Fertility,plant morphology,and transmission rates of the extra chromosome in single and double trisomics of Solanum tuberosum L. Group Tuberosum

Summary Initial single and double trisomics of S. tuberosum Group Tuberosum cv. Gineke were successfully crossed with and backcrossed to clones obtained through inbreeding of self-compatible dihaploids of the same variety. Some trisomics showed reduced flowering or flower abnormalities and contributed therefore only to a small extent. Berry-set and seed-set varied considerably. There was no relation between these phenomena, nor was there any relation between either berry-or seed-set and the identity of the extra chromosome in the female parent. Seed-set seemed to be influenced by the male parent. When a more inbred male parent was used in the crosses with trisomics this often resulted in less seed per cross. There was no clear relation between seed-set and stainability of the pollen grains, but both the strong selection for good pollen and the high level of self-compatibility, have apparently contributed to the success of the crosses. The double trisomic plants yielded less seed than most single trisomics. Only three of the single trisomics produced stainable pollen and two of them yielded progeny when used as male parent in crosses or selfings.In the progenies several of the trisomic types could be distinguished on the basis of plant morphology in the young seedling stage. For ten different trisomics the morphotype is being described. The average rate of female transmission of the extra chromosome was about twenty per cent, but there was a wide variation, both between and within the various trisomic types. The results indicated that for chromosomes 3 and 8 the rate of transmission was higher than the average value. In one out of two trisomic types male transmission of the extra chromosome occurred, with a rate of 4.7%. The possible causes for the observed differences in female transmission of the extra chromosome are being discussed.     

甘蓝型油菜三体、双三体和双四体的形态和细胞学特征

从甘蓝型油菜品种“Oro”×诸葛菜杂交后的一个混倍体杂种（2n=19~37）的小孢子再生植株中鉴定出一株2n=42的植株，此混倍体不含有诸葛菜染色体，故2n=42植株的细胞内没有诸葛菜染色体。用其花粉授予“Oro”后获得2n=39、40的植株。2n=39、40、42植株PMCs内染色体的主要配对方式分别为19Ⅱ+1Ⅰ、19Ⅱ+2Ⅰ和19Ⅱ＋2Ⅱ，后期Ⅰ的分离方式分别为20∶19、21∶19和21∶21。故2n=39、40、42为甘蓝型油菜的三体、双三体、双四体。最后讨论了这些种内非整倍体材料在油菜遗传研究中的意义。     

Pollen viability and meiotic behaviour in intraspecific hybrids of Hydrangea aspera subsp. aspera Kawakami group x subsp. sargentiana

Pollen viability and male meiosis in intraspecific hybrids of Hydrangea aspera subsp. aspera Kawakami group (2n = 2x = 36) and subsp. sargentiana (2n = 2x = 34) were investigated. Although it had been assumed that they were sterile, pollen viability was observed; it varied from 2.5% to 12.1%. The production of gametes with different chromosome numbers was implied by the analysis of the dispersion of the diameter distribution of pollen grains. Analysis of male meiosis made it possible to identify the origins with two major categories of meiotic aberrations: abnormal chromosome distribution (early chromosome migration at metaphase, lagging chromosomes at anaphase, micronuclei at telophase), leading to the formation of unbalanced tetrads and/or ones with supernumerary microspores; and abnormal spindle orientation in metaphase II (tripolar, fused and parallel spindles), leading to the formation of dyads or triads. The mode of 2n pollen formation is of the First Division Restitution type. The high level of parental heterozygosity that is normally associated with them should facilitate the transfer of a polygenic trait in breeding programme.     

