Review of Pennisetum section Brevivalvula (Poaceae)

Section Brevivalvula is one of five sections in the large tropical grass genus Pennisetum. It belongs to the tertiary genepool of P. glaucum (L.) R. Br., pearl millet, and consists of six morphological taxa: P. atrichum Stapf & Hubb., P. hordeoides (Lam.) Steud., P. pedicellatum Trin., P. polystachion (L.) Schult., P. setosum (Swartz) L. Rich. and P. subangustum (Schum.) Stapf & Hubb., which together form a polyploid and agamic complex. Four euploid (x = 9) and twelve aneuploid chromosome levels have been found till now; the polyploids are apomictic, while diploid populations of P. polystachion and P. subangustum are considered sexual. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cytological and geographical characterizations of Hemarthria

Summary Chromosme numbers were determined for 56 Hemarthria altissima (Poir.) Stapf et C. E. Hubb. introduction, forty of these were diploid (2n=18) and 16 were tetraploid (2n=36). These results, combined with previous findings, show that all but three of the tetraploids in the USDA Hemarthria altissima collection originated north of 20 S latitude. All other introductions collected throughout southern Africa were diploid. Meiosis was regular in a hexaploid, 6 tetraploid and 32 diploid introductions but a low frequency of quadrivalents was found in the teraploids. H. uncinata R. Br. and H. uncinata var. spathacea (Domin) Vickery were found to have 2n=36 chromosomes H. compressa (L.f.) R. Br., introduced from Japan, had 2n=54 chromosomes. No major cytological abnormalities exist in these Hemarthria species. Significant variation exists among the ploidy levels for cold tolerance and in vitro organic matter digestion to provide the basis for a forage improvement program.Joint contribution from the Department of agronomy. Institute of food and Agric. Sciences (IFAS), Univ. of Florida. Gainesville, Fl and, Plant Genetics and Germplasm Institute, USDA, Beltsville, MD Published as IFAS Journal Series No. 2849.     

Cytogeography and variation of stomatal size of Paspalum Glaucescens (Gramineae; Paniceae) in Southern Brazil

Paspalum glaucescens belongs to the informal group Plicatula, reproductively characterized by the dominance of tetraploid apomitic lines in most of its populations, with rare diploid, sexual counterparts. The species shows high phenotypic variation. Twenty nine Southern Brazilian accessions were cytologically and morphologically analysed. Most of the accessions were tetraploid (2n = 4x = 40). Meiotic study of three tetraploids showed their irregular behaviour. Eight accessions presented the diploid level (2n = 2x = 20).This can be considered a very high frequency of diploids in a member of the Plicatula group. While the tetraploids are concentrated at the highest elevations, diploids were detected mostly in the lowlands. Average stomatal sizes were quite distinct on different ploidy levels, being larger in tetraploids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analyses of phenotype and ARGOS and ASY1 expression in a ploidy Chinese cabbage series derived from one haploid

The aim of this research was to improve our understanding of how ploidy level influences phenotype and gene expression in Chinese cabbage (Brassica rapa L. ssp. pekinensis). Haploid plants (2n = 10) was induced by 0.2% colchicine to produce diploid (2n = 20) and tetraploid plants (2n = 40). The aneuploid (2n = 24) was also obtained by hybridization between diploid plants as the female and tetraploid plants. The ploidy levels of all plants were identified through chromosome counts and flow cytometry. Leaves and petals became larger as the ploidy level increased from haploid to diploid, and from aneuploid to tetraploid. Similarly, expression of ARGOS was regulated by genome size, increasing in parallel with the level of ploidy. Among the four ploidy types, expression was stronger in the floral buds than in the leaves. Expression by ASY1 also differed according to ploidy level, being highest in diploid plants, followed in order by tetraploids. Expression was similar between haploids and aneuploids at two stages—prior to and after meiosis—but was higher in the haploids during meiosis. When buds were compared within the same ploidy type at different stages, ASY1 expression was obviously higher during meiosis than either before or after. Our study demonstrated the generation and phenotype of a ploidy Chinese cabbage series derived from one haploid. Expression of genes ARGOS and ASY1 were modulated by genome size in this ploidy series, and the regulated patterns of the two genes was different.     

