1959 285
Cytotaxonomy of the Andropogoneae IV. Subtribe Sorgheae
RobertP. Celarier Departmentof Botanyand PlantPathology, Oklahoma Agricultural ExperimentStation, Oklahoma State University, Stiliwater,Oklahoma, U. S. A.
Received August 21, 1955
Previous reports in this series have reviewed the subtribes Dimeriinae, Saccharinae (Celarier 1956a), Ischaeminae, Rottboelliinae, and the Maydeae (Celarier 1957), as well as the genus Sorghum of the subtribe Sorgheae (Celarier 1958b). In this report all of the subtribe Sorgheae will be con sidered. In this, as in previous reports, the primary objective is the addition of new cytotaxonomic information dealing with the tribe, review the scattered literature on the subject, and to outline from this information a working hypothesis regarding phylogenetic relationships of the taxa involved. In the first report of the series the scope of the work, materials and methods, and a key to the subtribes were presented.
Subtribe V. Sorgheae Keng There has been quite a metamorphosis in the terminology of this group since Hackel's work in 1889 in which he considered all of this subtribe as merely a subgenus of Andropogon. Although generic names for most of the genera of this subtribe had been proposed previous to Hackel's mono graph, it was only after the work of Stapf (1919) that they became widely recognized as distinct from Andropogon. Stapf not only recognized them as distinct genera but grouped them together as the Sorghastrae under the subtribe Andropogoninae. More recently Keng (1939) proposed that they be given the status of a subtribe under the name Sorgheae. The following year Pilger (1940) independently came to the same conclusion and called his subtribe Sorgenae. The following genera are generally included in the subtribe: Sorghum Moench, Sorghastrum Nash, Cleistachne Benth., Lasiorrhachis Stapf, Astheno chloa Buse, Vetiveria Bory, Chrysopogon Trin., and Rhaphis Lour. In general the delimitations of these genera and their inclusion in the subtribe are rather well agreed on by Pilger, Stapf, and Bews. Stapf does however differ in two respects. He includes Sorghastrum under Sorghum as a subgenus, a procedure that was followed by Garber (1950) in a recent study of the genus . However, because of the extensive modification of the Cytologia24,1959 20 286 R. P. Celarier Cytologia 24 pedicellate spikelet, specific vegetative characters, and lack of any experimental evidence on the relationship of these taxa, Sorghastrum is retained as a distinct genus in this report. Stapf also placed the genus Asthenochloa (as Garnotiella Stapf) in the tribe Agrostideae. In this genus the pedicellate spikelet is completely reduced and consequently the major characteristic of the Andropogoneae (i. e. binate spikelets at each node) is more or less concealed. It is generally agreed that this led Stapf erroneously to place it outside the tribe (Bews 1929, Keng 1939). Keng differs from other workers in adding another genus, Pseudosorghum, to the subtribe, and by transferring Chrysopogon, Rhaphis (both included in his conception of Rhaphis) and Vetiveria (as Anatherum) to the subtribe Rottboelliinae. Although Pseudosorghum appears somewhat intermediate between Sorghum and certain members of the subtribe Bothriochloeae (see discussion) it is generally regarded as more closely related to the latter and is maintained there in this report. Because of the resemblance of the panicu late inflorescence of certain species of Chrysopogon and Sorghum it seems more desirable at this time to group them together in one subtribe, and since Vetiveria seems obviously closely related to Chr ysopogon both are treated here as members of the Sorgheae.
