Bilateral polyploidization inDactylis glomerata L. subsp.lusitanica: occurrence,morphological and genetic characteristics of first polyploids

Summary InDactylis glomerata L. subsp.lusitanica, triploid and tetraploid plants were obtained by bilateral sexual polyploidization in crosses between diploid parents known to produce 2n gametes. The polyploid and diploid progeny were compared for allozyme diversity (allele number and heterozygosity), phenological (pollen fertility, inflorescence emergence date), cellular (stomatic cell size) and morphological characters (vegetative biomass, seed weight, total seed number per plant, panicle number and seed number per panicle length) in four contrasting growing conditions. Stomatal cell size and the total number of alleles were significantly lower in diploids than in polyploids which sometimes recovered more than two distinct alleles at a locus via 2n gametes possessing heterozygous loci. Pollen fertility was similar in diploids and tetraploids, but significantly lower in the triploids. Seed weight was significantly higher in polyploids, although the average number of seeds per panicle length and the total number of seeds was higher in the diploid sibs. No phenological differences occurred among ploidy levels whereas such differences were observed inDactylis in all the natural areas of sympatry between diploids and their related polyploids. Our results provide evidence for an instantaneous effect of polyploidization on certain traits and suggest that natural selection would act subsequently on several other traits to allow the establishment of new polyploids.     

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.     

Bilateral sexual polyploidization in potatoes

Summary Bilateral sexual tetraploidization was achieved by intercrossing diploid Phureja × haploid Tuberosum hybrids. Both parents contribute gametes with the somatic number of chromosomes (diplogynoids and diplandroids). More than 100 tetraploid progeny appeared in nine 2x–2x families. The tetraploids are generally more vigorous and significantly outyield their diploid full-sibs. The superiority of the tetraploids is interpreted on the basis of the mode of diplandroid (2n pollen) formation by first meiotic division restitution (FDR). Heterozygosis, epistasis and genetic diversity, if present in the parental diploid genotype, are largely maintained in the 2n gametes formed by FDR. and syngamy brings about more opportunities for heterotic responses in conjunction with polyploidization. Differences in tuber yield among tetraploid clones within families were found to be statistically significant (P <0.05). Thus, unlike somatic chromosome doubling, which can merely increase chromosome numbers, or somatic hybridization, which could in addition bring about heterosis, sexual polyploidization is also associated with genetic variability. The degree of inbreeding and the genotypic structure in the population of newly arisen tetraploids is discussed. The relationship among asexual reproduction, preservation of favorable nonadditive genetic effects by FDR. restoration of sexuality, and polyploidization is explored. The possible evolutionary significance of these factors is emphasized.     

Occurrence, inheritance and use of reproductive mutants in alfalfa improvement

The widespread occurrence of 2ngametes (i.e. gametes with the somatic chromosome number) in the Medicago sativa-coerulea-falcata complex supports the concept that gene flow from diploid to tetraploid species occurs continuously in nature and plays a key role in alfalfa evolution. Breeders realized early that gene transfer between ploidy levels via 2n pollen and 2n eggs would have had potential use in cultivated alfalfa improvement. Cytological investigations provided insights into the types of meiotic abnormalities responsible for the production of 2n gametes. Alterations were defined as genetically equivalent to first (FDR) or second division restitution(SDR) mechanisms. For breeding purposes,data have proven that 2n gametes of the FDR type are more advantageous than those obtained by SDR for transferring parental heterozygosity and retaining epistatic interactions. The use of diploid meiotic mutants that produce 2ngametes is now recognized as one of the most effective methods available for exploiting heterosis and introgressing wild germplasm traits into cultivated tetraploid alfalfa via unilateral (USP) and bilateral sexual polyploidization (BSP) schemes. Both2n egg and 2n pollen producers could be used for direct gene transfer from wild diploid relatives into cultivated alfalfa by means of 2x-4x and4x-2x crosses. Although data have shown that forage yield improvement can be achieved when plants are sexually tetraploidized, problems related to reduced plant fertility and seed production remain largely unexplained. Apomixis has the potential of cloning plants through seed and thus provides a unique opportunity for developing superior tetraploid cultivars with permanently fixed heterosis and epistatic effects. A main goal in alfalfa breeding could be the introduction of functional apomixis (i.e. Apomeiosis and parthenogenesis) in cultivated alfalfa stocks. In the future, the efficiency of alfalfa breeding programs based on the use of reproductive mutants could be improved by direct selection at the genotype level using RFLPs and PCR-based markers. Suitable DNA markers and detailed linkage maps of alfalfa mutants should help to discover apomictic mutants and address basic genetic issues such as the extent of genomicre combination in polyploid hybrids and the effect of sexual polyploidization on heterosis. Molecular markers have recently been used in alfalfa for studying the inheritance of 2n gamete formation and identifying polymorphisms associated to genes involved in meiotic abnormalities. Molecular tagging of 2n egg and 2n pollen formation not only should explain the genetic control and regulation of these traits, but may also be an essential step towards marker-assisted selection of 2n gamete producers and implementation of USP and BSP breeding schemes. Future perspectives include strategies for the map-based cloning of genomic DNA markers,and screening of EST mini-libraries related to flowers at different developmental stages from meiotic mutants and wild-type scan lead to the identification of mRNAs and thus of candidate genes that control 2n gamete formation in alfalfa. This revised version was published online in July 2006 with corrections to the Cover Date.     

