Estimation of the coefficient of double reduction in the cultivated tetraploid potato

Summary Theoretical models to estimate the coefficient of double reduction in tetraploid organisms and the standard error of this estimate are derived. Using these models, we were able to estimate the coefficient of double reduction for several loci in tetraploid potatoes, Solanum tuberosum L., through examination of segregating isozyme loci in a series of 4x-2x crosses and in haploid progeny derived from six cultivated tetraploid potatoes. Tetraploid x diploid crosses are useful for estimating the frequency of double reduction because of the availability of homozygous diploid tester lines and the large number of tetraploid progeny generated via the functioning of 2n pollen. The strength of haploid analysis is the examination of diploid progeny. However, it is frequently difficult to obtain large numbers of progeny for testing. Based on our results, we conclude that double reduction occurs sporadically in tetraploid potatoes.     

Use of 2n pollen-producing triploid hybrids to introduce tetraploid Mexican wild species germ plasm to cultivated tetraploid potato gene pool

Summary Tetraploid (2n=4x=48) 2EBN Mexican wild species in the series Longipedicellata, which consists of Solanum fendleri, S. hjertingii, S. papita, S. polytrichon, and S. stoloniferum, were crossed with two 2EBN cultivated diploid (2n=2x=24) clones. The resulting triploid hybrids (2n=3x=36) produced 2n pollen (triplandroids) by the mechanism of parallel orientation of anaphase II spindles. The percentage of stainable pollen in 520 triploids ranged between 0 and 23.5%, with a mean of 2.7%. Triploids producing between 13.0 and 23.5% stainable pollen were crossed as staminate parents to the tetraploid cultivars, resulting in abundant pentaploid (2n=5x=60) and near-pentaploid hybrid progeny. Crosses of triploids with lower percentage of stainable pollen as pollen parent to the tetraploid cultivars did not yield fruit, unless rescue pollen from a tetraploid cultivar was added 2 days later. Pentaploid hybrids were selected among selfed tetraploid progenies using morphological and isoxyme markers transmitted from their cultivated diploid parents. These pentaploid hybrids were vigorous and had uniformly sterile pollen. They were female fertile and were crossed with tetraploid cultivars, yielding an average of 19 seeds per fruit. Triplandroids provide the opportunity of transferring 2EBN tetraploid Mexican wild species in the series Longipedicellata germ plasm into the 4EBN cultivated potatoes.Cooperative investigations of the ARS, USDA, and the Washington State University Agricultural Research Center, Prosser, WA 99350, USA. H/LA Paper No. 90-03, College of Agriculture and Home Economies Research Center, Washington State University, Pullman, WA 99164, USA     

Occurrence of 2n pollen and ps gene frequencies in cultivated groups and their related wild species in tuber-bearing Solanums

