studies on trisomics in a jute hybrid

Genetica (1972) 43:473-488

STUDIES ON TRISOMICS IN A JUTE HYBRID

P. K. DAS 1) and R. D. IYER Division of Genetics, I.A.R.I., Delhi-12, India

Received August 25, I97Z / Accepted July Io, I972

Fifteen red pigmented trisomics were isolated in the F~ generation from the cross Corchorus olitorius L. × C. capsularis L. In the Fs generation a few green trisomics were obtained; more of these were isolated from the backcross generation. A detailed morphological and cytological analysis of the trisomic hybr id populations derived from the F3 and F4 generations is presented. The trisomics were scored for several morphologically differentiat- ing characters and most of them were intermediate between the parental species, a few resembling the olitorius parent more. Cytological studies showed the formation of abnormal sporads in trisomics with different frequencies indicating a misdivision at meiosis. This imbalance a t meiosis results in a higher percentage of pollen sterility in the trisomics as compared with the parents. Analysis of Mx of meiosis showed t h a t there were: differences in the frequencies of the various chromosome configurations between the two categories of trisomics; significantly higher t r ivalent frequencies per PMC in the green trisomics; in contras t significantly higher univalent frequencies per PMC in the red trisomics. No significant difference in chiasma for- mat ion was observed between red and green trisomics, nor between trisomics and their parental species. I t appears t h a t segmental homology in the parental chromosomes has probably resulted in varying degrees of preferential pairing in the trisomic hybrid.

Introduction

In the genus Corchorus two economically valuable fibre-yielding species of Jute are C. capsularis ('White' Jute), and C. olitorius ('Tossa' Jute). Both species are distinguished by their morphological differences. C. capsularis is characterised by its branching habit of growth, being shorter than olitorius (average height 150.0 to 250.0 cm.), having smaller flowers with fewer stamina and producing globose fruits in bunches of 3 to 4. In contrast, C. olitorius is very tall (300.0 to 360.0 cm.), comparatively unbranched, having larger

1) Present address : Dept. of Ag. Bot., Universi ty College of Wales, Aberyst- wyth, Wales, U.K.

474 P. K. DAS AND R. D. I Y E R

flowers, producing cylindrical fruits in pairs or single. Of the two, olitorius produces superior 'Tossa' fibre with greater strength, yarn- length and lustre. The 'White' fibre of capsularis is weaker, shorter, without any lustre. However, C. capsularis is more adaptive in the sense that it can withstand floods, salinity and drought conditions, is less sensitive to photoperiods and shows better response to fertilizer application than C. olitorius. It was felt that if the desirable characters of the two species could be combined through hybridization, this would result in an ideal jute plant. SWAMINATHAN et al. (1961) succeeded in producing two interspecific hybrids by crossing two red pigmented varieties of both species in which olitorius was used as the female parent. The trisomics were obtained in the F~ generation and were red pigmented. They were maintained by selfing as well as back crossing with either of the parents. Back crossing was done with a view to ascertaining the crossability of trisomics with the parents. In the F8 generation of selfing of red pigmented trisomics a few green trisomic plants were isolated for the first time. Simultaneously, more green trisomics were obtained from the back cross generation. This classification of red and green trisomics was done purely on the basis of presence or absence of anthocyanin pigmentation on the plant. A detailed cytogenetic study of red and green trisomics was carried out over a period of two years. Our analysis suggests a very interesting difference between red and green trisomics in relation to chromosomal association of the extra chromosome in PMC's of both trisomics at M1. In the present paper, we report the analysis of two groups of trisomics and suggest a possible explanation for their origin.

Materials and Methods

The trisomic population studied here was isolated from fourteen progenies derived from the following four cultures: (A) Four F4 progenies of the F~ trisomics (B) F2 of back crosses of four other trisomics with C. olitorius var.

JRO 620 (red pigmented) as the male parent, (C) F2 back crosses of five other trisomics with C. olitorius var. C. G.

(green pigmented) as the male parent (D) F2 of back crosses of one trisomic with C. capsularis vat. JRC 412

(red pigmented) as the female parent.

TRISOMICS IN JUTE HYBRID 475

The trisomics were identified morphologically according to the scheme described by SWAMINATHAN & IYER (1961), and used by SACHAR et al. (1967) and IYER (1968) and labelled at the time of thinning, when the crop was a month old.

