Intergeneric Hybrids in the Bothriochloininae II Bothriochloa and Capillipedium

Home , Bothriochloa, Capillipedium, Capillipedium spicigerum, Chrysopogon

268 Cytologia 26

J. M. J. de Wet, D. S. Borgaonkar and H. R. Chheda

Department of Botany and Plant Pathology, Agricultural Experiment Station, Oklahoma State University, Stillwater, Oklahoma, U. S. A.

Received October 17, 1960

Members of the Bothriochloininae, subtribe Andropogoninae, are widely distributed throughout the tropics of the Old World. Bothriochloa intermedia (R. Br.) A. Camus and Capillipedium parviflorum (R. Br.) Stapf extend from Africa to the Pacific islands, whereas C. spicigerum S. T. Blake is confined to Australia. Morphological data presented by Harlan et al (1958) suggest that B. intermedia (R. Br.) A. Camus hybridizes with Capillipedium Stapf in nature. Artificially produced hybrids were studied, and compared with suspected natural ones.

Material and methods Hybrids were produced as described by Richardson (1958). Cytological data are based on studies of microsporocytes stained with aceto-carmine. Herbarium specimens are filed with the Department of Botany, Oklahoma State University.

Results The morphology of Bothriochloa O. Kuntze and Capillipedium Stapf is fully discussed by Stapf (1919) and Blake (1944). They resemble each other in spikelet structure, but differ in inflorescence characteristics. The inflores cence of Capillipedium is composed of strongly branched racemes, each of which articulates individually and never has more than 9 joints (9 sessile and 10 pedicellate spikelets). Bothriochloa is characterized by panicles which are often subdigitate, the racemes are seldomly branched, but if so the branches articulate with the primary raceme and the individual racemes are 15 or more jointed (15 sessile and 16 pedicellate spikelets). The two species of Capillipedium, used as male parents, differ from each other in the following salient morphological characteristics. Capillipe dium parviflorum (R. Br.) Stapf has a delicate panicle (Fig. 1) with the individual racemes reduced to a maximum of 3 sessile and 4 pedicellate spikelets and 2 intracarinal nerves on the lower glume of the sessile spikelet. A compact panicle, with individual racemes 3-9-jointed and 4-5 intracarinal

Supported in part by grant 10742, National Science Foundation. 1961 Intergeneric Hybrids in the Bothriochloininae II 269 nerves on the lower glumes is characteristic of C. spicigerum S. T. Blake (Fig 3). Hybrids between B. intermedia and C. parviflorum resemble C. spici gerum in spikelet structure and inflorescence characteristics (Figs. 3, 4). The

Figs. 1-6. Inflorescence morphology. 1, Capillipedium parviflorum (R. Br.) Stapf.

2, Bothriochloa intermedia (R. Br.) A. Camus. 3, Capillipedium spicigerum S. T. Blake. 4, B. intermedia•~C. parviflorum. 5, natural hybrid, B. intermedia•~C. spicigerum. 6. B. intermedia•~C. spicigerum.

inflorescence is strongly branched, espatheate and the lower glume of the sessile spikelet is sparsely hairy all over, depressed along the middle with 4-5 nerves between the keels. Hybrids differ from the natural species only

Cytologia 26, 1961 19 270 J. M. J. de Wet, D. S. Borgaonkar and H. R. Chheda Cytologia 26

in the maximum number of spikelet pairs per individual raceme, which is

Figs. 7-12. 7-9, cytology of B. intermedia•~C. parviflorum. 7, 20 bivalents. 8, 40 chro

mosomes during anaphase. 9, 2 bivalents and 36 univalents. 10-12, Cytology of B. inter

media•~C. spicigerum (2n=47). 10, 15 bivalents and 17 univalents. 11, 47 chromosomes during anaphase. 12, 9 bivalents and 29 univalents.

never more than 9 in C. spicigerum and never less than 14 in the artificial hybrids. 1961 Intergeneric Hybrids in the Bothriochloininae II 271

The hybrid progeny of a cross between B. intermedia and C. spicigerum cannot be distinguished, morphologically, from some natural hybrids collected in India (Figs. 5, 6). These plants resemble typical B. intermedia except for the strongly branched panicles and relatively few spikelet pairs per raceme. Bothriochloa intermedia and the two species of Capillipedium are characterized by 2n=40 chromosomes. During microsporogenesis the chro mosomes usually associate into pairs but occasionally a single multivalent and rarely as many as 16 univalents were observed. These "basic" species ap pear to be segmental allopolyploids as defined by Stebbins (1947). The cytology of the hybrids is summarized in Table 1. Three of the

Table 1. Cytology of parents and hybrids

* Range and average number of chromosome configurations are listed.

hybrids obtained from a cross between B. intermedia and C. parviflorum behave essentially like the parent species in respect to chromosome associa tion. The chromosomes usually associate into pairs (Fig. 7) and later chro mosome movement is completely regular (Fig. 8). Multivalents and univalents were encountered but only slightly more frequently than in the parents. One hybrid plant is characterized by an almost complete lack of chromosome pairing (Fig. 9). In this particular hybrid, perhaps through mutation, the ability of the chromosomes to pair preferentially within genomes was lost.

