Basic chromosome numbers and polyploid levels in some South African and Australian grasses ( Poaceae )

Chromosome numbers of 46 specimens of grasses, involving 24 taxa from South Africa and Australia, have been determined during the present study. For the first time chromosome numbers are given for Eragrostis sarmentosa (Thunb.) Trin. (n = 20). Panicum aequinerve Nees (n = 18), Digitaria argyrograpta (Nees) Stapf (n = 9) and D. maitlandii Stapf & C.E. Hubb. (n = 9). Additional polyploid levels are described for Diplachne fusca (L.) Beauv. ex Roem. & Schult. (n = 10) and Digitaria diagonalis (Nees) Stapf var. diagonalis (n = 9). B-chromosomes were observed in several different specimens. The presence of B-chromosomes often results in abnormal chromosomal behaviour during meiosis.


INTRODUCTION
regarded cytogenetics as an important element in the evaluation of relationships and in the determination of phylogenetic sequences in the angiosperms.In South Africa this useful taxonomic tool has not been used widely and plant cytogenetics can be considered to be one of the most neglected fields of botany.Thorough cytogenetic studies are restricted to a few economically important species and the most basic cytogenetic data, the chromosome numbers of the taxa.are not available for the majority of our indigenous species.Spies et al. 1989).The present paper reports on miscellaneous unpublished chromosome numbers and aims to determine w hether this information can contribute to our know ledge on the basic chromosome numbers and polyploid levels present in the South African Poaceae.

In an attempt to increase our cytogenetic knowledge of the South
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 nursery of the National Botanical Institute, Pretoria, where cyto genetic material was later collected and fixed.The material used and localities of origin are listed in Table 1.Voucher specimens are housed in the National Herbarium.Pretoria (PRE).
Young inflorescences were fixed in Carnoy's fixative (Carnoy 1886).The fixative was replaced by 707c ethanol after 2 4 -4 8 hours of fixation.Anthers were squashed in aceto-carmine (Darlington & La Cour 1976).Contrast between cytoplasm and chromosomes was enhanced by adding a small droplet of 45% acetic acid, saturated w ith iron acetate, to the stain immediately prior to making the squash [modification of method used by Thomas (1940)].Slides were made permanent by freezing them w ith liquid CO, (Bowen 1956).followed by dehydration in ethanol and mounting in Eupara!.An Olympus Vanox-S photo microscope and Ilford Pan-F film were used for the photomicrographs.At least ten cells per specimen were studied for each meiotic stage, except where otherwise indicated.

RESULTS AND DISCUSSION
The haploid chromosome numbers observed are listed with the voucher specimen numbers and their localities in Table 1.The classification of subfamilies and tribes follows Clayton & Renvoize (1986).Unless otherw ise in dicated.meiotic chromosome behaviour was normal.Spies 3746. 3749. 3751. 3752. 3754. 3755. 3756 & 3760  The genus Sporobolus R. Br. is cytogenetically com plex and basic chromosome numbers of x = 6, 9 and 10 seem to be present ( Davidse et al. 1986) The chromosome number of n = 18 observed for Brachiaria brizantha (A.Rich.)Stapf during this study, equals the lowest chromosome number reported for this species (Darlington & Wylie 1955;Ornduff 1967Ornduff -1969;;Fedorov 1969;Moore 1970Moore -1977;;Goldblatt 1981Goldblatt -1988;;Goldblatt & Johnson 1990).In addition to this number, a higher ploidy level of n = 27 has also been described in Fedorov (1969) and by Spies & Du Plessis (1987b), as well as by Basappa et al. (1987).The basic chromosome number, however, is considered to be x = 9 (Darlington & Wylie 1955;Ornduff 1967Ornduff -1969;;Fedorov 1969;Moore 1970Moore -1977;;Goldblatt 1981Goldblatt -1985;;Goldblatt & Johnson 1990).These results contradict the meiotic configuration of 12ii12j, observed by Nath et al. (1970), which suggests a basic chromosome number of 12 for the species.This seems to be the first report on the chromosome number of Panicum aequinerve Nees.The haploid chromosome number of 18 indicates a basic chromosome number of x= 9 for this genus and species.The absence of multivalents suggests an alloploid origin for this specimen (Figure 3A).In contrast to this basic number, we confirm numerous reports of a somatic chromosome number of 2n=32 for Panicum maximum Jacq.(Ornduff 1967(Ornduff -1969;;Fedorov 1969;Moore 1970Moore -1977;;Goldblatt 1981Goldblatt -1988;;Goldblatt & Johnson 1990).Contrary to these reports several other somatic numbers are reported in the same sources (2n=18,2 8 ,3 4 ,3 6 ,4 2 ,4 8 ,5 2 ,5 4 ).We found it very difficult to obtain well-spread meiocytes in this species and this may be a reason for the discrepancies in the chromosome numbers reported for this species.A re-investigation of the phylogenetic relationship between P. maximum and other Panicum species is necessary.1).

W * % _ ■CP i
This study included several cultivated specimens of D. eriantha.These cultivars are currently being evaluated for possible distribution as fodder crops by the Grassland Research Centre.Two of these 'cultivars' had two different ploidy levels.This indicates the variability present in these specimens and the need for a thorough cytogenetic inves tigation before these cultivars are released.
A basic chromosome number of x = 9 for the genus is supported by the presence of diploid specimens in all the species studied (Figure 3C).