Intergeneric hybrids and an amphiploid between Elymus canadensis and Psathyrostachys juncea

Summary Fifty four hybrid plants between Elymus canadensis and Psathyrostachys juncea were obtained by handpollination and embryo culture. The average cross compatibility between both species was 31.2 percent. One amphiploid plant was induced by colchicine treatment. The hybrid and amphiploid plants resembled P. juncea in appearance but showed a higher plant height and dry matter yield than the parents. The hybrids showed extremely low pollen stainability and were completely sterile. With the exception of one plant (2n=3x+1=22), all hybrid plants were allotriploids (SHN, 2n=3x=21). The amphiploid plant (SSHHNN, 2n=6x=42) showed 58.9% pollen stainability and 11.6% seed fertility.Mean chromosome associations of the hybrids and amphiploid at metaphase I were 0.02IV+0.06III+2.03II+16.91I and 0.07III+18.00II+5.85I, respectively. Lagging chromosomes, chromosome bridges, abnormal cytokinesis, and micronuclei were occasionally observed at the anaphase, telophase, or tetrad stage.     

2n Gamete formation in the genus Brachiaria (Poaceae: Paniceae)

Microsporogenesis of several Brachiaria species of the Brazilian collection at Embrapa Beef Cattle has been analyzed in detail. This paper reports abnormal cytokinesis in three accessions of three different species (Brachiaria humidicola, 2n = 4x = 36, Brachiaria decumbens, 2n = 4x = 36, and Brachiaria dura, 2n = 6x = 54). Chromosomes paired in bi-, tri-, and quadrivalents in these accessions, whereas chromosome segregation at meiosis I was characterized by exclusion of laggards as micronuclei. In a high number of meiocytes, the first sign of cytokinesis appeared only in metaphase II and did not divide the meiocyte into a dyad. Total absence of cytokinesis was also detected among meiocytes in the second division. Since in both cases the two metaphase plates were very close, they favored the rejoining of chromosome sets after anaphase II and formed a restitutional nucleus in telophase II. Second cytokinesis occurred after telophase II in most meiocytes. Monads, dyads, and triads with n or 2n nuclei were observed among meiotic products. The 2n gametes observed correspond to the first division restitution (FDR). The number of affected cells in each accession was variable, but the number of microspores with restitutional nucleus, including those scored in tetrads and the released ones, did not exceed 9%. Although polyploidy is common in the genus Brachiaria, its origin is still unclear. Current results suggest that 2n gametes may have contributed to the evolutionary history of the genus.     

Cytogenetical studies on African rice,Oryza glaberrima Steud. 3. Primary trisomics produced by pollinating autotriploid with diploid

Summary In order to promote cytogenetical studies on Oryza glaberrima (2n=2x=24), I produced primary trisomics in the progeny of the autotriploid. When the autotriploid was pollinated with the diploid, 136F1 seeds (5.8% of the number of spikelets pollinated) were obtained. The numbers of chromosomes of 31 surviving progeny varied from 24 to 28, with plants having 2n=25 occurring at the highest frequency (34.4%). The primary trisomics differed from one another as well as from the normal disomics in many aspects. The differences were attributed to a single extra chromosome in each trisomic type. Nine primary trisomics were classified into 8 types on the basis of morphological and reproductive features. Seeds were obtained from all primary trisomics except for Type D by self pollination, open pollination or pollination with the disomics. I was able to maintain 7 types of primary trisomics by seed propagation. The primary trisomics which are capable of expressing subtle genetic dissimilarities should be useful for studying the relationship between the two cultivated species of rice at the level of individual chromosomes.     

Failure of cytokinesis and 2n gamete formation in Brazilian accessions of Paspalum

Cytological analysis on 112 Brazilian accessions of Paspalum showed that 52 were affected by failure of first or second cytokinesis during microsporogenesis. When the failure of cytokinesis occurred only in the first division and in the second division the cytokinesis was normal, a dyad of microspores was formed. In most of them the two cells remained binucleate, but in some a restitutional nucleus was observed. When the first division was normal and the failure of cytokinesis occurred only in the second division, dyads and triads were observed. A restitutional nucleus in one or both cells of the dyad, or in the binucleate cell of the triad was also observed. The percentage of dyads and triads varied among accessions, reaching 15.75 of the sporads in some. The absence of cytokinesis indicates the possibility that the widespread occurrence of polyploidy in the genus Paspalum originates from 2n pollen grains. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