Chromosome numbers and microsporogenesis in Brachiaria brizantha (Gramineae)

The genus Brachiaria, native to the African tropical savannas, has achieved significance as a pasture grass in many tropical and subtropical countries, including Brazil. Many species and accessions are polyploid and apomictic, which complicates the improvement of breeding stocks through hybridization. In support of breeding programs, cytogenetic characterization, including chromosome counts and evaluation of the meiotic behavior in the accessions of the Brachiaria has been undertaken at the Embrapa Beef Cattle Center. In this study, 22 accessions of B. brizantha were analyzed of which one was found to be diploid (2n = 2x = 18), 18 were tetraploid (2n = 4x = 36) and three were hexaploid (2n = 6x = 54). The meiotic chromosome behavior was slightly irregular in the diploid and in some tetraploid accessions, and highly irregular in most tetra- and hexaploid accessions. Meiotic abnormalities were those common to polyploidy, i.e., multivalent chromosome association at diakinesis and irregular chromosome segregation leading to micronuclei formation in the tetrad stage. Low frequencies of multivalent chromosome associations among polyploids suggest that they may be segmental allopolyploids. This revised version was published online in August 2006 with corrections to the Cover Date.     

Occurrence of hexaploid males in Dioscorea alata L.

In the polyploid species Dioscorea alata, earlier studies have shown a prevalence of higher ploidy levels (2n = 60 and 80) restricted among female clones. Cytological screening of a number of rare flowering collections maintained at the CTCRI revealed the occurrence of hexaploids (2n = 60) among male clones for the first time. The hexaploid males were sparse flowering, showing irregular meiosis leading to very high pollen sterility. On the basis of the diploid chromosome number 2n = 20 in the Old World Dioscorea, the trivalent forming 2n = 60 male is considered as an autoallohexaploid.     

河北省桑属植物染色体倍数性研究

研究了桑属植物５个种３２个品种的染色体倍数性，发现宽城１０号等９个品种为三倍体（２ｎ＝３ｘ＝４２），其余为二倍体（２ｎ＝２ｘ＝２８）。     

芥菜型油菜×羽衣甘蓝种间杂种的获得及其性状表现

芸薹属内遗传和变异类型极其丰富,这为芸薹属植物种间杂交提供了条件。通过甘蓝(B. oleracea,2n=CC=18)和芥菜型油菜（2n=AABB=36）的种间杂交可以获得六倍体新物种,为油菜育种创造新的种质资源。本文选用芥菜型油菜和黄籽羽衣甘蓝(B. oleracea var. aceaphala,2n=CC=18)进行种间杂交,在10个杂交组合中,共授粉559朵花,     

Male fertility and cytology of triploid hybrids between tetraploidSolanum commersonii (2n=4x=48, 2EBN) and Phureja-Tuberosum haploid hybrids (2n=2x=24, 2EBN)

Summary Solanum commersonii Dun. is a diploid (2n=2x=24, 1EBN) wild species of potential value for potato breeding. It is a reproductively isolated species and cannot be crossed with Tuberosum haploids (2n=2x=24, 2EBN) or other diploid 2EBNSolanum species. In order to overcome the EBN barriers, triploid hybrids were produced between Phureja-Tuberosum haploid hybrids, which form 2n pollen grains by parallel spindles, and tetraploidS. commersonii. Microsporogenesis analysis of the triploids indicated a trend towards low values of chromosome distribution at Anaphase I; lagging chromosomes were often observed as well. Despite these abnormalities, the percentage of stainable pollen was very high, ranging from 5.0% to 74.3%. A high variation in pollen grain diameter was also evident. Parallel and tripolar orientation of spindles at Metaphase II of microsporogenesis was a common feature of all the triploids analyzed, but dyads and triads were observed at a very low frequency. Therefore, also the frequency of 2n pollen was very low; the different size of stainable pollen appears to represent the ploidy levels which are possible according to the distribution of chromosomes in Anaphase I. The results obtained also suggest thatS. commersonii could have minor genes acting at the end of meiosis in such a way that, despite the presence of parallel/tripolar spindles, dyads/triads are not formed.Contribution no. 124 from the Research Center for Vegetable Breeding.     