The trisomic population was scored with regard to plant habit and vigour, basal diameter, height (tall, medium-tall or short), pigmentation (light red throughout, only stipules red or fully green), leaf shape and size (length/breadth ratio), flower (stamen), fruit characters (very short curved, short and medium long), seed fertility and germi- nation percentage at room temperature. Seed fertility was recorded from five randomly taken fruits from each trisomic plant at harvest.

For the cytological analysis of the trisomics, buds were fixed in Carnoy's fixative to which a few drops of ferric chloride solution had been added as a mordant, and squash preparations made in propiono- carmine stain. Abnormalities in spore formation and pollen sterility percentage were recorded. Chiasma frequency and distribution of various chromosome configurations were analysed at M1 of meiosis.

Results

MORPHOLOGICAL STUDIES

Out of a total of 1512 plants raised from the 14 different trisomic lines, 176 plants were picked out as possible tfisomics on the basis of seedling and adult plant characters as described by SWAMINATHAN & IYER (1961.). SACHAR et al. (1967.) and IYER (1968.). Of these, 123 were subjected to a detailed morphological study. Broadly two types of trisomics, viz. light red and fully green, were recognised on the basis of the presence or absence of anthocyanin colour on the stem and stipules. In the former class were also included those which had no reddish tinge on the stem, but showed bright red stipules. Out of 123 possible trisomic plants a total of 111 plants were scored as red trisomics and only 12 plants were found to be green. Most of the trisomics either red or green were characterised by unbranched axis, and showed a wide range of variation in height (range 90.0 - 300.0 cm). In general, both red and green trisomics were found to be shorter than their diploid parents. However, some of the trisomics were as tall and vigo-


rous as the olitorius parent. Most of the red and green trisomics were found to be very weak and susceptible to disease and pest attack. The shape of the leaf in the majority of red and green trisomics was very characteristic in being oblong-ovate or linear-oblong, but the most interesting feature were the double filiform appendages at the base of the margins, as compared to single ones in the parents (Fig. l a-b). The serration of the leaf margin was found to be intermediate between the parental species. Although the general shape of the fruits in the red and green trisomics resembled that in C. olitorius, the former were distinctly shorter with undulated ridges which fused at some places (Fig. 1 c). Even the tallest and most vigorous trisomics showed marked- ly stunted fruits at maturity. The number of seeds per capsule was much lower in the red and green trisomics than in olitorius diploids. However, the green trisomics produced more sterile seeds than the red trisomics. Different morphological features scored for red and green trisomics are presented in Table 1.

From the foregoing the following conclusions are drawn. Trisomics form a class with distinct morphological features. The majority of both red and green trisomics occupy a position intermediate between the two parental species C. olitorius and C. capsularis, except in relation to leaf characters and, to some extent, internode length where the trisomics tend to resemble the capsularis rather than the olitorius parent. In respect of their non-branching habit and fruit character, the trisomic plants tend to resemble C. olitorius. They recall the F1 hybrid phenotype, especially in fruit shape and poor vigour in that the morphology of trisomics is, generally, intermediate between the parents.

Since normal diploid sister plants (disomics) of trisomics obtained from selfings and back crosses are very much similar to olitorius parents in different morphological characters they are not described separately. These disomics were as tall and vigorous as olitorius. They were comparatively less branched and produced cylindrical fruits in pairs or single like the olitorius parent. Their flower character (flower size and stamen number) was very much similar to that of olitorius. Different proportions of red and green disomics were found to segregrate in sells and back cross generations.

