Meiotic behavior of Adesmia DC. (Leguminosae-Faboideae) species native to Rio Grande do Sul, Brazil

SHORT COMMUNICATION

Meiotic behavior of Adesmia DC. (Leguminosae-Faboideae) species native to Rio Grande do Sul, Brazil

Liliana Gressler May Coelho and Alice Battistin

Departamento de Biologia, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria, Campus Universitário, 97.119-900 Santa Maria, RS, Brasil. Send correspondence to A.B.

ABSTRACT

Meiotic behavior in Adesmia DC. is described for the first time. The study encompassed twelve populations of seven Adesmia DC. species native to Rio Grande do Sul, Brazil. Populations with 2n = 2x = 20 are A. securigerifolia 9615, A. riograndensis 9590 (subnudae), A. latifolia 1568, 1775, 15025, A. bicolor JB-UFSM, A. incana var. incana 9636, 10288, A. punctata var. hilariana 6885, 10812, and A. tristis 10757. A. incana var. incana 9637 is a tetraploid with 2n = 4x = 40. The material was stained with 1% acetic orcein. The meiotic behavior of the populations studied was considered normal. The meiotic index (MI) and the estimates of pollen grain viability were above 95%, except for A. latifolia 1568 (MI = 89%). The present data indicate that these plants are meiotically stable and potentially fertile, apparently with no problems for use in programs of selection, crossing and viable seed production.

INTRODUCTION

The genus Adesmia DC., exclusively found in South America, consists of approximately 230 species, 17 of which occur in southern Brazil (Miotto, 1991). Cytogenetic studies have revealed that most species of this genus are diploid, with 2n = 2x = 20, and some are tetraploid, with 2n = 4x = 40 (Castronovo, 1945; Covas and Schnack, 1946; Covas, 1949; Krapovickas and Krapovickas, 1952; Covas and Hunziker, 1954; Hunziker et al., 1985; Miotto and Forni-Martins, 1994; Coelho and Battistin, 1996).

According to Allen and Allen (1981), Adesmia is the largest genus of Leguminosae plants in Argentina. Most species are good forage material and are also useful for soil cover and control of erosion.

In Southern Brazil, these plants have proven to be well adapted to the climate, growing in winter, which is the most critical season for cattle and sheep rearing. These factors, taken together with good nutritive quality, have attracted interest in these species.

In the present study we report data on the meiotic behavior and pollen viability estimates of 12 populations of seven Adesmia species.

MATERIAL AND METHODS

Seeds of populations collected in Rio Grande do Sul and in Santa Catarina (Table I and Figure 1) were allowed to germinate in a greenhouse (May 1994) and then transplanted to the field, where inflorescences were collected from October 1994 to January 1995. The inflorescences of populations 9615 of A. securigerifolia, 9590 of A. riograndensis, and 10288 and 9637 of A. incana var. incana were collected directly from the field in October and November 1996. The material was fixed in ethanol:acetic acid (3:1) for 24 h at 4°C and stored in 70% ethanol in a refrigerator until the time for slide preparation.

Figure 1
- Sites of occurrence of studied populations of species of Adesmia DC.

Meiotic cells from the anthers were stained with 1% acetic orcein in 2 to 10 inflorescences from each population. In the analysis of the phases, we recorded the chromosome associations at diakinesis and metaphase I, and we considered the cells in which 10 bivalents were observed to be normal, or 20 bivalents in the case of the tetraploid population. Chromosome disjunction was observed in anaphase and telophase I, with regular separation of 10 (20) chromosomes towards each pole being expected. Chromosome disjunction was also analyzed in anaphase and telophase II, and cells with equivalent distribution of 10 (20) single chromosomes towards each of the four poles were considered normal.

Tetrads and pollen grains were analyzed in four to 12 inflorescences from plants selected at random. Approximately 150 cells at the tetrad stage and 300 pollen grains per inflorescence were observed. On the basis of these counts, we calculated the meiotic index (Love, 1949), which indicates the percentage of normal tetrads (MI = number of normal tetrads x 100 / total number of cells analyzed). Pollen grain viability was estimated by staining with 1% acetic orcein.

RESULTS AND DISCUSSION

Table II summarizes the data concerning analysis of meiotic phases, meiotic index and estimates of pollen viability. Meiosis I was regular in the populations analyzed, with the formation of 10 bivalents in diploids and 20 bivalents in the tetraploid at diakinesis and/or metaphase I. Disjunction at anaphase and telophase I was normal (Figure 2). Population 10812 of A. punctata var. hilariana had 1.52% of the cells with laggard chromosomes, a fact that did not seem to affect the meiotic normality of the population since the meiotic index was above 95%.

