Extraction of AADD component of Triticum aestivum (AABBDD)

Hereditas 68: 151 ~ 158 (1971)

Extraction of AADD component of Triticurn aestivum (AABBDD) K. A. SIDDIQUI

Department of Agricultural Botany, The University, Reading, England]

(Received March 13, 1971)

A synthetic tetraploid, Tritieum aegilopoides X Aegirops sguarrosa (AADD), was crossed with seven varieties of Triticiim aestivum and with one synthetic hexaploid, Tritieum durum var. Carleton X Aegilops squarrosa. Two AADDB pentaploids were produced from 2 varieties of T. aestivum, Chinese Spring and A.T. 38 and a pentaploid AADDB hybrid was obtained from the cross involving the synthetic hexaploid, T. durum var. Carleton X Ae. sgiiarrosa. The pentaploid involving var. Chinese Spring was backcrossed to the hexaploid parent and a general backcross was attempted with the pentaploid from A.T. 38, but n o seed was obtained. The three generations of the synthetic tetraploid, T. aegilopoides X Ae. sqirarrosa were quite uniform morphologically, but there was marked variation in seed fertility. There is no evidence that variation in the fertility of the synthetic tetraploid was due to irregular meiosis or to the occurrence of aneuploids. The problems connected with the extraction of AADD component of T. aestivum are discussed.

Theoretically three tetraploid (2n = 4x = 28) com- ponents, AABB, BBDD and AADD can be extracted from any variety of the allohexaploid (2n = 6x = 42), Triticum aestivum, AABBDD. The extraction of the tetraploid component, AABB of T. aestivirm has been reported by many workers (KERBER 1964; SIDDIQIJI 1964; KALTSIKES et al. 1968). The first step in such a n extraction programme is the production of pentaploid hybrids. Since a large number of natural tetraploids with the genomic constitution AABB (e.g. varieties of Triticirm dirrum and Triticum dicoc- cum) are available it is easy t o produce AABBD pentaploids (SIDDIQUI 1969a). These pentaploids are fairly fertile for utilization in subsequent backcrosses (SIDDIQIJI 1969b).

Natural BBDD and A A D D tetraploids have not been reported in the Triticinae. It is therefore necessary to use synthetic amphiploids (tetraploids) for the production of the corresponding pentaploids. Such a n approach with respect to the BBDD component of T. aestivum has been reported earlier (SIDDIQUI 1964; SIDDIQUI and JONES 1969). The present paper describes an attempt to extract the tetraploid AADD component of T. aestivum. A synthetic tetraploid,

T. aegilopoides X Ae. squarrosa, AADD, produced by SEARS (1941) was used in this work. The behaviour of this synthetic tetraploid is also discussed .

Materials and methods Seven varieties of T. aestivum (Chinese Spring, Svenno, Peko, Koga, A. T. 38, C 518 and April Bearded) and one synthetic hexaploid ( T . durum var. Carleton X Ae. squarrosa), a11 of which have the genomic complement AABBDD, were crossed with the synthetic tetraploid ( T . aegilopoides X Ae. squarrosa) which has the genomes AADD. This tetraploid is called synthetic AADD in this work. The objectives were t o produce a number of pentaploid hybrids, and then t o backcross each of these with its hexaploid parent.

Most plants of the synthetic A A D D were almost completely male sterile, and therefore it was used mostly as female parent. A few reciprocal crosses were made. All the pentaploid hybrids

1 Present address see p. 158.

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152 K. A. SIDDIQUI

(2n = 35, AADDB) were backcrossed to the probably due mainly to the female sterility of the respective hexaploid parent, or, if this was not florets of the synthetic AADD. possible, to another variety of T. aestivum (“general backcross”, SIDDIQUI 1964). Since most of the pentaploids were male sterile they were used as female parents only in backcrossing.

In the winter of 1961 open pollination produced few seeds in the synthetic AADD and individual plants varied in this respect. Since this variation could affect the success of the backcrossina Dro-

No seed was obtained when the synthetic AADD was used as female parent in 1963, ir- respective of the variety of T. aestivum used as pollen parent or the number of pollinations made. Three other varieties of T. aestivum (Koga, April Bearded and A. T. 38) were used in addition in 1963. This complete failure of any seed setting in these crosses could be attributed either to - -

gramme it was decided to record the fertilities of individual plants, and also to select for higher fertility within this amphiploid.