Key to the genera of the Sorgheae AA. Spikelets in pairs or threes, pedicellate spikelet well developed or occasionally reduced to pedicel only. A. Spikelets dorsally compressed. I. Pedicellate spikelet often bisexual, lodicules ciliate at apex only...... Lasiorrhachis II. Pedicellate spikelets well developed, male or neuter, lodicules ciliate...... Sorghum III. Pedicellate spikelets reduced to pedicels only, lodicules not ciliate ...... So rghastrum B. Spikelets laterally compressed. I. Racemes with many pairs of spikelets, primary branch of panicle with several whorls...... Vetiveria II. Racemes mostly reduced to one bisexual sessile spikelet and two male or neuter pedicellate spikelets, rarely paired. 1. Awns long (except C. setifolius), leaves folded in bud ...... Chrysopogon 2. Awns short, leaves rolled, rhizomes slender and creep ing...... Rhaphis BB. Spikelets single on branch of axis, pedicellate spikelets and pedicels completely suppressed. A. Spikelets dorsally compressed, tall coarse grass. Cleistachne 1959 Cytotaxonomy of the Andropogoneae IV 287
B. Spikelets laterally compressed, low slender grass. Asthenochloa Three of the eight genera in this subtribe are monotypic. Two have rather restricted geographic distribution, Lasiorrhachis hildebrandii Stapf from central Madagascar and Asthenochloa tenera Base from Indonesia and the Philippine Islands; however, the third, Rhaphis acicularis Honda, is widely distributed through Asia and the Pacific World. Two genera, Sorghum and Chrysopogon, are of moderate size, both having more than twenty species, and both are widespread in the tropics of the Old World but essentially absent in the Americas.1 Sorghastrum with some 10-15 species is of special interest because of its geographical distri bution. It is widespread in the tropical and temperate regions of both Africa and the Americas but is not found elsewhere. In general the Sorgheae is a subtribe rather well known cytologically; however, two of the monotypic genera, Lasiorrhachis and Asthenochloa, have not been studied. Sorghum Moench Although a rather extensive review of this genus was given in the previous report (Celarier 1958b) a significant paper has been published in the interim (Sharma and Bhattacharjee 1957). In their report eighteen species were studied; one, S. elegans Snowden, for the first time. S. elegans is a member of the subseries Bicoloria of the Sativa series and has several varie ties in East Africa and one in West Africa. It was found to be 2n=20 with regular meiosis. Although the number and behavior of the chromosomes of these eighteen species were similar to previous reports (Celarier 1958b) there were several conclusions from this study that are new and important and will therefore be discussed briefly. A. Chromosome structure-Root tip studies were made by Sharma and Bhattacharjee (1957) from paraffin sections for all eighteen species. Idiograms based on the position of primary and secondary constrictions and relative size of chromosomes were made for all species. Twenty-three idiograms were shown (three for S. subglabrescens, three for S. durra, and two for S. roxburghii) and of these only two were similar (S. roxburghii Co. 2 and S. dochna). Ten major types of chromosomes were found and labeled A through J, but some of these major types had several minor differences (i. e. B, B1, B2, and B3). It is of interest to note that the three species in which more than one idiogram was prepared were all different. As mentioned previously S. rox burghii had one type similar to S. dochna whereas the other type was more like S. caffrorum. Three different idiograms were shown for S. durra. 1 The exact status of Sorghum trichoeladum from Mexico is somewhat obscure, but it does appear that Chrysopogon pauciflorus from Florida and Cuba is an indigenous part of the American flora. 20* 288 R. P. Celarier Cytologia 24
One type was more similar to S. nervosum than it was to the other "durras" and a second type was more similar to S. membranaceum. In the three types of S. subglabrescens two were rather similar to one another but the third was quite different from any of the other Sorghums. These structural differences in the chromosomes fit very well the genetics of species crosses in Sorghum (Celarier 1958b) but are difficult to reconcil with the cytological information in which the chromosomes of the hybrids are completely regular. However, only a few hybrids have been studied sufficiently to offer serious objections to these idiograms and more detailed studies must definitely be made. B. Chromosome size-Three chromosome sizes were recognized by Sharma and Bhattacharjee (1957) in the species studied, and were designated large, medium, and small. Two species, S. versicolor and S. purpureo sericeum, had large chromosomes and this is in agreement with previous reports (Celarier 1958b and Figs. 1 and 2). However the differentiation between medium and small sized chromosomes had not been recognized previously. The validity of this distinction is further suspect since two species, S. durra and S. subglabrescens, were represented in both categories. To this author it seems quite possible that these differences in size may have been the result of the environmental influences either at the time of collection or during dehydration and embedding. C. Chromosome fragments-Six species were found by