_??_1989 by Cytologia, Tokyo Cytologia 54: 73-78 , 1989

Cytomorphological Studies in Two New Biotypes of pedicellatum Trin.

Z. Vishnuvardhan and N. Lakshmi

Cytogenetics Laboratory, Botany Department Nagarjuna University, Nagarjunanagar-522 510, Accepted January 20, 1988

Pennisetum pedicellatum Trin. popularly known as 'Kyasuwa grass' or 'Deenanath grass' is a native of tropical and is probably an introduction in India (Bor 1960). It is a drought resistant annual weed with considerable economic importance as a soil binder and forage and is cultivated in different states of India . A perusal of existing literature revealed that the species is a polyaneuploid complex which is capable of maintaining efficiently an astonishing array of chromosome numbers 2n=30 , 32, 35, 53 (Chatterjee and Pillai 1970), 36, 48 and 54 (Nath and Swaminathan 1957, Joshi et al. 1959, Sharma et al. 1980) all derived from two base numbers x=8 and 9. The species can also exist in the form of distinct biotypes dif fering from each other mainly in leaf and inflorescence characters (Mukherjee and Chatterjee 1955, Chatterjee and Reddy 1974, Chatterjee and Das 1979). The different synonyms so far proposed for this species as well as different varietal classification (Chase and Niles 1962, Brunken 1979a, b) have probably been based on such minor morphological variations. The present study is based on cytomorphological investigations on two new biotypes of this species and an attempt has been made to understand the different cytogenetic mechanisms controlling the mutability and stability of the species and the role of chromosome numerical mosaicism in the differentiation of this polyaneuploid agamic complex.

Materials and methods

Two morphologically distinct biotypes, one with pink panicles and the other white were recognised in the wild population of P. pedicellatum growing in and around the campus of Nagarjuna University. A minimum of 10 plants at random of each form were used in the compilation of different morphometrics. Besides pollen fertility, seed set percentage, seed viability and germination percentage were also noticed. For meiotic studies young panicles were fixed in 3:1 alcohol-acetic acid and temporary slides were made by acetocarmine tech nique.

Results

a. Morphology: Of the two forms pink and white, pink is more prevalent. Although, in general morphology the two forms resemble one another, on detailed analysis they revealed several minor morphological differences (Figs. 1, 2 and Table 1). The pink form is char acterised by a cylindrical panicle with drooping tip, soft pink wool and dark green leaves while the white form revealed lance-shaped ear with straight pointed apex, soft white wool and light green leaves (Figs. 2, 3). b. Cytology: Cytological analysis has been made for a total of 10 random plants, five from pink and five from white forms. Out of these, one from pink and one from white turned out to be stabilized hexaploids with 2n=54 chromosomes (Fig. 4). In these, hexavalent was 74 Z. Vishnuvardhan and N. Lakshmi Cytologia 54 observed to be the highest association and formed in lowest frequency (Table 2). Lagging chromosomes and micronuclei were found to be common in anaphase and telophase stages. Pollen fertility was found to be high in both the hexaploids, 86% in pink and 80% in white. Meiotic analysis in the other eight plants revealed meiotic instability in the form of chro mosome numerical mosaicism. The chromosome number varied from 33-56 within the PMCs

Figs. 1-4. 1, Pink form. 2, White form. 3, Panicles of pink and white forms. 4, Metaphase I in white form with 54 chromosomes (1 VI+1 IV+4 III+15 II+2 I) •~2100. 1989 Cytomorphological Studies in Two New Biotypes of Pennisetum pedicellatum Trin 75 of white form and from 34-56 in pink form (Figs. 5-8). The frequencies of these varied chro mosome numbers are set out in Table 3. Of these, the numbers 45, 48 and 54 were observed to be in greater prevalence. In mosaics also hexavalent was the highest possible association, however, in cells showing lower numbers than 54 this association was absent. Second di visions were highly irregular with many dividing laggards and chromatin bridges. In mosaics of both white and pink forms, pollen fertility was low (75%) compared with hexaploids. There

Table 1. Survey of the main differences in vegetative and reproductive organs of different biotypes of P. pedicellatum

Table 2. Frequency of associations at diakinesis/metaphase I in hexaploids of P. pedicellatum

was no clear cut distinction in morphology between the mosaics and hexaploids. The species is a well established apomict and irregular meiosis is not a barrier to seed formation. c. Seed viability and germination: Seeds of the two forms were collected and their germination rate was studied under different storage periods. Seeds of white form did not germinate when they were kept for germination immediately after their collection, while pink form showed very low germination rate (1.33%). After 5 months storage, the pink and 10 Z. Vishnuvardhan and N. Lakshmi Cytologia 5 white forms showed 14% and 40% germination respectively. After 8-9 months, both form manifested maximum germination percentage (Table 4). Then onwards the pink form see showed decline in germination, while the other form remained on 91.68%. Seeds of pin form lost viability after two years and white form showed 22% germination. In all, whit form seeds showed high germination rate and longivity than the pink form.