Tribe Andropogoneae Dumort. Subtribe Sorghinae Bluff
A basic chromosome number of five in the Andro pogoneae is evident from both the literature and some of the Sorghum Moench specimens used during this study.A basic chromosome number of x=5 was observed in both & matarankense Garber & Snyder and S. stipoideum Gard ner & Hubb.These numbers correspond to the published numbers by Garber (1950Garber ( , 1954)), Garber & Snyder (1951) and Celarier (1956aCelarier ( , 1958)).Although meiosis was nor mal in most specimens (Figure 5A -C ), some cells formed rnicronuclei (Figure 5D).Abnormal meiotic behaviour was observed in one of the •>.stipoideum specimens, Spies 1740.Six bivalents were formed during diakinesis (Figure 4A).One of these biva lents was smaller than the rest and it is concluded that

Subtribe Ischaeminae Presl
Cytogenetic studies on Ischaemum afrum (J.F.Gmel.)Dandy seem to be restricted to our laboratories (Spies & Du Plessis 1987b).The formation of bivalents only during meiosis and the absence of specimens with a somatic chromosome number of ten indicate that this specimen can be considered to be a diploid (2n= 2x=20).These results are substantiated by reported chromosome numbers for other Ischaemum species (Darlington & Wylie 1955;Ornduff 1967Ornduff -1969;;Fedorov 1969;Moore 1970Moore -1977;;Goldblatt 1981Goldblatt -1985;;Goldblatt & Johnson 1990).However, the same reports suggest that x= 9 and x=19 should be considered secondary and tertiary basic chromosome numbers respectively in the genus.

Subtribe Andropogoninae Presl
The chromosome number of n=10 observed for Andropogon eucomus Nees, corresponds with the number published by Moffett & Hurcombe (1949) and Gould (1956).Previous studies by one of our laboratories revealed two different chromosome numbers for this species, i.e.
African flora, a cytogenetic study of the family Poaceae was initiated by the Botanical Research Institute during 1986 and is now continued at the National Botanical Institute, the Grassland Research Centre and the Department of Botany and Genetics at the University of the Orange Free State.Results were reported in previous publications in this series (Spies & Du Plessis 1986a.b. 1987a.b. 1988; Spies & Jonker 1987; Spies & Voges 1988; Du Plessis & Spies 1988; in the garden of the National Botanical Institute.Pretoria, (-C A ). Spies 1740.S. aff.stipoideum* 5 TRANSVAAL.-2528(Pretoria): cultivated in the garden of the National Botanical Instutute.Pretoria, (-C A ), Spies 1719.Subtribe Ischaeminae Ischaemum afrum 10 NATAL.-2832(Mtubatuba): 3 km from Hluhluwe to False Bay.(-A B ). Spies 2431.Subtribe Andropogoninae Andropogon eucomus 10 TRANSVAAL -2430 (Pilgrim's Rest): 17 km from Graskop to Sabie, (-D D ).Spies 1968 * Seed originally collected by M. Andrew in Australia.Subfamily Arundinoideae Tateoka Tribe Aristideae C.E. Hubb.The haploid chromosome number of n = 11 for Aristida congesta Roem.& Schult.subsp.congesta (Figure 1A, B) corresponds with published cytogenetic information on this taxon (De Winter 1965; Davidse et al. 1986; Spies & Jonker 1987).The occurrence of n = 11 as the lowest haploid chromosome number in the genus and the presence of multiples of 11 in other species of this genus (De Winter 1965; Spies & Du Plessis 1986a, 1987b; Viano & Bourreil 1987), support 11 as the basic chromosome number for both the genus Aristida L. and the tribe.The basic number of x = 11 for the tribe Aristideae is further supported by our observation of a Stipagrostis obtusa (Del.)Nees specimen with a haploid chromosome number of n = 2 2 + 0 -3 B (Figure 1C).Chromosome laggards were frequently observed (Figure ID) and it is suggested that the laggards represent the B-chromosomes, undergoing chromatid segregation.This is, to the best of our knowledge, the first report on the presence of B-chromosomes in this tribe.Polyploidy seems to be present in this species with our specimen being tetraploid and the one examined by Reese (1957) diploid (2n = 22).number of n = 10 for Diplachne fusca (L.) Beauv.ex Roem.& Schult.(Figure IE) is the lowest chromosome number yet described for this species and it supports a basic chromosome number of x = 10 for this species, genus, subtribe, tribe and subfamily.Published results indicate the presence of tetraploidy (Bir & Sahni 1986) and aneuploidy (Spies & Voges 1988).A basic chromosome number of x = 10 for Eragrostis Wolf is substantiated by the diploid E. cilianensis (All.)F.T. Hubb.specimen observed during this study.The presence of diploid and tetraploid specimens of this species is well documented(Fedorov 1969;Moore 1973 FIGURE 2 .-Cameralucida drawings of meiotic chromosomes in Sporobolus africanus.A, Spies 3201, n = 12, metaphase I; B, Spies 2529.n = 24, diakinesis; C, Spies 2393.n = 18 + 0 -6B, anaphase I with 6 B-chromosomes.Bar -10 ptm.

FIGURE 4 .
FIGURE 4 .-Meio tic chromosomes in a Sorghum stipoideum specimen with B-chromosomes, Spies 1740 A diakinesis with five bivalents and a B-chromosome bivalent; B, metaphase I with five bivalents and both B-chromosomes on the equatorial plate: C -E .metaphase I with five bivalents and both B-chromosomes on one s.de of the equatorial plate; F. metaphase I with five bivalents and the B-chromosomes on different sides of the equatorial plate; G, two telophase I cells with chromatid segregation of the B-chromosomes Bar = 10 "m