大豆雄性不育突变体NJ89-1的细胞学研究

通过对大豆雄性不育突变体NJ89-1不育株与可育株小 孢子母细胞减数分裂的比较研究,发现NJ89-1雄性不育株小孢子母细胞减数分裂高度变异,联会异常,出现单价体、染色体落后、染色体桥、染色体不均等分离等;在形成四分体的早期阶段,小孢子母细胞里见到微核,以后产生大小不等的二分体、三分体、四分体及多分体;单核小孢子     

Abnormal pollen development of bread wheat-<Emphasis Type="Italic">Leymus mollis</Emphasis> partial amphiploid

Summary Octoploid Tritileymus was the partial amphiploid obtained from Triticum aestivum × Leymus mollis, its chromosome constitution was 14 Leymus chromosomes and 42 wheat chromosomes. In the pollen development of Tritileymus, some abnormalities were observed, such as the absence of tetrad formation, cytomixis of microspores, irregular shape of some microspores and multi-germination pores, symmetrical first mitosis, chromosomes or chromatids randomly dispersed in the cytoplasm of microspore.     

Aneuploid and other cytological tester sets in rye

Summary Cytological tester sets include series of aneuploids (nullisomics, monosomics, trisomics of different types, tetrasomics), series of rearranged chromosomes (translocations, inversions, duplications, deficiencies) and series of chromosomes recognizable by specific microscopically visible markers (C-or other banding, molecular markers). In rye, only a few (mainly tertiary and telocentric) monosomics and no viable nullisomics have been found. Several sets of primary trisomics and some telocentric sets, usually not fully complete, have been developed, but few are still available for gene localization. A few tertiary trisomics have been derived from translocation heterozygotes. Extensively used are different sets of additions of rye chromosomes to wheat. A relatively widely distributed set of marked chromosomes is the Wageningen translocation tester set, complemented with translocations from different other institutions. A disadvantage of rye translocations is insufficient heterozygote semisterility. Series of otherwise rearranged chromosomes have not been reported. Sets of lines with chromosomes conspicuously differing from the standard C-banding pattern have been obtained. Molecular markers are available for most rye chromosome, but lack of heterozygosity, necessary for classification afterin situ hybridization is a restriction for use as cytological testers. In the cases of most translocations, C-banding andin situ molecular markers, each separate plant in a segregating population must be screened cytologically, whereas with aneuploid markers or with translocations having sufficient heterozygote semisterility, analyzing segregations is sufficient.     

Further cytological characteristics of a male-sterile mutant in soybean affecting cytokinesis and microspore development

A spontaneous male‐sterile mutation affecting microspore development has been found in BR97‐13509H line of the official Brazilian soybean breeding programme. Slightly abnormal and irregular chromosome segregation occurred in both meiotic divisions, albeit insufficient to explain total pollen sterility. The main cause of male sterility was the absence of cytokinesis after telophase II. Instead of the typical tetrads of microspores, four‐nucleate coenocytic microspores were formed. Coenocytic microspores resulting from the absence of cytokinesis have also been described in ms1 and ms4 male‐sterile soybean mutants, although with certain differential characteristics. In the BR97‐13509H mutant line, after interphase the four nuclei were rejoined in one or two metaphase plates and progressed through the first pollen mitosis. Pollen then underwent a progressive process of degeneration characterized by continuous cytoplasmic shrinkage. The second pollen mitosis failed to occur, and pollen sterility became total.     

