Contagens cromossômicas em espécies brasileiras de Paspalum L. (Gramineae)

Abstract

RESUMO -(Contagens cromossômicas em espécies brasileiras dePaspa/um L. (Gramineae».A partir de coletas de germoplasma de espécies de Paspa/um, realizadas nas cinco regiões do Brasil, e subseqüentes análises citológicas em mitose ou meiose, reportam-se os números de cromossomos de 107 acessos, distribuídos por 33 espécies, representativas de 13 dos grupos taxonômicos informais em que o gênero é tradicionalmente subdividido. No grupo Plicatula, sob intensa revisão taxonômica, 27 acessos são citados ainda sem identificação específica. A região sul é muito bem representada, com 65 acessos, seguida pela região centro-oeste, com 33. Os números cromossômicos de P. ji/(fo/ium (2n = 20), P. hartwegiallum (2n = 60), P. rhodopedum (2n = 40) e P. wetlsteillii (2n = 40 e 60) são relatados pela primeira vez. Também são novas as contagens de 2n = 50 para P. p/ellum e para uma forma de P. di/a/atum com anteras amarelas. Encontrou-se um novo acesso diplóide (2n = 20) de P. p/ica/u/um e mais um acesso de P. malldiocallum com 2n = 50, que discrepa do nível hexaplóide, mais freqüente na espécie. Outras contagens confirmam os números já conhecidos, estendendo sua representatividade geográfica.Palavras-chave -Paspa/um, Brasil, gramíneas, número somático, nível de ploidia ABSTRACT -(Chromosome counts in Brazilian species of Paspa/um L. (Gramineae)). Germplasm accessions obtained in collecting missions covering ali the five regions of Brazil were submitted to cytological analysis, either in mitosis or meiosis. Chromosome numbers are reported from 107 accessions of 33 species, representative of 13 ofthe informal taxonomic groups, in which the genus is traditionally divided. In the Plicatula group, under intensive taxonomic investigation, 27 accessions are mentioned without any specific identification. The Southem region is very well represented, with 65 accessions, followed by the West Central region, with 33. The chromosome numbers of P.ji/(fo/ium (2n = 20), P. hartwegiallum (2n = 60), P. rhodopedum (2n = 40) and P. wells/eil1ii(2n = 40 and 60) are reported for the first time. Also new are the reports of 2n = 50 for P. p/ellum and for a yellow-anthered form of P. di/ala/um. The new findings include an additional diploid accession of P. p/icatulum (2n = 20) and a second accession of P. malldiocanum with 2n = 50, a number in disagreement with the most frequent hexaploid levei in this species. Additional data confirm previous counts, thus extending their geographic amplitude.

Microsporogenesis in Paspalum conspersum Schrad. (Virgata group) with different ploidy levels

“…Accurate checking of passport data of the accessions cited by distinct authors (Table 1) confirms the conclusion of Pozzobon et al (2000) that references to 2n = 40 in this species can be traced to ill-identified specimens of P. regnellii Mez.…”

“…Previous tetraploid (2n = 4x = 40) reports for P. conspersum, associated with regular meiosis and sexual reproduction (Fernandes et al, 1974;Burson and Bennett, 1976), do not, in fact, refer to this species. On the contrary, hexaploidy (2n = 6x = 60) has been most commonly reported for true representatives of the species (Quarín, 1977;Quarín and Hanna, 1980;Pozzobon and Valls, 1987;Honfi et al, 1990;Pagliarini et al, 2001;Adamowski et al, 2005;Pozzobon et al, 2000Pozzobon et al, , 2008Hojsgaard et al, 2009). The 60-chromosome race of P. conspersum analyzed by Quarín and Hanna (1980) showed regular meiosis, with primarily bivalent pairing and a low percentage of univalents and quadrivalents.…”

Cytological and reproductive aspects in the Caespitosa group of Paspalum

“…In line with additional papers that cover a broader sampling, both in terms of accessions and geographical sites of origin of available Paspalum germplasm (HONFI et al, 1990;POZZOBON et al, 2000;MORRONE et al, 2006;HOJSGAARD et al, 2009), they document the fi nding of more than a single ploidy level in distinctive accessions of same species.…”

Cytogenetic analyses in Paspalum L. reveal new diploid species and accessions

“…Anachyris (MORRONE et al, 2000). Chromosome numbers of 2n=40 and 2n=60 were known for the species, the tetraploids being largely the most common (BURTON, 1940;GOULD, 1975;BURSON & HUSSEY, 1998;POZZOBON et al, 2000;PAGLIARINI et al, 2001).…”