Apart from the difference in anthocyanin pigmentation the red and green trisomics are very much similar in their morphological characters. The observations so far described prompt us to suggest, therefore,

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Figs. 1 a-f . Morphology and cytology of Comhorus: (a) Leaves of C. capsularis (Cc), C. olitorius (Co) and green tr isomics (GT). (Note the presence of p rominen t mult iple appendages of the base of the leaf margin) ; - (b) Leaves of C. capsularis

(Cc}, C. olitorius (Co) and red tr isomics (RT). The mult iple appendages can be clearly made out in RT; - (c) Capsules of C. capsularis (Cc), C. olitorius (Co) and of t r isomics (T). (Note a wide range of var ia t ion in f rui t l ength in trisomics, whose frui ts resemble those of t he olitorius parent . The t r isomic frui ts are cy- l indrical and s tun ted in size ; frui ts of capsularis are globose) ; - (d) Fi rs t meiotic me taphase of green tr isomic showing 611 + 1iii, t he t r iva lent is a chain ( - - - ) t y p e (× 4000); - (e) Fi rs t meiotic metaphase of green tr isomic showing 611 + lxlI in which t r iva lent is f ry ing pan type (-0). (× 2000); - (f) F i rs t meot ic me taphase of red t r isomic showing 7ii + 1i. Univa len t is ly ing apa r t (× 4000).

T R I S O M I C S I N J U T E H Y B R I D 479

that either the extra chromosome present in red and green trisomics is

one and the same, or different chromosomes with similar effects are involved. In an at tempt to clarify the situation the trisomics were further subjected to a cytological analysis.

C Y T O L O G I C A L S T U D I E S

Abnormalities in the/ormation o/spores. Abnormalities in the spore

formation after meiosis resulted in anything from monads to septads. Out of 344 cells analysed from red and green trisomics, 264 were normal tetrads and the remainder showed different types of sporads. The data on spore formation are summarised in Table 2. I t will be seen from the table that abnormal spores are formed in trisomics with different frequencies, thus indicating an imbalance in chromosomal

separation during reduction division.

TABLE 2

ABNORMALITY IN FULLY FORMED MICROSPORADS IN TRISOMICS

Sporad type Number of cells Percentage of total recorded

Monad 15 4.36 Dyad 10 2.90 Triad 7 2.03

Normal 264 76.74 TetradkAbnormal~ 6 1.74 Pentad 25 7.27 Hexad 7 2.03 Septad 10 2.90

Total: 344

Pollen sterility. Most of the trisomic plants showed a higher per-

centage of pollen sterility than either of the parents. The pollen fertility of the parents was 95.55 percent. A maximum of 52.17% sterile pollen grains was observed in the green trisomics, while in the red trisomics the percentage of pollen sterility ranged from 6.55 to 34.37%.

Chromosome association. Chromosome association was studied in the red and green trisomics at M1. In both classes of trisomics trivalents

480 P. K. DAS AND R. D. IYER

TABLE 3

M E A N F R E Q U E N C Y P E R P M C OF T H E D I F F E R E N T T Y P E S OF C H R O M O S O M E C O N F I -

G U R A T I O N

(For each plant 20 PMC's were analysed)

Plants 1 2 3 4 5 Mean

Chiasmata 14.00 14.10 14.00 14.00 14.00 14.0

Green I I I 0.833 0.877 1.000 0.833 0.907 0.890

trisomic II 6.167 6.185 6.000 6.208 6.419 6.195

I 0.166 0.0 0.0 0.166 0.139 0.094

Chiasmata 14.00 14.00 13.80 14.30 14.00 14.0

Red I I I 0.118 0.250 0.861 0.326 0.091 0.329

trisomic II 6.882 6.750 6.028 6.848 6.909 6.683

I 0.882 0.750 0.361 0.326 0.909 0.645

Disomie

C. olitorius

C. aapsularis

Chiasmata 14.00 14.00 14.00 14.00 14.00 14.0

I I I . . . . . .

I I 7.00 7.00 7.00 7.00 7.00 7.00

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Chiasmata 14.00 14.00 14.00 14.00 14.00 14.0

III . . . . . . II 7.00 7.00 7.00 7.00 7.00 7.00

I . . . . . .

Chiasmata 14.00 14.00 14.00 14.00 14.00 14.0

I I I . . . . . .

II 7.00 7.00 7.00 7.00 7.00 7 oo I . . . . . .

and univalents were observed in different frequencies (Fig. l d, e, f). In most of the trisomics trivalents were of the chain type (- - -),

only occasionally Y shaped and very rarely of the frying pan type O m (Fig. l d, e). In both trisomics ring and rod bivalents were form-

ed, rings being more frequent than rods as was also the case in the parents and disomics. No quadrivalents were seen. A summary of the distribution of chromosome configuration appears in Table 3. A ' t '

test (Table 4) was done to analyse the frequency distribution of the different types of chromosome configuration in red and green trisomics

as well as in parents and disomics.

