Cytological Studies on South Indian Araceae K. Ramachandran
Total Page：16
File Type：pdf, Size：1020Kb
Cytologia 43: 289-303, 1978 Cytological Studies on South Indian Araceae K. Ramachandran Departmentof Botany,University of Kerala,Trivandrum, India ReceivedSeptember 21, 1976 Araceae is a large family consisting of 1400-1500 species in 105 genera (Lawrence 1960), distributed largely in the tropics. The family includes three important tuber crops, viz. dasheen or taro (Colocasia esculenta Schott), tanier (Xanthosoma sagitti folium Schott) and elephantfoot yam (Amorphophallus campanulatus B1.) widely cultivated in most tropical countries. Other cultivated species of less importance are Alocasia indica and Typhonium trilobatum. The aim of the present investigation has been chromosome studies of cultivated and wild tuberous species of the Araceae. Cytological observations on 30 species, mostly indigenous to South India are pre sented in this paper. Karyological studies of four South Indian species of Amor phophallus have been reported elsewhere (Ramachandran 1977). Materials and methods All the materials investigated in the present study except Theriophonum minutum, Typhonium trilobatum and Arisaema wightii, were collected from different localities in Kerala, South India. Acetocarmine squashes of root tips and anthers fixed in 1:3 acetic alcohol were made according to the usual method. Root tips of plants with large or medium sized chromosomes were treated with 0.002M aqueous solution of 8-hydroxy quinoline at about 4•Ž for 3-4 hrs. and of plants with small chromosomes chilled for an hour in water at 4•Ž prior to fixation. For meiotic studies, parts of spadices with staminate flowers or stamens were directly fixed in acetic alcohol. The chromosome numbers of taxa determined in the present study are listed in Table 1. The tribes and genera have been arranged following Hutchinson's (1934) system of classification. The species have been arranged alphabetically. Classification of chromosomes as short (below 3ƒÊ), medium (3-6ƒÊ) and large (over 6ƒÊ) has been adopted from Delay (1951). Observations Acorns calamus Linn. (Sweet flag). This is a polymorphic species, wide-spread in the North temperate region, tropical Asia and Eastern North America. Materials examined in the present study were collected from shallow canals near Veli Lake, west of Trivandrum city. Root tip cells showed 45 chromosomes, which range between 0.75ƒÊ and 2.1ƒÊ in length (Fig. 1). Lasia spinosa Thw. It has a diploid chromosome number of 26 (Fig. 2). Chromo- 290 K. Ramachandran Cytologia 43 Table 1. Chromosome numbers in the Araceae comes vary from 1.6 to 2.7ƒÊ in length. Anaphyllum wightii Schott. The somatic complement consists of 26 chromosomes, which range between 1.8 and 5ƒÊ in length. A pair of chromosomes bear satellites 1978 Cytological Studies on South Indian Araceae 291 at the ends of long, thin connecting strands (Fig. 3). Meiosis is regular. Thirteen bivalents have been observed at first metaphase (Fig. 4). Pollen is 98% normal and the plant shows good seed setting. Dieffenbachia pieta Schott. Dieffenbachia is a tropical American genus. D. picta is found in shallow ditches in many localities in Trivandrum, and is evidently an escape from gardens. Materials of this species showed 2n=34 chromosomes (Fig. 5). They are large, between 4.0 and 10.7ƒÊ in length. Meiosis is regular. Seventeen bivalents have been found in PMCs at first metaphase (Fig. 6). However, no seed setting has been found in these plants. Steudnera discolor hort. This garden plant has a somatic complement of 56 chromo somes (Fig. 7). They range between 1.2 and 2.7ƒÊ in length, and most of them have median centromeres. Remusatia vivipara Schott. This species occurs at higher elevations in South India. Plants of this species showed a 2n chromosome number of 28. In length they range between 2.1ƒÊ and 3.3ƒÊ. Twelve pairs have median and the others submedian centromeres (Fig. 8). Colocasia antiquorum Schott. The tender leaves of this species are used as a vegeta ble. A few varieties differing chiefly in height of plant, pigmentation of petioles and veins, leaf blade and margin have been recognized. Cytological observations on two varieties, a diploid and a triploid are given below. C. antiquorum (diploid). This variety is characterised by green petiole and blade and light purple spot on the upper surface of leaf blade at the point of insertion of the petiole. Root tip cells of this variety showed 28 chromosomes, 2.5-4.8ƒÊ in length. Centromeres are median in six pairs and submedian in the others (Fig. 9). Meiosis is regular except for occasional lagging chromosomes at first anaphase. Fourteen bivalents are regularly found at first metaphase (Fig. 10). The pollen is 90% stainable with acetocarmine. C. antiquorum (triploid). This variety has dark purple petioles and veins and dark green leaf blades with purple margins. The somatic complement