Ten plants were grown in the summer of 1962, and ten plants from the progeny of the most fertile of these were grown in the autumn of 1962. The selection was repeated and a further ten plants of the next generation were grown in 1963. The segregation of seed fertility and of morphological characters was studied in each of

chance, or to environmental factors, or to the female sterility of the synthetic AADD.

The number of florets of the synthetic AADD pollinated during 1963 was almost 3 times greater, and with the disomic Chinese Spring it was about 4 times greater, than the number of florets pollinated during 1962. Thus the chance of getting hybrid seed should have increased in 1963. Also, the environmental conditions under which the plants were grown in the two summers were

these progenies.

Experimental results

practically the same. It is therefore unlikely that chance or environmental factors were the causes of failure.

Female sterility appears consequently to be the main cause of failure of seed setting in these crosses. The data in Table 3 indicate that the frequency of female sterile florets of the synthetic AADD was higher in 1963 than in 1962. 1. Production of pentaploids

The crossability of the synthetic AADD with Some of the plants produced dehiscent anthers varieties of T. aestivum, the germination of hybrid with viable pollen. Eighteen florets of the variety seed and the survival of pentaploid hybrids are A. T. 38 were crossed with this pollen and one reported in Table 1. hybrid seed was obtained.

During 1962, 322 florets of synthetic AADD Table 2 presents the results of crosses between were crossed with pollen from different varieties the synthetic AADD and a synthetic AABBDD, of T. aestivum. Hybrid seeds were obtained only T. durirm var. Carleton X Ae. squarrosa (Ca with the variety Chinese Spring. The hybrid Sq). Fifty-six florets of the synthetic AADD were seeds appeared normal: they were neither small pollinated in 1962 and 240 florets were pollinated nor wrinkled. Neither of the hybrid seeds from in 1963, but no seed was formed. Twelve florets the cross with monosomic XIX (6D) germinated, used in reciprocal crosses in 1962 did not produce whereas the single seed from the cross with the any seed. More reciprocal crosses were made in disomic germinated and developed into a normal 1963 and 9 seeds were obtained from the 80 plant. The failure of hybrid seeds from monoso- florets of the synthetic hexaploid that were pol- mic MA’ (6D) may have been due to aneuploidy, linated. since they could have been produced by 20 chromosome pollen grains.

The crosses of the synthetic AADD with the 2. First backcross varieties Peko, C 518 and Svenno did not produce any seed. More florets were pollinated with Peko (188) than with the other varieties (20 and 34). The failure of crosses with these three varieties.

A. The AD-Chinese Spring pentaploid, ( T . aegilopoides X Ae. squarrosa) X T. aestivum var. Chinese Spring, 2n = 35

and especially with Peko, may have been due in part to genetic incompatibility, but it was more

The single pentaploid hybrid produced from this cross in summer 1962 was backcrossed to the

Hereditas 68, 1971

AADD COMPONENT OF TRITICUM AESTIVUM 153

Table I . Hybridisation between synthetic A A D D and varieties of T. aestivum

Year Pollen parent variety No. florets No. seeds No. seeds No. seeds No. of pollinated obtained sown germinated hybrids

1962 I . Chinese Spring monosornic XIX (6D) 42 2

2. Chinese Spring (disomic) 38 I 3. Svenno 20 0 4. Peko 188 0 5. C518 34 0

Total 322 3

1963 I . Chinese Spring monosomic XVI (3D)

2. Chinese Spring (disomic) 3. Svenno 4. Peko 5 . C518 6. Koga 7. April Bearded 8. A.T. 38

14 150 200 158 86

238 54 28

Total 928 0

Reciprocal 8a. A.T. 38 18 I

Total 18 If69r;)

hexaploid parent, T. aestivum var. Chinese Spring. One hundred and sixty-four florets of the pentaploid were pollinated from disomic plants. Later when pollen from disomic plants was not available, 20 florets of the pentaploid were pollinated with Chinese Spring monosomic (2n = 41) XI V (IB). It was decided to make crosses in this direction because some of the earlier-formed ears of the pentaploid contained no anthers. It was also thought unlikely that sufficient viable pollen would be obtained from one single pentaploid plant to pollinate a reasonable number (say 150) florets of the hexaploid parent. Also, the work on the extraction of the AABB com-

2 0 I I 0 0 0 0 0 0

3 1

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0

I 1

I 1

ponent had indicated that more seeds are obtained if a pentaploid is used as a female parent. How- ever, these backcrosses of the AD-Chinese Spring pentaploid with the Chinese Spring disomic and monosomic produced no seed.

