1961 117

Interspecific and Intergeneric Hybrids of spontaneum L. I. Functioning of gametes .1

P. A. Kandasami

Sugarcane Breeding Institute , Coimbatore, Received June 27, 1960

Cytogenetical studies during the last 20 years have revealed that unreduced

gametes function in S. officinarum when used as a pistil parent in crosses

with S. spontaneum and reduced gametes function when Sclerostachya , Narenga, Erianthus etc. are used as staminate parents. This led Partha

sarathy (1946) to state that "when the genetical or family relationship is

near, reduced gametes function and when the relationship is more distant

the compatibility of the cross is presumably due to the functioning of the

non-reduced gametes". On this view, S. officinarum and Sclerostachya

should be considered as more closely related than S. officinarum and S.

spontaneum. Evidence of a fairly close relationship between S. officinarum

and Sclerostachya has in fact been found, 5 chromosomes of officinarum

having been found to be homologous with five of Sclerostachya (Parthasa

rathy 1948). Raghavan (1951a, b) pointed out a number of instances wherein

gametic contributions were not consistent with family relationships, e. g., crosses between S. officinarum on the one hand and Sorghum, Zea and even

Bambusa on the other which belong to different genera altogether and yet

contribute haploid gametes on each side, and crosses within the same genus,

namely, S. officinarum •~ S. spontaneum and S. officinarum •~ S. barberi wherein the gametic constitution was 2n+n. He also pointed out that the behaviour of the species S. barberi towards S. officinarum and S. spontaneum and of S. robustum towards S. officinarum and S. barberi was contrary to the view that gametic contribution depended on family relationship.

In the course of his work for the degree of M. Sc., the author had to carry out studies on a number of intraspecific, interspecific and intergeneric crosses. The type of gametic contribution observed in these crosses is discussed in this paper.

Material and methods

The material of study comprises varieties belonging to four species of

Saccharum, namely, S. officinarum, S. barberi, S. robustum and S. spon taneum and the allied genera, Sclerostachya fusca, Narenga porphyrocoma,

Erianthus ciliares and Sorghum. A few hybrid cane varieties, viz., Co.

1 Forms a part of the thesis submitted for M. Sc. degree of Madras University.

Cytologia 26, 1961 9 118 P. A. Kandasami Cytologia 26

205, Co. 285, Co. 421, Co. 467, POJ. 2725 and CAC 87 were also used in crosses. In all, forty three crosses were effected, S. spontaneum being one of the parents in all of them. The number of seedlings studied in each cross, the chromosome number in the offspring and the gametic contribution inferred are given in the Appendix. Eleven triploid seedlings (2n=96) obtained by selfing Saccharum spontaneum Coimbatore (2n=64) were also included in the study. The crosses were effected under bagged conditions. The bamboo tube technique (Raghavan 1953) was adopted in crossing to reduce chances of selfing. The seedlings were raised in cages to control contamination with foreign fluff. For determining mitotic chromosome numbers, root tips were fixed in Langlet's (1937) solution, washed, dehydrated and embedded according to LaCour's (1937) schedule. Microtome sections of root tips were cut 12 pin thickness and stained with gentian violet. For the study of meiotic chromosomes, aceto-carmine (Belling 1926) and acetic-orcein (LaCour 1941) smears of the pollen mother cells were prepared and permanent mounts of these were made.

Results

Comparative studies of the morphological and anatomical characters of the parents crossed and their progenies revealed the genuineness of hybridity of the latter. The meiotic and mitotic chromosome numbers of the hybrid seedlings also confirm their hybrid nature.

A critical study of the crosses and selfs effected indicate the functioning of n+n, 2n+n and deficient n+n gametes (Vide Appendix). In two crosses, viz., S. officinarum Var. Vellai •~ S. spontaneum Uganda-G. 3009 (Kandasami and Rao 1957) and S. officinarum Var. Manjri Red •~ S. spontaneum Ceylon

SH. 445, reduced gametes seem to have functioned on the S. officinarum side. This is the first finding of the kind in crosses in which S. officinarum is used as a pistil parent with S. spontaneum. Functioning of haploid gametes in a cross between S. officinarum and S. spontaneum (2n=96) was reported at about the same time by Sam Price (1957).

In general, haploid gametes have functioned in the intraspecific crosses of S. spontaneum, in interspecific crosses, S. barberi •~ S. spontaneum, S. robustum •~ S. spontaneum and their reciprocals. However, functioning of

2n+n as well as n+n gametes has been noticed in the self of S. spontaneum

Coimbatore. But, the former kind of gametes were far less as compared to the latter. Out of the two hundred and forty two selfed seedlings only

11 showed combinations of unreduced egg gametes with reduced male gametes

(Kandasami 1960). This tendency on the part of S. spontaneum Coimbatore was observed even in crosses with S. officinarum and other genera like 1961 Interspecific and Intergeneric Hybrids of Saccharum spontaneum L. 119

Sclerostachya, Narenga, Erianthus etc. (Vide Appendix) . With the exception of POJ. 2725, varieties having spontaneum chromosomes when crossed with S. spontaneum clones contributed haploid gametes . But, POJ. 2725 behaved differently with S. spontaneum Coimbatore and S . spontaneum Glagah as staminate parents. While it contributed a reduced gamete when crossed with the former an unreduced gamete was contributed when the latter was used in the cross. In the crosses Co. 421 with S. spontaneum Coimbatore and S. spontaneum Glagah as staminate parents deficient n gametes were contributed by Co. 421 as previously reported by Raghavan and Kandasami (1957). Moreover, the gametic contribution of different varieties even in the self same species is not perfectly similar. For example, when S. spontaneum Coimbatore is crossed with Saccharum, Narenga, Erianthus etc., unreduced gametes function while other spontaneum variants like SES. 184A, SES. 248 and Uganda-G. 3009 contribute reduced gametes.

