Cytologia 39: 525-529 , 1974
Karyotype Analysis in Moraea and Dietes
B. B. Chimphamba
Department of Biology, Chancellor College, University of Malawi, Limbe, Malawi
Received February 3, 1973
Moraea and Dietes are closely related African genera of the family Iridaceae with iris-type flowers without a perianth tube. The former genus consists of plants with corms and has about 60 species distributed mostly in Southern Africa with several species in Central and East Africa. The latter consists of evergreen rhi somatous forest-dwelling species and comprises only 6 species one of which is found in Australia (Goldblatt 1971). In the past the two genera were regarded as synon ymous because of their similar flowers. Unlike Iris, the two African genera are not well known horticulturally and in Malawi the few species that are cultivated as ornamentals are collectively known as "African irises" and sometimes "lilies" or "gladioli". As interest in the breeding of new forms continues to grow it is neces sary for the gardener to know the genetic affinities of the plants he is growing par ticularlyif hybridizations are to be made. The present study concerns karyotype analysisof some of the species grown in Malawi.
Materials and methods
Three Moraea species; M. schimperi (Hochst) Pichi Sermolli, M. polystachya (Thumb.)Ker. and M. thomsonii Bak. and two Dietes species, D. bicolor (Lindl.) Sweetand D. grandfora N. E. Br. were studied. The plants were collected in the field,though in some cases they were obtained from reliable horticultural sources. Theseare grown at Chancellor College, Limbe.
Chromosomes were studied from mitosis in root-tips. Actively growing root tips were pretreated with 0.1% aqueous colchicine solution for 3 to 4 hours, fixed for 15 to 30 minutes in fresh 1:3 acetic alcohol (1 part glacial acetic acid and 3 parts absolute ethyl alcohol), stored overnight in 90% alcohol, hydrolysed in normal hydrochloric acid at 60•Ž for 8 minutes and stained by the Feulgen squash method described by Darlington and La Cour (1942) for 2 hours. Squashing was carried out in a drop of 45% acetic acid . Slides were made permanent by the quick-freeze method of Conger and Fair child (1953). Photomicrographs were taken with a Carl Zeiss photomicroscope. In the illustrations the chromosomes were arranged in pairs according to homology exceptfor a single species where only the haploid complement has been represented due to the high chromosome number . Arrows were used in the photographs to showthe position of satellites where observed . 526 B. B. Chimphamba Cytologia 39
Results
The results are shown in Figs. 1 and 2. In Fig. 1, the four karyotypes (a) to (d) represent the chromosome complements of M. schimperi under different degrees
Fig. 1. a-d, Moraea schimperi (2n=12).
of chromosome contraction in order to reveal details of chromosome structure. In Fig. 2, karyotype (a) represents M. thomsonii, (b) represents M. polystachya and (c) and (d) represent D. grandiflora and the haploid complement of D. bicolor, respectively. A detailed chromosome analysis for the species is given in Table 1. 1974 Karyotype Aanlysis in Moraea and Dietes 527
Discussion
Chromosome counts of 2n=12 were observed in all the three species of Moraea and of 2n=20 and 2n=40 for D. grandiflora and D. bicolor, respectively. These
Fig. 2. a, Moreae thomsonii (2n=12); b, Moraea polystachya (2n=12); c, Dietes grandiflora (2n=20); d, Dietes bicolor (2n=40), the haploid complement only is shown. results,while confirming previous determinations by Riley (1962), Lewis (1964) and Goldblatt (1971), include also an additional species, Moraea thomsonii whose chromosomenumber of 2n=12 is reported for the first time. According to Gold blatt,M. schimperi consists of large and small chromosomes with the smallest chro mosomemeasuring only about half the size of the largest pair . This bimodality wasnot observed in any of the plants of this species studied by the present author , 528 B, B. Chimphamba Cytologia 39
including those collected from the Nyika Plateau where Goldblatt collected his material. Furthermore, in the idiogram presented by him the longest pair of chro mosomes is shown to be submetacentric. This feature was not observed during the present investigations even after varying the time of pretreatment of the root tips in colchicine to give different chromosome contractions at metaphase (Fig.1). Chromosome bimodality was, however, observed in both M. thomsoniiand M. polystachya. The karyotypes of these species were rather similar, the only visible difference being that the second longest pair of chromosomes in M. polystachya was distinctly acrocentric and had a satellite on the long arm whereas the correspond ing pair in M. thomsonii had none of these features (Fig. 2 a and b).
Table 1. Chromosome analysis in Morea and Dietes
In Dietes, the chromosomes of the two species differed from those of Moraea in two main respects. Fristly, many of the Dietes chromosomes were submetacent ric or metacentric. Secondly, they were on the whole smaller, ranging in size at metaphase after pretreatment from 2.5 to 5ƒÊ. The two genera were therefore different not only vegetatively but also cytologically. Within the genus Dietes the two species studied were different in chromosome number as well as in chro mosome morphology. D. bicolor with 2n=40 is a polyploid but the origin of this polyploidy has not been determined. Goldblatt suggests that the species is an allotetraploid on the account that its chromosomes can be paired and meiosis is normal. Natural hybridization between or within these genera has not been reported. It is doubtful if hybrids between Moraea and Dietes would be readily obtained in 1974 Karyotype Analysis in Moraea and Dietes 529 viewof the wide difference in the chromosomes of the two genera. Experimental crossesbetween and within these genera have proved unsuccessful (Goldblatt, litera ture cited). However, in view of the limited crosses made by this author it can not be concluded that interspecific and intergeneric hybridization is impossible. In Iris and Belamcanda the present author succeeded in obtaining fertile interspe cificand intergeneric hybrids only after many reciprocal crosses were made (Chim phamba 1970, 1972), and this success often involved the identification of compatible strains. The question is whether this method can be applied to Moraea and Dietes. Further research is being carried out by the author to obtain hybrids in these genera both at diploid and tetraploid level. Already, a 12 hour treatment with 0.1 colchicinesolution on seedlings of D. grandiflora has resulted in the doubling of the chromosomes of the shoots and roots. The plants are too immature to flower.
Abstract
This work is concerned with chromosome studies in three species of Moraea and two species of Dietes, all of which are being introduced into cultivation as orna mentalsin Malawi. Karyotype analysis for the species is given which has shown that the two genera are very different in chromosome morphology. The results, whileconfirming previous determinations of chromosome numbers in these genera have also added chromosome reports of Moraea thomsonii (Thumb.) Ker. which were unknown before. A preliminary report on the induction of polyploidy is givenand lines of further research to obtain interspecific and intergeneric hybrids are indicated.
Acknowledgements
This research work was carried out with the aid of grants and facilities offered by the Research Committee of the University of Malawi. This assistance is greatly appreciated with thanks. Thanks also go to the staff of the Department of Biology at Chancellor College for helping in various ways.
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