Sharma and Bhattacharjee (1957) to have somatic cells that contained chromosome frag ments. However there were never more than two fragments per cell, and none were found during the meiotic divisions. Also cells with other than the 2n number of chromosomes were found in somatic tissue but not in meiotic cells. D. Secondary associations-A detailed study of meiotic metaphase was made by Sharma and Bhattacharjee (1957) in four species and from these studies the frequency of secondary association of bivalents was tabulated. Unfortunately the method used in determining secondary associations was not given. The maximum number of associations per cell (i. e. the lowest number of groups of chromosomes) was four for all species. From these studies it was concluded that four is the basic number for the genus Sorghum. In the discussion of this report these authors mention that several species were studied that did not show this type of association but no data was presented for these. Secondary associations have been previously recorded for Sorghum (Kidd 1953, Merwine 1956), and Celarier (1958a) has pointed out that much more needs to be understood regarding the mechanism involved here. In general it appears to this author that the conclusions of Sharma and Bhattacharjee are controversial, but there is no question but that they are stimulating and challenging and must be taken into consideration in future 1959 Cytotaxonomy of the Andropogoneae IV 289 studies. They may well have opened the door to some of the bizarre genetic patterns found in Sorghum. Sorghastrum Nash This small genus with some 10-15 species has a very interesting dis junct geographical distribution. It is widespread in tropical Africa and also in tropical America but, except for a few species that extend into the temperate regions of North America, is not found elsewhere. Although over half of the species have been studied cytologically only one, S. nutans, has been sampled throughout much of its geographical range, and only two of the African species are known. A. AFRICANSPECIES 1. S. friesii Pilg. was studied by Moffett and Hurcombe (1949) and it was found to have forty somatic chromosomes. No meiotic studies were made. 2. S. rigidifolium Chippindall is recorded as being morphologically very similar to S. friesii but is generally a much larger plant. This species was studied by Garber (1950) from a seed collection made in Uganda and was found to be 2n=60. Meiosis was completely regular with 30 bivalents. B. AMERICANSPECIES 1. S. elliottii Nash is an uncommon species but widely distributed through the southeastern portion of the United States. It has been studied cytologically by Stebbins (reported by Myers 1947), Brown (1950), and Garber (1950) and all reported it to be 2n=20. Meiosis is completely regular. 2. S. secundum Nash, also of southeastern U. S., was studied by Garber (1950) and found to have regular meiosis with ten bivalents at diakinesis and metaphase I. 3. S. pellitum Parodi is a South American species studied by Saura (1948) and found to have twenty somatic chromosomes. 4. S. parviflorum Hichc. and Chase was reported by Saura (1948) as Andropogon agrostoides Speg. This South American species was also found to be 2n=20. 5. S. stipoides Nash was available for study from a seed collection made at Santa Maria, Brazil. Although the awns of this accession were only slightly longer than the sessile spikelet it nevertheless appears to belong to this taxon. It was found to be 2n=20 with completely regular meiotic behavior (Fig. 3). 6. S. nutans Nash is widely distributed in the Americas from Canada to Argentina and is part of the ecological climax of the Great Plains of the United States. It was first studied cytologically by Church (1929) and was found to be 2n=40. This number was confirmed both by Gould (1956) and in the present report. Gould reported on five accessions from Texas and in the present 290 R. P. Celarier Cytologia 24
Figs. 1-12. Chromosome behavior in the Sorgheae. 1350•~. Photographs 4 and 5 were taken from slides made permanent six years previously by the TBA method (Celarier, 1956. Stain Tech. 31: 155-157), and all others were taken from temporary mounts. 1, metaphase I in Sorghum nitidum A-6100 from the Ryukulu Islands with five large bivalents (one bivalent has already begun to separate). 2, metaphase I of S. niloticum var. kavirondense A-4842 from Ethiopia with ten medium sized bivalents. 3, diakinesis of Sorghastrum stipoides A-1374 from Brazil with ten bivalents. 4 , diakinesis in S. nutans A-2275 from Kansas, U. S. A. with twenty bivalents. Two bivalents interlocking at arrow. 5, metaphase I in S. nutans A-2275 with twenty bivalents (two overlappings at arrow). 6, metaphase I of Vetiveria zizanioides A-4828 from New Delhi, India with ten bivalents. 7, metaphase
I of V. zizanioides A-4828 showing the clumping of two bivalents . 8, metaphase I of V. zizanioides A-4498 from the Punjab of India with three configurations of two bivalents each that are believed to be associations due to clumping. 9, late anapase I of V. zizanioides A-4828 with 10:10 distribution of the chromosomes. 10, metaphase I of V. filipies A-6566 from Queensland, Australia with twenty bivalents. 11, diakinesis of V. filipies A-6566 with either twenty bivalents or one quadrivalent at arrow. 12, metaphase I of Chrpsopogon
