Abstract We report the in vitro induction of polyploids from two cassava cultivars by colchicine treatment. Shoot nodal segments, collected from in vitro cultivated plants of Porquinho and Vassourinha cultivars, were used as explants. Explants were treated in liquid media without and with colchicine (0.05, 0.10 or 0.15%), at 90 rpm, in the dark, for 48 or 96 h. Normal-like and putative-polyploid phenotypes were recovered from in vitro culture, for both cultivars. All plants from the putative-polyploid group were confirmed as tetraploids by flow cytometry and root tip chromosome counting, whereas no association was found between ploidy level and phenotype in normal-like plants. Mixoploids were also recovered from both cultivars. Vassourinha was more responsive to colchicine treatment than Porquinho. Tetraploid plants have fewer, but bigger, stomata guard cells than those in diploids. Colchicine at 0.10% for 96 hours induced a high number of tetraploids in both cultivars.

Malpighia emarginata Sessé e Mociño ex DC., ou acerola, é uma planta silvestre originada do sul do México, América Central e região norte da América do Sul. A espécie foi introduzida no Brasil há cerca de 60 anos e o País é o maior produtor mundial. Embora os frutos da acerola tenham alto valor comercial, pois são uma importante fonte natural de vitamina C, pouco se conhece sobre os cromossomos da espécie. Estudos prévios mostraram que a maioria das espécies de Malpighia é diploide, incluindo M. emarginata com 2n = 20. No presente trabalho, foi confirmado o número cromossômico da acerola e foi descrito, pela primeira vez, o seu cariótipo, provendo a identificação dos homólogos para a construção do ideograma. Os cromossomos da acerola são pequenos (1,71 a 2,56 µm) e metacêntricos, com exceção do cromossomo 2, que foi classificado como submetacêntrico. Além disso, definiu-se um protocolo para produzir plântulas enraizadas in vitro para estudos mitóticos, o qual pode, igualmente, ser usado para a micropropagação da acerola.

Malpighia emarginata Sessé & Mociño ex DC. or West Indian cherry (acerola) is a wild plant originated in southern Mexico, Central America and the northern region of South America. The species was introduced to Brazil about 60 years ago and now the country is the world's biggest producer. Even though the fruits of acerola have high commercial value, as they are an important source of the natural vitamin C, very little chromosome information is available for this species. Previous studies showed that most Malpighia species are diploids, including M. emarginata with 2n = 20. In the present paper, the chromosome number of acerola was confirmed, and for the first time, its karyotype was described, providing the identification of the homologues for the ideogram construction. The acerola chromosomes are small (1.71 to 2.56 µm) and metacentric with the exception of chromosome 2 that is classified as submetacentric. In addition, it is recommended a protocol to produce rooted-plantlets in vitro for mitotic studies that could be also used for micropropagation of acerola.

The chromosomes of Crotalaria juncea, a legume of agronomic interest with a 2n = 16 karyotype composed of metacentric chromosomes, were analyzed using several cytogenetic techniques. C-banding revealed heterochromatic regions around the centromeres in all chromosomes and adjacent to the secondary constriction on the chromosome 1 short arm. Fluorescent staining with the GC-specific chromomycin A3 (CMA) highlighted these heterochromatic regions and a tiny site on the chromosome 1 long arm while the AT-specific stain 4'-6-diamidino-2-phenylindole (DAPI) induced a reversed pattern. Staining with CMA combined with AT-specific distamycin A (DA) counterstaining quenched the pericentromeric regions of all chromosomes, but enhanced fluorescence was observed at the heterochromatic regions around the secondary constriction and on the long arms of chromosomes 1 and 4. Fluorescence in situ hybridization (FISH) revealed 18S-5.8S-26S rRNA gene sites (45S rDNA) on chromosomes 1 and 4, and one 5S rDNA locus on chromosome 1. All the rDNA sites were co-located with the positive-CMA/DA bands, suggesting they were very rich in GC. Silver staining revealed signals at the main 45S rDNA locus on chromosome 1 and, in some cells, chromosome 4 was labeled. Two small nucleoli were detected in a few interphase cells, suggesting that the minor site on chromosome 4 could be active at some stages of the cell cycle.

