Cytologla 37: 155-161, 1972

Chromosome Numbers in edule

B. T. Roach1 ReceivedJuly 16, 1970

Within the diverse Saccharum, there exists a small group of clones charac terised by production of peculiar swollen and aborted inflorescences . The known geographical range of clones of this type includes Fiji, New Guinea, Indonesia and Malaysia. Clones of this group are cultivated by the indigenous peoples of these areas and the aborted inflorescence , which forms a cauliflower-like mass in the sheath, is used as a vegetable. Classification of these clones has remained an enigma to both workers and taxonomists. Although there have been rare reports of normal development of the inflorescence of some of these clones (Warner and Grassl 1958), classification has of necessity been made on vegetative characters alone. For convenience, the classification of this group as Saccharum edule Hassk. by Jesweit (1925) and Grassl (1946) has been fairly generally accepted. As clones of this group are of little direct economic value and abortion of the inflorescence prohibits their use in breeding programmes, there is relatively little published information on chromosome numbers of S. edule. This paper reports chromosome numbers of 9 clones of S. edule and the pos sible origin of S. edule is discussed.

Review of Literature Chromosome counts which are available in the literature for clones of S. edule are listed in Table 1, together with the origin of the clones. There are obvious anomalies in the counts reported by different authors for the clones 28NG38, 28NG201, Duruka memanu and Fiji 1. The chromosome counts reported by Grassl (1946) and Artschwager (1948) were from unpublished studies of chromosome counts in the files of the Division of Sugar Investiga tions of the United States Department of Agriculture. A number of other workers, for example, Moriya (1944, 1950), Parthasarathy et al. (1946), Price (1957) and Price and Daniels (1968) have been unable to agree with counts from this source. Erroneous counts from this source have been responsible in the past for the assumption of undue cytological complexity in Saccharum robustum Brand. & Jesw. ex Grassl, as noted by Price (1957). It also seems probable that counts from this source may have confused rather than clarified our knowledge of S. edule.

Materials and methods

Clones of S. edule used in this study were derived from the variety collection maintained at the Colonial Sugar Refining Company's Experiment Station at 1 Plant Breeder, C. S. R. Field Experiment Station, Macknade, Queensland Australia. 156 B. T. Roach Cytologia 37

Table 1. Previously published chromosome numbers in S. edule

Table 2. Chromosome numbers of some clones of S. edule

Macknade, Queensland. They had been introduced from various sources and the geographical origin of the clones is shown in Table 2. The source of clones SE15, SE34, SE78 and SE97 is probably not well known in sugarcane literature. These clones are selections from a much larger collection made in New Guinea under the direction of J. S. Womersly, Chief of the Division 1972 Chromosome Numbers in Saccharum edule . 157

of Botany, Department of Forests , Lae, during the 1950's. At the request of the Fiji Government, these selected clones were introduced into Fiji in 1960 through the Colonial Sugar Refining Company's quarantine facilities in Sydney , Australia and Lautoka, Fiji. The numbers are Womersly accession numbers , whilst the SE prefix (Saccharum edule) was added by the Colonial Sugar Refining Company in Sydney.

For chromosome counts, cuttings were germinated at approximately 30•Ž.

Germinating buds were pre-treated with 0 .2% colchicine and fixed in 1:3 acetic alcohol. Following hydrolysis for 10 minutes in 1N hydrochloric acid, leaf tissue was squashed in aceto-orcein.

Results and discussion Results of chromosome counts are shown in Table 2. The count of 2n=70 for 28NG201 confirms the count of Bremer (1934) rather than the count of 2n=84 -88 reported by Artschwager (1948). It was also possible to confirm exactly the count of 2n=70 reported by Price and Daniels (1968) for Fiji 1, for which Artschwager (1948) reported 2n=68-70.

Figs. 1-3. 1, somatic metaphase in SE97. 2n=60. •~1800. 2, somatic metaphase in clone SE15. 2n=70. •~1800. 3, somatic metaphase in clone SE34. 2n=80. •~1800.

The count of 2n=60 for the clone SE97 is the first reported instance of this chromosome number in S. edule. The chromosome complement of this clone at somatic metaphase is shown in Fig. 1. Mitotic metaphase of clones SE15 (2n=70) and SE34 (2n=80) is shown in Figs. 2 and 3 respectively. From the chromosome counts now available for S. edule, it seems probable that erroneous unpublished chromosome counts, which were quoted in the literature, have suggested undue cytological complexity in this species, as they did in S. robu stum. 158 B. T. Roach Cytologia 37