montanus A-3032 from the Punjab of India with ten bivalents. 1959 Cytotaxonomy of the Andropogoneae IV 291 study accessions from Kansas, Missouri, and Oklahoma are included (Table 1). All were found to have regular meiosis with twenty bivalents at diaki nesis and metaphase I (Figs. 4, 5) and 20: 20 distribution of the chromosomes to the daughter cells. Saura (1948) reported 2n=20 for a South American representative of the species. Vetiveria Bory This is a small genus, probably with fewer than ten species, but is widespread throughout the Old World tropics. One species , V. zizanioides, has been extensively cultivated for its aromatic roots, and is now widely distributed throughout the tropics of the world. This genus is very closely related to Chrysopogon and differs principally in having many jointed racemes. There are intermediate forms such as V. fulvibarbis from Africa, and V. filipes and allied species from Australia that have been placed in both genera by different taxonomists. Only three species are known cytologically. 1. V. zizanioides Nash was first studied by Janaki Ammal (1945) from an Indian collection and was found to have twenty somatic chromosomes . This number was confirmed by Sikka and Mehra (1956) and in the present report with five accessions across North India from Assam to the Punjab. All accessions are essentially normal in meiotic behavior and ten bivalents are usually seen at diakinesis and metaphase I (Fig. 6). Occasionally group ings of four chromosomes are found (Figs. 7, 8) but it appears unlikely that this is due to physical pairing of the chromosomes. Although this is seen to some extent in all accessions it is much more frequent in A-4498 from the Punjab in India. There is also a tendency for the metaphase plates to clump in this species. Anaphase and telophase I are quite regular (Fig. 9). 2. V. lawsoni Blatter and McCann from southwest India was also studied by Janaki Ammal (1945) and was found to be 2n=20. No meiotic studies were made. 3. V. filipes C. E. Hubb. is an Australian endemic that is of special interest because of its somewhat intermediate morphological position between typical Vetiveria and Chrysopogon. One accession of this species from Queensland was studied and found to be 2n=40. Meiosis was essentially normal with 20 bivalents (Fig. 10) but there was extreme clumping of the chromosomes at metaphase I. Also an occasional cells was found that might be interpretated as 18 II and one IV (Fig. 11). Anaphase and telophase I was normal. Chrysopogon Trin. This is one of the larger genera of the Sorgheae with approximately 25-30 described species. It is widespread throughout the Old World tropics with numerous species in Africa, Asia, and Australia. There is a single Table 1. Cytology of the Sorgheae Table 1. Cytology of the Sorgheae (cont'd) 294 R. P. Celarier Cytologia 24
annual species found in America, C. pauciflorus Benth. ex Vasey, and because of its unique distribution deserves much more serious attention. The morphological variation in this genus is quite large and is of special interest since there are intermediate types between it and Vetiveria, Rhaphis, and Para-Sorghum of the Sorgheae and also Capillipedium of the Bothrio chloeae. It is the opinion of the author that experimental studies with these materials might be very rewarding. Cytologically the genus is poorly known, only five species having been studied. 1. C. rnontanus Trin. was first studied by Krishnaswamy (1941) from an Indian collection and was found to have twenty somatic chromosomes. This number has been confirmed by Janaki Ammal (1945), Mehra (1955), Sikka and Mehra (1956) and the present report. Mehra (1955) reported on six accessions from India and five were found to be 2n=20 but the sixth was 2n=80. All were completely regular at meiosis. In the present study three accessions from India were found to be 2n=20. The meiotic behavior is completely regular with ten bivalents (Fig. 12) and 10: 10 distribution of the chromosomes (Fig. 13). The South African variety tremulier was studied by de Wet and Anderson (1956) and was also found to be 2n=20. 2. C. zeylanicus Thw. was studied by Janaki Ammal (1945) from an Indian collection. It was found to have twenty somatic chromosomes but no meiotic studies were made. 3. C. gryllus Trin, was reported to be 2n=40 by Avdulov (1931), and this number is confirmed in this report in four accessions from Iraq and Turkey. Meiosis was normal in all accessions with 20 bivalents at metaphase I. 4. C. archeri Stapf is a desert species distributed through North Africa, Arabia, and into India. One accession from the Rift valley in Ethiopia was studied and found to have forty somatic chromosomes. The meiotic behavior was regular with 20 bivalents at diakinesis and metaphase I (Fig. 14) and 20:20 distribution of the chromosomes to the daughter cells (Fig. 15). 5. C. latifolius S. T. Blake is an Australian endemic apparently re stricted to Northern Territory and Western Australia. One accession was studied and was found to have 2n=20 with ten bivalents at metaphase I (Fig, 16) and regular anaphase (Fig. 17). Rhaphis Lour. Only one species, R. acicularis Honda, is generally recognized but at least one other species, Chrysopogon setifolius Stapf, is also known without a well developed awn, which has been one of the most used characters to separate the two genera. However R. acicularis seems rather distinct in several vegetative characteristics. This species is widely distributed throughout Southeast Asia and the Pacific Islands. It apparently has a long history in 1959 Cytotaxonomy of the Andropogoneae IV 295