Assignment of Endosperm Balance Numbers to the tuber-bearing Solanums and their close non-tuber-bearing relatives

The Endosperm Balance Number (EBN) of over 80 species and subspecies of the tuber-bearing Solanums and their close non-tuber-bearing relatives representing 13 taxonomic series has been determined, with no species assigned to more than one EBN level. Among North American species, most diploids are 1EBN, most tetraploids are 2EBN and all hexaploids are 4EBN; however, among South American species most diploids are 2EBN, most tetraploids are 4EBN and again all hexaploids are 4EBN. Thus species may be isolated from others of the same ploidy level by EBN differences, e.g., 4×(2EBN) from 4×(4EBN), while other species differing in ploidy but having the same EBN may be intercrossed, e.g., 4×(2EBN) and 2×(2EBN). Chromosome doubling or 2n gametes can be used to make a lower EBN species compatible with a higher EBN species. These findings also explain the major crossing difficulties previously inherent in the use of North American species in potato improvement. They also have direct implications for potato improvement, barring the occurrence of other incompatibility barriers. Any 4×(4EBN) cultivar is endosperm compatible and thus will cross with 4×(4EBN) and 6×(4EBN) species. The 2×(2EBN) haploids of 4×(4EBN) cultivars likewise will hybridize with 2×(2EBN) and 4×(4EBN) species. All 2×(1EBN) species are crossable with 2×(2EBN) haploids through 2n gametes or chromosome doubling.Cooperative investigation of the U.S. Department of Agriculture, Agriculture Research Service, and the Wisconsin Experiment Station.     

The importance of Endosperm Balance Number in potato breeding and the evolution of tuber-bearing Solanum species

Summary Endosperm failure is considered the primary reason for the lack of success in intra-and interspecific crosses. The Endosperm Balance Number (EBN) hypothesis is a unifying concept for predicting endosperm function in intraspecific, interploidy, and interspecific crosses. In the EBN system, every species has an effective ploidy (EBN), which must be in a 2:1 maternal to paternal ratio in the endosperm for crosses to succeed. The knowledge of EBN is very useful in the transfer of genes from exotic germplasm, and in the development of new breeding schemes in potato. The paper describes the strategies for introducing 2x(1EBN), 2x(2EBN), 4x(2EBN) and 6x(4EBN) germplasm into the cultivated 4x(4EBN) potato gene pool. A new methodology for producing 4x(4EBN) and 2x(2EBN) chromosome addition lines is also discussed. EBN has evolutionary importance in the origin of tuber-bearing Solanums. The role of the EBN in the origin of diploid and polyploid potato species, and as a barrier for hybridization and speciation of sympatric species within the same ploidy level is demonstrated. The origin of 3x and 5x cultivated tuber-bearing Solanums may also be explained using the EBN concept. EBN has been reported to exist in other plant species: alfalfa, beans, blueberries, rice, soybeans, squashes, tomato, forage legumes, grasses, ornamentals and Datura stramonium. This indicates that EBN may have broad application and could be useful for germplasm transfer and breeding in other crop species.     