Discussion

The results presented above go to show that there is a general pattern

of gametic contribution for individual varieties of different Saccharum species

though it is variable to some extent according to partners involved in crosses

with them and, at times, even in the reciprocal crosses of the self-same

varieties. At least in S. officinarum, which contributes either n or 2n

gametes according as the male partner is S. robustum or S. spontaneum, there is reason to believe that both types of gametes may be being produced

simultaneously but are selectively fertilised. In the cross S. officinarum •~

S. spontaneum SES. 248 (2n=40), functioning of 2n+n gametes is noticed

while in the cross S. spontaneum SES. 184A (2n=40) •~ S. officinarum (which

can be taken as similar to a reciprocal of the former cross) functioning of

haploid gametes of both the parents is seen. The relationship between the

male and the female in a cross cannot be closer than in a self. In the

present studies, it has been pointed out that differential behaviour with regard to gametic contribution is observed even in selfs of some of the spontaneums.

Further, it is known that in the interspecific crosses, S. officinarum •~

S. spontaneum and S. officinarum •~ S. barberi in which functioning of 2n+n gametes is inferred, the F1 progeny is pollen fertile. On the other hand, in the intergeneric crosses, S. officinarum •~ Sclerostachya, Narenga and

Erianthus wherein haploid gametes of the parents are supposed to function, the F1 seedlings are completely pollen sterile. Thus it would appear that the relationship inferred on the basis of gametic contribution (Parthasarathy

1946) is contrary to the view that fertility of progeny is an index of close relationship or otherwise between the parents involved in the crosses. For these reasons, it would appear that gametic contribution cannot be a sure indication of genetic relationship between the parents.

9* 120 P. A. Kandasami Cytologia 26

However, in the case of the different species studied the pattern of behaviour of each clone is more or less uniform but for a few exceptions. Out of 481 studied 18 were exceptions, 7 in officinarums, 11 in spontaneums, nil in barberi and nil in robustum. Therefore, it may be possible to use gametic contribution of a clone as an additional criterion together with other criteria such as morphological and anatomical characters for identification of its species. For such purposes, crosses of the clone will have to be made with at least a few different types of the spontaneums.

Summary

The paper relates to the observations made on the gametic contributions from the male and female sides in a number of intra and interspecific crosses in Saccharum and crosses with allied genera. The findings are as below:-

1. Chromosome numbers in all F1s of intraspecific crosses involving five S. spontaneum variants, namely, S. spontaneum (Coimbatore), S. spon taneum (Glagah), S. spontaneum (Holes I), S. spontaneum SES 248 and S. spontaneum S. H. 546 (Egypt) indicated functioning of only haploid gametes on the part of both the parents.

2. When S. spontaneum Coimbatore was selfed, a few giant forms with three times the haploid chromosome number of the parent were obtained in addition to a large number of diploid plants with n+n gametic con stitution. The functioning of diploid egg gametes is therefore to be inferred in the former.

3. The species S. barberi and S. robustum were also found to contri bute only haploid gametes in both way crosses with S. spontaneum variants.

But, S. officinarum was generally found to contribute the diploid egg gametes in crosses with S. spontaneum, except when crossed with certain variants

G. 3009-Uganda (2n=120) and S. spontaneum S. H. 445-Ceylon (2n=128).

4. In crosses between S. spontaneum and a few hybrid cane varieties having some spontaneum chromosomes in their genetical make up the functioning of only haploid gametes was observed. However, one instance of functioning of diploid egg gamete on the part of the pistil parent, POJ.

2725 and two cases, viz., Co. 421 •~ S. spontaneum Coimbatore, Co. 421 •~

S. spontaneum Glagah wherein egg gametes with a deficient haploid number had functioned were noticed.

5. Functioning of both 2n+n and n+n gametes was observed in interspecific as well as intergeneric crosses, viz., S. spontaneum •~ S. offi cinarum and S. spontaneum •~ Sclerostachya, Narenga and Erianthus.

6. The functioning of n+n as well as 2n+n gametes was noticed in crosses between different varieties belonging to the same species and even in selfs. It would therefore, appear that gametic contribution is unsuitable as a criterion of genetic relationship between the types involved in crosses .

7. It may be possible to use the gametic contribution of a clone as 1961 Interspecific and Intergeneric Hybrids of Saccharum spontaneum L . 121 an additional criterion along with morphological and anatomical characters for identification of its species .

Acknowledgement

My grateful thanks are due to Dr. T. S . Raghavan, Retired Second Cane Breeding Officer, Sugarcane Breeding Institute , Coimbatore and late Shri N. L. Dutt, ex-Director, Sugarcane Breeding Institute, Coimbatore for their guidance in conducting the investigations . I am highly thankful to Dr. N. R. Bhat, Director, Sugarcane Breeding Institute, Coimbatore for critically going through the manuscript and making helpful suggestions in the writing of the paper.

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and Kandasami, P. A. 1957. Breeding behaviour of Co. 421 in relation to its cyto

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numbers in interspecific hybrids. Bot. Gazette, 118: 146-159. 122 P. A. Kandasami Cytologia 26

Appendix 1961 Interspecific and Intergeneric Hybrids of Saccharum spontaneum L. 123

(Continued)

CBE-Coimbatore SES-Spontaneum Expedition Scheme