2n gametes in potato species and their function in sexual polyploidization

Summary The extent and pattern of polyploidy in the tuber-bearing Solanums varies among the many taxanomic series that have been identified in this subsection of Solanum. While several series appear to be entirely diploid, others exhibit a range of ploidy levels from 2x to 6x, and some contain only polyploid species.In many diploid, triploid and tetraploid species 2n gametes (gametes or gametophytes with the sporophytic chromosome number) have been detected. Both 2n eggs and 2n pollen occur. 2n gametes provide the opportunity for unilateral and bilateral sexual polyploidization. The genetic determination and consequences of sexual polyploidization strongly suggest that 2n gametes have been the major instrument in the polyploid evolution of the tuber-bearing Solanums. Somatic doubling of species and interspecific hybrids appears to be of very limited importance.New evidence for the occurrence of 2n eggs and 2n pollen in many species is reported, and data from the literature are added to illustrate the widespread distribution of 2n gametes throughout the subsection. A very high correlation is found between polyploidy and 2n gametes, and its significance is discussed. Proof is presented for the occurrence of alleles governing 2n pollen production in the cultivated tetraploids, providing additional evidence for the hypothesis that 2n gametes have been involved in their origin.Multiple unilateral and bilateral sexual polyploidizations are proposed for the origin of the cultivated tetraploids: this accounts for the large variability encountered in this group, which closely resembles that of the related diploids. Similar evolutionary pathways are hypothesized for the other polyploid complexes in the subsection.A scheme is proposed in which participation of both 2n and n gametes link together all ploidy levels in the tuber-bearing Solanums, thus overcoming the ploidy barriers and providing for gene flow throughout the sympatric species of the subsection.Paper No. 2093 from the Laboratory of Genetics. Research supported by the College of Agricultural and Life Sciences, a gift from Frito-Lay, Inc., and grants from NIH (GM 15422) and The International Potato Center. Plant materials, unpublished chromosome counts and technical help of IR-1 are gratefully acknowledged.     

Somatic hybridization between Solanum tuberosum and species of the S. nigrum complex: Selection of vigorously growing and flowering plants

Fusion experiments were performed between diploid (2n = 2x = 24) or tetraploid (2n = 4x = 48) potato genotypes and four species of the Solanum nigrum complex, namely S. nigrum (2n = 6x = 72), S. villosum (2n = 4x = 48), S. chenopodioides (2n = 2x = 24) or S. americanum (2n = 2x = 24 and 2n = 6x = 72). All five accessions of the S. nigrum-species were successfully hybridized with at least one of the potato genotypes. Somatic combining abilities were influenced by the ploidy level as well as the genotype of the parental species. The use of kanamycin or hygromycin resistance as cell-selectable markersystem had no influence on somatic combining ability, but such markers can be useful to improve efficient selection of somatic hybrids in sufficient numbers. At least 20% of the hybrids of each successful combination performed well in vitro. However, only 60 genotypes out of 761 somatic hybrids were vigorous as well as flowering in the greenhouse. Analysis of the DNA content of somatic hybrids could be used as a criterion for the indirect selection in vitro of hybrids that were vigorous in the greenhouse. Flowering somatic hybrids of S. nigrum (+) 2x potato and S. americanum (+) 4x potato were selected with the aim of introgression of resistance traits after recurrent backcrossing with cultivated potato. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ploidy races in Actinidia chinensis

Summary Ploidy levels were examined in 26 accessions of Actinidia chinensis: 20 accessions were diploid (2n=2x=58) and 6 accessions were tetraploid (2n=4x=116). There was no evidence of variation in ploidy level within an accession. Our results are consistent with tetraploid A. chinensis coming from a restricted part of China.Interploid crosses within A. chinensis produced only low numbers of seedlings which were mainly triploid. Crossing hexaploid A. deliciosa with pollen of tetraploid A. chinensis produced a large family of plants and those checked were pentaploid.Counts on 83 genotypes of different ploidy levels (2x, 3x, 4x, and 5x) confirmed that the basic chromosome number in Actinidia is 29.     