Summary The gene frequency for parallel spindles (ps) was estimated from the frequency of plants producing 2n pollen in three cultivated groups: 2x Phureja (phu), 2x Stenotomum (stn), and 4x Andigena (adg), as well as in four related wild taxa: 2x Solanum brevicaule (brc), 2x S. sparsipilum (spl), 4x S. gourlayi (grl) and 4x S. gourlayi-S. infundibuliforme hybrids (grl-ifd). Plants with more than 1% large pollen were considered as 2n pollen producers. Observations of meiosis in a sample of 2n pollen-producing plants indicated that parallel spindles is the mechanism of 2n pollen formation. The number of plants with 2n pollen among the total examined was 228 plants (15.5%) of 1,473 in 2x spl, 31 (26.7%) of 116 in 2x brc, 92 (17.4%) of 528 in 2x stn, 665 (22.1%) of 3,008 in 2x phu, 731 (51.4%) of 1,421 in 4x adg, 591 (41.2%) of 1,436 in 4x grl, and 36 (64.3%) out of 56 in 4x grl-ifd. The ps gene frequencies assuming Hardy-Weinberg equilibrium were: 0.393 for 2x spl, 0.462 for 2x brc, 0.417 for 2x stn, 0.470 for 2x phu, 0.847 for 4x adg, 0.801 for 4x grl, and 0.895 for 4x grl-ifd. Twenty-five adg clones were randomly selected from a large population and were crossed with 2x clone W5295.7, which produces 2n pollen by parallel spindles (ps). The 4x progenies from 4x×2x crosses were used to determine the genotypes at the ps locus by screening 10–20 plants in each family for 2n pollen. Based on chromosome segregation at the ps locus, 9, 14, 1, and 1 clones were nulliplex, simplex, simplex or duplex, and duplex, respectively. The frequency of the ps gene in the adg population was estimated to be 0.825 and 0.815 for chromosome and chromatid segregation, respectively. The high frequencies of 2n pollen and the ps gene in cultivated 2x and 4x groups, and in wild taxa closely related to them, provide evidence for sexual polyploidization in the tuber-bearing Solanums.Paper No. 3032 from the Laboratory of Genetics. Research supported by the College of Agriculture and Life Sciences; International Potato Center; USDA, SEA, CGRO 84-CRCR-1-1389; and Frito Lay, Inc.     

Discovery of a synaptic mutant in potato haploids and its usefulness for potato breeding

Summary A synaptic mutant was found in haploids (2n=2x=24) extracted from the Mexican potato variety Atzimba (2n=4x=48). The mutant is inherited as a simple Mendelian recessive, designated sy4. Meiotic abnormalities of the mutant during microsporogenesis include: poor synapsis at pachytene; high frequency of univalents at diakinesis; elongated and curved spindles and univalents being scattered over the spindles at metaphase I and anaphase I; abnormal chromosome distribution at anaphase I; and production of sterile pollen, presumably due to unbalanced chromosome complement. The expression of sy4 in megasporogenesis was also detected. The sy4 mutant is very useful for potato breeding when combined with another meiotic mutant, parallel spindles (ps), because haploids homozygous for sy4 and ps produce fertile 2n pollen which transmit almost intact genotypes of the parents to the progenies. Thus, the meiotic mutants provide a powerful breeding method for maximizing heterozygosity and epistasis. They can also provide a very efficient method of transferring diploid germplasm, which has desired characteristics efficiently combined at the 2x level, to tetraploids. Many haploids have been identified with 2n pollen production by ps alone or by sy4 and ps, vigorous growth and good flowering, and a high level of resistance to late blight. The importance of a further search for meiotic mutants and their use for breeding is discussed.     

Apomixis and ploidy barrier suppress pollen-mediated gene flow in field grown transgenic turf and forage grass (Paspalum notatum Flüggé)

Bahiagrass (Paspalum notatum Flüggé) is the predominant forage grass in the southeastern US. The commercially important bahiagrass cultivar ‘Argentine’ is preferred for genetic transformation over sexual diploid cytotypes, since it produces uniform seed progeny through apomixis. Pseudogamous apomictic seed production in Argentine bahiagrass may contribute to transgene confinement. It is characterized by embryo development which is independent of fertilization of the egg cell, but requires fertilization with compatible pollen to produce the endosperm. Pollen-mediated gene transfer from transgenic, glufosinate-resistant apomictic bahiagrass as pollen donor at close proximity (0.5–3.5 m) with non-transgenic sexual or apomictic bahiagrass cultivars as pollen receptors was evaluated under field conditions. Hybridization frequency was evaluated by glufosinate herbicide resistance in >23,300 seedlings derived from open-pollinated (OP) pollen receptor plants. Average gene transfer between transgenic apomictic, tetraploid and sexual diploid bahiagrass was 0.03%. Herbicide-resistant hybrids confirmed by immuno-chromatographic detection of the PAT protein displayed a single copy bar gene identical to the pollen parent. Hybrids resulting from diploid pollen receptors were confirmed as triploids or aneu-triploids with significantly reduced vigor and seed set as compared to the parents. Transmission of transgenes to sexual bahiagrass is severely restricted by the ploidy difference between tetraploid apomicts and diploid sexual bahiagrass. Average gene transfer between transgenic apomictic tetraploid and non-transgenic, apomictic tetraploid bahiagrass was 0.17%, confirming a very low frequency of amphimixis in apomictic bahiagrass cultivars. While not providing complete transgene containment, gene transfer between transgenic apomictic and non-transgenic bahiagrass occurs at a much lower frequency than reported for other cross-pollinating or facultative apomictic grasses.     

