Cytogenetics of Chilean land plants (Embryophyta): state-of-the-art and prospects / CItogenética de plantas terrestres Chilenas (Embryophyta): estado del arte y perspectivas

ABSTRACT Chile is located in the south-western region of South America along the Pacific Ocean and contributes to the worldwide flora with ca. 6,120 species of Bryophyta, Pteridophyta, Pinophyta, Gnetophyta, and Magnoliophyta (1.9% of worldwide total species), exhibiting high endemism across all plant divisions. Little is known about the genetic diversity of Chilean land plants worldwide, including their cytogenetic and molecular characteristics. In 2012 we published the first state-of-the-art review in Cytogenetics of Chilean Angiosperms. The article gathered 78 publications from 1924 to 2010 accounting for approximately 139 species (2.8% of total Chilean species). The aim of this paper was to review the advances in cytogenetic studies of Chilean land plants, reporting additional cytogenetic data for species of four botanical divisions until 2020. Cytogenetic data were searched in the CPCD (Chilean Plants Cytogenetic Database). In total, we found 180 publications from both Chilean and foreign researchers. To date, cytogenetic data have been reported for 499 Chilean land plant species (8.2% of total) belonging to 244 genera and 117 families. In this context, the 2001-2020 period has been among the most productive regarding publications, with 74 available reports that include 163 additional species. Based on chromosome numbers, angiosperms and bryophytes registered the greatest diversity with 55 and 29 different 2n, respectively; both divisions having the greatest number of studied species. Given the importance of increasing information on Chilean land plants, it is expected that more publications will contribute to the knowledge of their cytogenetic diversity in the near future.

RESUMEN Chile está ubicado en la región suroeste de América del Sur a lo largo del Océano Pacífico y contribuye a la flora mundial con aproximadamente 6.120 especies de Bryophyta, Pteridophyta, Pinophyta, Gnetophyta y Magnoliophyta (1,9% del total de especies en todo el mundo), que presentan un alto endemismo en todas las divisiones de plantas. Poco se conoce sobre la diversidad genética de las plantas terrestres chilenas en todo el mundo, incluidas sus características citogenéticas y moleculares. En 2012 publicamos la primera revisión sobre el estado del arte en Citogenética de Angiospermas Chilenas. El artículo reunió 78 publicaciones desde 1924 hasta 2010, que representan aproximadamente 139 especies (2,8% del total de especies chilenas). El objetivo de este trabajo fue revisar los avances en estudios citogenéticos de plantas terrestres chilenas, reportando datos citogenéticos adicionales para especies de cuatro divisiones botánicas hasta el 2020. Los datos citogenéticos se buscaron en el CPCD (Base de Datos Citogenéticos de Plantas Chilenas). En total, encontramos 180 publicaciones sobre citogenética de plantas terrestres chilenas, con datos citogenéticos para 499 especies (8,2% del total) pertenecientes a 244 géneros y 117 familias. En este contexto, el período 2001-2020 ha sido uno de los más productivos en cuanto a publicaciones, con 74 artículos disponibles que incluyen 163 especies adicionales. Basado en los números cromosómicos, angiospermas y briófitos registran la mayor diversidad, con 55 y 29 2n diferentes, respectivamente; ambas divisiones tienen también el mayor número de especies estudiadas. Dada la importancia de incrementar la información sobre plantas terrestres chilenas, se espera que más publicaciones contribuyan al conocimiento de su diversidad citogenética en un futuro próximo.