Crosses between Beta intermedia bunge and B. vulgaris L.

Summary A tetraploid annual male sterile form of Beta vulgaris L. (2n=4x=36) was crossed with the wild beet species Beta intermedia Bunge (2n=36). The resulting F₁-plants were male sterile annuals being two or three times back-crossed to diploid and tetraploid sugar and fodder beets in the next years. Apart from tetraploid material (36 chromosomes) hexaploid (54 chromosomes) and a number of aneuploid plants developed.The results obtained justify the conclusion that, at a tetraploid level the material mostly propagates apomictically after the F₁ generation. The presence of penta-, hexa-, septa-and even octaploid plants might be explained by assuming that no meiosis has taken place in the crossing partners. Triploid plants are sometimes found in the progeny of hexaploid material and may presumably be considered haploids. Moreover some pentaploid plants were found in the progeny of the open pollinated F₁ which after two generations of bagging are still pentaploids although they produce no pollen. This is another clear indication of apomictic reproduction.The tetraploid generation from the cross between the hexaploid material and diploid sugar beets probably contains the best prospects for breeding.     

Variation of chromosome numbers and essential oil components of plants derived from anther culture of the diploid and the tetraploid in Pelargonium roseum

Summary Anthers of the diploid (2n=77) and the colchi-tetraploid (2n=154) Pelargonium roseum were cultured in vitro. In both ploidy level anthers containing uninucleate or binucleate microspores were incubated on a modified White's medium. Calli formed were then subcultured on Murashige and Skoog's medium for organoid differentiation. Plants developed from organoids were transferred to filter paper bridges and after that transplanted into pots. Plants derived from anthers of the tetraploid had diploid chromosome number. Wide variation of their essential oil components suggested their genetic heterogeneity. Further, high correlations between different seasons in the rate of essential oil components showed that the wide variation was due to genetic differences. Therefore, these plants probably originated from pollen grains. On the other hand, plants derived from anthers of the diploid had diploid chromosome number. Small variation and low correlations between different seasons in essential oil components indicated their genetic homogeneity. Their origin was ascribable to the somatic tissues of the mother plant. It is concluded that in plant species in which usual sexual reproduction is difficult, anther culture of chromosome-doubled plants will give a useful method for obtaining genetic variation.     

Cytology and reproductive behavior of diploid, tetraploid and hexaploid germplasm accessions of a wild forage grass: Paspalum compressifolium

Summary Fourteen germplasm accessions of Paspalum compressifolium native from southern Brazil were cytologically and embryologically analysed. The study revealed that one accession was diploid (2n=20), twelve were tetraploid (2n=40) and one was hexaploid (2n=60). This is the first report of diploid and hexaploid cytotypes for this species. Studies on microsporogenesis, megasporogenesis, and embryo sac development indicated that the diploid cytotype had regular meiotic behavior and reproduces sexually. Tetraploid cytotype usually had an important proportion of chromosomes that associated as quadrivalents during meiosis and reproduced by mean of aposporous apomixis. The hexaploid cytotype showed irregular meiotic behavior with about one third of the chromosomes associated as multivalents and reproduced by aposporous apomixis. Thus, P. compressifolium could be an agamic complex. Breeding in this complex is possible due to the presence of diploid sexuals which can be treated by colchicine and pollinated by apomicts.     