19* 272 J. M. J. de Wet, D. S. Borgaonkar and H. R. Chheda Cytologia 26

Nonhomology may then explain the chromosome behaviour in this particular hybrid plant. Hybrids between B. intermedia and C. spicigerum behave essentially like those with C. parviflorum in respect to chromosome association. One plant, however, has 2n=47 chromosomes (Figs. 10, 11, 12) which associate into as many as 21 bivalents during microsporogenesis with the remaining ones present as univalents or 4 of these forming a single tetravalent. This hybrid plant could have received the extra chromosomes from either one or both parents. Morphological data provide no conclusive evidence to support either assumption. Aneuploidy could be expected as both parents are characterized by some degree of chromosomal abnormalities during micro sporogenesis.

Discussion Morphologically Bothriochloa O. Kuntze and Capillipedium Stapf are closely related, but appear to represent true taxonomic units, each charac terized by the constancy of its morphological type. Celarier and Harlan (1957) indicated that tetraploid (2n=40) species of these genera are faculta tive apomicts. Natural hybridization apparently only takes place at the tetraploid level, thus after the species became apomictic. Cytological studies in the artificial hybrids suggest close homology between the chromosomes of these two genera. This, however, may not be completely true. In hybrids between Bothriochloa and the related genus Dichanthium, Celarier et al (1960) demonstrated that the chromosomes of the haploid genomes of any one of these genera can pair among themselves. Intergeneric hybridization between Bothriochloa, and both Capillipedium and Dichanthium is closely correlated with their apomictic mode of reproduction. The question now arises whether these genera should be united and the "species" of each regarded as microspecies , in the sense of Gustafsson (1947) and Stebbins (1950), centered around three large macrospecies. From a taxonomic point of view this will lead to chaos rather than serve any useful purpose in classification. Capillipedium and Dichanthium, whether sexual diploids or apomictic polyploids, do not hybridize with each other, or at least may be crossed only with great difficulty. Within "genera" Gustafsson's concept of circle microspecies could serve a useful purpose.

Summary Artificial hybrids between tetraploid (2n=40) Bothriochloa intermedia (R. Br.) A. Camus and both Capillipedium parviflorum (R. Br.) Stapf and C. spicigerum S. T. Blake were produced and studied. The cytology of the hybrids suggests close homology between the chromosomes of Bothriochloa O. Kuntze and Capillipedium Stapf. Each genus, however, is characterized by the unity of its morphological type and it is suggested that chromosome 1961 Intergeneric Hybrids in the Bothriochloininae II 273 pairing may take place autosyndetically. Capillipedium spicigerum S. T. Blake could have originated from a hybrid between B. intermedia (R. Br.) A. Camus and C. parviflorum (R. Br.) Stapf backcrossed to the latter species.

Literature cited

Blake, S. T. 1944. Monographic studies in the Australian Andropogoneae, 1, including revisions of the genera Bothriochloa, Capillipedium, Chrysopogon, Vetiveria, and Spathia. Univ. Queensland papers II: 1-62. Celarier, R. P., de Wet, J. M. J., Borgaonkar, D. S. and Harlan, J. R. 1960. Intergeneric hybrids within the Bothriochloininae 1. Bothriochloa intermedia and Dichanthium annulatum. Cytologia 26: 170-175. - and Harlan, J. R. 1955. Studies on Old World Bluestems, Okla. Agr. Exp. Sta. Tech. Bull. T-58: 1-31. - and - 1957. Apomixis in Bothriochloa, Dichanthium and Capillipedium. Phytomor. 7: 93-102. Gustafsson, A. 1947. Apomixis in higher plants. iii. Biotype and species formation. Lunds Univ. Arsskr. 44: 183-370. Harlan, J. R., Celarier, R. P., Richardson, W. L., Brooks, M. H. and Mehra, K. L. 1958. Studies on Old World Bluestems II. Okla. Agr. Exp. Sta. Tech. Bull. T-72: 1-23. Richardson, W. L. 1958. A technique of emasculating small grass florets. Indian Jour. Gen. Pl. Breed. 18: 69-73. Stapf, O. 1919. Gramineae, in Prain, D., Flora of Tropical Africa 9: 248-298. Stebbins, G. L. 1947. Types of polyploids: Their classification and significance. Adv. in Genet. 1: 403-429. - 1950. Variation and evolution in plants. Columbia Univ. Press, N. Y.