Session - Thursday, ~ 3 r d April, 2.30 p.m.

MR. K. R. GARD, Chairman

~h~ Chairman invited MR. STEVENSON to present his paper.

Paper

THE USE O F SELFING AND INBREEDING WITH SUGARCANE - G. C. STEVENSON

B.W.I. Central Sugar Cane Breeding Station, Barbados

INTRODUCTION

The sugarcane varieties at present in commercial cultivation are, with few ex- ceptions, the results of spectacular advances in breeding which followed the large-scale use of interspecific hybridisation within comparatively recent years. They are, of course, propagated vegetatively, being mainly=complex polyploids and aneuploids which are cytologically unstable. The breeding methods by which they were developed are ad- mittedly empirical, requiring the annual production of very large seedling populations and the use of a rigorous testing technique. Such advances as have been made in Barbados are due to the use of male-sterile types as seed-bearing parents, followed by selection based on the progeny test applied to seedling populations of known parentage, when subjected to a full West Indian growing season. These methods are continuing to provide variety improvement. Moreover, it is reasonably anticipated that further advances are possible for many years, particularly as the range of variability in parent material has been as yet only partially explored, and many introductions of new and valuable varieties to the breeding plots are being made.

The potential value of a more fundamental approach to sugarcane breeding has long been recognised by geneticists. Theoretical considerations of selfing and line-breeding have been made by ST EVENS ON^^^ who had previously pointed out the problems to be overcome in using breeding material of so complex a c$tological constitutionz3. I t is concluded, however, that there is justification for research into the development of more precise breeding methods, but that such work should be, for the present, complementary to the successful methods now in use, as it may be many years before commercial varieties are obtained.

Considerable advances have been made during recent years -in the cytological analysis of sugarcane types: it is shown below that in some instances a knowledge of the cl~romosome constitution of varieties has revealed relationships unsuspected previously, and that where there is ~ncomplete male-sterility of "female" varieties, or occasional occurrence of apomyctic seedlings in the populations, parentages of varieties produced by empirical breeding methods must be regarded as putative only. In such cases the method of analysis by progeny testing loses its validity, and a serious limitation to progressive advance in breeding is introduced.

The use of inbreeding and line-breeding has been followed by useful advances in the yield and quality of many plant species. I t is also in general use for animal breeding:

References f i p 519-520.

CANE BREEDING SECTION

for instance, recent work points to the value of the method for increasing egg-production in fowls. The genetical and statistical principles underlying the inbreeding method have been presented by FISHER^^, and it is not proposed to review here the results obtained in plant breeding generally. They are well enough known in the case of maize, for which perhaps the most spectacular yield increases have been obtained.

Homozygous inbred lines are comparatively easy to develop in self-fertile diploids, and are a pre-requisite for the production of improved hybrids by the method under consideralion. In the case of sugarcane, which is far more complex cytologically, the process is likely to be slower and less straightforward, but there is no theoretical reason why success should not be obtained eventually. The following sections aim to set out the cytological basis for pure-line development in sugarcane, and to describe some aspects of the use which has already been made of selfs and inbreds in breeding work and in commercial cultivation.

CYTOLOGICAL

The genus Saccharum exhibits a very wide n~orphological and cytological range. Its forms are particularly diverse in the tropics of the Old World, where it is endemic. Five species - S . oficinarum, S . spontaneum, S . robustum, S . barberi and S . sinense - are recognized, but recent research has shown that only the first three are to be regarded as truly distinct species. S . barberi and S , sinense are probably hybrid forms which arose naturally from S . oficinarum and various forms of S. s$ontaneum long ago13"z2. At Coimbatore, an interesting attempt is being made to elucidate the origin of S , barberi by back-crossing repeatedly to S . spontaneum and S , oficinarhm. By these means it is hoped to reduce the chromosomes of these two species in the supposed hybrid to their basic numbers. S . robustum, only comparatively recently discovered, and whose range in morphology has not yet been fully explored, can as yet be given only tentative species status. GRASSL~~ regards it as a possible ayestor of S . oficinarum in the New Guinea area.

All species and hybrids of Saccharum are inter-fertile to some extent, and conse- quently it is a simple matter to produce hybrid seedling populations, which will show considerable variation and can be subjected to a selection procedure for variety develop- ment. I t is on account of this inter-fertility that the empirical breeding methods in general use have been elaborated, and have been successf~~l in yielding improved varieties. S. sinense shows a considerable degree of sterility, and consequently has been little used in breeding work, and there is a large range in fertility experienced in derivatives from crosses involving the various S . s$ontaneum forms.