The origin of polyploids via 2n gametes in Vaccinium section Cyanococcus

Summary The production of 2n pollen (pollen with the sporophytic chromosome number) was evaluated in 4x and 6x taxa of Vaccinium section Cyanococcus. Mean frequencies of 2n pollen producers were 17.1% and 8.3% in natural 4x and 6x populations, respectively. The frequency of 2n pollen producers in the 4x species ranged from 8.6% (V. angustifolium) to 23.8% (V. pallidum). Level of 2n pollen production was genotypically variable (1% to 37.4%). The widespread occurrence of 2n pollen in 2x, 4x and 6x taxa suggests that sexual polyploidization was widespread and responsible for the origin of the polyploid species found in this genus. The frequency of 2n pollen producers was not significantly different between the 4x species and their putative 2x ancestors. These results support the origin of 4x and 6x taxa as a consequence of sexual polyploidization. Polyploids derived from sexual polyploidization would be expected to have increased fitness and flexibility due to the mode of 2n pollen formation. In blueberry species the predominant mode of 2n pollen formation is genetically equivalent to a first division restitution mechanism (FDR). FDR 2n pollen transmits a high percentage of the heterozygosity and a large fraction of the epistasis from the 2x parent to the 4x offspring.     

Genetic variation in the agamic species complex of Pennisetum section Brevivalvula (Poaceae) from West Africa: ploidy levels and isozyme polymorphism

Some characteristics of the species complex Pennisetum section Brevivalvula are polyploidy and apomixis. Four euploidy levels (x = 9) were assessed by DAPI-flow cytometry for 304 plants of the section, distributed among five species: P. hordeoides (2n = 36, 54), P. pedicellatum (2n = 36, 45, 54), P. polystachion (2n = 18, 36, 45, 54), P. setosum (2n = 54), and P. subangustum (2n = 18, 36, 54). The geographical distribution of the ploidy levels seems to be related to major ecological zones of West Africa. The hilly regions displayed a higher ploidy diversity than the others; diploid populations of the annual species P. polystachion and P. subangustum were found. Genotypic variation expressed by isozyme polymorphism did not show any significant difference between the diploid, sexual populations and the polyploid, apomictic populations of these two species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Variation of DNA methylation and phenotypic traits following unilateral sexual polyploidization in <Emphasis Type="Italic">Medicago</Emphasis>

Sexual hybridization is an important generator of biodiversity and a powerful breeding tool. Hybridization can also overcome ploidy barriers when it involves 2n gametes, as in the case of unilateral sexual polyploidization (USP) that has been utilized in several crops, among which alfalfa. This research was aimed at gaining insights into the effects of USP on genome methylation and on phenotypic traits in alfalfa, an important forage species. The Methylation-Sensitive Amplified Polymorphism technique was used to estimate the cytosine methylation changes occurring in a tetraploid (2n = 4x = 32) USP progeny from crosses between a diploid Medicago sativa subsp. falcata genotype that produces 2n eggs and a cultivated tetraploid Medicago sativa subsp. sativa variety. De novo methylation or demethylation in the USP progeny were observed for 13% of the detected genomic sites, indicating that methylation changes can be relevant. USP plants showed larger surface area of the leaf epidermis cells than both parents, but this did not result in larger leaf size or higher plant biomass. They displayed significant higher ovule sterility than the tetraploid parent, but normal fertility was observed in crosses with unrelated male testers. We conclude that hybridization and sexual polyploidization resulted in novel variation in terms of remodeling of the methylation landscape as well as changes in phenotypic traits in alfalfa.     

Investigation on Evolutionary Relationships of the Subgenomes in Interspecific Triploid Cotton via Meiotic FISH

We report in this paper primary studies on interspecific species of cotton vis GISH (genomic in situ hybridization).We use interspecific triploid hybrids (F1 from hybridization of allotetraploid cultivated species with diploid A,D,or C genome species) and two cultivated tetraploids to study the chromosome paring during meiosis of pollen mother cellls (PMCs) and to estimate the consequences on synapsis between these three subgenomes after synthetic polyploid formation.     