The occurrence and frequency of 2n pollen in three diploid solanums from Northwest Argentina

Summary A group of wild, tuber-bearing species from Northwest Argentina, belonging to the series Tuberosa, Solarium spegazzini Bitt. (spg, 2n=2x=24), S. gourlayi Hawkes (grl, 2n=2x=24 and 2n=4x=48) and S. oplocense Hawkes (opl, 2n=6x=72), and Cuneolata, S. infundibuliforme Phil (ifd, 2n=2x=24), is being used to investigate the mode of origin of polyploids in the genus Solanum. 2n gametes have been detected in the diploid species ifd and spg and in a diploid race of grl, using cytological and breeding approaches. Twenty-two introductions of spg, 8 of grl and 26 of ifd have been tested for 2n pollen; 59%, 63% and 54% of them, respectively, had at least one 2n pollen producing plant. These introductions comprised 238, 76 and 235 plant respectively, of which 20, 16, and 32 plant produced 5% or more 2n pollen. The mechanism of 2n pollen formation was determined in several plant of 2x spg, 2x grl and 2x ifd. All of them were found to form diplandroids via parallel spindles. This mechanism, which gives meiotic products genetically equivalent to first division restitution gametes, is under control of the Mendelian recessive ps. The results suggest that the allele ps is widely distributed in natural populations of the three diploids, and that its frequency is very high. These species are seen as valuable material for population genetic studies, and for the eventual incorporation into a breeding scheme involving sexual polyploidization via 2n gametes.     

Unreduced gametes in diploid Medicago and their importance in alfalfa breeding

Summary In the genus Medicago, it is known that 2n gametes have been important in the evolution and breeding of cultivated alfalfa, which is a natural polysomic polyploid (2n=4x=32), however little is known on the frequency of male and female 2n gametes in diploid relatives of alfalfa. To obtain data on the frequency of 2n gametes, more than 12,000 2x–4x and 4x–2x crosses were made in 1982 at Madison (USA). Diploid parents in crosses were from four populations of M. coerulea, two of M. falcata and one diploid population of cultivated M. sativa which was derived by haploidy. The tetraploid seed parent in the crosses was a male-sterile M. sativa clone and vigorous tetraploid M. sativa plants were used as pollen parents. Each of 274 diploid plants was utilized both as male and as female. Of the 548 cross combinations, 266 crosses produced variable quantities of seeds which were sown in 1983 in a greenhouse at Perugia (Italy); the plants were subsequently space transplanted in the field in 1984. The identification of ploidy level of these genotypes was made on the basis of morphological characters, plant fertility, pollen stainability and chromosome counts.Of the 515 plants analyzed, the majority behaved as normal tetraploids indicating that many diploid plants produced 2n gametes. Diplogynous and diplandrous gamete production was not correlated with each other, which indicated a different genetic control of 2n sporogenesis in the 2 sexes. Only 4 F₁ triploid plants confirmed the presence of a very effective triploid block in alfalfa. In consequence, bilateral sexual polyploidization is a more likely alternative for the origin of tetraploid alfalfa than triploid bridges. The present study showed that it is possible to efficiently identify genotypes able to produce high frequencies of 2n gametes within natural populations of diploids Medicago that are useful in alfalfa breeding.Part of this study was conducted at the Agronomy Department, University of Wisconsin, Madison, Wis, USA, while one of us (F. Veronesi) was in receipt of financial assistance provided by the National Research Council of Italy; part was conducted at Centro di Studio per il Miglioramento Genetico delie Piante Foraggere, C.N.R., Perugia, Italy. The paper was presented at the Eucarpia Fodder Crops Section Meeting, Svalöv, Sweden, 16–19th September 1985     