In Saccharum oficinarum, the so-called "noble canes", the usual chronlosome number is 80, and meiosis is regular. Univalents are only occasionally seen. Hence fertility is high. Male-sterility is rare, and most varieties are used as male parents in controlled breeding work. A number of aberrant forms in S. oficinarum have been reported: many of the original chewing canes from the Pacific Islands show go, 100, or some other number16, and undoubtedly some such naturally occurring varieties pre- viously ascribed to S. oficinarum are of hybrid origin. Occasionally 120 chromosomes are found in varieties originally raised from seedls. The latter are doubtless explained by a chromosome doubling in the female embryo-sac, a phenomenon not infrequently met with when S , oficinarum is used 'as female parent in interspecific hybridisation with S . s$ontaneuslnz (q.v. infra.).

G. C. STBVENSON

The various forms of S. s@ontaneum occur in a wild state, and are particularly diverse in India, where the cultivated hybrid varieties of the so-called S. bavberi and S. sinense originated. There is a considerable range in chromosome number within S. spo~taneunz, forms with 64, 80, 96 and 112 being typical of different ecological areas. Other numbers, too, have been reported, and there seems no doubt that the origin of several of the forms now in existence must have been by natural hybridisation between the simpler representatives within the speciesle. S. spontaneum, in all its forms, is

strongly male-fertile, and consequently is used as pollen-parent in controlled breeding worB.

Saccharurn robustum is ill-defined as yet, and a number of the forms which have been assigned to it are probably of hybrid origin. The type form, 28 NG. 251, which was the first of the species to be described after the United States expedition to New Guinea in 1928, has 84 chromosomes, is cytologically regular, and is highly male-fertile in crosses with the "female" varieties of S. o@ci?zarum.

The cytology of interspecific hybrids in Sacclzarum has been studied by several investigators, and the pioneer worli of BREMER~ has been corroborated and extended. BREMER first described the cytology of oficinarum-s$ontaneum hybrids, in which "nobilisation", or chromosome doubling on the female side occurs in the o@cinarum gametes in the first cross and the second generation back-cross. He also coined the apt word which has come to be generally used in referring to the phenomenon.

NARAYANASWAMY~~ first described a fusion of the two inner megaspore nuclei, which resulted in diploid megaspores, particularly in S. o@cinarum. BREMER'S recent interpretatlqn6 follows similar lines but depends upon a splitting of the chromosomes in the innermost megaspore cell aiter a normal reduction division. In either case the phenomenon is post-meiotic, with consequent important genetic implications, and JANAICI A M M A L ~ ~ has shown that parthenogenetic seedlings, presumably derived from such diploid eggs, show considerable variation. DARLING TON^ is inclined lo suspect the functioning of supernumerary aposporous embryo-sacs in S. o@cinaruvn when crossed with S. spontaneuvn, but the writer has so far been unable to find any evidence in support of such a theory from his preparations in Barbados. There is some evidence that oc- casionally diploid male gametes may function. It is interesting to note that although the process does not normally take place in intervarietal crossing within S. o@cinarum, occasional individuals from such parentage have been reported to show 120 chromo- somesls*. In the individuals from o@cinarum-robusturn crosses, the "nobilisation" process has not been seen. This indicates some homology between the chromosome sets of the two species, and also explains why in breeding work the development of satisfactory commercial varieties is slower by the use of these back-crosses than in the case of the ~flcinavurn-spontaneum line.

PARTHASARATHY~~ considers that the functioning of reduced gametes in interspecific hybridisation is evidence of close genetic or family relationship, and that when the relationship is distant, compatibility in crosses may be effected by the functioning of unreduced gametes. The theory has some points to commend it, but breaks down in the case of the cross S, oficinarum x Sclevostachya, where reduced female gametes function,

* LI and MA (loc. cit.) list the noble cane variety E.K. z as showiilg 120 chromosomes, with meiotic configuratioil a t first mefaphase 57 I1 + 6 I. It is not clear, however, why in another paper ill the same publication they show the same variety as hairing 80 chromosomes in the pedigree of P.0. J. 2725.

References p p . 519-520.

512 CANE BREEDING SECTION

indicating a possible close affinity, whereas the first back-cross is effected by the function- ing of unreduced eggs. Moreover, cases are known in which, in the same intergeneric cross, both reduced and unreduced gametes are able to functionzz.