Effect of high temperature on the production of 2n pollen grains in diploid roses and obtaining tetraploids via unilateral polyploidization

To integrate the gene pool of a wild species (primarily diploid) into a cultivated pool (primarily tetraploid), a crossing between a dihaploid cultivated rose and a hybrid of Rosa wichurana allowed to obtain interspecific diploid hybrids that produced 2n pollen grains. A return to a tetraploid level sought by breeders can then be considered using sexual polyploidization, obtained by crossing a tetraploid cultivated rose with these hybrids. Application of a high‐temperature regime led to a small but significant increase in the percentage of 2n pollen grains in these hybrids of up to 4.6%. This result was obtained by applying high temperatures close to 32°C during the day to plants cultivated in a glasshouse during recurrent cycles of bloom. Crosses were made between an unreleased tetraploid hybrid tea rose, as a female, and the diploid hybrid that produces the most 2n pollen grains. Tetraploid (42.1%) and triploid (57.9%) offspring were obtained. The use of these 2n pollen grains of the first division restitution type should facilitate the introgression of complex traits of interest.     

Transfer of resistance to potato cyst nematode (globodera pallida) into cultivated potato Solanum tuberosum through first division restitution 2n pollen

Genetic resistance to potato cyst nematode is considered as one of the most effective means of increasing yield and reducing nematode infestation levels in potato fields. In this study, resistance to this nematode was successfully transferred from diploid tuber-bearing Solanums to the tetraploid gene pool using a 4x-2x breeding approach. More specifically, resistance from Solanum vernei, S. sparsipilum and haploids of S. tuberosum group Andigena was introgressed into conventional tetraploid clones, using first division restitution (FDR) 2n gametes. Furthermore, some of the FDR diploid parents had similar breeding values as advanced resistant tetraploid clones which were developed only after several cycles of selection against the potato cyst nematode. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluation of FDR diploid and tetraploid parents in potato under two different day-length environments

Five tetraploid clones of potato were crossed to each of eight diploid first division restitution (FDR) 2n pollen producers and four tetraploid males using a line × tester mating design. A total of 59 families were obtained and evaluated under long days at Rhinelander (USA). A subset of 49 families were grown under short days at four Peruvian locations. Tuber yield (kg per plant) of 4x-2x families was similar to, or greater than, that of 4x-4x families in short day environments. The diploid clones had breeding values greater than or equal to those of the tetraploid clones. Only families derived from FDR 2n pollinators combined high tuber yield with stability and high dry matter content. Reciprocal recurrent selection would be the best breeding scheme, in which the diploids are testers of the tetraploids and vice-versa. Intra-population improvement could be achieved through phenotypic recurrent selection. The best materials from both breeding pools could then be crossed to produce tetraploid hybrids through unilateral sexual polyploidization (4x-2x crosses).     

Relevance of unilateral and bilateral sexual polyploidization in relation to intergenomic recombination and introgression in <Emphasis Type="Italic">Lilium</Emphasis> species hybrids

Sexual polyploids were induced in diploid (2n = 2x = 24) interspecific F1 hybrids of Longiflorum × Asiatic (LA) and Oriental × Asiatic (OA) Lilium hybrids by backcrossing to Asiatic (AA) parents as well as by sib-mating of the F1 LA hybrids. A majority of the BC1 progenies were triploid and the progenies from sib-mating were tetraploid or near tetraploids. Genomic in situ hybridization (GISH) technique was applied to assess the intergenomic recombination in the BC1 populations of LA and OA hybrids obtained after unilateral sexual polyploidization. A total of 63 LA (LA × AA and AA × LA) and 53 OA hybrids were analysed. LA hybrids were originated through the functioning of 2n gametes either as 2n eggs or 2n pollen while those of OA hybrids originated through functional 2n pollen of diploid OA genotype. In both type of crosses, a majority of the progenies had originated through First Division Restitution (FDR) mechanism of functional 2n gamete either with or without a cross over. However, there were nine LA- and four OA-genotypes where Indeterminate Meiotic Restitution (IMR) was the mechanism of 2n gamete formation. Based on GISH, total amount of introgression of Longiflorum and Oriental genome into Asiatic genome was determined. Most of the BC progenies exhibited recombination and the amount of recombination was higher in LA hybrids as compared to OA hybrids. Intergenomic recombination was also determined cytologically in the 16 plants of sib-mated LA hybrids where both parents had contributed 2n gametes. Based on these results the nature of interspecific lily hybrids obtained from uni- and bilateral sexual polyploidization leading to allotriploid and allotetraploid formation is discussed in the context of introgression and intergenomic recombination.     