T R I S O M I C S IN J U T E H Y B R I D 481

TABLE 4

THE t-TEST FOR THE FREQUENCY DISTRIBUTION OF THE DIFFERENT TYPES OF

CHROMOSOME CONFIGURATION IN RED (RT) AND GREEN (GT) TRISOMICS AND

PARENTAL (P) SPECIES

Configuration Item df t

I II GT-RT 4 4.912* * II GT-RT 4 4.127"

GT-P 4 12.761"* RT-P 4 1.926 N.S.

I GT-RT 4 4.516"*

*) Significant at 5% **) Significant at 1%

N.S. Not significant Disomics are not included in the present analysis separately since only 7ix are formed in PMC's of disomics as in the parental species.

From the analysis the following points emerge: (1) there is a signi-

ficant difference in the mean frequencies of trivalents, bivalents and

univalents between red and green trisomics (Fig. 2), (2) trivalent

frequency at the expense of bivalents and univalents is significantly

higher in the green trisomics (P>/ 0.01); on the other hand, (3) bivalent and univalent frequency are significantly higher in the red

trisomics (P>/0 .5 and P>~ 0.01 respectively), and (4) there is a signi-

ficant difference in bivalent formation between green trisomics and parents as well as disomics (P>/ 0.001).

Chiasma [requency. The mean chiasma frequencies for parents,

disomics and trisomies are given in Table 3. There are no significant differences in chiasma frequency between either the two trisomic

types or between the trisomics and parents or disomics. This shows tha t the presence of extra chromosomes does not cause any change in the

mean cell chiasma frequency but of course the mean frequency per chromosome is lower in the trisomics.

482 P. K . D A S A N D R. D . I Y E R

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Fig. 2. Formation of trivalents (3) and univalents (1) in two classes of jute trisomics at MI. A significantly higher number of trivalents (3) are formed in green trisomies. Univalents (I) and bivalents (2) are significantly more numer-

ous in red trisomics.

Discussion

The first report on a trisomic jute plant was by NANDI (1937) who recorded its spontaneous occurrence in C. capsularis. Following the observation of gametes containing eight and six chromosomes he

suggested that trisomics might have arisen due to mating of an abnormal egg cell (n + 1 = 8) with a normal pollen grain ( n = 7). The trisomics we are concerned with, are of interspecific hybrid origin (SwAMINATHAN 6: IYER, 1961). Altogether 15 trisomics were isolated in the F2 generation from the F1 hybrid of the interspecific cross between C. olitorius × C. capsularis made by SWAMINATHAN et al. (1961). The cytological analysis of the F1 hybrid showed the occurrence


of Iiii + 511 q- 1I in some cells and 611 -~- 21 in other (SwAMINATHAN & IYER, 1961 ; SACHAR, 1962). The irregular chromosome pairing in the F1 hybrid seems to be responsible for the formation and functioning of gametes with aneuploid chromosome number and the occurrence of trisomics in the F~ generation of the interspecific hybrid (SWAMINA- THAN • IYER, 1961; SACHAR et al., 1967; IYER, 1968.). The trisomics analysed here are the derivatives of the F~ trisomics. The trisomics isolated at F2 were either selfed or back crossed with either of the parents.

The present study indicates that in accordance with the findings of NANDI (1937) in a C. capsularis trisomic, AVERY & BLAKESLEE (1948) in Dalura trisomics, TSUCHIYA (1960) in barley, SEN (1965) in rice, and of GILL et al. (1970) in pearl millet the chief feature of the trisomic hybrids of jute is the reduction in growth rate and vigour, in the ma- j ority of the trisomic population analysed here. The trisomic mutant of C. capsularis found by NANDI (1937) had smaller, deeply serrated and narrower leaves without any appendages at all but with shorter petioles. Stamina were fewer in number, some of them transformed into petaloid structures. The trisomic hybrids described here have unbranched stems resembling those in the C. olitorius parent. The most striking feature occurring uniformly in both red and green trisomics is the leaf type, with the glossy linear-oblong lamina slightly curved outwards, and prominent double appendages present at the base of the leaf margin (Figs. 1 a-b). These appendages actually represent extended outgrowths of the last few pairs of teeth, and in some trisomics as many as four such extended 'whiskers' have been noted on each side. This appears to be a variable character because in some leaves the double appendages occur only on one side, the other being single. Another marked feature is the fruit morphology of the trisomic plants. It is observed that both green and red trisomics are characterised by cylindrical fruits of the olitorius type, but shorter in size. The trisomic studied by SACHAR et al. (1967) and IYER (1968) also showed such fruit morphology, leaf type and growth habit. It seems that these morphological features can be taken as phenotypic markers for not only red trisomics but green trisomics also. In fact, suspected trisomics identified by such phenotypic markers were always found to be trisomics following cytological analysis (IYER, 1968).