In interspecific hybrids, meiosis is frequently irregular. There is typically a number of unpaired chromosomes, which may or may not be included in the gametes, as they often tend to lag behind the bivalents at first anaphase. Such failure of chromosome pairing is due to lack of homology, and is to be expected in interspecies hybrids. The fact that the univalents are probably derived from the s$ontaneum parent in crosses involving nobilised'hybrids, and that they are likely to carry desirable genes, is significant in relation to the rate at which variety improvement may be attained in breeding.

Chromosome behaviour on selfing is dependent upon the extent to which meiosis departs from the regular. In varieties of S , ofici~zarum, selfing gives rise preponderately to 80-chromosome individuals, and i,s as regular as is to be expected in a polyploid species, where duplicated chromosome sets are present. Progress towards homozygosity is likely, for evident reasons, to be slower in polyploids than .in diploids.

In interspecific hybrids, where a number of univalents occur at meiosis, selfing results in progeny which may vary from one to another in chromosome number. Varying figures are formed at meiosis, and, in addition, univalents may or may not be included in the gametes. Consequently, selfed progeny may show more or less chromosomes than the parent, or the same number. Populations which have been examined show, in fact, most individuals with less chromosomes than the parent, due no doubt to the frequent non-inclusion of univalents in gamete formation. LI and MA^^ record for four selfs of P.O. J. 2878 (zn 121) the following chromosome numbers: 123, 121, 118, 112. Two other selfs of P.O. J. 2878 examined in Barbados27 showed 119 and 118 respectively. Five selfs of B. 41211, another nobilisation of S. s$ontaneum derived,from both Indian (zn 64) and Javan (zn 112) forms, and having itself 123 chromosomes, showed 121,120,120,120 and

VARIATION IN *HYBRID CROSSED AND SELFED SEEDLING POPULATIONS

Variation observed in seedling populations is due to differences in environment and differences in genotype. EVANS^^ showed in Mauritius that in a clonal population of the variety R.P. 6, where variation was environmental only, stool weights varied from 1.5 to 112.9 lb. with a mean of 35.3 lb. and a coefficient of variability 49.8. ST EVENS ON^^ showed, also in Mauritius, that a plant-cane population of the variety M. 134132, established from single-eye cuttings, showed a coefficient bf variability 39.9 at the time of reaping. In seedling populations, genetic variation, upon which progressive advance by selection depends, is superimposed upon this wide environmental variation. In the field, it is impossible to distinguish in any individual first year seedling the contributions made by environmental and genetic variation in the phenotype, for the usual statistical methods are only applicable at later stages in the testing procedure. I t is for this reason that selection of first-year seedlings based on weight per stool, and made without the necessary safeguards, may be disappointing and unreliable.

Variation in seedling populations in comparison with that in clonal material was studied in Mauritius by ST EVENS ON^^. By means of a randomised layout, it was possible to obtain an estimate of differences in genetic variation between populations from different parentages. I t was shown that the trosses yielding the highest selection per-

G. C. STEVENSON 5I3

centages did not always show the widest degrees of genetic variation, but were generally characterised by a high mean population performance. In Barbados at the present time pgressive improvement in first year populations is being achieved by the use of seedling performance figures as a guide to the choice of parent varieties.

Selfs have so far been comparatively little used in breeding work with sugarcane. I t has been usual to provide for the maximum possible variability by using intervarietal and interspecific crosses, and there is a good deal of justification for such action. With the "noble cane" (S . oficinarum) varieties, which formed the bull< of the world breeding material until comparatively recent times, there is little doubt that crossing is preferable to selfing for direct production of new varieties, particularly where, as in Barbados, there has been some degree of pure line development in the early breeding worl~l9. Here, indeed, crosses between individuals in different "lines" are shown to be preferable to crosses within the same line. The situation is different, however, now that the great majority of the commercial varieties and breeding canes are interspecific hybrids, often of complex genealogy. On cytologica1 grounds, it is to be expected that a considerable degree of variation might be shown in selfed populations from such varieties.

Variation in a selfed population in comparison with that in crosses is well illustrated by analysis ef data recorded in Barbados in 1933. In that year selfs from the variety B(3o)L. 7, a nobilisation of P.O. J. 2364, were planted at random among individuals from crossed populations, and individual records of stool weight and sucrose in juice were made for batches of seedlings twice during the crop season-early and late. Diagrams of frequency distribution for stool weight and juice quality have been prepared from the data, and are presented in-Figs. 1-4. The crosses used for comparison are: Ba. 11569~ Ba. 6032, Ba. 11569 x B. 417, M.E. 157 x B.H. ro(12) and P.O. J. 2725 x Ba. 6032, of which the first two are "noble cane" crosses (S . oficinarunz) and the others nobilisations of S. spontaneum (112-chramosome Javan form).