Figs. 13-20. Chromosome behavior in the Sorgheae. 1350•~. 13, anaphase I of Chrysopogon montanus A-3032 with 10: 10 distribution of the chromosomes. 14, metaphase I of C. arche-ri A-4515 from Ethiopia with twenty bivalents. 15, anaphase I of C. archeri A-4515 with 20: 20 distribution of the chromosomes to the daughter cells. 16, metaphase I of C. latifolius A-2656 from Australia with ten bivalents. 17, anaphase I of C. latifolius A-2656 in which the twenty chromosomes are clearly seen. 18, metaphase I of Rhaphis acicularis A-6405 from Tockali, Japan with ten bivalents. 19, diakinesis of Cleistachne sorghoides A-5453 from Southern Rhodesia with eighteen bivalents (two bivalents lying together at arrow might be interpretated as a quadrivalent). 20, metaphase I of C. sorghoides A-5453 with eighteen bivalents. All these chromosomes, except in fig. 1, are recorded as medium in size but
notice that figs. 19 and 20 are considerably larger than the others, 296 R. P. Celarier Cytologia 24 the Pacific World and is considered endemic on most of the islands. This species and Ischaemum hyrone Hitchc. are the only species in the Andro pogoneae believed to be endemic in Hawaii (Degener, 1933, 1940, Whitney et al. 1939). The species was first studied cytologically by Janaki Ammal (1945) and found to have twenty somatic chromosomes. This number was confirmed in this study from one accession from Japan. Meiosis was found to be es sentially normal (Fig. 18) but occasionally a cell was seen that might be interpretated as having a quadrivalent. Cleistachne Benth. This genus consists of only a very few species and is apparently re stricted in distribution to East Africa and West India. In many respects it has the most highly specialized floral morphology in the Sorgheae. Only one species, C. sorghoides Benth., has been studied cytologically. Garber (1950) first studied it from a collection made in Uganda and in this report an accession from Southern Rhodesia was analyzed. In both the 2n number was found to be 36, and the meiotic behavior was essentially regular (Fig. 19, 20).
Discussion and conclusions There seems to be an obvious relationship between the Sorgheae and the Bothriochloeae and it appears likely that the former may have been derived from the latter. Although the precise relationship of these subtribes is far from clear, it does appear that the genus Pseudosorghum occupies a somewhat intermediate position. There are several distinct patterns of morphological variation within the subtribe Sorgheae and they all suggest that the primitive or ancestral type would have the following characteristics: paniculate inflorescence, many jointed racemes, well developed pedicellate spikelet, callus short and obtuse, palea small, with a basic chromosome number of five. Quite early there must have been a differentiation into two more or less isolated types, one with the spikelets dorsally compressed and the other laterally compressed. In general, modifications within these two groups seem independent of one another; however, there may have been occasional transfer of genes (or chromosomes) from one to the other. Also there are some suggestions of the addition of germplasm from other sources. In the group with dorsally compressed spikelets the genus Pseudosorghum represents the nearest approach to our hypothetical ancestral type that is known to the author. In this genus the inflorescence is a compact panicle, with many jointed racemes and with subsessile secondary racemes. The pedicellate spikelet is well developed and the callus is short and obtuse. The basic chromosome number is five (or ten) and the chromosomes are medium in size. 1959 Cytotaxonomy of the Andropogoneae IV 297
From something similar to Pseudosorghum it appears that two types may have been derived. One, Lasiorrhachis, shows the beginning of the modification of the pedicellate spikelet and in the species L. hildebrandtii (Hack.) Stapf all stages of suppression of the pedicellate spikelet may be found (Keng 1939). Otherwise this small genus seems to be isolated both geographically and genetically. The second derived type is examplified by the subgenus Eu-sorghum in which the inflorescence is an open panicle, the rhachis joints are reduced, and the racemes are all well peduncled. As mentioned in the previous report of this series (Celarier 1958b) the status of the subgenera Heterosorghum and Chaetosorghum is somewhat obscure. However, in several characters they appear to be intermediate between Eu-sorghum and Sorghastrum, and it is possible that they were derived from Eu-sorghum with a reduction of the pedicellate spikelet until only the glumes remain. The subgenus Chaetosorghum is similar to the subgenus Para-Sorghum in many respects, especially in regard to the simple panicle branches and well developed awn, and may conceivably represent an intermediate phylogenetic position between Heterosorghum and Para-Sorghum. Sorghastrum represents a continuation, from Heterosorghum, of the reduction of the pedicellate spikelet in which the spikelet is completely sup pressed, and shows a further reduction in the number of raceme