DNA content and cytogenetic characteristics of Gymnocalycium quehlianum (Cactaceae) along an altitudinal gradient / Contenido de ADN y características citogenéticas de Gymnocalycium quehlianum (Cactaceae) a lo largo de un gradiente altitudinal

ABSTRACT Important changes in vegetation types occur along elevational gradients. The genus Gymnocalycium is endemic to southern South America, and its species are distributed along elevational gradients. In particular, Gymnocalycium quehlianum is a globular cactus endemic to the Sierras de Córdoba. Studying cytogenetic aspects and DNA content in populations throughout their distribution is key to understanding the species. DNA content and cytogenetic characteristics were analyzed in four populations of G. quehlianum (615, 744, 948 and 1257 masl). The genome size in the four populations varied between 3.55 and 4.30 pg. The populations were diploid (2n = 22). All populations showed the karyotype formula of 10 metacentrics (m) + 1 submetacentric (sm). The species presented symmetrical karyotypes and constitutive heterochromatin CMA+/DAPI- associated with nucleolar organizing regions, always found in the first pair of m chromosomes. The 18-5.8-26S rDNA locus is found in the terminal regions of the first pair of chromosomes m, and the 5S locus is adjacent to the 18-5.8-26S locus. A tendency for DNA content to decrease with increasing altitude was observed.

RESUMEN A lo largo de los gradientes altitudinales se producen cambios importantes en los tipos de vegetación. El género Gymnocalycium es endémico del sur de América del Sur y sus especies se distribuyen en gradientes altitudinales. En particular, Gymnocalycium quehlianum es un cactus globular endémico de las Sierras de Córdoba. Estudiar aspectos citogenéticos y de contenido de ADN en las poblaciones a lo largo de su distribución es clave para comprender a la especie. En cuatro poblaciones de G. quehlianum (615, 744, 948 y 1257 msnm) se analizaron el contenido de ADN y las características citogenéticas. El tamaño del genoma en las cuatro poblaciones varió entre 3,55 y 4,30 pg. Las poblaciones resultaron diploides (2n=22). Todas las poblaciones presentaron la fórmula del cariotipo de 10 metacéntricos (m) + 1 submetacéntrico (sm). La especie presentó cariotipos simétricos y heterocromatina constitutiva CMA+/DAPI- asociados con regiones organizadoras nucleolares, que siempre se encontraban en el primer par de cromosomas m. El locus de ADNr 18-5.8-26S se encuentra en las regiones terminales del primer par de cromosomas m y el locus de 5S está adyacente al locus 18-5.8-26S. Se observó una tendencia del contenido de ADN a disminuir con el aumento de la altitud.

Citogenética comparativa de Physalis peruviana en tres poblaciones cultivadas de Cajamarca, Perú / Comparative cytogenetics of Physalis peruviana from three cultivated populations from Cajamarca, Peru

Resumen En este trabajo se caracteriza y compara citogenéticamente Physalis peruviana "aguaymanto" de poblaciones cultivadas de la región Cajamarca: San Pablo, Celendín y Cajabamba. El número cromosómico más frecuente en las tres poblaciones fue 2n = 4x = 48 con frecuencias de 60, 50 y 34% en las poblaciones de San Pablo, Celendín y Cajabamba respectivamente. En menor frecuencia se encontró casos de aneuploidía somática. Los resultados permitieron distinguir cada población a partir de su fórmula cariotípica 17m+4sm+3t, 24m y 20m+2sm+2t que identifican a San Pablo, Celendín y Cajabamba respectivamente. Los cariotipos fueron caracterizados por la longitud total del complemento haploide (HCL) y los índices de simetría (S%), asimetría (A) y asimetría intra e intercromosómica (A1 y A2). El mayor valor de HCL se describió en San Pablo. Celendín presentó el mayor grado de simetría (S%=53.226 y A= 0.177), mientras que los cariotipos de San Pablo y Cajabamba fueron descritos como los más asimétricos. Se concluye que la condición más frecuente es la tetraploidía; aunque se evidencia diferente morfología cromosómica entre los cariotipos de las tres poblaciones.