Fig. I. Weight distribution curves for selfs and crosses. Early reaping.

I t is seen from the diagrams that the distribution curves for the selfs do not differ appreciably in form from those for the crossed seedlings. Also, mean population perfor- References @ p . 519-520. 33

found to give very good performance figures, and selection percentages from them as * first year seedlings were comparativeiy high.

G. C . SlhVhNSUN

election of potential commercial varieties. Detailed performance figures are not available for selfs raised in later years, as

selfing has been little used in the general breeding programme, and then mainly as a means to check observations on male sterility. For the 1952 reaping season, however, a population of selfs from B. 41227 (a tri-species hybrid) raised for cytogenetical study, had been grown for selection with the general population of crosses. These selfs were

- B (30) L7 self5

-0- ME 157 x BH 10 (12) -x- POJ 2725 x Ba 6032

Fig. 4. Sucrose per cent juice distribution curves for selfs and crosses. Late reaping.

show any reduction in vigour-or quality. Sugarcane breeders who maintain, in justifi- cation of the use of male-fertile varieties as seed ~a ren t s . that anv selfs which might

Selfs in first-year populations from interspecific hybrids do not, therefore, necessarily

" occur in the seedling populations would be recognizable through lack of vigour, are under a delusion which is without doubt due to experience with, or theoretical consider- ations of, plant material less complex cytologically. With selfs from the varieties of S. oficinarum, the so-called "noble canes", on the other hand, recent observations in Barbados would appear to indicate that some 102s of vigour is evident even in the first generation. Similar conclusions have been reached, it is understood, from observations made in Australia arid Hawaii. Such results are to be expected on cytological grounds, and are in conformation with the theory that progress towards homozygosity by selfing will be more rapid in S. oficinarum than in interspecific lines.

Refevences p p . 519-520.

516

REEDING C A N E S

show lack of vigour in proof of this is the s cultivation in the West Indies,

B. 3337 was selected in 1933 from the seedling population discussed in the preceding section. I t was never grown on a large scale in Barbados, but achieved great popularity in Trinidad, being.the major commercial variety in 1951, and representing 37 % of the area reaped. Yields in excess of 80 tons of cane to the acre have been recorded for B. 3337 in Trinidad, and it ratoons well and recovers rapidly from damage by the froghopper pest. As a breeding cane in ~arbados , B. 3337 has been used extensively as a male parent, and has produced several seedlings which are up to commercial standard. Two of these are in use on estates in Barbados and elsewhere in the West Indies, and others are still undergoing trials.

B. 37172 was until recently regarded as being from the cross P.O. J. 2878 x B. 2935, the latter a "noble" variety. Cytological examination has shown, however, that its chromosome number is 119, and that it almost undoubtedly arose as a self of P.O. J. 2878, which is known to shed appreciable quantities of pollen sometimes, and to be un- satisfactory as a female parent for this reason. B. 37172 is a standard commercial variety in large-scale cultivation at present in Trinidad, Jamaica, Guadeloupe, St. Lucia and other parts of the West Indies. I t is particularly useful where rainfall is very high, for under such conditions it outyields most other varieties and gives cane of very good juice quality. I

Thus, two selfs are at present contributing largely towards the sugar production of the West Indies. Others are under trial in Barbados, and may later be grown commer- cially.

The Indian variety Co. 421, which until recently was grown quite extensively in British Guiana, was originally thought to be from the cross P.O. J. 2878 x B. 3412, and therefore a nobilisation of the famous Javan variety. I t was shown at Coinibatore, however, that its chromosome number is 118, so that (as in the case of B. 37172) the recorded parentage must be incorrect. DUTT and RAO~O found from previous records that during the breeding season in question, P.O. J. 2878 had been also crossed, in the same row, with a S. sflontaneum nobilisation, Co. 285 (zn IIZ), and they conclude that Co. 421 may have arisen as a chance pollination of P.O. J. 2878 by this variety. They do not, however, appear to have considered the possibility of a self of P.O.J.2878, which the present writer thinks more likely. The morphological and cytological characteristics of Co.421 could be satisfactorily explained by its origin from such a selfing. C0.421 is being used extensively in the breeding work: in Barbados, and has given a number of varieties which show great promise.