Origin of chloroplast DNA diversity in the Andean potatoes

Summary Wide chloroplast DNA (ctDNA) diversity has been reported in the Andean cultivated tetraploid potato, Solanum tuberosum ssp. andigena. Andean diploid potatoes were analyzed in this study to elucidate the origin of the diverse ctDNA variation of the cultivated tetraploids. The ctDNA types of 58 cultivated diploid potatoes (S. stenotomum, S. goniocalyx and S. phureja), 35 accessions of S. sparsipilum, a diploid weed species, and 40 accessions of the wild or weed species, S. chacoense, were determined based on ctDNA restriction fragment patterns of BamHI, HindIII and PvuII. Several different ctDNA types were found in the cultivated potatoes as well as in weed and wild potato species; thus, intraspecific ctDNA variation may be common in both wild and cultivated potato species and perhaps in the higher plant kingdom as a whole. The ctDNA variation range of cultivated diploid potatoes was similar to that of the tetraploid potatoes, suggesting that the ctDNA diversity of the tetraploid potato could have been introduced from cultivated diploid potatoes. This provided further evidence that the Andean cultivated tetraploid potato, ssp. andigena, could have arisen many times from the cultivated diploid populations. The diverse but conserved ctDNA variation noted in the Andean potatoes may have occurred in the early stage of species differentiation of South American tuber-bearing Solanums.     

Reducing the tetraploid non-nodulating alfalfa (Medicago sativa) MnNC-1008(NN) germ plasm to the diploid level

MnNC-1008(NN) (referred to as MN-1008) is a tetraploid alfalfa mutant with two recessive genes (nn ₁ and nn ₂ )conditioning the non-nodulating trait. The tetraploid level (2n=4x=32) of this Medicago sativa germ plasm was reduced to the diploid (2n=2x=16) level using the 4x-2x genetic cross originally described as a workable method for the induction of haploidy in alfalfa by T. E. Bingham. In our experiments more than 7000 emasculated flowers of a single non-nodulating MN-1008 mutant alfalfa plant with purple petals were cross-pollinated with pollen from a single, diploid, yellow-flowered alfalfa plant. Mature seeds from these crosses were collected and germinated, after which the plants were subjected to morphological and cytogenetic analyses as well as to DNA fingerprinting. Out of 26 viable progeny, 6 were hybrid plants, 19 proved to be self-mated derivatives of MN-1008, while one descendant turned out to be a diploid (2n=2x=16), purple flowered, non-nodulating plant denoted as M. sativa DN-1008. This diploid, non-nodulating alfalfa plant can serve as starting material to facilitate the comprehensive morphological, physiological and genetic analysis (gene mapping and cloning) of nodulation in order to learn more about the biology of the symbiotic root nodule development. To produce diploid, nodulating hybrid F₁ plants, DN-1008 was crossed with a diploid, yellow-flowered M. sativa ssp. quasifalcata plant. An F₂ population segregating the nn ₁ and nn ₂ genes in a diploid manner, in which the genetic analysis is more simple than in a tetraploid population, can be established by self-mating of the F₁ plants.     