Diversity in ploidy levels and nuclear DNA amounts in Korean Miscanthus species

Because of its high biomass productivity and nutrient-use efficiency, Miscanthus spp. have emerged as promising bioenergy crops. Polyploidism in Miscanthus species is important because it allows non-native countries to cultivate sterile types, such as triploid M. × giganteus, in order to prevent ecosystem disturbance. Although M. sacchariflorus and M. sinensis are considered to be native to Korea, China, and Japan, accurate information describing the ploidy levels of these species has not yet been well established. To evaluate rough ploidy levels, 215 accessions of Miscanthus species were estimated by relative fluorescence intensities of DAPI-stained nuclei. After evaluation of rough ploidy levels, 20 plants were randomly selected by species and ploidy levels, and ploidy levels were examined by counting chromosomes, estimating propidium iodide-stained DNA content with flow cytometry, and measuring sizes of stomata and caryopsis. Among the 20 plants examined, 3 were diploid and 6 were tetraploid M. sacchariflorus (4.56 ± 0.01 and 8.90 ± 0.14 pg/2C nuclear DNA content, respectively), while 6 were diploid and 3 were triploid M. sinensis (5.40 ± 0.18 and 8.29 ± 0.33 pg/2C nuclear DNA content, respectively). One plant was a putative triploid M. × giganteus having 7.31 pg/2C nuclear DNA content, which was similar to an M. × giganteus plant from Illinois, USA having 7.23 pg/2C nuclear DNA content. We confirmed the occurrence of diploid and tetraploid M. sacchariflorus and M. sinensis plants as well as a putative triploid M. × giganteus native to Korea. Thus, measurement of the size of stomata and caryopsis allowed prediction of ploidy levels in the field and laboratory.     

The Use of Stomatal Chloroplast Number for Rapid Determination of Ploidy Level in Maize

The usefulness of using the chloroplast number in epidermal guard cells as an indirect ploidy indicator was evaluated on seed-grown and tissue culture-derived maize plants. For seed-grown plants, two maize genotypes (B89 and R75) which had both diploid and tetraploid seeds available were used as experimental materials. The ploidy levels of seed-grown plants were confirmed by flow cytometric analysis of nuclear suspensions from these plants. For regenerated plants, haploid and diploid levels were examined and the ploidy levels of these plants were determined by chromosome counts of cells from root tips. A positive relationship between the chloroplast number and ploidy level was observed for both seed-grown and regenerated plants. The stomatal guard cells of tetraploid plants had nearly double the number of chloroplasts as the diploid plants. Similar results were found from the regenerated plants. The differences in the mean chloroplast number between diploid and tetraploid seed-grown plants and between haploid and diploid regenerated plants were highly significant. The results of this study demonstrate that counting chloroplasts in guard cells can be an efficient means of screening a large number of plants for ploidy levels. In addition, this study suggests the possibilities of using this method for detecting contaminated seed lots by different ploidy seed and for distinguishing plants of different genotypes.     

竹叶兰和香港毛兰的核型分析

采用压片法研究了竹叶兰〔Arundina graminifolia（D.Don) Hochr〕和香港毛兰〔Eria gagnepainii Hawkes et. Heller.〕的染色体数目和核型。结果表明：竹叶兰的染色体数目2n=40,有2条随体,其核型公式为：2n=2x=40=16m+22sm+2st,染色体相对长度组成为2L+18M2+18M1+2S;香港毛兰染色体数目2n=36,核型公式为2n=2x=36=28m+8sm,染色体相对长度组成为4L+18M2+12M1+2S。两者均为二倍体,染色体主要由中部和近中部着丝点染色体组成。核型分类前者为1A型,后者为2B型,都较为对称。     

Chromosome localisation of genes for resistance to Heterodera schachtii, Cercospora beticola and Polymyxa betae using sets of Beta procumbens and B. patellaris derived monosomic additions in B. vulgaris