Abstract In this work, we characterized cytogenetically Physalis peruviana "aguaymanto" and cultivated populations of the Cajamarca region: San Pablo, Celendín and Cajabamba are compared. The most frequent chromosomal number in the three populations was 2n = 4x = 48 with frequencies of 60, 50 and 34% in San Pablo, Celendín and Cajabamba respectively. Few cases of somatic aneuploidy were found. Our results let distinguish the populations by its karyotypic formula 17m + 4sm + 3t, 24m and 20m + 2sm + 2t (San Pablo, Celendín and Cajabamba respectively). Karyotypes were characterized by the total length of the haploid complement (HCL) and the indices of symmetry (S%), asymmetry (A) and intra and interchromosomal asymmetry (A1 and A2). The highest value of HCL was described in San Pablo. Celendín presented the highest degree of symmetry (S% = 53.226 and A = 0.177), while the karyotypes of San Pablo and Cajabamba were described as the most asymmetric. We concluded that the tetraploidy is most frequent condition; although there is evidence of different chromosomal morphology between the three populations.

Chromosome number variation in part of the flora of protected wild areas in the Araucania region of southern Chile / Variación del número cromosómico en parte de la flora de áreas silvestres protegidas en la región de la Araucanía, sur de Chile

ABSTRACT An analysis was made of the correspondence between species diversity and chromosome number (CN) diversity across 13 Protected Wild Areas (PWA) in the Araucanía Region of southern Chile, encompassing 84 plant species with available cytogenetic data. Our aim was to establish whether higher species diversity within a PWA entails higher CN variation as based on the index of chromosome number heterogeneity (ICNH). The CN data were extracted from databases for Chilean plants, and the ICNH for the flora of each PWA was calculated. Results showed that in nine PWA the species diversity clearly correlates with CN diversity. However, four PWA do not fit this trend. The percentage of species with CN data varied between 9.6% and 24.5% among PWA, with 11 PWA presenting percentages higher than 11%. A 27.3% of the Chilean vascular plant species with available cytogenetic data were studied here for the 13 PWA. The results obtained by studying one part of the flora with available CN data suggest that the PWA could be an important reservoir of genetic diversity at a chromosome level, thus justifying the protective role of the PWA as biodiversity conservation sites.

RESUMEN Se realizó un análisis de la correspondencia entre la diversidad de especies y la diversidad de números cromosómicos (CN) en 13 Áreas Silvestres Protegidas (PWA) en la Región de La Araucanía en el sur de Chile, incluyendo 84 especies de plantas con datos citogenéticos disponibles. El objetivo fue establecer si una mayor diversidad de especies dentro de un PWA implica una mayor diversidad en CN expresado en base al Índice de Heterogeneidad Cromosómica (ICNH). Los CN de cada especie se extrajeron de bases de datos para plantas chilenas y se calculó el ICNH para la flora de cada PWA. Los resultados mostraron que en nueve PWA la diversidad de especies se correlaciona claramente con la diversidad de CN. Sin embargo, cuatro PWA no se ajustan a esta tendencia. El porcentaje de especies con datos de CN varió entre 9,6% y 24,5% entre PWA, con 11 PWA presentando porcentajes superiores al 11%. Un 27,3% de las especies de plantas vasculares chilenas con datos citogenéticos disponibles fueron estudiadas para las 13 PWA. Los resultados obtenidos al estudiar parte de la flora sugieren que las PWA serían un reservorio importante de diversidad genética a nivel cromosómico como se muestra aquí, justificando así el papel protector de las PWA como sitios de conservación de la biodiversidad.

Chilean plants cytogenetic database: coverage, features and usages / Base de datos citogenéticos de plantas Chilenas: cobertura, características y usos

Chilean Plants Cytogenetic Database (CPCD) is a resource available on line in electronic format, which provides a cytogenetics catalogue for continental and insular Chilean vascular plants. In this report, we made reference to the CPCD, discussing aspects on its coverage, features and usages. Currently, the database stores cytogenetic information for 247 species, 107 genera, and 55 families belonging to Pteridophyta, Pinophyta, and Magnoliophyta.

