_??_1987 by Cytologia, Tokyo Cytologia 52: 487-491 , 1987

Cytomorphological Studies of Three Species of Linn. from South India

J. Christopher, P. Sam Raj and K. Gongadharan Pillai Departmentof Botany,University of Kerala, Kariavattom,Trivandrum, India AcceptedMay 7, 1986

Paspalum Linn. is the second largest genus of the tribe Paniceae with about 400 species (Chase 1929), distributed in the tropical, sub-tropical and warm-temperate regions of the world. Several species are important fodder grasses and P. scrobiculatum, known as "kodo" is a minor cultivated in India. Three species of this genus, P. scrobiculatum, P. com mersonii and P. orbiculare (Bor 1960) are widely distributed in Southern India. Recently Clayton (1975) who has studied the morphological characters and habit of these grasses from natural populations of West Africa suggested that these three species should be considered as varieties of a single species P. scrobiculatum complex since the distinguishing characters are quite unreliable in the West Aftrican specimens. For the present study, samples of these three species were collected from the natural populations (both cultivated and wild) from different localities of Southern India. Cytological studies have been made with a view to ascertain whether these three taxa showing diverse morphological characters and distinct variation in habit (Figs 1, 2, 3) could be co-related with any cytological distinction.

Material and methods P. commersonii and P. orbiculare were collected from natural populations found in dif ferent regions of South India. The seeds of the cultivated species, P. scrobiculatum were ob tained from Tamil Nadu Agriculatural University, Coimbatore. The were maintained in numbered pots at the Botanic Garden, University of Kerala, Kariavattom Campus. Meiotic studies were made from PMCs for which young spikelets at appropriate stage of development were fixed in Carnoy's fixative. Somatic preparations were made from root tips and the standard aceto-carmine smear-technique is used for the present investigation. Four to five plants of each species were investigated. Voucher specimens were deposited in the herbarium of the Botany Department.

Observations Paspalum commersonii Forst (Figs. 1 and 2) This is a perennial species distributed in the tropics and sub-tropics of the Old World. It is found in wet places throughout India ascending the hills up to 1600m. It commonly occurs both as hydrophyte and terrestrial ecotypes. The terrestrial form is rather erect, reaching a height of about 0.5m (Fig. 1), while the aquatic form has more succulent culms and grows to about 1.5m in length, rooting at the nodes (Fig. 2). For the present study both ecotypes were collected from the sub-rubs of Trivandrum. The meiotic behaviour of the PMCs has been studied in detail in the two populations. During prophase the chromosomes showed total asynapsis and late prophase and metaphase I stages showed 60 univalents (Figs. 8, 9). After metaphase I, all the chromosomes organised to 488 J. Christopher, P. Sam Raj and K. Gangadharan Pillai Cytologia 52

form a restitution nucleus (Fig. 10) which proceeded directly to the second division in which the univalents divided equationally. As a result, 60 daughter chromosomes were observed segregating to opposite poles (Fig. 11). These two groups of anaphase chromosomes formed two nuclei at telophase (Fig. 12) and subsequently dyads were formed (Fig. 13). The dyads develop into diploid pollen grains which eventually disintegrate.

Root tip cells of both ecotypes consistently showed 60 chromosomes which are small in size ranging in length from 1ƒÊu to 1.7ƒÊ with median or sub-median constrictions (Fig. 5). The earlier reports on the chromosome number of this species are 2n=20 (Tateoka 1956), 2n=40

(de Wet and Anderson 1956, Moffett and Hurcombe 1949, Singh and Godward 1960, Larsen 1963) and 2n=60 (Christopher and Abraham 1976).

P. scrobiculatum Linn. "Kodo millet" or "Vargu" This is cultivated in poorer soils of South India for the grain which is eaten under the name "Kodo" . Meiosis showed 20 bivalents in PMCs at diakinesis and metaphase I (Fig. 7). Ana

phase I separation was found to be normal and pollen fertility was estimated to be 82 percent.

Figs. 1-3. 1, Paspalum commersonii. Terrestrial ecotype. •~1/12. 2, P. commersonii. Hy drophyte ecotype. •~1/12. 3, P. orbiculare. •~1/4.

A high percentage of seed-set was also observed. The previous reports on the chromosome number of this species also show 2n=40 (Avdulov 1928, Krishnaswamy 1951, Larsen 1963, Hiremath and Dandin 1975 and Christopher and Abraham 1976).

P. orbiculare Lam. (Fig. 3)

This is a perennial grass with culms creeping and rooting below (Gamble 1934) and dis tributed in S. E. Asia generally. It occurs throughout India in waste places both in the plains and hills and materials for study were collected from the Karyavattom Campus and Trivan drum (Fig. 3).