Selfs have been used with considerable success as breeding canes in Australia. The varieties Trojan, Orion and Akbar were raised from a cross between a self of Korpi and Co.270, while 31M.Q.228, which was a parent of Eros and Vesta, was from a self of Korpi crossed with Badila. These breeding lines were regarded as so successful that a long-range programme of selfing for pure line produ'ction was begun in 192813. Although the work was interrupted during the war years, it is understood to1 have been since

References &b. 519-520.

G. C. STEVENSON 517

In view of the above considerations, it can be concluded that first-generation selfs from interspecific hybrids can be used with success, both as commercial varieties and in breeding work. Such is not the case with selfs from S . o@cinavum varieties. Nor is it considered likely that later-generation selfs from the hybrids would be of immediate use commercially, as progress towards homozygosity would almost certainly be associa- ted with some loss of vigour. The results of work now in progress in Barbados should produce useful information on this subject.

THE USE O F INBREEDING

Judging from published work, there have been few comprehensive studies on the use of inbreeding with sugarcane. Workers at the Canal Point Station, Florida, U.S.A., many years ago proposed a programme of selfing, crossing and back-crossing to build up stocks of known constitution3, but the results do not appear to have been publish- ed, and the work is no longer in psogress, so that it is impossible to comment upon any results which might have been obtained. Correspondence with the Station in 1g4g2, and a visit made there by the writer in 1950, showed that other lines of work had super- seded the original programme, and there was no data as to whether the onset of male- sterility or the super-abundance of non-arrowing clones had brought the work to a conclusion. Either could become a limiting factor to progress under the sub'tropical *conditions of Florida.

The potential danger of inbreeding when using varieties of S . oficinarum for imme- diate development of new commercial types was recognized by McIntosh at an early stage in the work at the Barbados Station. He was able to distinguish five "1ines"'within the Barbados "noble" varieties, which had been evolved by selection of seedlings from open-pollinated arrowslO. Crosses between varieties in different lines were shown to be more successful than those within any line. This is understandable on the assumption that some degree of homozygosity had resulted from the line development.

With the large-scale use of nobilisation and crossing between complex interspecific hybrids, chromosome numbers are higher and parent varieties embody far more segre- gating genes than in S , oficinavum crosses. Selection in selfed and inbred seedling popu- lations is therefore quite effective in this type of breeding work. Cytologically, it is known that irregular meiosis may account for chromosome alterations in such selfing and inbreeding, and that within the limits set by linkage, which damps the expression of variability in polygenic inheritance, the results may be equally as effective as in out- crossing. Several well-known and widely grown commercial varieties are more or less closely inbred, as is shown below.

P.O. J.2878, perhaps the best known, and at one time probably the most popular commercial variety in the world, is inbred to some extent, having P.o.J.100 on both sides of its pedigree :

I P.O. J.2878

References pp . 519-520.

518 CANE BREEDING SECTION

P.O. J.2878 is undoubtedly the best of the series of seedlings raised from P.O. J.2364 xE.K.28 in Java. The female parent, P.O. J.2364 (zn 148) may have 30 or more uni- valent~ at'meiosis, and with E.IC.28 gave seedlings with chromosome numbers ranging from 107 to 121. P.O.J.2878 has 121, and therefore includes a high proportion of the univalents fyom P.O. J.2364, many of which are almost certainly derived from S. sfion- taneum, and carry some desirable characters. P.O. J.2878 is still one of the best breeding varieties in the world, being the parent of such useful varieties as P.O. J.2961 and P.O.J. 3016 in Java, B.37172, B.41227 and B.4362 in Barbados, Co. 421 in India, M.134132 in Mauritius, F.IIO and F.116 in Taiwan, H.32-8560 in Hawaii, Eros, Jason and Vesta in Australia, M.L.3-18 in Cuba, and M.336, P.R.902, P.R.905 and P.R.1000 in Puerto Rico.

P.o.J.3016, a more recent Javan variety, is very closely inbred:

Kassoer I

P.O. J.100 I I

An analysis of this interesting pedigree shows that the same two varieties-P.O. J.- 2364 and E.K.28-are maternal grandparents and paternal great-grand-parents, and only eight varieties from a possible thirty are represented in a four-generation pedigree. P.O. J.3016 has, however, only ~ o g chromosomes, and there has been a loss of several derived from S. sfiontaneuun, which carry resistance to mosaic disease among other characters. The variety is closer in its characteristics to the "noble" canes than is P.O. J.2878, and is, in fact, susceptible to mosaic disease.