The pentaploid was grown from November 1962 to June 1963, under artificial conditions in the winter and under normal daylight conditions from March 1963 to June 1963. It also produced some new tillers during the spring of 1963. Later tillers of cereals normally produce little or no seed, but one seed was obtained after self-pollination of the pentaploid. The pollen fertility was 40%) in this pentaploid.

Table 2. Hybridisation between the synthetic A A D D and the synthetic hexaploid wheat, T. durum var. Carleton X Ae. squarrosa ('Ca Sq')

Year Cross No. florets No. seeds No. seeds No. seeds No. pollinated obtained sown germinated hybrids

1962 1 . AADDx'CaSq' 56 0 0 0 0 2. 'Ca Sq' x AADD 12 0 0 0 0

1963 I . A A D D x ' C a S q ' 240 0 0 0 0 2. 'Ca Sq' x AADD 80 9 9 9 9

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154 K. A. SIDDIQUI

B. The A. T. 38 - AD pentaploid, T. aestivum var. A. T. 38 X (T. aegilopoides X Aegilops squarrosa) , 2n = 35 The A. T. 38 - AD pentaploid hybrid from the cross made in 1963 (Table 1) produced heads about one month later than the hexaploid parent, T. aestivum var. A. T. 38 and therefore the backcross to the actual parent was not possible. Another variety of T. aestivum, Chinese Spring, was used to pollinate 180 florets of the pentaploid, but no seed was obtained.

Pollen fertility of the pentaploid (43%) was determined from anthers of a spike on a later tiller. Fourteen florets of this spike were allowed to self-pollinate, but no seed was obtained.

3. The AD-Chinese Spring pentaploid progeny

One seed obtained from the self-pollination of the AD-Chinese Spring pentaploid hybrid was aneuploid, with 30 chromosomes.

4. Segregation in the synthetic allotetraploid AADD ( T . aegilopoides X Ae. squarrosa)

The three generations of the amphiploid were quite uniform morphologically but there was marked variation in seed fertility. The seed setting following controlled self-pollination in each of the three generations is presented in Table 3. All ten plants in each generation were grown under similar conditions.

More than 1350 florets were selfed during the summer of 1962. Six of the ten plants (nos. 1 - 10) were completely sterile and the percentage of florets containing seed in the other four varied from 0.5 to 50. Plant number 2 had the highest seed set (50%). Ten plants (nos. 1 1 -20) were grown from the seed of plant number 2, and 1480 florets were selfed during the autumn of 1962. The percentage of florets containing seed varied from 0 to 34, and 7 of 10 plants were completely sterile.

During the summer of 1963, ten plants were

Table 3. Segregation for seed fertility in the synthetic tetraploid T. aegilopoides X Ae. squarrosa (self-pollinated)

Summer 1962

Plant No. I 2 3 4 5 6 7 8 9 10 Total or mean

No. florets selfed 144 34 18 200 220 200 150 120 136 150 1.327 No. seeds obtained 0 17 6 1 10 0 0 0 0 0 34 % seed set 0 50 33 0.5 5 0 0 0 0 0 2.47

Autumn 1962 Progeny of Plant No. 2

Plant No. I I 12 13 14 15 16 17 18 19 20 Total or mean

No. florets selfed 120 170 150 180 50 200 130 120 160 200 1,480 No. seeds obtained 0 2 0 4 17 0 0 0 0 0 23 % seed set 0 I 0 2 34 0 0 0 0 0 I .55

Summer 1963 Progeny of Plant No. 15

Plant No.

No. florets selfed 200 250 100 150 100 160 170 160 200 50 1,540 No. seeds obtained 0 0 0 0 20 0 2 0 0 0 22

seed set 0 0 0 0 20 0 I 0 0 0 I .42

Hereditas 68, 1971


obtained from plant number 15 which had the highest seed set (347,) in the second generation; 1540 florets were selfed. The percentage of seed set varied from 0 to 20 and 8 of 10 plants were completely sterile. Even in plants which produced seeds most spikes were completely sterile.

There appears to be difference in the total seed set (seed set on population basis) during the summer of 1962 (2.5:,) and the autumn of 1962 ( l .5 ,") , but the total seed set (1.4%) was rather lower during the summer of 1963. These results show that selection for fertility has been completely ineffective. There were considerable differences in seed set between different spikes in fertile plants, which suggests that much of the sterility is not under direct genetic control.