A new cytotype of Jacobaea vulgaris (Asteraceae): frequency,morphology and origin

Jacobaea vulgaris subsp. vulgaris (syn. Senecio jacobaea subsp. jacobaea) constitutes an intricate polyploid complex distributed in Europe. Four cytotypes have been reported in this species, three with euploid (diploid, tetraploid and octoploid; 2n=20, 40 and 80) and one with aneuploid (2n=32) chromosome numbers. Here we report that the diploid chromosome number (2n=20) reported from Bulgaria is due to misidentification with Jacobaea aquatica. On the other hand, we have discovered a new, hexaploid (2n=6x=60) cytotype within J. vulgaris subsp. vulgaris using flow cytometry. The new cytotype occurs within four sympatric populations of otherwise tetraploid and octoploid plants in Pannonia (one locality in the eastern Czech Republic and two localities in southwestern Slovakia) and in Podillya (one locality in western Ukraine). The frequency of hexaploid individuals within 76 studied populations is very low (only 10 of 693 analysed plants), and hexaploids probably represent hybrids between tetraploid and octoploid plants. Three mixed populations with hexaploid plants were subjected to detailed morphological and pollen fertility analyses. Multivariate morphometric analysis reveals partial separation of tetraploid and octoploid plants, whereas hexaploid individuals are similar in morphology to octoploids. In comparison with tetraploids, octoploids and hexaploids exhibit slightly longer ray florets, involucral bracts and tubular florets and more hairy outer achenes. Hexaploid plants display larger pollen grains and lower pollen fertility compared to tetraploids and octoploids.     

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

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 cultivars, suggest that it can be used as a simple and reliable method of obtaining homozygous tetraploid potatoes.     

Single cross alfalfa (Medicago sativa L.) hybrids produced via 2n gametes and somatic chromosome doubling: experimental and theoretical comparisons

Summary The potential breeding value of 2n gametes from diploid alfalfa (2n = 2x = 16) was tested by comparing single cross alfalfa hybrids produced via 2n = 2x gametes from diploids versus n = 2x gametes from somatic-chromosome-doubled, tetraploid counterparts. Three diploid clones, designated 2x-(rprp), homozygous for the gene rp (conditions 2n gamete formation by a first division restitution mechanism) were colchicine-doubled to produce their tetraploid counterparts, designated 4x-(SCD). These six clones were crossed as males to the same cytoplasmic male sterile clone. Yield comparisons of progeny from the six clones demonstrated a significant yield increase of the hybrid progeny from 2n = 2x gametes from the diploids over the hybrid progeny from n = 2x gametes from the chromosome doubled tetraploid counterparts. The yield gain ranged from a 12% increase to a 32% increase. Theoretical comparisons indicated the 2n = 2x gametes from diploids would have 12.5 to 50% more heterozygous loci, on average, than the n = 2x gametes derived from somatic doubling. These results confirm the importance of heterozygosity on alfalfa yield, and the results demonstrate that 2n gametes formed by first division restitution offer a unique method for producing highly heterotic alfalfa hybrids.     

Allozyme variability and phylogenetic relationships in the cultivated potato (Solanum tuberosum) and related species