Figure 2
- Meiosis in populations of Adesmia DC.: A) diakinesis in A. securigerifolia 9615; B) telophase II in A. riograndensis 9590; C) telophase I in A. latifolia 1568; D) telophase I in A. latifolia 1775; E) diakinesis in A. latifolia 15025; F) diakinesis in A. bicolor JB-UFSM; G) metaphase I in A. incana var. incana 9636; H) diakinesis in A. incana var. incana 9637; I) telophase II in A. incana var. incana 10288; J) telophase I in A. punctata var. hilariana 6885; K) anaphase II in A. punctata var. hilariana 10812. The bar is 2 µm.

At meiosis II, there was a predominance of cells with regular anaphasic and telophasic division. A few cells with the formation of only three poles with chromosomes occurred in A. riograndensis, A. bicolor JB-UFSM and A. punctata var. hilariana 6885, with 2 poles having 10 chromosomes and 1 pole having 20 chromosomes.

The meiotic index was higher than 95% in most of the populations studied (Table II), except for A. latifolia 1568, which had a meiotic index of 89%. The most frequent abnormalities observed at the tetrad stage were irregular triads (3 cells), pentads (5 cells) and irregular tetrads, i.e., with cells of different sizes (2>2, 3>1). A. incana var. incana 9636, diploid population, had 4% of cells at the tetrad stage with irregularities, especially triads, indicating the formation of unreduced gametes, which can indicate a possible mechanism of origin of tetraploid populations (as A. incana var. incana 9637).

According to Love (1949), plants with an MI above 90% are meiotically stable and their use in crosses poses no problem. By being meiotically stable, these plants guarantee the maintenance of successive generations through seeds. A. latifolia 1568 probably would pose no problems if used in crosses since, in addition to having regular disjunction at meiosis, it has an MI very close to 90%.

The method used to estimate pollen viability (Table II) showed a high percentage of viable pollen (>96%), reflecting meiotic regularity and high meiotic index, i.e., indicating that these plants can be considered potentially fertile. A superestimation of pollen grain viability by the method of staining probably occurred. Only in vitro germination provides a measure more accurate of this parameter (Mendes, 1994).

A. riograndensis 9590, A. bicolor JB-UFSM, and A. punctata var. hilariana 6885 and 10812 had a small percentage of meiotic irregularities, MI higher than 95%, and a pollen viability higher than 96%, indicating that these irregularities probably are not significant in terms of plant reproduction.

A. latifolia is a species of wide dispersion (Figure 1) and is well adapted to markedly different temperatures, especially during the cold season. The wide adaptation of this species is not associated with meiotic irregularities in the populations studied (1568, 1775, 15025).

The observed normal chromosome behavior during meiosis observed in the populations studied suggests high seed fertility, if the same behavior also occurs in the female part (ovules). The plants probably will not present problems in terms of the production of viable seeds, if we exclude other factors independent of meiosis that might affect seed formation, such as physiological or environmental factors.

RESUMO

Doze populações de sete espécies de Adesmia DC. das séries subnudae, bicolores e psoraleoides, nativas do Rio Grande do Sul, Brasil, foram estudadas pela primeira vez, quanto ao comportamento meiótico: A. securigerifolia 9615 e A. riograndensis 9590 (subnudae), com 2n = 2x = 20 cromossomos; A. latifolia populações 1568, 1775, 15025, A. bicolor JB-UFSM, A. incana var. incana populações 9636, 9637, 10288, A. punctata var. hilariana populações 6885, 10812 (bicolores), todas com 2n = 2x = 20, com exceção da população 9637 de A. incana var. incana, tetraplóide com 2n = 4x = 40 e A. tristis 10757, com 2n = 2x = 20 (psoraleoides). As inflorescências foram fixadas em etanol:ácido acético (3:1) por 24 horas a 4°C e conservadas em etanol 70%. O material foi corado com orceína acética 1%. O comportamento meiótico das populações analisadas foi considerado normal. Os índices meióticos (MI) e as estimativas da viabilidade dos grãos de pólen situaram-se acima de 95%, com exceção de A. latifolia 1568 (MI = 89%). Os dados obtidos indicam plantas meioticamente estáveis e potencialmente férteis, provavelmente sem problemas para uso em programas de seleção, cruzamentos e produção de sementes viáveis.

(Received May 26, 1997)

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Publication Dates

• Publication in this collection
  23 Feb 1999
• Date of issue
  Sept 1998

History

• Received
  26 May 1997