The evidence now available suggests that S. edule may consist of a relatively simple polyploid series with occasional aneuploids. There have been two main theories for the origin of S. edule. Lennox (1938) and Brandes et al. (1938) proposed that these clones were variants of S. robustum. Certainly the hard rind and dry pith of these clones resemble S. robustum. Ste venson (1965) also considered that S. edule had arisen as the result of mutations. S. robustum consists of two main cytological types, namely those with 2n=60 and 2n=80 chromosomes (Price 1957). It has also been shown (Price 1965) that clones with 2n=70 chromosomes occur in New Guinea. There thus exist in New Guinea, forms of S. robustum and its derivatives which could have given rise to clones presently recognised as S. edule by mutation at the level of a single chro mosome or gene. Whilst the change from the normal inflorescence of S. robustum to that of S. edule is a drastic one, radical changes from relatively minor mutations have been recorded in other (Stebbins 1950). However mutation to the S. edule form would confer complete sterility. It would thus seem necessary to assume that similar mutations occurred in all precursor forms of the present range of S. edule types. A hybrid origin for S. edule has been proposed by Price (1963) and Grassl (1964). Grassl (1946) considered that the Fijian forms were different from those of New Guinea and originally pro posed them as deri vatives of Erianthus maximus Brongn. In a later article Grassl (1965) sug gested that the 2n= 70 chromosome forms had arisen Figs. 4-5. 4, partial emergence of infloresence in clone 63MQ810R.

5, spikelet detail of 63MQ810R. •~14. from a backcross of an F1 of S. officina rum (2n=80)•~Miscanthus floridulus (Labill.) Warb. (2n=38) to S. officinarum with a n=30 gamete from the F1 functioning. However Price and Daniels (1968) consider that S. edule was introduced into Fiji by the migrating ancestors of the 1972 Chromosome Numbers in Saccharum edule . 159

Fijians and that possibly only two clones were introduced . Grassl (1965) proposed that the New Guinea forms had arisen from crosses of Miscanthus floridulus with S . robustum, with both 2n=60 and 2n=80 chromosome forms of S. robustum involved. The Maprik area of New Guinea was considered the most likely centre of origin, as the greatest number of clones and the most extensive plantings occur in that area (Grassl 1964). Janaki Ammal (1941) con sidered that the S. edule clone Taboe Trebeq was a hybrid between Saccharum and a member of the Maydeae.

Four unusual clones, with chromo some numbers in the

range 2n=48-50 and thought to be pos

sible intergeneric hy brids, have been re

ported previously

(Roach 1968). These clones, which were found as seed

lings amongst the normal progeny of

crosses of S. offici narum•~S. sponta

neum, are thought to have arisen from

pollen contamina tion of the S. offici

narum parents by some other genus

(possibly Pennisetum or Imperata). Two

of these clones, 63 Figs. 6-7. 6, detail of inflorescence of S. robustum clone 57NG22.

MQ192R and 63 •~ 14. 7, detail of inflorescence of S. edule clone SE15. •~30. MQ810R, regularly produce aborted inflorescences and in this respect resemble miniature forms of S. edule. In the 1969 flowering season, several inflorescences of 63MQ810R developed further than usual and partly emerged from the sheath. The type of inflorescence produced and spikelet detail are shown in Figs. 4 and 5. The inflorescence retains some similarity to a Saccharum inflorescence (Fig. 6) in having both sessile and pedicellate spikelets. However, both spikelets are sterile, being devoid of any reproductive organs. The rachis and pedicel are greatly swollen and fleshy in comparison to the thin, hard structures in Saccharum. Length of the pedicel and the distance between successive spikelets along the rachis are also greatly increased. 160 B. T. Roach Cytologia 37

Whilst the inflorescence of 63MQ810R differs markedly from that of S. edule (Fig. 7), it indicates that the inflorescence can be greatly modified as the result of a single cross. S. edule is a cultivated species and it seems probable that the indi genous peoples in its areas of origin would have selected and retained naturally occurring forms with the largest and most palatable inflorescences. Thus the clones presently found in these areas may represent the extremes of naturally occurring forms. Clones of S. edule have been rather difficult to maintain in the variety collec tion at Macknade and their lack of vigor suggests they may have poor survival value under natural conditions. Thus many forms of S. edule which were less desirable as a source of food may have become extinct. Whilst the hybrid origin of S. edule seems the most likely explanation at pre sent, suggestion of putative parents at this stage would be little more than specula tion. Results of this and previous work show that forms with 2n=60, 2n=70 and 2n=80 chromosomes occur. As it seems probable that the basic number of the Andropogonae is x=5 (Celarier 1956), the range of putative parents for S. edule is probably considerable.

Summary

Chromosome numbers of nine clones of S. edule are reported. Six of the clones were found to have 2n=70 chromosomes and two had 2n=80 chromosomes. The remaining clone was found to have 2n=60 chromosomes, this being the first reported instance of this chromosome number in S. edule. The cytological complexity in this species, suggested by earlier chromosome counts, may be incorrect. S. edule probably consists basically of a simple polyploid series, with occasional aneuploids. The probable origin of this species is discussed. It seems possible that the clones presently recognised as S. edule may have resulted from intergeneric hybridi sation.

Acknowledgements

I wish to thank the Colonial Sugar Refining Company Ltd. for permission to publish the results of this investigation.

Literature cited

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