RESUMO

Cynodon dactylon is characterized by taxonomic and systematic complexity, and polyploidy is one of the factors responsible for its genetic and morphological diversity. The aim of the present study was to compare karyotypes of C. dactylon cytotypes based on fluorescent banding and nuclear DNA content. The nine C. dactylon accessions evaluated were obtained from the Active Germplasm Bank (BAG) of the United States Department of Agriculture (USDA). Roots were pretreated with cycloheximide, fixed in Carnoy's solution and subjected to enzymatic digestion. Slides were prepared by the dissociation and air-drying technique. The fluorescent banding pattern was obtained using chromomycin A3 (CMA)/4,6-dimidino-2-phenylindole (DAPI) staining and DNA content was estimated by flow cytometry. The chromosome number of the accessions ranged from 2n = 2x = 18 to 2n = 5x = 45. Chromosomal polymorphism was observed based on the distribution and number of heterochromatic bands, with CMA+ bands located in the pericentromeric position and DAPI+ bands mainly in the terminal position. PI477004-26 (2n = 3x = 27) and PI291966-27 (2n = 4x = 36) had the highest and lowest number of DAPI+ bands, respectively. The number of CMA+ bands was stable, as only PI477004-26, PI291966-27 and PI289750-10 (2n = 5x = 45) showed variation. There was no direct correlation between an increase in the ploidy level and an increase in the percentage of heterochromatic regions, mainly in relation to A-T-rich blocks. The chromosomal banding variation found reinforces the notion of allopolyploidy occurrence in C. dactylon and demonstrates the genomic complexity of this species regard to repetitive DNA content.

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RESUMO

Cynodon is a genus of plants with forage potential that has attracted the interest of breeders. These species have high morphological variability in a large number of varieties and cytotypes, hampering identification. This study aimed to determine the karyotype asymmetry index among accessions of Cynodon to discriminate between them. Karyotype symmetry was based on three estimates, which were compared. The basic number for the genus is x = 9. The results of the chromosome count and DNA quantification, respectively, were as follows: two diploid accessions (2n = 2x = 18 and 1.08 ± 0.094 to 1.17 ± 0.036 pg DNA and ± standard deviation), one triploid accession (2n = 3x = 27 and 1.63 ± 0.017 pg DNA), four tetraploid accessions (2n = 4x = 36 and 1.88 ± 0.069 to 2.10 ± 0.07 pg DNA), and one pentaploid accession (2n = 5x = 45 and 2.55 ± 0.098 pg DNA). C. incompletus var. hirsutus had the longest total length of the haploid lot (29.05 µm), with chromosomes that ranged from 1.7 to 6.2 µm in length. On the basis of the karyotype asymmetry indices, the accessions were divided into two groups: 1) C. dactylon var. dactylon, C. transvaalensis, C. dactylon var. polevansii, three accessions of Cynodon sp, and C. nlemfuensis; and 2) C. incompletus var. hirsutus. This is the first description of tetraploidy in C. transvaalensis. The karyotypic data facilitated a determination of the degree of proximity between the accessions.

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RESUMO

Cynodon dactylon (L.) Pers. var. dactylon (common bermudagrass) is widely distributed geographically between approximately 45°N and 45°S latitude, penetrating to approximately 53°N latitude in Europe. The extensive variation of morphological and adaptive characteristics of the taxon has been substantially documented, but information is lacking on DNA molecular variation in geographically disparate forms. The genetic diversity of 51 wild accessions of bermudagrass from southwest China (Sichuan, Chongqing, Yunnan, Guizhou, and Tibet) and 8 African bermudagrass was analyzed using amplified fragment length polymorphism molecular markers. A total of 670 polymorphic bands were detected with 11 primer combinations, of which 663 (98.74%) bands were found to be polymorphic. The genetic similarity among the accessions ranged from 0.64-0.96 with an average of 0.78. All 59 wild accessions were clustered into 5 eco-geographic groups, and nearly all accessions from the same area were classified into the same group and were found to be associated with their geographical distributions. Therefore, complex geographical and ecological environments are important factors for the genetic structure and geographical distribution of C. dactylon.

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Objetivou-se por meio deste trabalho comparar o processo de secagem, em forno de microondas e em estufa de ventilação de ar forçada, bem como seus efeitos sobre a composição química de diferentes genótipos pertencente ao gênero Cynodon (Tifton 85, Jiggs, Russel, Tifton 68 e Vaquero) colhidos em diferentes idades de corte (28, 48, 63 e 79 dias). O delineamento experimental utilizado foi o de blocos casualizados em esquema de parcelas subdivididas, com 4 repetições. Não foi observada diferença (P>0,05) entre os métodos analisados sobre a composição química dos genótipos em estudo. O aumento da idade de corte influenciou negativamente (P<0,05) os teores de proteína bruta das diferentes partes da planta. Houve aumento significativo (P<0,05) dos teores de matéria seca, fibra em detergente neutro, fibra em detergente ácido e produção de matéria seca com o aumento da idade de corte. O uso do forno de microondas é uma alternativa rápida e precisa na obtenção do teor de matéria seca das forragens, mostrando eficiência semelhante ao método de secagem em estufa de circulação de ar forçada. Os genótipos apresentaram melhores resultados de composição química quando manejados na idade 28 dias.

The aimed of this work was to comparing the drying process in a microwave oven and forced air ventilation, as well as their effects on the chemical composition of different genotypes of the genus Cynodon (Tifton 85, Jiggs, Russell, Tifton 68 and Vaquero) collected at different ages cutting (28, 48, 63 and 79 days). The experimental design was a randomized block in a split-plot design, with 4 replicates. There was no difference (P>0.05) between the methods analyzed on the chemical composition of the genotypes studied. Increasing age cutoff negatively influenced (P<0.05) the crude protein content of the different plant parts. A significant increase (P<0.05) of dry matter, neutral detergent fiber, acid detergent fiber and dry matter production was observed with increasing age cut. The use of the microwave oven is a quick and precise method obtain the dry matter content of the fodder showing efficiency similar to the method of drying in an oven with forced air circulation. The genotypes showed better chemical composition results when handled at age 28 days.

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RESUMO

Fifty-five wild accessions of bermudagrass (Cynodon dactylon) were collected from southwest China (Sichuan, Chongqing, Yunnan, Guizhou, and Tibet), and their genetic diversity was analyzed using simple sequence repeat markers. A total of 267 polymorphic bands were detected with 18 primer combinations. The genetic similarity among the accessions ranged from 0.688 to 0.894 with an average of 0.797. All 55 wild accessions were clustered into 7 eco-geographic groups. Our data showed that the dendrogram was almost in accordance with geographic distribution, and accessions from the same collection sites tended to be clustered into the same group. A genetic differentiation analysis revealed that the percentage of genetic variance was 70.07 and 29.93% within and among groups, respectively. Finally, we discuss the implications of these results for C. dactylon in southwest China.

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