The Australian sugarcane breeders have used the inbreeding method. Fbr instance, the variety Pindar has in its pedigree 28M.Q.1370, produced from a Badila seedling, Q.813, back-crossed to Badila itself.

In Barbados, some of the varieties in commercial cultivation have been produced from a mild inbreeding programme. An example is B.41211, which occupies about 10%

p.0. j .236~ ~ . k . 2 8 I

I P.O. J.2878 P.O. J.2722

u I

P.O. J.2940

I I

of the cane area in the island at present:

M.B. Ba.11569 S. s#ontaneum I I I I

I I

Close inbreeding has not been practised in the general breeding programme in Barbados for a number of reasons. At present, however, nqw that suitable parent Refevences 9p. 519-520.

G. C. STEVENSON

I / material from interspecific hybridisations involving a number of distinct genealogical

1 lines is available, there is reason to suppose that planned inbreeding methods would satisfactory results.

DISCUSSION

The effects of selfing, and the use in breed~ng of pure liiles developed by selfing in a number of successive generations, have been studied comprehensively In a number of slmple d~ploids. The pioneer worlr was done in the Uilited States w ~ t h malze, and ~t is In that crop that the most spectacular yield Increases have been obta~ned by the use of hybr~ds ~nvolving two or more selfed llnes It is usual In the early stages of pure l ~ n e development, and before homozygos~ty IS reached, to encounter a loss of v~gour. This loss vanes between individual lines developed from the same foundation parent, and although on theoretical grounds a pure l ~ n e equally as vigorous as the original parent is possible, the chance of its occurrence IS remote, for yield IS polygenlc, and oil account of hnlrage and the uncovering of deleterious recessives, it is unlilrely that all favourable factors would be comb~ned in one genotype. For a statistrcal treatment of the factors associated with yield decreases in selfed lines, the reader is ~eferred to Fisher's "Theory of Inbreeding" 12

In sugar cane, there is no reason to suppose that S oficznarum vaneties would behave d~fferently from simple d~ploid plants on selfing, although on account of polyploidy ~t is lilrely that pure 11ne development would be slower It has been shown above that there is, In fact, some loss in vlgour on selfing S offcznavum varieties, but the worlr in Barbados has not yet progressed far enough to indicate how long the development of homozygosrty, so far as yield factors are concer~~ed, will take.

Some account has been given above of the extent of variability met with In selfs from inter- specific aneuploids of sugarcane I t was concluded that loss of vlgour need not occur 111 the early stages of a selfed line, and that such selfed i~ldividuals can serve a useful purpose both as commercial variet~es and for breed~ng Further progress with the development of selfed lr~ies from interspeclfic hybrids must depend upoil chromosome behavioui a t meiosis Failure of pairlilg is usually due to lacli of homology 111 the chromosomes, aud IS to be expected ~n species hybrids As the chromosomes are so small, it is impossible to d~s t i i~gu~sh under the microscope those derlved from d~ffereilt specles, but ~t is l~lrely that the un~valents, 111 the case of sugarcane hybrrds, are fiorn the S . spontaneum ancestor In any event, such univalents are lilrely to be lost in the early stages of pure hne development, due to non-mclus~on in the gametes, so that eventual l~nes will probably be closer to the "noble" canes than were the foundation vanetles. T h ~ s may or may not be des~rable, according to the type of variety envisaged from the eventual combinatioil of selfed lines

The assumptioi~ of a stable chromosome constitution IS a pre-requis~te to pure line development, and the charactei~st~cs of each line will naturally depend upon which of a number of possibihties lalies place 111 the early stages of ~ t s development by selfing In this connect~on, work with species hybrids In other genera is significant in Nzcotzana, for instance, ClauseilG found that on selfing a hybrid from dzgluta x Tabacum, the dzgluta chromosomes were eliminated 111 a few generations On the other hand, ~t IS known that 111 Crepzs a true-breeding i~lterspecific hybrid can be extracted a t the F4 generat~on, whose cytolog~cal stab~lity is explained by autosyildes~s resulting from the polyplold nature of one of the parent species' In sugarcane, it IS to be expected on theoretical grounds that selfed lines embodying a t least a proportion of the s+ontaneum chromosomes could be produced, as some autosyndetic pairlng among such chromosomes IS likely. Similarly, and for reasons already given, it IS to be ant~cipated that pure lines representing different degrees of "i~obilisatlon" could be developed from the same foundat~on hybrid

REFERENCES

BRANDES, E. W. 1950. Rept. of Proc. I n t . Soc. of Sug. Tech. 7th Congvess, Brisbane. BRANDES, E W . 1949. Correspondence. BRANDES, E. W. and SARTORIS, G. B. 1937. Sugarcane: Its Origin and Improvement. U.S.D.A. Yearboolr for 1936.

