_??_1990 by Cytologia, Tokyo Cytologia 55: 315 -319 , 1990

Genome Homology and Origin of sumatrense (Gramineae)

S.C. Hiremath1, G. N. V. Patil2 and S. S. Salimath1

1 Department of Botany, Karnatak University, Dharwad, 2Department of Botany , Anjuman Science College, Bhatkal, India

Accepted December 22, 1989

Panicum sumatrense Roth. is a minor cultivated in India, Ceylon, Pakistan, Burma and South East Asian countries. This millet forms an important part of tribal agriculture in eastern ghats of India. It is commonly known as sama millet or little millet and is drought resistant quick growing cereal of 90 days. Panicum psilopodium Trin. is a wild grass distributed throughout the Indian sub-continent. It is found as a weed in sama millet cultivation. Morphologically it is similar to cultivated taxon P. sumatrense. De Wet et al. (1983) from comparative morphological studies merged both P. psilopodium and P. sumatrense into a single species P. sumatrense Roth. and the two former taxa were given subspecific rank. P. sumatrense subsp. sumatrense includes morphologically variable cultivated forms and P. sumatrense subsp. psilopodium (Trin.) De Wet. comb. nova is a wild taxon. Based on mor phometric analysis De Wet et al. (1983) suggested that P. psilopodium may be the putative progenitor of cultivated sama millet P. sumatrense. Cytogenetics of Panicum and their wild relatives is poorly understood. The basic chromosome number is x=9 and evidences have been presented to show that this number has originated from x=10. Polyploidy is common in this genus ranging from tetraploid to 12 ploid level (Chennaveeraiah and Hiremath 1990). Knowledge regarding genome relations in these species is not known. Present investigation was undertaken to determine the genomic homology between P. sumatrense or sama millet and P. psilopodium to elucidate the origin and domestication of cultivated taxon P. sumatrense.

Material and method

The seed material of cultivated species Panicum sumatrense was obtained from Dr. See tharam, Minor millets Coordinator, University of Agricultural Sciences, Bangalore. The wild species P. psilopodium was collected from natural population. The identifications of these species were confirmed by Royal Botanic Gardens, Kew (U. K.). One set of vouchered specimen has been filed at the above herbarium and another set is available in the herbarium, Department of Botany, Karnatak University, Dharwad, India. Both the species are self pollinated. Florets were hand emasculated according to the technique of Nelson 1984 with suitable modifications. Spikes were fixed in Carnoy's fluid

(6:3:1) and microsporocytes were stained with 1% aceto-carmine. Slides were made per manent using Celariar's (1956) acetic acid butyl alcohol series. Pollen viability was estimated on the basis of stainability of pollen in aceto-carmine glycerine mixture.

Results

Crossability Crossability data is given in Table 1. Hybrids were obtained in both the directions. However, only in P. sumatrense•~P. psilopodium combination all the hybrid seeds germinated 316 S. C. Hiremath, G. N. V. Patil and S. S. Salimath Cytologia 55 and reached to maturity. In reciprocal cross out of 6 seeds only 3 germinated but they failed to reach to maturity. Hybrids were confirmed through genetic marker characters.

Morphology The comparative morphological characters of the parents and their hybrids are given in Table 2 and Figures 1 to 3. The female parent P. sumatrense is tall, stem thick, leaves broad, panicle long semi lax, spikelets many, nonshattering, glumes green, stigma white and upper lemma acute. The male parent P. psilopodium is short, stems medium in thickness, leaves narrow, panicles small lax, spikelets few shattering, glumes, stigmas purple and upper lemma apiculate.

Table 1. Results of interspecific hybridization in P. sumatrense and P. psilopodium

Table 2. Morphological characters of P. sumatrense, P. psilopodium and their F, hybrids

Table 3. Chromosome pairing in Panicum sumatrense, P. psilopodium and their F, hybrids

The hybrids resembled their parent P. sumatrense with regard to nonshattering spikelets. They were intermediate between both the parents with respect to several quantitative charac ters like height, thickness of stem, leaf width and spikelet number. The hybrids are like male parent in having purple glumes and stigma.

Cytology Meiotic behaviour is perfectly normal in both the parents. Regular 18 bivalent formation 1990 Genome Homology and Origin of Panicum sumatrense 317 is observed in female parent P. sumatrense and male parent P. psilopodium (Figs. 4 5). In the hybrids meiotic process is apparently normal. Mean chromosome pairing of 17.9II+ 0.035IV per cell was found in 200 cells analyzed. About 96% of the PMCs showed 18 bivalents. A single quadrivalent was noticed in 7 cells (3.5%). Univalents were conspicuously absent.

