Lidia Poggio

GENOME SIZE AND NUMERICAL POLYMORPHISM FOR THE B CHROMOSOME IN RACES OF MAIZE (ZEA MAYS SSP. MAYS, POACEAE)

Twenty-one native populations (1120 individuals) of maize from Northern Argentina were studied. These populations, which belong to 13 native races, were cultivated at different altitudes (80-3620 m). Nineteen of the populations analyzed showed B chromosome (Bs) numerical polymorphism. The frequency of individuals with Bs varied from 0 to 94%. The number of Bs per plant varied from 0 to 8 Bs, with the predominant doses being 0, 1, 2, and 3. Those populations with varying number of Bs showed a positive and statistically significant correlation of mean number of Bs with altitude. The DNA content, in plants without Bs (A-DNA)(2n = 20), of 17 populations of the 21 studied was determined. A 36% variation (5.0-6.8 pg) in A-DNA content was found. A significant negative correlation between A-DNA content and altitude of cultivation and between A-DNA content and mean number of Bs was found. This indicates that there is a close interrelationship between the DNA content of A chromosomes and doses of Bs. These results suggest that there is a maximum limit to the mass of nuclear DNA so that Bs are tolerated as long as this maximum limit is not exceeded.

Is maize B chromosome preferential fertilization controlled by a single gene

In previous work, genotypes for high and low B chromosome transmission rate were selected from a native race of maize. It was demonstrated that the B transmission is genetically controlled. The present work reports the fourth and fifth generations of selection and the F1 hybrids between the lines. The native B is characterized by a constant behaviour, with normal meiosis and nondisjunction in 100% of postmeiotic mitosis. It is concluded that genetic variation for B transmission between the selected lines is due to the preferential fertilization process. The F1 hybrids show intermediate B transmission rate between the lines. They are uniform, the variance of the selected character being one order of magnitude lower than that of the native population. In addition, 0B × 2B and 2B × 2B crosses were made to study the effect of the presence of B chromosomes in the female parent, resulting in non-significant differences. Several crosses were made both in Buenos Aires and in Madrid to compare the possible environmental effect, but significant differences were not found. Our results are consistent with the hypothesis of a single major gene controlling B transmission rate in maize, which acts in the egg cell at the haploid level during fertilization. It is also hypothesized that maize Bs use the normal maize fertilization process to promote their own transmission.

Localization of the genes controlling B chromosome transmission rate in maize (Zea mays ssp. mays, Poaceae)

In previous papers we found that the frequency of B chromosomes in native races of maize varies considerably in different populations. Moreover, we found genotypes that control high and low transmission rates (TR) of B chromosomes in the Pisingallo race. In the present work crosses were made to determine whether the genes controlling B-TR are located on the normal chromosome set (As) or on the B chromosomes (Bs). We made female f.0B × male m.2B crosses between and within high (H) and low (L) B-TR groups. The Bs were transmitted on the male side in all cases. The mean B-TR from the progeny of f.0B (H) × m.2B (H) and f.0B (H) × m.2B (L) crosses was significantly higher than that from f.0B (L) × m.2B (L) and f.0B (L) × m.2B (H) crosses. The results show that the B-TR of the crosses corresponds to the H or L B-TR of the 0B female parents irrespective of the Bs of the male parent. This indicates that B-TR is genetically controlled by the 0B female parent and that these genes are located on the A chromosomes.

Chromosome and morphological studies in the Mimosa debilis complex (Mimosoideae, Leguminosae) from southern South America

Mimosa debilis Humb. & Bonpl. ex Willd. and M. nuda Benth. were grouped in specific and infraspecific complexes. Both taxa showed exomorphological similarities, with conflicts in their taxonomic circumscription and present different ploidy levels. The objective of the present contribution was to analyse chromosome numbers of different populations and to evaluate morphological characters of specimens from Paraguay, Argentina and boundary regions. Chromosome numbers of M. debilis var. debilis (2n = 2x = 26 and 2n = 4x = 52) confirmed previous reports, whereas those of M. nuda var. glaberrima (2x = 26, 4x = 52), M. nuda var. gracilipes (2x = 26, 4x = 52) and M. nuda var. nuda (4x = 52) are presented for the first time. Variation was observed in habit, foliar and floral morphology and was correlated with the chromosome number and the geographical distribution of the taxa. Groups with stable morphological characters and restricted geographic distribution were identified. Also, the results showed a pattern of hybrid swarms and polyploids of different origin that may explain the existence of taxonomic conflicts in the M. debilis–M. nuda species complex. On the basis of these results, M. nuda should be included in the synonymy of M. debilis.

Ploidy levels and their relationships with the rainfall in several populations of Patagonian species of Berberis L.

Abstract The ploidy levels and pollen staining of 68 populations belonging to 13 species of the genus Berberis L., growing in the Argentinian Patagonia under different environmental conditions, were analyzed as a part of a multidisciplinary study to obtain information about the evolutionary history of the genus. The chromosome number at Berberis bidentata, B. cabrerae, B. chillanensis, B. darwinii, B. empetrifolia, B. ilicifolia, B. linearifolia, B. micro-phylla, B. montana, B. parodii and B. serrato-dentata is 2n = 28, whereas B. buxifolia and B. heterophylla have 2n 56. The relationship between ploidy levels and rainfall showed that, contrarily to the species with 2n = 28, B. buxifolia and B. heterophylla (2n =56) grow in areas where the rainfall range is low. The opening of new habitats for colonization as a result of climatic change provides an ecological opportunity for the polyploids to exploit their inherent advantage.