* BREMER, G. 1928-34. De cytologie van het Suilrerriet. Arch. Suilierindus. Nederland Indie, Med. Proefsta. Java-Su~kerindus. BREMER, G. 1948. PYOG. 8th I n t . Genetzcs Congress Stockholm. ' CLAUSEN, R. E. 1928 Unzv. Calif. Pub . Bot . 2 : 177. ' DARLINGTON, C. D. 1937. Recent Advances in Cytology. J. and A. Cl~urcl~ill.

DARLINGTON, C. D. 1951. Correspondence. DEERR, N. 1949. The History of Sugar. I . Chapman and Hall.

lo DUTT, N. L. and RAO, J. T. 1950 Coimbatore Canes in Cultivation. The Indian Central Sugarcane Committee, New Delhi.

CANE BREEDING SECTION

l1 EVANS, H. I934 Sug. Res. Stat. Mauritius, Bull. 3. l2 FISHER, R. A. 1949. The Theory of Inbreeding. Oliver aud Boyd. l3 GARD, K. R. 1950. Re@. proc. 7th Gong. Int. Soc. Sug. Teclz. Brisbane. l4 GRASSL, C. 0. 1946. Jour. Arnold Arb. 27. l5 GRASSL, 'C. 0. 1951. Correspondence. l " ~ ~ ~ ~ r ~ AMMAL, E. K. 1936, Ind. Journ. Agric. Sci. 4 : 7. l7 JANAKI AMMAL, E. K. 1943. JOUY. Genetics 45. l8 LI, H. W. and MA, T. H. 1951. List of the Chromosomal Numbers of Sugarcane Varieties and

Sugarcane Relative Plants. Rept. Taiwan Sug. Exfit. Stn. NO. 7. Is M c h ~ o s a , A. E. S. 1932 Agric. Jour. Barbados Dept Scz. and A ~ V ~ C . I (I). 20 NARAYANASWAMY, S. I940 Ind, Journ. AgrXc. Sci. 10.

PARTHASARATHY, N. 1947. Journ. Ind. Bot. Soc. Iyengar Comm. Vol. 22 SINGH, T. S. N. 1934. Ind. Joum. Agric. Sci. 4. 23 STEVENSON, G. C. 1943. The Present aud Potential Value of Sugarcane Breeding. Emp. Jour. Exp.

Agric. XI : 41. 24 STEVENSON, G. C. 1945. Sixteenth Ann. Refit. Sug. Res. Stn. Mauritius. 25 STEVENSON, G. C. 1950 Rept. Proc. 7th Cong. Int. Soc. Sug. Tech. Brisbane.

STEVENSON, G. C. 1950. PVOC. Meetzng of B. W.I. Sug. Tech. Jamazca. STEVENSON, G. C. 1952. Unpublished.

DISCUSSION

THE CHAIRMAN, in opening the discussion, complimented the author on hls paper, which he thought raised many points which were of interest and importance to all sugarcane breeders. In referring to selfed populations from P 0 J 2878 raised in Queensland, he observed that there had not beell any wide variatioil between individuals, and that 111 general, crossed seedlings with this variety as one parent, had been more vigorous He aslted whether this had been the experience in Baibados

MR. STEVENSON said that selfs from different varieties did differ in populatioil vigour and in the extent of variability betweed indlvlduals He had not examined sufficient selfs from P . 0 J 2878 to make any useful comparisoil with those from other varieties

MR DE SORNAY asked how many seedlings were usually obtaiiled m selfed,populations in Bar- bados In Mauritius the experieilce had beell that very few seedlings were obtained, and iiidicatlons were that they were inferior 111 weight and sucrose content to those obtaiiled from crossks, though no sigilificant difference could be established

MR STEVENSON replied that in Barbados the numbers of seedlings obtained from different selfings varied from none to several thousands. There was sometimes self-sterdity although pollen production appeared to be normal In most cases selfed populations of a few hundreds had beell obtained without difficulty. In reply to MR GRASSL, he described how selfiilg was carried out in the ilormal bleeding lanterns, which remained in positloll until the fuzz was ready for removal During the flowering period, the arrows were gently shaken by tapping the stalks, in order to ensure a good pollen shed