Discovery of 2n gametes in tetraploid oat Avena vaviloviana

Summary Sexual polyploidization via the action of 2n gametes (gametes with the sporophytic chromosome number) has been identified as the most important evolutionary mode of polyploidization among plant genera. This study was conducted to determine whether 2n gametes are present in the tetraploid level of the genus Avena (2n=4×=28) Twenty tetraploid Avena lines, representing four species and one interspecific hybrid, were screened for pollen grain size in order to differentiate between n and 2n pollen. Avena vaviloviana (Malz.) Mordv. line PI 412767 was observed to contain large pollen grains at a 1.0% frequency. Cytogenetic analyses of pollen mother cells of PI 412767 revealed cells with double the normal chromosome number (i.e., 56 chromosomes at metaphase I and anaphase I). The mode of chromosome doubling was found to be failure of cell wall formation during the last mitotic division that preceded meiosis. The resulting binucleate cells underwent normal meiotic divisions and formed pollen grains with 28 chromosomes. Based on the formation and function of 2n gametes, three models involving diploid and tetraploid oat lines are proposed to describe possible evolutionary pathways for hexaploid oats. If stable synthetic hexaploid oat lines could be developed by utilizing 2n gametes from diploid and tetraploid oat species through bilateral sexual polyploidization, the resulting hexaploids could be used in breeding programs for transferring genes from diploids and tetraploids to cultivated hexaploids.     

Cytological mechanism of 2n pollen formation and unilateral sexual polyploidization in Lolium

Summary Plants of Lolium perenne, L. multiflorum and L. hybridum (331, 51 and 18, respectively) were screened for 2n pollen production. The screening was based on the size differences that are expected to be found between n and 2n pollen of a plant. It was found that 28 plants of perennial ryegrass-belonging to 13 cultivars-produced produced pollen grains of heterogenous size (big and small). The estimated frequency of big pollen grain production was higher than 10% in ten out of 28 plants and in three of them it reached a value of 100%. Eight plants obtained from two 4x × 2x crosses, in which the male parent had been previously identified as producing pollen grains of heterogenous size, was tetraploid. The cytological mechanism of big pollen grain formation observed in three plants consists in the lack of spindle formation and, consequently, of chromosome migration in anaphase II. From these breeding and cytological results, it was concluded that the big pollen grains observed were viable 2n pollen grains. The nuclei of the 2n pollen grains produced by this mechanism are genetically equivalent to those formed by the restitution of the second meiotic division. The value of these gametophytes in a breeding program of Lolium is discussed.     

波斯小麦×节节麦杂种F_1直接形成双二倍体的细胞遗传学研究

波斯小麦(Triticum carthlicum,AABB)与节节麦(Aegilops tauschii,DD)杂交,杂种 F_1出现可育性。不同组合的自交结实率21.25—39.72%。细胞学研究表明,可育性是由于杂种 F_1通过两种途径形成了未减数配子:第一,一部分花粉母细胞第一次分裂消失,只发生第二次分裂。即21条染色体集中到赤道面上之后,姊妹染色单体均等分离并移向     

Chromosome number and microsporogenesis in a pentaploid accession of Brachiaria brizantha (Gramineae)

Chromosome number, microsporogenesis and mode of reproduction are described for an accession of Brachiaria brizantha, a grass of African origin. Cytological analysis revealed that the accession BRA005886 is pentaploid (2n = 5x = 45), with a base number of x = 9. Multivalent chromosome associations, from tri‐ to pentavalents, were recorded in diakinesis, and the further meiotic behaviour was highly irregular as well. Most abnormalities were related to irregular chromosome segregation commonly found in polyploids. Micronuclei were observed following telophases I and II. Some micronuclei near the cell wall were released as microcytes, whereas others remained in the tetrad. Other meiotic abnormalities, such as cell fusion and the absence of cytokinesis causing the formation of dyads and triads were also recorded. Binucleate microspores and 2n microspores resulting from nucleus restitution were observed among the normal ones. Limitations of this accession for use in hybridization programmes are discussed.     

Investigations on the breeding behaviour of aneuploids of guava

Summary The breeding behaviour of aneuploids of guava (Psidium guajava L.) such as trisomic, tetrasomic, and higher aneuploids has been studied. Reciprocal crosses between aneuploids and diploids indicated less than 100% crossability. The aneuploids when used as male parents crossed less frequently than as female parents and certain aneuploids crossed more readily than others. Differences were observed in fruit size, fruit weight, and seed number in the reciprocal crosses.The extra chromosome was found to be transmitted through both the egg cell and the pollen. However, the frequency of transmission was greater through the egg cell than the pollen. As high as 26% transmission of extra chromosomes were obtained through the egg cell. There was no clear cut difference between trisomics and higher aneuploids with regard to the frequency of transmission of extra chromosomes.     