Gene frequencies at 13 isozyme loci were determined in three South American taxa of cultivated potatoes [the diploid group (gp.) Stenotomum, the diploid subgroups (subgp.) Goniocalyx, and the tetraploid gp. Andigena ofS. tuberosum], in the diploid weed speciesS. sparsipilum, and in most of the main cultivars now raised in the Northern Hemisphere (the tetraploid gp. Tuberosum ofS. tuberosum). High levels of genetic variability (mean number of alleles per locus, percentage of polymorphic loci, and mean heterozygosity) were detected, being higher in tetraploid potatoes. An equilibrium among the evolutionary factors which increase genetic variability and artificial selection for maximum yield would explain the high uniformity of heterozygosity values we observed in both Andigena (0.36 ± 0.02) and Tuberosum (0.38 ± 0.01) cultivars.—The low value of genetic distance (D = 0.044) between Stenotomum and Goniocalyx does not support the status of species forS. goniocalyx.—In most isozyme loci, the electromorphs of gp. Andigena were a combination of those found in both gp. Stenotomum andS. sparsipilum, suggesting an amphidiploid origin of gp. Andigena from that two diploid taxa. The presence in Andigena of unique electromorphs, which were lacking in both gp. Stenotomum andS. sparsipilum, suggests that other diploid species could be also implied in the origin of tetraploid Andean potatoes. Furthermore, since Andigena were more related to Stenotomum (D = 0.052) than toS. sparsipilum (D = 0.241), the autopolyploidization of Stenotomum individuals and the subsequent hybridization with gp. Andigena may also have occurred. Thus, our study suggests a multiple origin (amphidiploidy, autoploidy, and hybridization at tetraploid level) of gp. Andigena.—Most of the electromorphs of gp. Tuberosum were also found in gp. Andigena; both the direct derivation of that group from the Andean tetraploid potatoes and the repeated introgression provided by breeding programmes could explain this result. However, the allele c of Pgm-B, present in 30 out of 76 Tuberosum cultivars from Northern Hemisphere as well as in 3 Chilean Tuberosum cultivars, lacks in the 258 Andigena genotypes sampled, suggesting that Chilean germplasm could have taken part in the origin of at least the 39% of the potato cultivars from Europe and North America analyzed here.—The distanceWagner procedure provides an estimate of a 30% of heterogeneity in the evolutionary divergence shown by different groups of cultivated potatoes. Diploid groups show a higher (22.5%) evolutionary rate than tetraploids, which can be attributed to both tetrasomic inheritance and facultative autofecundation that exists in Andigena and Tuberosum groups. Thus, artificial selection acting since 10000 years has not resulted in a higher rate of molecular evolution at the isozyme level in the tetraploids.     

Desynapsis in diploid and tetraploid clones of ryegrass

Desynapsis is described in diploid and tetraploid plants of perennial ryegrass. The plants were derived by repeated cloning of a single mixoploid (2n=14 and 28) detected among colchicine-treated seedlings. The diploid and tetraploid clones varied in degree of desynapsis, chiasma number, and fertility. The variation among the clones was probably environmental. The progeny of the mixoploid parent included dipoids, tetraploids, and an aneuploid. One diploid and the aneuploid were desynaptic and originated perhaps by selfing. Apparently a single recessive gene determined desynapsis. The role of synaptic genes in controlling the chemical structure and function of nucleoprotein macromolecules is discussed.     

Chromosome doubling of 2x Solanum species by oryzalin: method development and comparison with spontaneous chromosome doubling in vitro

A potato breeding scheme implies the possibility of ploidy level manipulation either by reducing the chromosome number of cultivars from 48 to 24 to be able to cross them with diploid related species or by doubling diploid material to reach the generally optimal tetraploid level. In vitro spontaneous chromosome doubling is widely used but can lead to somaclonal variation. Since oryzalin has proven to be efficient as a chromosome doubling agent on potato cell suspension cultures, we tried this herbicide on various Solanum species and interspecific diploid hybrids. A 24 h dip in a 28.8 M aqueous oryzalin solution applied on apical buds was the most efficient treatment in terms of tetraploid plant production (mean = 4.1 tetraploid plants for 10 treated buds over 4 genotypes). However 50–100% of the regenerated tetraploid plants acclimatized after in vitro treatment proved to be chimaeric. Consequently, a selection procedure in the progeny was necessary to obtain real and stable doubled clones and final yields were low. This technique is easy to apply and could be a good alternative to chromosome doubling by spontaneous in vitro regeneration in the case of refractory genotypes especially where somaclonal variation is problematic. Percentage of tetraploids among the regenerated plants varied from 6 to 29% with the oryzalin doubling technique while it varied from 20 to 78% by in vitro spontaneous doubling for five diploid genotypes. An observation of the progeny indicated that chimaeras were more frequent using oryzalin (50–100% of the initially supposed tetraploid plants) than when chromosomes doubled spontaneously (4–67% of the initially supposed tetraploid plants).     