DR BRETT enquired whether sib-ciossing was used MR STEVENSON explained that in certain cases where desirable seedlings were pollen-sterile,

both sib-crosses and back-crosses had been used There was no theoretical oblection to this, but progress towards pure line productloll would be slowed down, and pollen-fertile individuals were always preferred if suitable ones were available

MR. GRASSL observed that work of this nature might well be done on a co-operative basls, a number of Stations worlung on different breeding liiles

THE CHAIRMAN stated that in Queenslaild s&lection in inbred lines for high quality had been started, but difficulties had been experlenced on account of sterility and non-flowering

DR WARNER said that in Hawaii one oblection to the selfing method was that selection must be through flowering types, and flowering was regarded as detrimental in commercial cane under theii co~lditio~ls

MR. STEVENSON agreed that flowers were necessary for continuing the development of an iilbiecl line, but poiilted out that the same llmitatioil existed in ally breeding method, and need not be more serious in inbreeding than in out-crossing There appeared to be no reason why 11ght-flower~ng inbred liiles could not be developed, which on inter-crossing a t a later stage might yield light-flowering or 11011-flower~ng hybrlds for commercial use

MR. GRASSL spoke of the potential value of inbred liiles m which such features as mosaic dlsease iesistance were present in a homozygous form

THE CHAIRMAN referred to DR CHILTON'S paper on the effect of temperature on pollen-pro- duction, and suggested that temperature control might be effective In lilducing pollell production in varieties which were ilormally pollen-sterile

G. C. STEVENSON 5z1

DR. CHILTON thought that temperature might have an effect not only on the production, but also on the quality of seedling populations. MR. GRASSL agreed.

MR. DE SORNAY said that in his opinion this effect, althoughpossibly of some application in sub- tropical areas where pollen product@ was limited by low temperatures, was ,of little importance in the tropical areas.

MR. STEVENSON, summlng up the discussion on factors affecting pollen production, said it should be borne in mind that male-sterility could be attributed to two causes - genetic, due to a brealrdown In meiosls, and environmental, due to the suppression of anthesis. Some varieties always shed pollen freely, and some did not shed a t all, where the cause was genetic. In between was a range in which shedding was effected by environmental condltlons, and might be improved experi-

THE CHAIRMAN enquired how many chromosome counts ~t was necessary to make in order to establish the number accurately.

MR. STEVENSON replled that it would depend upoil the technique employed, the quality of the preparations used, and the type and adjustment of the microscope. With the modern methods of pre-treatment, whereby cl~romosomes could be contracted and spaced, accurate counts could be made easily with practice He relied malnly on somatic mitoses, as these were easily obtained a t any time of the year, and was inclined to suspect meiotlc counts in interspecific material on account of the difficulty of dlstinguishillg univalent chromosomes from bivalents, and of the occurrence of precocious splitting.

The Chairman presented the following paper in the absence of the authors.

Paper

CANE COLLECTING IN NEW GUINEA IN 1951

J. H. BUZACOTT and C. G. HUGHES

Bureau of Sugar Ex$erinzent Stations, Queensland

INTRODUCTION

Theisland of New Guinea, which abuts on the equator from the north-eastern corner of the Australian continent, has long been a happy hunting ground for the cane collector. The natives there have cultivated noble canes in their gardens as an important item of diet for a very long time and, as an added interest to the modern cane explorer, the non- noble saccharums also occur in wide variety. In the coastal areas there is an abundance of non-nobles growing wild, indicating that perhaps this island is the centre or one of the centres of origin of the genus; the central highland areas, in marked contrast, apparently have no wild canes occurring naturally and the non-nobles in that region, because of their value for fences around the gardens, are almost as much products of the native agriculturalists' selection as are the nobles.

There is no doubt that various unrecorded introductions of cane were made into Australia from New Guinea in the early years of the sugar industry in this country but the first official collecting expedition was organized in 1893 In that year, E. COWLEY, an officer of the Queensland Department of Agriculture, twice visited New Guinea and collected canes along the Gulf of Papua on the southern shore of the island. The next expedition has from the same Department and under the charge of H. TRYON, an en- tomologist and pathologist; it returned in 1896 with, amongst other varieties, the famous noble cane Badila which to this day is an important contributor to Queensland's sugar yield. I t came from Milne Bay at the eastern tip of the island. A third expedition (in 1908)