No abstract

Somatic chromosome numbers of 131 accessions belonging to 55 Paspalum species from subtropical South America have been determined. All species had x = 10 as a basic chromosome number, except P. almum which had x = 6. Six ploidy levels were found among species with tetraploidy as the most frequent condition. New diploid and octoploid counts were reported. For Paspalum lilloi and P. glabrinode (both 2n = 2x = 20), and for P. ellipticum, P. erianthoides, P. ovale and P. remotum (all 2n = 8x = 80) sporophytic chromosome numbers are presented for the first time. Records that differ from previously reported counts are given for the following species: P. paucifolium (2n = 2x = 20), P. ceresia (2n = 6x = 60), P. conjugatum (2n = 6x = 60), P. alcalinum (2n = 6x = 60) and P. aff. arundinellum (2n ? 1 = 5x ? 1 = 51). These chromosome data are discussed in light of ploidy-level variation and implications for breeding systems within and among species.

Karyotypes of 18 populations belonging to eight of the southernmost species of South American Crotalaria were examined. All had x = 8, except C. incana which had x = 7. Diploid, tetraploid and octoploid species were found. The octoploid is a new record and is the highest ploidy level detected so far in the genus. Species within the same ploidy level could be distinguished by quantitative karyotype parameters and by the size and position of the satellites. From an evolutionary point of view, our results support a decrease of the basic chromosome number by dysploidy. Polyploidy is one of the more important mechanisms of chromosome change, even though some structural rearrangements may explain variations of the karyotype formula. Gigas effects, due to polyploidy, were evident in the length of the stomatal guard cells and in pollen size, but were less clear in seed weight. Nucleotype effects, caused by the DNA quantity in a nucleus, were also evident for pollen and stomatal guard cell size and seed weight, although only in diploids with x = 8 for the latter character. Chromosome data are further discussed in the light of the infrageneric systematic arrangement.

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.

Chromosome numbers, meiotic behaviour and karyotypes in 27 populations belonging to four species of Commelina L. from north-east Argentina and Paraguay have been studied. The basic number of chromosomes in all accessions is x = 15. For C. platyphylla Klotzsch ex Seub. (2 n = 2 x = 30) the chromosome number is reported for the first time.A new ploidy level (2 n = 6 x = 90) is presented for South American accessions of C. diffusa Burm. f. Commelina erecta L. and C. obliqua Vahl are tetraploids (2 n = 4 x = 60). Chromosomes behave regularly at meiosis and pair as bivalents in diploid and polyploid accessions. Chiasma frequency and distribution is reported for each species. The karyotype descriptions of C. platyphylla (18m + 12sm), C. obliqua (30m + 26sm + 4st) and hexaploid C. diffusa (38m + 44sm + 8st) are reported here for the first time. The data suggest an allopolyploid condition for tetraploids of C. erecta and C. obliqua.