During the course of the present study an interesting observation


was made. The majority of trisomics either red or green occupy an intermediate position between two parental species, olitorius and capsularis in different morphological characters (Table 1). On the other hand, the majority of disomics (normal diploid sister plants of trisomics) are skewed towards the olitorius female parent in different morphological features. SWAMINATItAN & IYER (1961) also observed such skewed segregation in F2 and F8 plants of the F1 hybrid. They found that the recombinant phenotypes died at the seedling stage, probably due to lethal gene combinations. They suggested that ge- homes of C. olitorius and C. capsularis have differentiated in the direction of increased coherence, which automatically decreased the possibility of effective recombination. In that situation it is difficult to appreciate why trisomics would be in between two parental species in the expression of different morphological characters. It seems that the extra chromosome present in the trisomics plays an impor- tant role so far as different morphological characters are concerned. It may be possible that a certain amount of recombination takes place since the F1 hybrid showed 1iii + 511 + 1i in some cells and 61i + 2i in others, and that the extra chromosome present ensures the survival Of recombinants (which otherwise could have died) due to a gene dosage effect. However, the majority of the trisomics either green or red showed a change in negative direction from the normal diploid sister plants (disomics). For instance, both green and red trisomics had shorter height, thinner stem, smaller flowers with fewer stamina and smaller fruits. It can be assumed that the physiological action of a chromosome as a whole could account for the characters of a trisomic type varying from a diploid in the same direction (GooD- SPEED • AVERY, 1939).

The interesting feature is the recovery of fully green types from the selfed progeny of pigmented trisomic plants. At this point it would be useful to recall that the two parents of the original cross, from whose progeny the trisomics were obtained, were pigmented types. Two explanations are possible for this situation. One is that of chance outcrossing of the red trisomic with a fully green variety of C. olitorius growing in the same field. The partial sterility of the trisomics could enhance the possibility of natural crossing (ROY, 1965). Alternatively, the pigmentation may not be controlled by a single gene but by a series of independent genes (PATEL et al., 1944). Let us represent the


genotype of the C. olitorius parent as AApp and of the C. capsularis parent as aaPP, A and P being the genes for pigmentation in the two species respectively, and assume that the presence of at least one dominant gene is essential for the expression of pigmentation. The hybrid between these would be AaPp and the trisomic hybrid may be represented as AaaPp. Four types of gametes with one extra chromosome are possible from such a trisomic plant, namely, Aap, aaP, Aap and aap. As an egg cell with an extra chromosome functions normally in jute (NANDI, 1937; SACHAR et al., 1967) we further assume that only pollen carrying normal complements of chromosomes functions, then we would have four types of male gametes, namely, AP, Ap, aP, and ap. So, on selfing, the phenotypic ratio between red and green trisomics would be 15:1. Thus, it is not surprising to get green trisomics from the selfed progenies of red trisomics. However, the present situation is further complicated due to the appearance of two types of red trisomics where one type shows only red stipules whereas the other is red throughout. Unless a detailed genetic study is available to establish the genetics of pigmentation the present explanation is only tentative.