Possible pathways of the gene flow inTaraxacum sect.Ruderalia

Reproductive behaviour and the pathways of gene flow among ploidy levels were studied experimentally inTaraxacum sect.Ruderalia. Diploid, triploid and tetraploid individuals were sampled from mixed diploid — polyploid natural populations. 136 experimental hybridizations between the plants of different ploidy levels were performed. Seeds resulting from these crosses, those obtained from isolated anthodia as well as from open pollinated anthodia (both from cultivated and wild plants) were subjected to the flow-cytometric seed screening (FCSS) to determine ploidy levels in the progeny and to infer breeding behaviour of maternal plants. Three possible pathways of the gene flow were studied: (A) fertilization of sexuals by pollen of apomicts, (B) B_III hybrid formation, (C) facultative apomixis. Diploid maternal plants when experimentally crossed with triploid pollen donors produced diploids and polyploid progeny, while when pollinated with a mixture of the pollen of diploids and triploids or insect pollinated, no polyploids were discovered. It seems that in the mixture with the pollen of diploids, the pollen of triploids is ineffective. Tetraploids produce hybrids much easier with diploid mothers and their role in wild populations requires further study. Triploid mothers, even those with subregular pollen did not show traces of facultative apomixis. B_III hybrids were present in the progeny of both triploids and tetraploids, in tetraploids in quite high percentages (up to 50% of the progeny in some crosses).     

Risk assessment of transgenic apomictic tetraploid bahiagrass,cytogenetics, breeding behavior and performance of intra-specific hybrids

Pollen-mediated gene transfer from stress tolerant or herbicide-resistant transgenic plants may cause environmental or agronomic problems. Apomictic seed production found in some bahiagrass cultivars may serve as a natural transgene containment system. Under greenhouse conditions, the average gene transfer frequency from an herbicide-resistant apomictic tetraploid to a population of sexual diploid bahiagrass genotypes or apomictic tetraploid bahiagrass was 0.16% when the transgenic pollen donor was placed at 0.5–1.5 m distance from the non-transgenic pollen receptors. The herbicide-resistant hybrids were characterized for transgene integration, expression and ploidy, by Southern blot analysis, immuno-chromatography and flow cytometry, respectively. Hybrids resulting from open pollination of non-transgenic diploid female plants with transgenic tetraploid male plants were triploids or near-triploids, with 2n = 26–34. These hybrids displayed a wide range of phenotypic variability, including some non-persistent or non-flowering dwarf-type hybrids with good vigor, or hybrids with vegetative growth similar to non-transgenic plants, but with significantly reduced seed set. Non-flowering aneu-triploids with good vigor/field performance will provide the highest level of transgene containment. Embryo sac analysis of pollinated spikelets confirmed a high proportion of aborted ovules. An apospory-linked RFLP marker was detected in 13 of the 15 near-triploid hybrids. All flowering aneuploid hybrids displayed significantly reduced seed set, and none of the sexual near-triploid hybrids produced any seeds. All tetraploid gene transfer events carried the apospory-linked RFLP marker, suggesting that despite the presence of the aposporus locus, a low degree of sexuality co-exists in apomictic tetraploid cultivars. Thus, tetraploid apomictic bahiagrass does not provide complete transgene containment, although intra-specific gene transfer is drastically reduced compared to sexually reproducing perennial grasses.     

Untersuchungen zur Karyologie und Mikrosporogenese vonPelargonium sect.Pelargonium (Geraniaceae)

The chromosome numbers of the 24 species of sect.Pelargonium were determined from field collected and cultivated plants of known localities in S. Africa. Twelve species are diploid (2n = 22), eight tetraploid (2n = 44), one hexaploid (2n = 66), and three octoploid (2n = 88). The chromosome numbers correlate well with the proposed subdivision of sect.Pelargonium. Its chromosomes are relatively small (1.0–1.5 µm) in comparison to most of the other sections, and its diploid karyotype is considered to be primitive. The occurrence of the basic number x = 11 in this section, in other sections of the genus, and in related genera (Monsonia, Sarcocaulon) leads to the conclusion that x = 11 probably is basic for the whole genus. — The pollen meiosis, microsporogenesis and pollen fertility of the diploid species is normal, with the exception of one, possibly young taxon from the Greyton Nature Reserve. The tetraploid species could be of autoploid origin, the higher polyploids exhibit a mixed auto-alloploid nature. — The 20 diploid and tetraploid species have a relatively small distribution range, most of them occur in the SW. Cape Province of South Africa. This area may therefore be considered as the centre of origin of the genus. Three of the four high polyploid species occupy rather large areas.