Beet cyst nematodes (BCN, Heterodera schachtii), Cercospora beticola, and rhizomania, caused by the beet necrotic yellow vein virus (BNYVV) and vectored by the soil-borne fungus Polymyxa betae, are the most serious diseases of sugar beet ( Beta vulgaris subsp. vulgaris). The wild Beta species of section Procumbentes are known to be completely resistant to H. schachtii, C. beticola and P. betae. Alien monosomic additions (2n=19), plants of cultivated beet (2n=18) carrying different individual chromosomes of B. procumbens (2n=18) or B. patellaris (2n=36), were tested in greenhouse experiments for resistance to these pathogens. Gene(s) conferring full resistance to the beet cyst nematode in B. patellaris are located on chromosome 1.1, and the other tested chromosomes of B. patellaris are not involved in the expression of resistance. Artificial inoculation under greenhouse conditions, with in vitro produced inoculum of C. beticola and spot-percentage rating of the disease intensity, showed that the high level of resistance that was observed in the wild species B. procumbens and B. patellaris was not found in any of the monosomic additions tested. It was suggested that genes on various chromosomes of the wild species are needed to express full resistance, and that the chromosomes of group 7 of B. patellaris and chromosome 7 of B. procumbens have the largest effect. The greenhouse tests for resistance to P. betae in B. patellaris derived monosomic additions showed that the addition families of group 4.1 have a strong partial resistance, while the addition families of group 8.1 appeared to be completely resistant to the pathogen. Resistance to P. betae in the two wild species as well as in the two resistant addition types did not exclude infection with BNYVV, but resulted in a considerable reduction of the virus concentration. It was concluded that resistance to the vector would complement virus resistance, and may provide a more effective and durable control of rhizomania. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of reproductive isolation between pearl millet (Pennisetum glaucum (L.) R.Br.) and P. ramosum, P. schweinfurthii, P. squamulatum, Cenchrus ciliaris

Crosses between pearl millet lines and Pennisetum ramosum, P. schweinfurthii, P. squamulatum or Cenchrus ciliaris were observed for the frequency and development of zygotes, the possibility of embryo rescue, and the fertility of F1 hybrids obtained. Eight per cent of the ovules from diploid millet × P. ramosum crosses showed small embryos which could not be rescued. However, 59% of the ovules from tetraploid millet × P. ramosum crosses showed well-developed embryos that were easy to rescue 14 days after pollination. F1 hybrids were male sterile but female fertile when pollinated by diploid millet. Both diploid and tetraploid millet ovules showed the presence of hybrid zygotes after pollination with P. schweinfurthii at rates ranging from 25% to 45%. The diploid millet× P. schweinfurthii hybrid zygotes often developed almost normal seeds giving, without embryo rescue, totally sterile plants. The tetraploid millet × P. schweinfurthii hybrid embryos were normal but the endosperm was severely defective. A hybrid obtained by embryo rescue was totally sterile. A diploid millet-P. schweinfurthii amphidiploid was obtained by somatic embryogenesis associated with colchicine treatment during callogenesis. This amphiploid plant was male sterile, but gave many seeds when pollinated by a tetraploid millet and few seeds when pollinated by a diploid millet. P. squamulatum pollinating diploid millets produced proembryos with large undifferentiated endosperms in 73% of the ovules. A normal seed set was observed on tetraploid millets pollinated by P. squamulatum and the resulting F1 hybrids were partially male and female fertile. Backcrosses of these hybrids were much more fertile when pollination was from a tetraploid millet rather than from a diploid millet. C. ciliaris pollinating a diploid millet showed, in 60% of the ovules, proembryos and endosperms similar to those observed with P. squamulatum and no hybrid could be rescued. Crosses with a tetraploid millet could not be attempted due to the pistil-pollen incompatibility of tetraploid millets available with C. ciliaris. Ploidy levels of mating partners do not seem to influence pistil-pollen compatibility, but play a major role in post-zygotic abortion. With adequate ploidy levels of parents, and embryo rescue, it seems that the pearl millet gene pool can be considerably enlarged by germplasm from many other species.