Karyotype studies in Mimosa (Mimosoideae, Leguminosae) from Southern South America and ecological and taxonomic relationships

Abstract In this work we studied the chromosome number and karyotype formula of seven species of Mi- mosa L. (Mimosoideae, Leguminosae). The chromosome number 2n = 2x = 26 for M. detinens Benth., M. hex- andra M. Micheli, M. ostenii Speg. ex Burkart and M. xanthocentra Mart. var. mansii (Benth.) Barneby are new records, while the chromosome number 2n = 2x = 26 for M. debilis var. debilis, M. urugüensis Hook. and Arn. and M. uliginosa Chodat and Hassl. confirm previous records. Karyotype formulae revealed the existence of metacentric and submetacentric chromosomes, and the chromosomal asymmetry indexes did not show significant differences between taxa. The chromosome length of xerophilous and endemic M. detinens and M. ostenii differed from the rest of species, indicating that this parameter could have taxonomic value. In addition, the relationship between total chromosome length and climatic parameters showed that diploid species of marginal areas of distribution have a larger chromosome size, and that this could be related with mechanisms of ecologi- cal adaptation.

Meiosis and pollen grain development in Isolepis cernua f. cernua (Cyperaceae)

In this paper, cytogenetic studies and pollen grain development of Isolepis cernua (Vahl) Roem. & Schult. f. cernua (Cyperaceae) from Argentina are presented. The somatic chromosome number found is 2n= 54, being different from previous reports. Primary constrictions have not been observed, suggesting that they are holocentric chromosomes, as in many species of the family. The meiotic behaviour was described showing n= 27 and axial orientation of some of the bivalents. Three of four pollen nuclei degenerate while one of them completes the mitosis. These processes originate the pseudomonad, a characteristic feature in the Cyperaceae. This fact does not affect the pollen fertility wich is 98%.

Cytogenetic studies of Southern South-American Ilex

Abstract The dioecious genus Ilex (Aquifoliaceae) has been poorly studied from a cytogenetic point of view. Chromosome numbers of only ca. 5% of the species have been reported. In the present work the chromosome number of eight taxa from Argentina and Brazil are presented: Ilex taubertiana Loes., I. integerrima (Vell.) Reissek and I. pseudobuxus Reissek present 2n = 40, being this the first report for these species. A diploid number of 40 is also confirmed for I. paraguariensis A. St. - Hil, I. brevicuspis Reissek, I. dumosa Reissek and I. theezans Reissek, and 2n = 80 for I. argentina Lillo. Species with 2n = 40 (n = 20) show a regular meiotic behaviour with 20 bivalents, while I. argentina also shows a regular meiosis with 40 bivalents. Those individuals of I. paraguariensis analyzed in the present paper do not show a heteromorphic bivalent as previously reported and ascribed to sex chromosomes.

Nucleolar organizer activity and competition in Tricepiro Don Rene INTA, a synthetic forage crop

Abstract The nucleolar organizer activity and the presence of rDNA zones were studied in Tricepiro Don René INTA, a synthetic forage crop (2n=42,6x, AABBRR with introgression of Thinopyrum in 6A chromosome). The use of pTa71 probe revealed the presence of six rDNA zones but Ag-NOR indicated the presence of only four NORs (nucleolus organizer regions). Differential amphiplasty phenomenon could explain the inactivity of some rDNA zones. Simultaneous use of FISH (pTa71 probe) and DAPI banding analysis indicated that the chromosomes with rDNA zones belong to two rye and to four wheat chromosomes. The maximum number of nucleoli observed in somatic cells and the number of chromosomes with secondary constrictions agreed with the four active NORs detected with the Ag-staining method. The use of the pSc119.2 probe allowed to recognize that chromosomes with secondary constrictions are the wheat chromosomes IB and 6 B. The results obtained using classical and molecular cytogenetics lead us to conclude that this crop has a similar behavior to that observed in hexaploid triticales in relation to the phenomenon of amphiplasty. Furthermore, the complexity of genetic interactions between wheat and rye genomes described in triticales, are not modified by the presence of Thinopyron introgression in Tricepiro Don René INTA.

Variability in the amount of homoeologous pairing among F1 hybrids

Genes involved in the exclusive pairing of homologous chromosomes have been described in several polyploid species but little is known about the activity of these genes in diploids (which have only one dose of each homoeologous genome). Analysis of the meiotic behaviour of species, natural and artificial hybrids and polyploids of Glandularia suggests that, in allopolyploids where homoeologous genomes are in two doses, regulator genes prevent homoeologous pairing. The different meiotic phenotypes in diploid F1 hybrids between Glandularia pulchella and Glandularia incisa strongly suggest that these pairing regulator genes possess an incomplete penetrance when homoeologous genomes are in only one dose. Moreover, the meiotic analysis of natural and artificial F1 hybrids suggests that the genetic constitution of parental species influences the activity of pairing regulator genes and is mainly responsible for variability in the amount of homoeologous pairing observed in diploid hybrids. In Glandularia, the pairing regulator genes originated in South American diploid species. The cytogenetic characteristics of this genus make it a good model to analyse and explore in greater depth the activity of pairing regulator genes at different ploidy levels.