La Base de Datos Citogenéticos de Plantas Chilenas (CPCD) es un recurso disponible en formato electrónico en línea, que provee de un catálogo citogenético para plantas vasculares de Chile continental e insular. En esta comunicación hacemos referencia a la CPCD, discutiendo aspectos sobre su cobertura, rasgos y usos. Actualmente, la base de datos contiene información citogenética para 247 especies, 107 géneros y 55 familias pertenecientes a Pteridophyta, Pinophyta y Magnoliophyta.

Cytological and genome size data analyzed in a phylogenetic frame: Evolutionary implications concerning Sisyrinchium taxa (Iridaceae: Iridoideae)

Abstract Sisyrinchium is the largest genus of Iridaceae in the Americas and has the greatest amount of cytological data available. This study aimed at investigating how genomes evolved in this genus. Chromosome number, genome size and altitude from species of sect. Viperella were analyzed in a phylogenetic context. Meiotic and pollen analyses were performed to assess reproductive success of natural populations, especially from those polyploid taxa. Character optimizations revealed that the common ancestor of sect. Viperella was probably diploid (2n = 2x =18) with two subsequent polyplodization events. Total DNA content (2C) varied considerably across the phylogeny with larger genomes detected mainly in polyploid species. Altitude also varied across the phylogeny, however no significant relationship was found between DNA content changes and altitude in our data set. All taxa presented regular meiosis and pollen viability (> 87%), except for S. sp. nov. aff. alatum (22.70%), suggesting a recent hybrid origin. Chromosome number is mostly constant within this section and polyploidy is the only source of modification. Although 2C varied considerably among the 20 taxa investigated, the diversity observed cannot be attributed only to polyploidy events because large variations of DNA content were also observed among diploids.

Meiotic behavior during microsporogenesis of Alchornea triplinervia (Sprengel) Müller Argoviensis / Comportamento meiótico durante a microsporogênese de Alchornea triplinervia (Sprengel) Müller Argoviensis

The Alchornea triplinervia specie belongs to the Euphorbiaceae family, one of the main families of the Brazilian flora. In order to contribute to a better understanding of the specie, a counting of chromosome number and the microsporogenesis analysis of A. triplinervia were done. The inflorescences were collected in the municipalities of Paranavaí and Diamante do Norte, State of Paraná, Brazil, and the slides were prepared by squashing technique and staining with 1% acetic carmine. The analysis were performed using an optical microscope and showed a chromosome number for the specie equal to 2n=8x=72. Irregularities in the chromosome segregation process were the main meiotic abnormalities, presenting typical polyploid behavior. Other irregularities were observed; however, at low frequency without compromising the pollen grain formation of the analyzed plants.

A espécie Alchornea triplinervia pertence à família Euphorbiaceae, uma das principais famílias da flora brasileira. Visando a contribuir para um melhor entendimento da espécie, foi realizada a contagem do número de cromossomos e a análise da microsporogênese de A. triplinervia. As Inflorescências foram coletadas nos Municípios de Paranavaí e Diamante do Norte, no Estado do Paraná, Brasil, sendo as lâminas preparadas pela técnica de esmagamento e coradas com carmim acético 1%. As análises foram realizadas ao microscópio óptico, revelando um número cromossômico para a espécie igual a 2n=8x=72. Irregularidades no processo de segregação dos cromossomos foram as principais anormalidades meióticas, mostrando comportamento típico de poliploides. Outras irregularidades foram observadas, porém, em baixa frequência, não comprometendo a formação dos grãos de pólen das plantas analisadas.

Botanical aspects of Heteropterys umbellata (Malpighiaceae): a cytological and palynological approach

The genus Heteropterys is one of the major genera in Malpighiaceae. However, few cytological and palynological studies were reported. The present work described for the first time the chromosome number, heterochromatin pattern, meiotic behavior, pollen viability and palynological aspects of Heteropterys ubellata, a very spread species. One large Brazilian population was evaluated using conventional techniques for meiotic studies and acetolyse to access the pollen morphology. The species showed 2n = 20 chromosomes, normal meiotic development and viable pollens. Great blocks of heterochromatin were observed around the centromers. DAPI staining was positive for centroeric heterochroatin, hile CMA3 ark as observed just at terinal regions of one pair of hoologues chromosomes. This result and the presence of one chromosome pair attached to the nucleoli during the pachytene and diakinesis suggested the presence of only one pair of NORs. Palynological analysis revealed that pollen grains are apolar, 6 porate and with colpoids associated to all pores. The pollen content was positive for the starch test, and the exine was rugulate with little psilate regions.