consists of 42 chromosomes. They are smaller (1.7-3.8ƒÊ) than those of the diploid (Fig. 11). C. esculenta Schott. Popularly known as taro or dasheen, this is an important tuber crop, extensively cultivated in many tropical and subtropical countries. Over 1000 horticultural varieties are grown in different parts of the world (Greenwell 1947). Seventeen varieties were assembled during the present study, which include 3 from Assam, 2 from Andhra Pradesh and one from Nepal, the other 11 being from Kerala State. Seven of these varieties (6 from Kerala and 1 from Nepal) were diploids (2n=28) and the others triploids (2n=42). Cytological observations on 292 K. Ramachandran Cytologia 43 1978 Cytological Studies on South Indian Araceae 293 two South Indian varieties, a diploid and a triploid are given below. C. esculenta (diploid). "Chutti". This is a medium sized plant, growing up to one metre in height. Leaves are green except for a pink spot on the upper surface of the blade at the point of insertion of the petiole. Fig. 12 shows the somatic chromosomes (2n=28) of this variety. Chromo somes vary in length between 2.1ƒÊ and 4.8ƒÊ. Centromeres are median in five pairs and submedian in the others. Meiosis is largely regular. Fourteen bivalents are found at first metaphase (Fig. 13). The mean number of xta per bivalent, averaged from 20 metaphase I plates is 1.7. Precocious separation of dyads at metaphase I and laggards at anaphase I are observed in a small proportion of cells. The pollen is 95% well formed (Fig. 14) and their fertility was confirmed by germination tests in 100ppm aqueous solution of boric acid. C. esculenta (triploid). "Kari Chembu". The plant grows to over 1.2 metres in height. Petioles and veins are purple. The somatic chromosome number of this variety is 42. They range in length between 2.1ƒÊ and 4.3ƒÊ (Fig. 15). PMCs show varying numbers of trivalents, bivalents and univalents at first metaphase (Fig. 16). The number of univalents ranges between 2 and 8. Analysis of 17PMCs showed a mean of 4.3 univalents per cell. Chromosomes lag at ana phases of both divisions. The pollen shows a wide range in size, About 33 are well-filled (Fig. 17). Sterility in Colocasia: Both C. antiquorum and C. esculenta are propagated ex clusively by vegetative means and sexual reproduction is not known. The sterility in C. antiquorum was investigated by Mayeda (1932) and Banerji (1934, 1937). Mayeda found certain irregularities in microsporogenesis to which he attributed the apparent sterility. Banerji confirmed Mayeda's findings. However, in the diploid varieties of both species of Colocasia investigated in the present study, the course of meiosis was regular and pollen fertility, as determined by staining and germination tests, was also high. The development of fruits and seeds also appeared normal. The embryos, though small, were well-formed. However, the seeds fail to germinate under natural conditions. It was shown that the embryos can be grown in culture medium (Abraham and Ramachandran 1960). This work has opened up possibilities of breeding in this crop so far considered impossible. Figs. 1-17. All figs, except 14 and 17, •~1000. Figs. 14 and 17 •~320. 1, Acorus calamus, 2n=45. 2, Lasia spinosa, 2n=26. 3, Anaphyllum wightii, 2n=26. 4, prometaphase in a PMC of A. wightii showing 13 bivalents. 5. Dieffenbachia pieta, 2n=34. 6, metaphase I in a PMC of D. pieta showing 17 bivalents. 7, Steudnera discolor, 2n=56. 8, Remusatia vivipara, 2n=28. 9, Colocasia antiquorum, 2n=28 (diploid). 10, metaphase I in a PMC of diploid C. antiquorum showing 14 bivalents. 11, C. antiquorum, 2n=42 (triploid). 12, C. esculenta, 2n=28 (diploid). 13, meta phase I in a PMC of diploid C. esculenta showing 14 bivalents. 14, pollen of diploid C. esculenta. 15, C. esculenta, 2n=42 (triploid). 16, metaphase I in a PMC of triploid C. esculenta showing trivalents, bivalents and univalents. 17, pollen of triploid C. esculenta showing the large proportion of sterile pollen. 294 K. Ramachandran Cytologia 43 1978 Cytological Studies on South Indian Araceae 295 Alocasia fornicata Schott. Materials of this species showed 2n-42 chromosomes (Fig. 18). In length, they vary between 2.6ƒÊ and 6ƒÊ. Alocasia indica Schott. This species is cultivated in South India. Its starchy root stock grows to large dimensions, up to 2.5 metres in height and a diameter of 30cm. It has a diploid chromosome number of 28 (Fig. 19). The chromosomes measure 3.6ƒÊ to 5.9ƒÊ in length. Ten pairs have median and the others submedian centromeres. Alocasia montana Schott. Root tip cells showed 28 chromosomes (Fig. 20). Their length ranges between 3.3ƒÊ and 5.5ƒÊ. Centromeres are median in all the chromo somes. Caladium bicolor Vent. Caladium is a tropical American genus. C. bicolor is one of the two species of Caladium commonly grown in gardens. It is now commonly met with in many localities, occupying waste lands and is an escape from gardens.