Foram conduzidos experimentos visando à otimização de procedimentos para preparações citológicas de pontas de raiz com alta freqüência de metáfases mitóticas, apresentando cromossomos com morfologia nítida, em espécies pertencentes a dois gêneros de plantas, Passiflora (Passifloraceae) e Crotalaria (Leguminosae). Para o acúmulo de metáfases, bem como de prófases e prometáfases com cromossomos bem condensados, foram avaliados pré-tratamentos de raízes, em que foram utilizadas diferentes combinações de 8-hidroxiquinolina, inibidor do fuso mitótico, com cicloheximida, inibidor da síntese protéica. As preparações foram coradas pelo método de Feulgen. Os melhores resultados foram obtidos com o tratamento com 8-hidroxiquinolina a 300ppm combinado com cicloheximida a 3,125ppm, por 1 hora e 30 minutos para as espécies de Passiflora, e a combinação de 8-hidroxiquinolina a 300ppm + cicloheximida a 6,25ppm também durante 1 hora e 30 minutos para as espécies de Crotalaria. Esta investigação ilustra a situação de dois gêneros de plantas em que a adequação de pré-tratamentos diferiu entre os grupos, e é fundamental para estudos envolvendo comparação do cariótipo das espécies, sobretudo para a detecção de marcadores cromossômicos evidenciados por meio de métodos diversos de citogenética (bandamento-C, bandamento com fluorocromos e hibridação in situ fluorescente).

Experiments were carried out aiming to optimize procedures for cytological preparations of root tips with high frequency of metaphase cells showing clear features of chromosome morphology, in species belonging to two genera of plants, Passiflora (Passifloraceae) and Crotalaria (Leguminosae). For the accumulation of metaphases, as well as prophases and prometaphases with well condensed chromosomes, pretreatments of root tips with different combinations of 8-hydroxiquinoline, a mitotic fuse inhibitor and with cycloheximide, a protein synthesis inhibitor, were evaluated in Feulgen stained preparations. The treatments with 8-hydroxiquinoline at 300ppm + cycloheximide at 3.125ppm, and with 8hydroxiquinoline at 300ppm + cycloheximide at 6.25ppm, both for 1 hour and 30 minutes, were more effective respectively for Passiflora and Crotalaria species. This investigation illustrates a case of differences of pretreatment procedures between two genera of plants, as well as represents a basic work for studies involving the comparison of the karyotype of species belonging to these genera, and especially, for the detection of chromosome markers via several cytogenetic methods (C-banding, fluorescent-chromosome banding and in situ hybridization).

Com o objetivo de estudar a variabilidade genética intra-específica em Oncidium varicosum Lindl. (Orchidaceae - Oncidiinae), foram avaliadas cinco populações de Minas Gerais, coletadas em Alfenas (AL), Estiva (ES), Pedra do Coração (PC), Pedra Branca (PB) e Pouso Alegre (PA). Foram considerados 22 caracteres florais, medidos a partir de "vouchers" (fichas florais), empregando-se métodos estatísticos univariados e multivariados (análise discriminante canônica - CDA e análise de agrupamento a partir de distância de Mahalanobis). Houve diferença significativa (p < 0,05) entre populações, pelo teste F, para 13 caracteres. O primeiro eixo canônico separou a população PA de PB e de PC. Os indivíduos de PA são menores que os de PC, que são menores que os de PB. AL se sobrepôs a PA, ES e PC pelo primeiro eixo, mas se separou completamente de PA e quase que totalmente das demais populações de acordo com o segundo eixo canônico, por apresentar características como colunas compridas e espessas, sépalas laterais compridas e estreitas e ovários mais curtos. De acordo com a análise de agrupamento, novamente a população AL divergiu das demais. Observou-se que as populações ES, PC e PB são mais próximas entre si, seguidas da população de PA. O padrão de variabilidade genética observado não parece estar relacionado a diferenças de latitude. Entretanto, parece estar associado a diferenças de longitude, embora este único fator pode não ser suficiente para explicá-lo.

Five populations of Oncidium varicosum Lindl. (Orchidaceae - Oncidiinae) collected in Minas Gerais at Alfenas (AL), Estiva (ES), Pouso Alegre (PA), Pedra do Coração (PC) and Pedra Branca (PB), were examined with the aim of studying the intraspecific genetic variability. Twenty-two floral characters were measured from vouchers, using univariate and multivariate statistical methods (canonical discriminant analysis - CDA and cluster analysis using Mahalanobis distance). Significant differences (p < 0,05) among populations, by the F test, were observed for 13 characters. The first canonical axis separated population AL from PB and PC. The PA individuals are smaller than those of PC, which are smaller than those of PB. AL overlapped PA, ES and PC by the first axis, but was completely separated from PA and almost totally from the other populations according to the second canonical axis, for presenting characteristics such as longer and thicker columns, longer and narrower lateral sepals and shorter ovaries. According to the cluster analysis, AL diverged again from the other populations. Populations ES, PC and PB are closer to each other, followed by PA. The pattern of genetic variability observed does not seem to be related to different latitudes. However, it seems to be associated to longitudinal differences, although this single factor may not be enough to explain this pattern.