The cytological analysis in the present study indicated distinct differences in number and type of chromosome associations at meiosis° I between red and green trisomic hybrids. The frequency of trivalents is significantly higher in green than in red trisomics. On the other hand, the red trisomics form a significantly larger number of univalents which in fact supports the findings of SACHAR et al. (1967) who observed mostly 711 + 1i in trisomics of the F2 generation. 51ANDI (1937) also recorded the occurrence of 711 + 1i at metaphase-I in the trisomic mutant of capsularis studied by him. At present it is not very clear how more trivalents are formed in the PMC's of the green trisomics. I t can only be assumed that the differential behaviour of the extra chromosome in red and green trisomics is due to the difference in homology between the chromosomes of the parental species. In fact, chromosomes of capsularis are larger than those of olitorius. In C. capsularis chromosome size ranges from 3.7 to 1.7~, in olitorius from 2.7 to 1.3 [~ (SHARMA • ROY, 1958). The F1 hybrid of the interspecific cross between these two species showed l lii + 511 + 1i in some cells and 611 + 21 in others (SWAMINATHAN • IYER, 1961 ; SACHAR, 1962). I t seems that the chromosomes of the two species are not wholly


homologous and thus pairing among partially homologous segments may give rise to varying degrees of preferential pairing. The higher

frequency of trivalent formation in green trisomics is probably due to total affinity while the frequent occurrence of a univalent extra

chromosome in the red trisomics may have resulted from varying degrees of preferential pairing in the hybrid.

The question is whether the same chromosome or different chro-

mosomes are involved in the red and green trisomics. The striking morphological similarity for different characters between the red and

green trisomics would suggest that either the same chromosome or different chromosomes with the same effect are involved. If the latter is true one should expect that the same genetic processes are in operation for different characters and therefore, different characters are influenced by the same genes. I t is difficult to conceive how different chromosomes would have genes with similar effects which in turn, would control different morphological characters in order to produce such a remarkable resemblance in different morphological

features between the red and green trisomics. On the other hand, the differences in chromosome configurations as observed in the red and

green trisomics at MI of meiosis would indicate that the extra chromosome present in the PMC's of the red and green trisomics is not one and the same. In fact, green trisomics form more trivalents in their PMC's.

Whereas more univalents are formed in the PMC's of the red trisomics. If the same chromosome is involved one should not expect such a

significant difference in chromosome association (Tab. 4). This situation can further be illustrated by the fact that the percentage of pollen sterility in the case of green trisomics is almost twice that of

the red trisomics. In this connection it is to be noted that the green trisomics showed a higher percentage of seed sterility than the red trisomics (Tab. 1). I t would thus appear from the present study that

most likely two different chromosomes are involved in the red and green trisomics. At present we do not know which chromosomes of the parental species are associated with the two classes of trisomics. To understand this it is necessary to investigate in detail their chromosome morphology and that of the two parental species C. olitorius and C. capsularis somatic karyotype or pachytene analysis.

The present investigation indicates the possibility of obtaining different kinds of trisomic plants. Since trisomics obtained from the


cross C. olitorius × C. capsularis may be complex due to segmental differences in the chromosome sets of parents, it would be worth while initiating attempts to produce them from crosses between auto- tetraploids and diploids. Since haploids occur occasionally in jute (JACOB & SEN, 1961), they could also be used in the establishment of trisomic series. The available knowledge about the linkage groups (GHOSE, 1957) shows that linkage analysis in jute is still in the element- ary stage. The development of a trisomic series in jute will greatly facilitate linkage analysis. The isolation of trisomics can also be used in developing substitution lines which will help in the selective addition of the desirable chromosomes of one parent to the genome of the other. This is of great importance since interspecific hybrids in this crop are difficult to obtain.

REFERENCES

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GHOSE, R. L. M. (1957). Linkage studies in rice and jute. Ind. J. Genet., 17: 329-335.

GILL, B. S., S. S. VlRMANI & J. L. MINOCHA (1970). Primary simple trisomics in pearl millet. Can. J. Genet. Cytol., 12: 474-483.

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SEN, S. K. (1965). Cytogenetics of trisomics in rice. Cytologia 30: 229-238.


SHARMA, A. K. & M. ROY (1958). Cytological studies on jute and its allies. I . Agronomia lusit. 20: 5-15

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SWAMINATHAN, M. S., R. D. IY~R & K. SVLB~A (1961). Morphology, cytology and breed ing behaviour of hybrids between Corchorus olitorius and C. ¢apsularis. Curt. Sci. 30: 67-68.

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studies on trisomics in a jute hybrid

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