joints. This line of development terminates with the genus Cleistachne in which the pedicel itself is suppressed and the number of raceme joints is reduced to one. The same extreme reduction of the pedicellate spikelet and number of raceme joints is seen in Asthenochloa, and in this genus the palea and lodicules are absent. However, the sessile spikelets of Asthenochloa are laterally compressed and it may conceivably represent the final stages of reduction in the other line of development. However, since this group does not have intermediate stages showing the reduction of the pedicellate spikelet, no convincing conclusions can be drawn. The second main line of development, with spikelets laterally compressed, is presented in this subtribe by Vetiveria, Chrysopogon and Rhaphis. Some forms of Vetiveria, such as V. zizanioides, may be considered as the most primitive and possibly the ancestral form. It has panicle branches of the inflorescence simple; numerous and many jointed racemes; pedicellate spikelet well developed; callus short, obtuse, and glabrous; and awns small or absent. Some of the characters of Vetiveria, such as the muricate glumes and glabrous callus, are indications to some authors (Keng 1939) of a relationship outside of the subtribe. There is certainly a possibility that Vetiveria may contain some germplasm from outside sources. However, there seems to be no question but that it is closely related to Chrysopogon and in the author's opinion there is reason to believe that some gene exchange between the two is still occurring. 298 R. P. Celarier Cytologia 24
The typical condition in Chrysopogon has fewer racemes, rhachis joints reduced to one, palea small or occasionally absent, callus elongated and bearded, and awns well developed. Between these two typical types are found species that represent almost all intermediate conditions (i. e. Chryso. pogon sylvaticus, Vetiveria fzlipes, etc.). Also there are types of Chrysopog-on that are very similar to Capilli pedium of the Bothriochloeae and differ principally in having laterally com pressed spikelets, long callus, and absence of a longitudinal groove in the pedicel. Because the intermediate types are most abundant in poorly col lected Southeast Asia, and since no exhaustive morphological study has yet been made on the few collections from that area, it is quite possible that other intermediate types may be found. The relationship between these two remains somewhat obscure. Suggestions of relationship are also seen between Chrysopogon and the subgenus Para-Sorghum. They are similar in their paniculate inflorescence with panicle branches simple; with few racemes whose joints are occasionally reduced to one in Para-Sorghum; with a callus that is long, pointed, and bearded; and with well developed awns. They are, however, different in several significant characteristics and the relationship between the two is very uncertain. The subgenus Stiposorghum is very similar to Para-Sorghum and was probably derived from it by continued development of callus and
awns. The genus Rhaphis seems to be little more than an extreme modification of Chrysopogon in which the awns are poorly developed and the callus has been extensively modified. In general two lines of modification are clearly seen in the Sorgheae. One is the reduction of the pedicellate spikelet until even the pedicel is suppressed, and the other is the reduction of the number of joints (nodes) of the raceme until only one remains. Several other modifications are in dicated but none are as clear cut as these. It should be emphasized again that these morphological suggestions of relationship are entirely hypothetical, but they do indicate several places where experimental studies should be attempted. These paths of relation ship are diagrammatically summarized in Fig. 21. The basic chromosome number of the Sorgheae is relatively uncompli cated when compared with other subtribes of the Andropogoneae; never theless, there are several problems. The evidence strongly supports five as the basic number (Garber 1950, Celarier 1956b) especially since Para-Sorghum and Stiposorghum have several species with n=5. All of the species that have been studied, except Cleistachne sorghoides, have somatic numbers that are multiples of five. However 2n=20 is by far the most common number encountered and in all cases, except Para-Sorghum and Stiposorghum, be have cytologically as diploids. Consequently ten must be considered to be 1959 Cytotaxonomy of the Andrypogoneae IV 299
Fig. 21. Diagram of relationships in the Sorgheae Primitive type 300 R. P. Celarier Cytologia 24