Screening <Emphasis Type="Italic">A. ventricosa</Emphasis> populations for 2n gametes

Sexual polyploidization via the formation of 2n gametes has been acknowledged as the most significant evolutionary mode of polyploidization among plant species. The present study was conducted in order to determine whether 2n gametes are present in the C-genome diploid Avena ventricosa Bal. ex Coss., a species that contributed to the evolution of the cultivated hexaploid species (Avena sativa L). Individual plants belonging to four different Cypriot populations, were screened for pollen grain size variation with the aim to distinguish 2n gametes. Avena ventricosa ARI00-845 was identified to produce large pollen grains at a low percentage (1.21%). Subsequent analysis using flow cytometry confirmed the presence of 2n gametes in the pollen. Cytogenetic analyses of pollen mother cells revealed cells with twice the typical chromosome number at metaphase I (i.e., 28 chromosomes). We postulate that irregularities in cell wall formation preceding meiosis could have contributed to the mode of chromosome doubling.     

Formation of 2n gametes in durum wheat haploids: Sexual polyploidization

Allopolyploidy, resulting from interspecific and intergeneric hybridization accompanied by sexual doubling of chromosomes, has played a major role in the evolution of crop plants that sustain humankind. The allopolyploid species, including durum wheat, bread wheat, and oat, have developed a genetic control of chromosome pairing that confers on them meiotic regularity (diploid-like chromosome pairing), and hence reproductive stability, and disomic inheritance. Being natural hybrids, they enjoy the benefits of hybridity as well as polyploidy that make them highly adaptable to diverse environments. Despite the complexities of sexual reproduction, it is widespread among plants and animals. Sexual polyploids are highly successful in nature. Sexual polyploidization is far more efficient than somatic chromosome doubling. Sexual polyploidization effected by functioning of unreduced (2n) gametes in the parental species or in their hybrids has been instrumental in producing our grain, fiber, and oilseed crops. Evidence is presented for the occurrence of sexual polyploidization in durum haploids. ThePh1-induced failure of homoeologous pairing is an important factor in the formation of first division restitution(FDR) nuclei and 2n gametes. The evolutionary and breeding significance of sexual polyploidization is discussed. It is emphasized that three factors, viz.,sexual reproduction, allopolyploidy, and genetic control of chromosome pairing,jointly constitute a perfect recipe for cataclysmic evolution in nature. This revised version was published online in July 2006 with corrections to the Cover Date.     

木薯有性四倍体遗传稳定性分析

木薯作为中国重要的经济作物,其优良品种的选育一直是木薯科研工作的重点,而多倍体的巨型性特点为其育种提供了新的思路,目前多倍体研究大多是体细胞加倍,有性多倍化研究起步较晚,而本课题组通过2n配子有性活体杂交,成功获得了首例木薯有性四倍体植株。为了研究木薯有性四倍体的遗传稳定性,本研究分别采用:田间的农艺性状观测(生长稳定期)、流式细胞术、叶片染色体计数、蛋白质含量测定/蛋白质聚丙烯酰胺凝胶电泳以及淀粉含量测定等方法进行鉴定。结果显示:木薯有性四倍体各株系农艺性状均保持了母株器官巨型性的多倍体特征;流式细胞仪分析显示,木薯有性四倍体各株系叶片DNA含量均为二倍体亲本(SC5)的两倍,相对应的叶片染色体数目也为二倍体亲本(SC5)的两倍,且视野中四倍体细胞所占比例均在90%以上;各株系蛋白质含量均小于二倍体对照组,且有性多倍体株系电泳谱带基本相似;在淀粉含量测定中,其各株系淀粉含量均小于对照组,且各株系之间含量波动较小。本研究结果表明木薯有性四倍体植株具有较好的遗传稳定性,对木薯多倍体品种的选育具有重要意义。     

