Arachis hypogaea, a synthetic amphidiploid {[A. batizocoi K9484 × (A. cardenasii GKP10017 × A. diogoi GKP10602)]4×} was used as donor parent to generate a backcross population of 78 progeny. Three hundred seventy RFLP loci were mapped onto 23 linkage groups, spanning 2210 cM. Chromatin derived from the two A-genome diploid ancestors (A. cardenasii and A. diogoi) comprised mosaic chromosomes, reflecting crossing over in the diploid A-genome interspecific F1 hybrid. Recombination between chromosomes in the tetraploid progeny was similar to chromosome pairing reported for A. hypogaea, with recombination generally between chromosomes of the same subgenomic affinity. Segregation distortion was observed for 25% of the markers, distributed over 20 linkage groups. Unexpectedly, 68% of the markers deviating from expected segregation showed an excess of the synthetic parent allele. Genetic consequences, relationship to species origins, and significance for comparative genetics are discussed.

Use of half-tetrad analysis to discriminate between two types of 2n egg formation in a potato haploid

The ratio of the first division restitution (FDR) to second division restitution (SDR) 2n eggs was estimated in 4182t, a haploid (2n = 2x = 24) of Solanum tuberosum L. that produces 2n eggs by the two modes. The segregation of three genes previously mapped relative to their centromeres, Pgm-2 (2.0 cM), Mdh-1 (33.5 cM), and 6-Pgdh-3 (30.1 cM) was analyzed in the tetraploid offspring of a 2x × 4x cross. Based on the segregation of the Pgm-2 locus, 39.7% of the progeny originated from FDR 2n eggs and 60.3% from SDR. Segregation patterns of the two distal loci within the FDR-derived 4x subpopulation indicated that the gene–centromere recombination rate during megasporogenesis was significantly reduced for Mdh-1 when compared with a previous estimate during microsporogenesis. In the SDR-derived 4x subpopulation, the gene–centromere recombination rates for Mdh-1 and 6-Pgdh-3 were not significantly different from previous estimates. Tetraploid progeny generated from one 2x × 4x cross where the 2x parent produces 2n gametes by two modes can be used to make an unbiased comparison of the potential breeding value of FDR and SDR gametes.Key words: potato, megasporogenesis, first division restitution, second division restitution, isozyme.