of very great evolutionary importance regardless of what the lowest basic number may actually be. The one species of Cleistachne that has been studied cytologically is 2n=36 and is regarded as having a basic number of nine. This is most easily visualized as having been derived from 2n=20 with the loss of one pair of chromosomes followed by chromosome doubling, or as an amphidi. ploid derived from crossing two species with n=9. Because of the meiotic regularity of C. sorghoides the latter seems more likely. However it is also possible that the n=9 types may have been derived as amphidiploids follow ing crosses of two types, one with n=5 and the other n=4. This latter consideration becomes more palatable since Celarier and Paliwal's (1957) report of a species in the Andropogoneae with n=4, and Sharma and Bhattacharjee's (1957) conclusion from secondary associations that four is the basic number for Sorghum. Despite these recent reports the evidence still remains overwhelmingly in favor of five as the basic chromosome number for the subtribe, and this seems to offer the most acceptable working hypothesis at this time. The chromosome size referred to in this report are rather general and refer to the metaphase I condition. Those species with metaphase I chromo somes larger than five microns in length are considered large, those of three microns or less are small, and all in between are regarded as medium. With this crude separation everything so far studied, with the exception of Para-Sorghum and Stiposorghum , are regarded as medium in size. Most of these are essentially similar in size (Figs . 2-18) but C. sorghoides is ap preciably larger than the others (Figs. 19, 20) being slightly greater than four microns in length. The exact significance of the evolution of chromosome size in the Sorgheae is not clear. However the fact that all the species with the larger chromosomes are highly specialized morphologically can be used as argument for a phylogenetic increase in chromosome size. If this is actually the case it appears to be in contradiction to what was seen in the subtribe Sac charinae (Celarier 1956a). However both trends seem to be fairly well established in the Gramineae and it has been suggested (Stebbins 1950) that this change in chromosome size is probably reversible . On the whole polyploidy is widespread in the Sorgheae but it appears to be of relatively less importance than in the other subtribes studied. As suming five to be the basic number there is an extremely high frequency of tetraploids but additional polyploidy is uncommon . Most of the tetraploids behave cytologically as diploids (amphidiploids) , except that most tetraploid species in Para-Sorghum and Stiposorghum behave as autotetraploids. Although there is still a great need for routine chromosome studies of the different genera and species , especially cytogeographical studies of some of the major complexes, there is enough information available to suggest 1959 Cytotaxonomy of the Andropogoneae IV 301 certain hybridization problems that require immediate attention. Crosses between different species are needed in all genera and practically none have been made and thoroughly analyzed. Also crosses need to be attempted between species in the different subgenera of Sorghum. This seems essential to a clear understanding of this complex genus. Several previous attempts to make these hybrids have met with failure (Karper and Chisholm 1936, Ayyanger and Ponnaiya 1941, Garber 1950) but none of these studies were exhaustive. Also there is some evidence to suggest that certain intergenetic crosses might be possible, especially between certain types of Chrysopogon with both Vetiveria and Para-Sorghum. Because of its intermediate position crosses should be attempted with Pseudosorghum and selected members of both the Bothriochloeae and the Sorgheae. Also crosses between subtribes might be possible if certain members of Chrysopogon and Capillipedium were used. It is the author's opinion the proper selection of parents is of paramount concern to the success of such a hybridization program. In conclusion it should be mentioned that the Sorgheae seems to suffer the same major deficiency of all members of the Andropogoneae so far studied; namely, insufficient collections of the taxa involved from specific geographical areas-usually Southeast Asia.
Summary 1. A review of the cytology of the Sorgheae (excluding Sorghum) is presented. Chromosome behavior at meiosis is discussed whenever available. 2. An artificial key is given for the eight genera. All but two have been studied cytologically and these are both monotypic. One is the primitive Lasiorrhachis and the other the very specialized Asthenochloa. 3. Of the eighteen species reported, seven are studied meiotically for the first time. 4. Five is concluded to be the most likely basic chromosome number for the subtribe, but one species (Cleistachne sorghoides) is 2n=36 and is considered to have a basic number of nine. 5. Although polyploidy is common it seems to be less frequent than in other subtribes. 6. Noticable differences in chromosome size are seen in different genera and subgenera but their relationship to phylogeny is not certain. 7. A discussion of the phylogenetic patterns of the subtribe is presented. In general these patterns are rather direct with what appears to be two distinct lines of development. However, there are several suggestions of interconnections between these lines that need additional study. 8. It is suggested that the time is ripe for detailed hybridization studies between species within the different genera, between the subgenera in Sorghum, between selected genera, and in a few cases between subtribes.
Cytologia 24, 1959 21 302 R. P. Celarier Cytologia 24
Literature cited
Avdulov, N. P. 1931. Karyo-systematische Untersuchung der Familie Gramineen. Bull.
Appl. Bot., Genet., and Pl. Breeding Suppl. 43.
Ayyanger, G. N. R. and B. X. W. Ponnaiya. 1941. Studies in Para-Sorghm Snowden-the
group with bearded nodes. Proc. Indian Acad. Sci. 14 (B): 17-24. Bews, J. W. 1929. The World's Grasses. London.