O gênero Heteropterys é um dos maiores gêneros entre as Malpighiaceae. Entretanto, poucos estudos citológicos e palinológicos foram relatados. O presente trabalho descreveu pela primeira vez o número cromossômico, o padrão heterocromático, o comportamento meiótico, a viabilidade polínica e aspectos palinológicos de Heteropterys umbellata, uma espécie muito disseminada. Uma grande população brasileira foi estudada utilizando técnicas convencionais para o estudo de cromossomos meióticos e acetólise para acessar a morfologia polínica. A espécie apresentou 2n = 20 cromossomos, desenvolvimento meiótico normal e pólens viáveis. Grandes blocos de heterocromatina foram observados ao redor dos cen-trômeros. A coloração com DAPI foi positiva para a hetero-cromatina centromérica, enquanto marcas com CMA3 foram observadas somente em um sítio terminal de um par de cromossomos homólogos. Este resultado e a presença de um par de cromossomos associados a um nucléolo durante o paquíteno e diacinese sugerem a presença de somente um par de RONs. A análise palinológica revelou que os grãos de pólen são apolar, com 6 poros e colpóides associados a todos eles. O conteúdo polínico foi positivo para o teste de amido e a exina mostrou-se rugulada com poucas regiões psiladas.

Mitotic karyotype of the tropical freshwater crayfish Procambarus (Austrocambarus) llamasi (Decapoda: Cambaridae)

In Mexico, the biology of Procambarus has been more studied than the biology of other Cambarids because of its diversity and potential use in aquaculture. We determined the karyotype of the Mexican tropical freshwater crayfish Procambarus (Austrocambarus) llamasi from 189 metaphase spreads from gill tissues of 17 adults. They had 98-120 chromosomes (mode 2n=120 chromosomes). There are 60 pairs of monoarm, telocentric chromosomes. Sex chromosomes were not detected and we propose that the P. llamasi karyotype can be used to distinguish this species from other Mexican crayfish. Additionally, we suggest using karyological data in aquaculture and conservation biology. Rev. Biol. Trop. 58 (2): 655-662. Epub 2010 June 02.

El género Procambarus ha recibido mayor atención en los estudios de los principios fundamentales de su biología debido a su diversidad en el territorio mexicano y potencial uso en acuicultura. El cariotipo típico del acocil tropical mexicano Procambarus (Austrocambarus) llamasi, se estudió mediante 189 dispersiones cromosómicas en metafase del tejido branquial de 17 adultos tratados con la técnica citológica de inmersión. Encontramos un amplio número de cromosomas, que variaron entre 98-120 elementos cromosómicos, con número modal diploide de 2n=120 elementos cromosómicos. El cariotipo del acocil tropical esta constituido por 60 pares de cromosomas monorrámeos, todos los centrómero están en la región telocéntrica de los cromosomas. En las metafases mitóticas de hembras y machos no fueron identificados cromosomas sexuales. Sugerimos considerar la estructura cromosómica del cariotipo como una herramienta citotaxonómica así como el empleo de datos cariológicos para propósitos de acuicultura y conservación del acocil tropical.

Chromosome number and microsporogenesis of two accessions of Brachiaria dura Stapf (Poaceae) / Número de cromossomos e microsporogênese de dois acessos de Brachiaria dura Stapf (Poaceae)

The two accessions of B. dura analyzed (DU01 and DU02) are hexaploid (2n = 6x = 54), derived from x = 9. Meiotic abnormalities, such as precocious chromosome migration to the poles, laggards and micronuclei, were recorded in low frequency in both accessions. The few multivalent chromosome association at diakinesis and meiotic stability suggested that hexaploidy probably resulted from chromosome doubling. In DU02, chromosome transfer (cytomixis) among meiocytes, involving part or the entire genome was observed. The implication of these findings for the Brachiaria breeding is discussed.