Figs. 1-7. 1, panicle of female parent Panicum sumatrense. 2, panicle of P. sumalrense•~P.

psilopodium F1 hybrid. 3, panicle of male parent P. psilopodium. 4, diakinesis in female parent P. sumatrense with 18 bivalents. 5, diakinesis in male parent P. psilopodium with 18 bivalents. 6, diakinesis in F1 hybrid with 18 bivalents. 7, diakinesis in F1 hybrid with 16 bivalents and 1 quadrivalent (arrow). Figs. 1-3. •~2/3 N. S.. Figs. 4-7. •~1200. 318 S. C. Hiremath, G. N. V. Patil and S. S. Salimath Cytologia 55

Frequencies of different chromosome configurations are given in Table 3 and Figures 6, 7. Anaphasic separation of chromosomes at first and second division was normal. Tetrad forma tion was also regular.

Fertility Pollen fertility was found to be 99% in female parent P. sumatrense and 96% in male parent P. psilopodium. In the hybrids about 90% of the pollen was assessed good. In the parents seed setting is 88% in P. sumatrense and 82% in P. psilopodium. The hybrids are highly fertile with 84% seed set.

Discussion The basic chromosome number and attendant genes comprise a genome (Jackson 1985). In eukaryotes two or more genomes derived from parental gametes form the chromosome complement or karyotype (Grant 1987). Various methods have been developed to assess genome affinity between different taxa. Some of the methods are karyotype analysis, chromo some pairing in species hybrid, chromosome banding techniques, natural karyotype, seed protein profile, isoenzyme studies, DNA/DNA hybridization and restriction endonuclease studies. These have been briefly reviewed by Patil (1988). Classical method of genome analy sis is through chromosome pairing in the F1 species hybrid (Kihara 1930). Using this method genomic relations have been elucidated in large number of crop and their wild relatives (Simmonds 1976). Chromosome pairing is known to be under genetic control (Riley and Chapman 1958) as exemplified by Ph gene in bread wheat or affected by environmental factors (Solbrig 1968). With these limitations in mind this method is still considered to be the best in assessing the genome homologies between different taxa (Kimber et al. 1981). Panicum sumatrense is widely cultivated in Indian subcontinent. In eastern ghats of India it forms an important part of tribal agriculture. P. psilopodium is distributed throughout India. In eastern ghats of north Andhra Pradesh it grows as a weed in the cultivation of sama millet and forms fertile hybrids. Morphologically cultivated millet P. sumatrense and P. psilopodium are similar but can be separated by several diagnostic characters. The hybrids resembled their female parent P. sumatrense with regard to nonshattering spikelets. They were intermediate between both the parents with respect to several quantitative characters. The hybrids were like male parent P. psilopodium in having purple glumes and stigma. The hybrids were vigorous and highly fertile. Thus morphological similarity, sympatric distribution and formation of fertile hybrids in nature suggest that P. psilopodium may be the putative progenitor of sama millet P. su matrense. Introgression of genes between these two species appears to be common in eastern ghats of Andhra Pradesh (De Wet et al. 1983). Regular 18 bivalents were found in both the parents P. sumatrense and P. psilopodium. These two taxa are allotetraploids. Univalent and multivalent formations are absent in both the parents. In the hybrids mean chromosome pairing of 17.7II+0.035IV per cell was found in 200 cells analyzed. About 96% of the PMCs showed 18 bivalents formation. Univalents were conspicuously absent. Preponderance of 18 bivalent formation in the hybrids strongly indicated that genomes of P. sumatrense and P. psilopodium are basically similar and are fully homologous. Thus P. sumatrense might have originated from P. psilopodium through se lection and further cultivation. Genomic notation of AABB is proposed for these two species. Presence of a single quadrivalent in the hybrids (3.6%) shows that the genomes of P. sumatrense and P. psilopodium are differentiated by one reciprocal translocation. The pollen and seed fertility in the hybrids is 90% and 84% respectively. It is evident here that trans 1990 Genome Homology and Origin of Panicum sumalrense 319 location is not the major isolating barrier between these two species . However, it is worth while to investigate the isolating mechanisms which restrict the free flow of genes between these two taxa. Since the progenitor species P. psilopodium and sama millet P. sumatrense are sympatric and introgression appears to be common in the eastern ghats of Andhra Pradesh adjoining to Orissa, it is probably here that P. sumatrense might have been domesticated .

Summary Interspecific hybrids between Panicum sumatrense and P. psilopodium were produced and analyzed to assess the genome homology between these two taxa. Meiotic behaviour was perfectly normal in both the parental species, P. sumatrense and P. psilopodium. Regular 18 bivalents were observed in the parents and they are allotetraploid. Both the parents are fully fertile. In the hybrids a mean chromosome pairing of 17.9II+0.035IV per cell was found in 200 cells analyzed. About 96% of the PMCs contained 18 bivalents. Regular 18 bivalent formation in the hybrids strongly suggests that the genomes of P. sumatrense and P. psilopodium are basically similar and are fully homologous. Thus P. sumatrense or sama millet might have originated from wild taxon P. psilopodium through selection and further cultivation. Presence of a single quadrivalent in the hybrid indicates the genomic divergence and differentiation in these two species through one reciprocal translocation.

References

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