厚轴茶雄性不育株花药败育的生物学特性和细胞学研究

为明确厚轴茶(Camellia crassocolumnaH. T. Chang)雄性不育株花器发育形态、花药和花粉败育时期及兵细胞学特征,利用体视显微镜、石蜡切片技术、染色体制片和DAPI染色法,对厚轴茶雄性不育株和可育株开花迚程、花器形态、花药发育过程、花粉母细胞减数分裂及小孢子发育过程比较观察。结果显示,厚轴茶花属于完全花,花药其四室、呈蝶形,花药壁发育为基本型,绒毡层细胞其双核,于四分体时期形成分泌型细胞,单核花粉期开始降解,花粉母细胞经过减数分裂Ⅰ、减数分裂Ⅱ和胞质分裂后形成四面体型四分体,小孢子呈三角形,成熟花粉为二细胞型花粉。花蕾发育早期,不育株雄蕊发育正常,与可育株无明显差异。花蕾发育后期,不育株花丝弯曲,花药粘连、干瘪、褐化、坏死,不裂药。不育株减数分裂期绒毡层细胞异常增生、排列混乱,单核至双核花粉期绒毡层延迟降解。不育株花粉母细胞减数分裂过程中存在环状单价体、滞后染色体、染色体桥、染色体缺失、不均等分离、微核和多分体等异常现象。不育株小孢子胞质紊乱,单核期花粉粒相互粘附,花粉壁皱缩变形,花粉细胞质和细胞核模糊不清,成熟花粉细胞空瘪凹陷。研究结果表明,厚轴茶雄性不育花器形态属雄蕊萎缩型和花药异常型,花药发育受阻于减数分裂至单核花粉期,存在花粉母细胞败育型和单核败育型。单核花粉期是兵花药败育的主要时期。花药绒毡层异常发育和延迟降解,花粉母细胞减数分裂染色体行为异常,小孢子和花粉粒发育异常可能是兵花药败育的主要原因。     

Cytogenetics of Cultivated Bougainvilleas. IX. Precocious Centromere Division and Origin of Polyploid Taxa

Precocious centromere division at metaphase I leading to diploid gamete formation has been observed in three cultivars. Some of the PMC's are characterized only by rod bivalents whose centromeres split at metaphase I. After passing to respective poles, the already divided centromeres fall apart at telophase I, with the result that each pole has unreduced number of 34 chromosomes. There is no second division and such cells form dyads which give rise to diploid pollen grains. Such unreduced pollen are 100 per cent fertile because of reduced (or no) recombination between hamoeolugous genomes and the presence of two sets of chromosomes. Thus, triploids or even tetraploids can arise when such pollen grains are involved in tertilization with reduced or unreduced egg of other cultivars.     

Primary trisomics in Moss Verbena

Summary Four, out of the maximum of 5 possible, primary trisomics have been identified karyomorphologically. These are Pseudo Normal, Slender, Semi Erect and Weak, trisomic for C, A, B and D chromosomes respectively. The trisomics are reasonably distinguishable from one another on the basis of qualitative and quantitative characters, like growth habit and rate, stem thickness, internode length, size and shape of leaves and flowers and fertility. The most common type of association at meiosis is 5II+1 I followed by 1 III+4 II. The trisomics differ in the number and type of trivalents. There is a significant increase in range and number of ring bivalents in all trisomics particularly in Slender. This is attributable to a correspondingly significant increase in chiasma frequency. The reasons for this are not clear. Anaphase segregation is ordinarily normal and pollen fertility is high except in Semi Erect in which it is correlated with segregational errors. Although, seed setting is apparently normal in all except Slender, yet germinability is very poor. Greater phenotypic effects and lesser tolerance to the addition results in trisomics for the long submedian and satellited A and medium submedian D chromosomes than for B and C chromosomes.