Untersuchungen zur Karyologie und Mikrosporogenese der GattungPelargonium, 1.     

Successive domestication and evolution of the Andean potatoes as revealed by chloroplast DNA restriction endonuclease analysis

Five chloroplast DNA (ctDNA) types (W, T, C, S, and A) have previously been identified in the Andean tetraploid cultivated potatoes (Solanum tuberosum ssp. andigena) and three types (C, S, and A) in diploid cultivated potatoes (S. stenotomum). In this study, ctDNA types were determined for an additional 35 accessions of S. stenotomum and 97 accessions of putative ancestral wild species (15 of S. brevicaule, 26 of S. bukasovii, 4 of S. candolleanum, 25 of S. canasense, 17 of S. leptophyes, and 10 of S. multidissectum). The first five ctDNA types were also identified in S. stenotomum. The wild species were also polymorphic for ctDNA types except for S. brevicaule, which had only W-type ctDNA. T-type ctDNA was not found in any of the wild species and could have originated from W-type ctDNA after S. stenotomum arose. The other types of ctDNA evolved in wild species. The geographical distribution of each ctDNA type indicated that A-type ctDNA arose in central Peru and T-type ctDNA in the Bolivia-Argentine boundary. It is implied that potatoes were successively domesticated and that, in parallel, several wild species were differentiated from time to time and place to place from the ancestral species complex. Subsequent sexual polyploidization formed a wide ctDNA diversity among the Andean tetraploid potatoes, and selection from them formed the limited ctDNA diversity found in Chilean tetraploid potatoes (ssp. tuberosum).Hawkes' (1990) classification system is tentatively adopted throughout this text. Synonyms indicated by Hawkes (1990) for the species names described by various authors are presented in parentheses.     

Autonomous cell death, temperature sensitivity and the genetic control associated with resistance to cucumber mosaic virus (CMV) in diploid potatoes (Solanum spp.)

Cucumber mosaic virus (CMV) is a commonly occurring plant virus that causes severe damage in many crops, including the diploid crop species tomato and pepper (Lycopersicon spp. and Capsicum spp., respectively) of the family Solanaceae, but it is neither common nor economically important in cultivated potatoes (Solanum tuberosum; Solanaceae). Resistance to CMV was examined in two diploid (2n=2x=24), highly heterozygous potato populations (Solanum spp.; Solanaceae) consisting of 76 and 126 progeny. Resistance to long-distance transport of CMV controlled by one locus with a major effect and functional at a low temperature (18°C) but overcome at a high temperature (28°C) was identified in one population. In the other population, resistance was controlled by two loci with major effects. In both populations, additional genes with minor effects were probably also involved. Induced resistance to CMV, associated with autonomously developing cell death lesions (Anl) previously not known in potato, was expressed in one parental line. The mechanisms of resistance to CMV may be associated with an inherent or developmental lack of host factors required for compatible CMV-host interactions in viral long distance transport and/or inability of CMV to efficiently suppress the host gene silencing mechanism in potatoes. Polyploidy (gene dose) and high heterozygosity (multiple homologous genes) of potato cultivars may be significant in conferring the durable resistance to CMV. These data provide explanations why CMV is not common and economically important in cultivated potatoes, even though CMV commonly occurs in other crops, weeds and wild plants in potato production areas. Received: 11 February 1999 / Accepted: 25 March 1999