Cytogenetic studies in some representatives of the subfamily Pooideae ( Poaceae ) in South Africa . 1 . The tribe Aveneae , subtribe Aveninae

This is a report on chromosome numbers for 14 species of the subtribe Aveninae. which is largely naturalized in South Africa. This is the first chromosome number report for Helictotrichon longifolium (Nees) Schweick. (n = 14). H. longum (Stapf) Schweick. (n = 14). H. namaquensis Schweick. (n = 14) and Lophochloa cristata (L.) Hyl. (n = 7, 21/2. 14). The subtribe has a basic chromosome number of seven, and fewer ploidy levels occur in the naturalized species in South Africa than in the same species in other parts of the world. All tetraploid specimens were alloploids.

The Pooideae is, for the largest part, introduced to southern Africa.The majority of species belonging to this subfamily is restricted to either the winter rainfall area of South Africa or to high altitude areas.The tribe Aveneae Dumort.comprises 57 genera and approximately 1 050 species in the world (Clayton & Renvoize 1986).Most South African representatives (18 genera and 59 species) are naturalized (Gibbs Russell et al. 1990).Clay ton & Renvoize (1986) subdivided the tribe into four subtribes, i.e.Duthieinae Potztal, Aveninae Presl.Phalaridinae Rchb.and Alopecurinae Dumort.The genera representing these subtribes are listed in Table 1.
The aim of this study is to determine the chromo some numbers, polyploid levels and meiotic chrom o some behaviour of the South African representatives of the tribe Aveninae.These results will eventually be com pared with results of indigenous and endemic taxa to compare the frequency of polyploidy between indige nous and introduced grasses.

MATERIAL AND METHODS
Cytogenetic material was collected in two different ways for the purpose of this study.The material was either collected and fixed in the field, or living material was collected in the field and transplanted in the nurseries of either the National Botanical Institute (Pretoria) or the Department of Botany and Genetics, University of the Orange Free State (Bloemfontein), where cytogenetic material was collected and fixed.The material used and their localities are listed in Table 2. Voucher specimens are housed in the Geo Potts Herbarium.Department of Botany and Genetics, University of the Orange Free State, Bloemfontein (BLFU) or the National Herbarium, Pretoria (PRE).
Young inflorescences were fixed in Camoy's fixative (Camoy 1886).The fixative was replaced by 70% ethanol after 24-48 hours of fixation.Anthers were squashed in 2% aceto-carmine (Darlington & LaCour 1976).Slides were made permanent by freezing them with liquid COt (Bowen 1956), followed by dehydration in ethanol and mounting in Euparal.An Olympus Vanox-S or Nikon Mi crophot photomicroscope and Ilford Pan-F film (ASA 50) were used for the photomicrographs.At least ten cells   per specimen were studied for each meiotic stage, ex cept where otherwise indicated.
Meiotic chromosome counts are given as haploid (n) numbers to conform to the style set out by the editors of the Index to plant chromosome numbers series, published by the Missouri Botanical Garden.
Koeleria capensis is indigenous and the only repre sentative of the genus Koeleria in South Africa (Gibbs Russell et al. 1990).This study revealed two ploidy levels for this species, diploid and tetraploid, thus con firming previous results (Goldblatt 1981(Goldblatt , 1983(Goldblatt , 1985(Goldblatt , 1988;;Goldblatt & Johnson 1990, 1991).The tetraploid specimens were restricted to the southern Cape, near Bredasdorp.Their chromosome configurations con curred with the expected configurations for the 2:2 model with an x-value of 1.These specimens are con sequently alloploids.
Lophochloa is represented by two naturalized species in South Africa, L. cristata and L. pumila (Desf.)Bor (Gibbs Russell et al. 1990).This is, to the best of our knowledge, the first report on chromosome numbers for L. cristata, which has at least two different ploidy levels, diploid and tetraploid.One specimen (Spies 4965) with abnormal chromosomal behaviour was observed.This specimen is either a triploid or it contains up to seven B-chromosomes.The additional chromosomes do not dif fer morphologically from the 'normal' chromosomes.However, since the number of additional chromosomes seems to differ from one cell to another (Figure 6 are alloploids.This study confirms the diploid status al ready described for L. pumila (Goldblatt 1981(Goldblatt , 1983(Goldblatt , 1985(Goldblatt , 1988;;Goldblatt & Johnson 1990,1991).However, we found no confirmation for a basic chromosome number of 13 for Lophochloa as often reported (Goldblatt 1981(Goldblatt , 1983(Goldblatt , 1985(Goldblatt , 1988;;Goldblatt & Johnson 1990, 1991).
The subtribe Aveninae is largely naturalized in South Africa.The exceptions are the genus Helictotrichon and the species Holcus setiger and Koeleria capensis.The subtribe has a basic chromosome number of seven, and less ploidy levels occur in the naturalized species in South Africa in comparison to the same species in other parts of the world.This may be attributed to the intro duction of these species.The species deviating from the basic chromosome number of the subtribe need to be investigated thoroughly.

FIGURE
FIGURE 4.-Photomicrographs of meiotic chromosomes in some representatives of the genera Holcus and Koeleria.A, Hol South Africa and two species are recognized in this country, i.e. A. caryophyllea and A. cupaniana (Gibbs Russell et al. 1990).Both species are dip loid, n = x = 7 (Table South Africa (Gibbs Russell et al. 1990).All A. barbata specimens studied, are tetraploid.This supports the different ploidy levels, ranging from diploid to hexa ploid, previously described (Goldblatt 1981, 1983, 1985, 1988; Goldblatt & Johnson 1990, 1991).These results may indicate that a single introduction, or several introduc tions from the same ploidy level, of A. barbata, occurred.Avena byzantina is hexaploid, thus supporting the chro mosome number previously described (Morikawa 1982).The high frequency of ring bivalents and the absence of any multivalent suggests an alloploid origin for both spe cies.This alloploid origin is confirmed by the correspond ing values obtained during this study and when the expected chromosome associations for the 2:2 model of Kimber & Alonso (1981) is determined.The x-value of 1 indicates no relationship between the chromosomes of the two different genomes.

FIGURE 6 -
FIGURE 6 -Photomicrographs of mciotic chromosomes in Lophochloa cristata, Spies 4965.A-R, various cells indicating the difficulty to determine whether the additional chromosomes are B-chromosomes or whether they represent a third genome.Scale bar: A-R, 10 fun.

TABLE 1 .
-List of subdivisions of the tribe Aveneae, indicating the genera and number of species present in southern Africa Edwards & Leistner (1971)s L. 6 TABLE 2.-Haploid chromosome numbers of representatives of the subtribe Aveninae (Poaceae.Pooideae, Aveneae) in southern Africa with the voucher specimen numbers and their specific localities, arranged according to the system ofEdwards & Leistner (1971)A.fatua L.