Numerically unreduced (2n) gametes and sexual polyploidization in Actinidia

This is the first report on the production of numerically unreduced (2n) gametes in Actinidia species. Their occurrence was apparent from direct observations of microporogenesis in 2x, 3x, 4x and 6x plants and was inferred from ploidy analysis of progenies from 4x-2x and 2x-4x crosses. Both male and female plants were found to produce 2n gametes. 2n gamete producers were detected only in interploidy crosses. The observed frequency of 2n gametes was either similar to or towards the lower end of the ranges reported for other genera. The role of sexual polyploidization in the evolution of the genus is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Trifluralin-mediated polyploidization of <Emphasis Type="BoldItalic">Rosa chinensis minima</Emphasis> (Sims) Voss seedlings

Many diploid rose species and cultivars possess valuable traits that can be introgressed into modern tetraploid cultivars. Interspecific, interploidy crosses are possible, but triploid hybrids typically have limited fertility, hindering further breeding and selection. Tetraploidizing diploids before mating with tetraploids can alleviate fertility barriers. The efficiency of trifluralin was investigated for polyploidization of Rosa chinensis minima (2n = 2x = 14) seedlings. Treatments were trifluralin at 0.086% and 0.0086%, colchicine (0.5%), and distilled water and contained 2% dimethyl sulfoxide and a surfactant. Approximately 5 l of the treatment solution was applied to the apical meristem of seedlings (N = 337, 82–85 per treatment) in the process of cotyledon expansion. Guard cell length, pollen diameter, and root tip squashes of rooted cuttings were used to detect polyploidy in meristematic layer (L)I, LII, and LIII, respectively. Trifluralin (0.086%) was the most effective treatment for polyploidization (LI 20.2%, LII 12.9%, LIII 12.9%), followed by trifluralin (0.0086%) (LI 10.6%, LII 7.1%, LIII 4.7%) and colchicine (LI 2.4%, LII 0%, LIII 0%). Polyploidization consistently occurred from LI inward. Polyploids as a group had reduced pollen stainability and a lower leaflet length to width ratio than diploids. In addition, two diploid seedlings were identified which produce 2n pollen. Considerations in selecting germplasm and generating somatically-induced polyploids from seedlings versus clones for use in breeding are discussed.     

Evidence of sexuality in induced tetraploids of Brachiaria brizantha (Poaceae)

Difficulties in obtaining new breeding lines of Brachiaria (Trin.) Griseb., an important forage grass in Brazil, are mostly related to differences in ploidy among the accessions, and to apomixis, an asexual mode of reproduction. Usually, sexual accessions are diploid while apomicts are polyploid. Induced tetraploids of Brachiaria brizantha (A. Rich.) Stapf have been successfully obtained and this paper presents the results of a study of their reproductive modes and fertility. Despite frequent meiotic aberrations during microspore development, the induced tetraploids produced viable pollen and produced progeny after controlled self-pollination. Similarly to the original diploid sexual progenitor, embryo sacs of the Polygonum type with confirmed meiotic origin were present in the induced tetraploids suggesting chromosome doubling did not alter the reproductive mode. The embryo sac of the Polygonum type was also observed in progenies obtained after self and open pollination. Nevertheless, embryo sacs of the Polygonum and the Panicum types within the same ovule were observed in some progenies obtained after open pollination, probably having resulted from hybridization with tetraploid, apomictic plants. Indeed, the compatibility of the progeny with tetraploid, apomictic B. brizantha was confirmed by the formation of mature caryopses after controlled pollination. Evidence is presented that the induced tetraploids and their progeny are sexual plants and that they are compatible with natural tetraploid B. brizantha. The induced tetraploids will be useful for analyses of apomictic inheritance as well as in the development of sexual tetraploid lines in Brachiaria breeding programs.