Figs. 5-8. 5, Diakinesis with 52 chromosomes (1 IV+23 II+2 I) . •~2250. 6, Diakinesis showing 56 chromosomes (1 VI+3 IV+1 III+16 II+3 I) . •~2250. 7, Diakinesis with 50 chromosomes (2 IV +20 II+2 I). •~2250. 8, Anaphase I showing 22:23 segregation . •~2000. 1989 Cytomorphological Studies in Two New Biotypes of Pennisetum pedicellatum Trin . 77

Discussion

The varient forms recognised in P. pedicellatum , pink and white are considered as two distinct ecotypes since they maintained their distinctiveness genetically . The presence of two base numbers within the species, polyaneuploid series and intraplant aneuploidy suggest that P. pedicellatum is a dynamic and rapidly evolving species . The prevalence of meiotically unstable mosaics compared to polyploid forms in the population suggests that intra-individual aneuploidy is contributing in bringing about genetic variation in the species . Amphimixis and apomixis co-existed in the species and the latter is an added dividend to the active evolu tionary state by virtue of which it can tolerate any amount of genetic imbalance without inter

Table 3. Percentage of cells with varying number of chromosomes in chromosomal numerical mosaics of P. pedicellatum

Table 4. Germination percentage of seeds of two biotypes of P. pedicellatum under different storage conditions

ruption to the seed formation. Khokhlov (1970) while pointing the significance of apomixis in the evolution of higher plants remarked that apomicts are characterised by their cosmopolitism, high viability, ability to compete with other annual forms, high mutation rate, absence of characteristics of degeneration and extinction, absence of stability in chromosome numbers and higher seed productivity. Muntzing (1967) and Zavadskii (1966) pointed out the signifi cance of apomixis in evolution by saying that the path of progressive evolution in the methods of reproduction of is not a transition from amphimixis to apomixis but the development of the whole system of reproductive methods, including xenogamy and apomixis mutually sup plementing and protecting each other. 78 Z. Vishnuvardhan and N. Lakshmi Cytologia 54

All the evolutionary advantages of an apomictic species can be seen in P. pedicellatum plants studied here since the plants are healthy, highly vigorous and had high aggressive capacity. Of the two, the white form showed high percentage of seed set, germination and longivity. These are additional advantages for this form to spread rapidly than the other and in due course of time the white form may dominate the pink by exploiting these advantages. The presence of two base numbers in the species and aneuploid series suggest the role of hybridization in the differentiation of the species. In short it can be concluded that polypolidy coupled with hy bridization and apomixis might have played an important role in creating genetic variation and ecotype differentiation in the species.

Summary

Two distinct ecotypes, pink and white have been recognised in P. pedicellatum. They differed from one another in ear shape, colour, number of involucels per panicle and bristles per involucels. Cytological studies revealed the existence of hexaploid chromosome number 2n=54 in some and chromosome numerical mosaicism in others. It is concluded that this is a dynamic and rapidly evolving species showing differentiation of new ecotypes. The genetic mechanisms underlying this diversification are polyploidy, meiotic instability and co-existance of apomixis along with amphimixis.

References

Bor, N. L. 1960. The grasses of Burma, Ceylon, India and Pakistan. Paragamon Press, London p. 344. Brunken, J. N. 1979a. Cytotaxonomy and evolution in Pennisetum section Brevivalvula (Gramineae) in tropical Africa. Bot. J. Linn. Soc. 79: 37-49. - 1979b. Morphometric variation and the classification of Pennisetum section Brevivalvula (Gramineae) in tropical Africa. Bot. J. Linn. Soc. 79: 51-64. Chase, A. and Niles, C. D. 1962. Index to grass species. Vol. 3. GK Hall and Co. Chatterjee, A. K. and Das, A. P. 1979. Cytomorphological studies of the biotypes of Pennisetum pedicellatum Trin. Caryologia 32: 5-14. - and Pillai, G. K. 1970. Apomixis in Pennisetum pedicellatum Trin. Sci. Cult. 36: 667-669. - and Reddy, B. M. 1974. Wild grass flora in and around Indian Institute of Technology Khargapur Campus. The Harvester 16: 7-10. Joshi, A. B., Patil, B. D. and Manchand, P. L. 1959. Chromosome number in some grasses. Curr. Sci. 28: 254-255. Khokhlov, S. S. 1970. Apomixis and breeding: Translation of 'Apomiksis i selektsiya' by B. R. Sharma, Amerind Publ. Co. Pvt. Ltd., New Delhi. Mukherjee, S. K. and Chatterjee, B. N. 1955. Culture of Pennisetum pedicellatum in Bihar for forage and soil conservation. J. Soil and Water Convserv. in India. 3: 161-163. Muntzing, A. 1967. Genetika (Genetics) Nysl. Moscow. Nath, J. and Swaminathan M. S. 1957. Chromosome numbers in some grasses. Indian J. Genet. 17: 102. Sharma, C. M., Sinha, P. K. and Singh, A. P. 1980. Cytomorphological studies in Pennisetum pedicellatuin: in 'Trends in Genetical Research of ' Ed. V. P. Gupta and J. L. Minocha P. A. U . Ludhi ana pp. 205-209.