Os dois acessos de B. dura analisados (DU01 e DU02) são hexaplóides (2n = 6x = 54), derivados de x = 9. Anormalidades meióticas como migração precoce de cromossomos para os polos, cromossomos retardatários e micronúcleos foram observados em baixa frequência em ambos os acessos. A presença de poucas associações cromossômicas em diacinese e a estabilidade meiótica sugere que a hexaploidia provavelmente resultou de duplicação cromossômica. No acesso DU02 observou-se transferência de cromossomos (citomixia) entre meiócitos, envolvendo parte ou todo o genoma. As implicações destes resultados para o melhoramento de Brachiaria são discutidas.

Chromosome studies in Orchidaceae from Argentina

The center of diversity of Argentinean orchids is in the northeast region of the country. Chromosome numbers and karyotype features of 43 species belonging to 28 genera are presented here. Five chromosome records are the first ones at the genus level; these taxa are Aspidogyne kuckzinskii (2n = 42), Eurystyles actinosophila (2n = 56), Skeptrostachys paraguayensis (2n = 46), Stigmatosema polyaden (2n = 40) and Zygostates alleniana (2n = 54). In addition, a chromosome number is presented for the first time for 15 species: Corymborkis flava (2n = 56), Cyclopogon callophyllus (2n = 28), C. oliganthus (2n = 64), Cyrtopodium hatschbachii (2n = 46), C. palmifrons (2n = 46), Galeandra beyrichii (2n = 54), Habenaria bractescens (2n = 44), Oncidium edwallii (2n = 42), O. fimbriatum (2n = 56), O. pubes (2n = 84), O. riograndense (2n = 56), Pelexia ekmanii (2n = 46), P. lindmanii (2n = 46) and Warrea warreana (2n = 48). For Oncidium longicornu (2n = 42), O. divaricatum (2n = 56) and Sarcoglottis fasciculata (2n = 46+1B?, 46+3B?), a new cytotype was found. Chromosome data support phylogenetic relationships proposed by previous cytological, morphologic and molecular analyses, and in all the cases cover some gaps in the South American literature on orchid chromosomes.

Reproductive system of Eriocnema fulva Naudin (Melastomataceae), an endemic species of Minas Gerais state, SE Brazil

Eriocnema fulva Naudin is a perennial herb, endemic to Minas Gerais state, SE Brazil, found on humid, shaded rocky riverbanks in montane semideciduous seasonal forests. The species is threatened, but information regarding its biology is still lacking, although such information is fundamental to any management plan. We aimed to evaluate the reproductive system of Eriocnema fulva in the Jambreiro Forest (19° 58'-59' S and 43° 55'-52' W, 800-1100 m altitude), municipality of Nova Lima, by experiments carried out in 1997 and 1998. The flowers are white, and flowering is of the steady state type, occurring once a year from November to December. Anthers are poricidal, and pollen is the only resource for visitors. The chromosome number is n = 17 during meiosis. The species is self-compatible, but does not produce fruits by spontaneous self-pollination or agamospermy; it requires pollen vectors and buzz pollination in order to produce fruits. Cross-pollination is the main reproductive strategy of E. fulva, and is accentuated by the small number of flowers (one or two in each plant) opened per day. Although the population studied was shaded by forest canopy, the seeds needed light to germinate. Germination ratio was lower in germination cabinet on filter paper (14 percent after 30 days) than in greenhouse on soil brought from the forest (47 percent after 25 days). Although the fruit is a capsule and the seeds are small, dispersion (anemochory or hydrochory) does not seem to occur at long distance, as it is the case for other Melastomataceae species with similar syndrome.