Brown, W. V. 1951. Chromosome numbers of some Texas grasses. Bull. Torrey Bot. Cluo.
78: 292-299.
Celarier, R. P. 1956a. Cytotaxonomy of the Andropogoneae I. Subtribes Dimeriinae and
Saccharinae. Cytologia 21: 272-291.-
1956b. Additional evidence for five as the basic chromosome number of the Andro
pogoneae. Rhodora. 58: 135-143.- 1957. Cytotaxonomy of the Andropogoneae II. Subtribes Ischaeminae, Rottboelliinae,
and the Maydeae. Cytologia 22: 160-183.-
1958a. Cytotaxonomic notes on the subsection Halepensia of the genus Sorghum. Bull.
Torrey Bot. Club. 85: 49-62.-
1958b. Cytotaxonomy of the Andropogoneae III. Subtribe Sorgheae, genus Sorghum.
Cytologia 23: 395-418.-
and R. L. Paliwal. 1957. Basic chromosome number of four in the Subfamily Panicoideae
of the Gramineae. Science 126: 1247-1248.
Church, G. L. 1929. Meiotic phenomena in certain Gramineae II. Paniceae and Andro
pogoneae. Bot. Gaz. 88: 63-84.
Degener, 0. 1933. Flora-Hawaiiensis. vol. 1.-
1940. Flora-Hawaiiensis, vol. 4 . deWet, J. M. J. and L. J. Anderson. 1956. Chromosome numbers in Transvaal grasses.
Cytologia 21: 1-10.
Garber, E. D. 1950. Cytotaxonomic studies in the genus Sorghum. Univ. of Calif. Publ. in Bot. 23: 283-361.
Gould. F. W. 1956. Chromosome counts and cytotaxonomic notes on grasses of the tribe
Andropogoneae. Amer. Jour. Bot. 43: 395-404.
Hackel, E. 1889. Andropogoneae in de Candolle , A. Monographiae Phanerogamarum VI. Paris.
Janaki-Ammal, E. K. 1945. in Darlington and Janaki-Ammal, Chromosome Atlas of culti vated plants. London.
Karper, R. E. and A. T. Chisholm. 1936. Chromosome number in Sorghum. Amer. Jour.
Bot. 23: 369-374.
Keng, Y. L. 1939. The gross morphology of Andropogoneae. Sinensis 10: 274-343.
Kidd, H. J. 1953. Secondary chromosome association in Eu-sorghum and its probable causes
(Read at the A. I. B. S. meetings in Madison, Wisconsin).
Krishnaswamy, N. 1941 . Untersuchungen zur Cytologie and Systematik der Graminee. Bot. Centralblatt 60: 1-56.
Mehra, K. L. 1955. Chromosome races in Chrysopogon montanus . Current Sci. 24: 95-96. Merwine, N. C. 1956. A cytogenetic study of a hybrid in the genus Sorghum: Sorghum
vulgare Pers.•~S. halepense (L .) Pers. Ph. D. Dissertation, Mississippi State College.
Moffett, A. A. and R. Hurcombe . 1949. Chromosome numbers in South African grasses.
Heredity 3: 369-373 .
Myers, W. M. 1947. Cytology and genetics of forage grasses. Bot. Rev. 13: 319-421.
Pilger, R. 1940. Gramineae III: Unterfam . Panicoideae in Engler U. Prant. Die Natiir lichen Pflanzenfamilien vol . 2, Leipzig.
Saura, F. 1948. Cariologia de Gramineas en Argentina . Univ. Nac. Buenos Aires Fac. de
Agron. y. Vet. 12: 51-67 . 1959 Cytotaxonomy of the Andropogoneae IV 303
Sharma, A. K. and D. Bhattacharjee. 1957. Chromosome studies in Sorghum 1. Cytologia 22: 287-311. Sikka, S. M. and K. L. Mehra. 1956. Cytological studies in the tribe Andropogoneae, Gramineae. Proc. 43 Indian Sci. Cong. Part IV: 18-19. Stapf, O. 1919. Gramineae in Prain, D., Flora of Tropical Africa. vol. 9. London. Stebbins, G. L. 1950. Variation and evolution in plants. Columbia Univ. Press, New York. Whitney, L. D., Hosaka, E. Y., and Ripperton J. C. 1939. Grasses of Hawaiian ranges. Hawaii Agr. Exp. Sta. Bull. 82, 148 pp.
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