Meiosis showed 20 bivalents in PMCs at diakinesis and metaphase I (Fig. 6). All col lections had regular meiotic metaphase pairing, normal anaphase I separation and good stain ability of mature pollen and a high percentage of seed set. Mitotic studies revealed 40 chromo somes ranging in length between 1ƒÊ and 2ƒÊ, with median or sub-median centromeres (Fig. 4). The earlier reports on this species are 2n=20 (Chen and Hsu 1961) and 2n=60 (Tateoka 1956 and Hsu 1964); Nath et al. (1970) have reported 2n=54 in this species from India. 1987 ThreeSpecies of PaspalumLinn. from SouthIndia 489

Discussion Paspalum is a large genus of about 400 species and the chromosome numbers of about 85 species reported so far range from 2n=20-160 (Darlington and Wylie 1955, Fedorov 1974). Most of the previous reports are in multiples of 10 which is the predominant basic number of this genus (Hiremath and Dandin 1975). Of the three species of Paspalum now studied, two

Figs. 4-13. 4, P. orbiculare. Mitosis, 2n=40. 5, P. commersonii. Mitosis, 2n=60. 6, P. orbi culare. Meiosis, n=20. 7, P. scrobiculatum. Meiotic metaphase I, n=20. Figs. 8-13. P. com mersonii. The stages of meiosis. •~1000. 8, prophase showing 60 univalents. 9, metaphase I

showing 60 univalents. 10, restitution nucleus. 11, anaphase II. The univalents have divided equationally and segregate to opposite poles. 12, telophase II. 13, a dyad. •~1000. 490 J. Christopher,P. SamRaj and K. GangadharanPillai Cytologia52 are tetraploids (2n=40) and one is a hexaploid (2n=60). Meiosis is found to be quite normal in P. scrobiculatum and P. orbiculare. However, in P. commersonii, total asynapsis has been observed in most of the PMCs and dyads of microspores are formed which eventually dis integrated resulting in total pollen sterility. An appreciable amount of seed set has been ob served in this species, which means seeds are formed independent of fertilization. This ob viously shows that the seeds are formed by some apomictic means. Incidentally apomictic development of the embryo has been reported in many species of Paspalum (Smith and Raleigh 1948, Narayanswamy 1954, Snyder 1957, etc). In P. secans, Snyder (1957) reported meiotic irregularities such as complete asynapsis of the chromosomes and the production of dyads of microspores. Smith and Raleigh (1948) and Irene et al. (1968) have reported irregular meiosis in P. dilatatum which is assumbed to be of hybrid origin propagated by apomictic means. However Gottschalk and Kaul (1980) have assumed that asynapsis is controlled by a polygenic system. Meiotic irregularities resulting in the break-down of microsporogenesis have been reported in apomictic grasses by other investigators also (Stebbins 1950, Nygren 1954, Snyder 1957, etc). Brown and Emery (1958) have recorded that apomictic species of grasses are most ly polyploids as in all angiosperms and ecologically apomixis is often found in weedy grasses. P. commersonii the presently studied apomictic species, is also a perennial polyploid and wide spread weed. There is considerable taxonomic confusion in the classification of these three species. Bor (1960) considers that the most obvious taxonomic distinction between these grasses is the dif ference in the number of nerves in the lower lemma and the annual or perennial habit. On morphological basis also these three species appear to be distinguishable, since they are highly divergent in form, habit and some morphological characters. P. scrobiculatum is the annual cultivated crop while P. commersonii, which some what resembles the former species in habit, is perennial, widely distributed and with a large range of habit growing as mesophyte or hydrophyte. But P. orbiculare is a distinct species with creeping culms and rooting at the nodes (Gamble 1934). The present cytological study has shown that P. scrobiculatum and P. orbiculare have re gular meiosis with n=20 and 2n=40, while in P. commersonii which has a somatic number of 2n=60, the meiosis is very irregular and apomictic. Clayton (1975) who studied the natural populations of these three species from West Aftrica, however suggests that the difference in lower lemma nervation stressed by Bor (1960) is not a reliable diagnostic character for dis tinguishing these three species as this character is highly variable and merges with one another in the West African specimens. Further, Clayton finds that the inflorescence character in the cultivated P. scrobiculatum merges completely with P. commersonii. The present cytological evidence indicates that the annual cultivated species P. scrobiculatum and the wild perennial species P. commersonii, showing close resemblances in morphological characters, inflorescence and habit (Clayton 1975) are distinct species. The latter appears to be of hybrid origin with apomictic as well as vegetative methods of reproduction. P. orbiculare is also distinct from the other two species in cytological and morphological characters.

Summary Cytological studies have been made on three species of Paspalum, two of which were col lected from natural populations while P. scrobiculatum is a cultivated species. P. commersonii consists of forms with diverse morphological varieties, occurring either as mesophyte or hy drophyte. P. scrobiculatum and P. orbiculare show regular meiosis with n=20 and 2n=40 . In contrast, in P. commersoniiwhich has a somatic number of 2n=60 meiosis is very irregular with total asynapsis of chromosomes. This species is probably of hybrid origin and apomictic . 1987 Three Speciesof Paspalum Linn. from South India 491

The results of the present cytological studies clearly indicate that variations in morphological characters and habit shown by these species are correlated with cytological distinctness. The refore these three taxa deserve separate specific rank as suggested by Bor (1960).

Acknowledgement

The authors are thankful to Dr. C. A. Ninan, Professor and Head, Department of Botany, for facilities and encouragement.

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