Eriocnema fulva Naudin é uma planta herbácea, perene, endêmica no estado de Minas Gerais, sendo encontrada em paredões rochosos úmidos, ao longo de riachos sombreados pela Floresta Estacional Semidecídua Montana. A espécie é ameaçada de extinção e não existem informações sobre a sua biologia, embora sejam fundamentais para um plano de manejo. Com o objetivo de avaliar o sistema de reprodução, foram feitos experimentos em 1997 e 1998 em uma população na Mata do Jambreiro (19° 58'-59' S e 43° 55'-52' W, 800-1100 m de altitude), no município de Nova Lima. As flores são brancas e a floração é do tipo steady state, ocorrendo uma vez ao ano durante novembro e dezembro. As anteras são poricidas e o pólen é a única recompensa para os visitantes. O número cromossômico encontrado na meiose foi n = 17. A espécie é autocompatível, não produz frutos por autopolinização espontânea nem por agamospermia, mas requer obrigatoriamente vetores de pólen e polinização vibrátil. A polinização cruzada é a principal estratégia reprodutiva de Eriocnema fulva, sendo acentuada devido ao pequeno número de flores abertas por dia, apenas uma ou duas em cada planta. Embora as populações estejam localizadas em ambientes sombreados e úmidos, as sementes precisam de luz para germinar, sendo fotoblásticas positivas. A taxa de germinação em papel de filtro na câmara de germinação foi menor (14 por cento após 30 dias) que em solo da floresta na casa de vegetação (47 por cento após 25 dias). Embora o fruto seja do tipo cápsula com sementes pequenas, a dispersão (anemocoria ou hidrocoria) parece não ocorrer a distâncias longas, como é observada em outras espécies de Melastomataceae com síndrome de dispersão semelhante.

Microsporogenesis in Brachiaria dictyoneura (Fig. & De Not.) Stapf (Poaceae: Paniceae)

icrosporogenesis was analyzed in five accessions of Brachiaria dictyoneura presenting x = 6 as the basic chromosome number. All accessions were tetraploid (2n = 4x = 24) with chromosome pairing in bi-, tri-, and quadrivalents. The recorded meiotic abnormalities were those typical of polyploids, including precocious chromosome migration to the poles, laggard chromosomes, and micronucleus formation. The frequency of these abnormalities, however, was lower than those reported for other polyploid accessions previously analyzed for other Brachiaria species. Cell fusion and absence of cytokinesis were also recorded in some accessions, leading to restitutional nucleus formation in some cells. Genetically unbalanced microspores, binucleate, and 2n microspores were found among normal meiotic products as results from these abnormalities. The limitation in using these accessions as pollen donor in interspecific crosses with sexual species with x = 7 or x = 9 in breeding programs is discussed.

Microsporogenesis in tetraploid accessions of Brachiaria nigropedata (Ficalho & Hiern) Stapf (Gramineae)

The genus Brachiaria (Trin.) Griseb. has achieved considerable importance to cattle production systems, as a result of the good production and adaptation of a few cultivars to poor and acid soils of the Brazilian savannas. Many of its species and accessions are polyploid and apomictic, which limits direct hybridization. To assist the breeding program, cytogenetic characterization has been undertaken on the accessions of Brachiaria collection at the Embrapa Beef Cattle Research Center. In this study, chromosome number and meiotic behavior are reported for the Brachiaria nigropedata (Ficalho & Hiern) Stapf collection. The 20 available accessions are tetraploid (2n = 4x = 36). Chromosomes paired preferentially as bivalents, but quadrivalents were found in high frequencies in some cells. Meiotic behavior was, in general, irregular, and varied among accessions. Most accessions presented more than 20% of abnormal tetrads. The most common meiotic abnormalities were those related to irregular chromosome segregation due to polyploidy, leading to micronuclei formation in the tetrad stage. A low frequency of other meiotic abnormalities such as the absence of cytokinesis, chromosome stickiness, cell fusion, anaphase bridges, and chromosome transfer among microsporocytes were also recorded in some accessions. Limitations of these accessions for use in hybridization programs are discussed.