Discussion The Triticum aegilopoides X Ae. squarrosa amphiploid (AADD) that was used in the present crossing experiments was produced by SEARS (1941). No other synthetic A A D D has been reported. SEARS recorded a seed set of 76,; in the year 1939/40, when this amphiploid was first produced. It was not stated whether this seed resulted from open pollination or from controlled self-pollination. The seed set obtained from self- pollination in the present work averaged from 1 to 3 per cent. There appears to have been a considerable fall in the fertility of this allotetraploid. This makes it difficult to maintain the tetraploid. Similar difficulties have also been encountered in a comparable synthetic tetraploid, Triticum monococcum X Aegilops speltoides, AABB (SID- DIQUI 1969a; SEARS 1970, pers. comm.). This synthetic tetraploid (AABB) produced only 26 seeds on self-pollination of 156 florets during one year. In the next year no seed was obtained after the self-pollination of 355 florets and thus this synthetic AABB tetraploid was also too sterile to maintain (SIDDIQUI 1969a).

The apparent fall in the fertility of the synthetic tetraploid AADD may be due in part to environmental differences. The growing conditions used by SEARS in Missouri were probably different from those at Reading, and this difference may affect the fertility. The results in Table 3 show that although the plants of the synthetic tetra-

ploid were grown in two different seasons, summer and autumn during 1962, and also in 1963 few seeds were produced at any time. Never- theless, it is possible that the fertility of this synthetic tetraploid is markedly affected by the growing conditions.

SEARS (1941) studied meiosis in the allotetraploid and found on an average, 1.00 univalents, 12.66 bivalents, 0.16 trivalents and 0.30 quadriva- lents. A similar frequency of bivalents was observed in 25 cells of this tetraploid in 1961.

There is no evidence that variation in the fertility of the synthetic AADD is due to irregular meiosis resulting in aneuploid progeny. The chromosome numbers of allotetraploid plants that were grown were not checked, but meiosis was studied in some plants and in each case the plant had 28 chromosomes. Further, the chromosome number of all the hybrid seedlings in which this tetraploid was involved, with T. aestivum, with (T. durum var. Carleton X Ae. squarrosa) and with Secale cereale, was euploid. OKAMOTO (1957) also examined hybrids between this tetraploid and T. aestivurn var. Chinese Spring for studying the asynaptic effects of chromosome V (5B). He found that the fertility of the F1 hybrids was extremely low and that no seed was obtained (OKAMOTO, pers. comm. 1964). He did not re- port aneuploidy in the synthetic tetraploid. There- fore there is no evidence that variation in the fertility of the synthetic allotetraploid, AADD, is due to irregular meiosis or to the occurrence of aneuploids.

WAGENAAR (1969) has reported a clear rela- tionship between the observed pattern in fertility and meiotic chromosome behaviour in re- sponse to selection for fertility in a spontaneously produced amphiploid of Triticum crassum X T. turgidum. However, reduced fertility in plants cannot always be explained in terms of meiotic irregularities (RILEY and CHAPMAN 1957). In a study of meiotic and reproductive behaviour of hexaploid Triticales, considerable meiotic irregu- larity during microsporogenesis had little or no effect on percent seed set (SISODIA et al. 1970). They observed that meiotic instability increased with delayed seeding, but this increase was with- out concomitant influence on either pollen via- bility or spike fertility.

The low fertility observed in the plants of the tetraploid was apparently due to male sterility. Most anthers were imperfectly developed. They

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156 K. A. SIDDIQUI

did not dehisce and the pollen fertility in the usual sample of 500 grains was found (by staining) to be less than 5 per cent. Some anthers dehisced in two spikes only, on two different plants. About 80% of the pollen from these anthers was stain- able. That some spikes occasionally produce fertile pollen suggests that male sterility in most spikes is the expression of genic sterility in particular environments.

Female sterility may also affect seed production, but unlike male sterility it is not apparent before seed is formed, either by self-pollination or by cross-pollination. More than 1450 pollinations (Tables 1 and 2) in which fertile pollen (95 - 100%) from varieties of T. aesfivum and from a synthetic hexaploid was used produced no seed. There was no sign of seed breakdown and therefore no sign that fertilisation had oc- curred. This suggests that the tetraploid is also female sterile.

Segregation of amphiploids for fertility and other characters has been reported by many workers (GAJEWSKI 1953; GRANT 1954; GERSTEL and PHILLIPS 1958). GAJEWSKI found a situation in the progeny of a synthetic amphiploid (Geum rivule X G. macrophyllum) similar to one reported in this work for the synthetic amphiploid, AADD. There was variation in fertility but there was very little segregation of the morphological characters which differentiated the parental spe- cies. Multivalents were not found in this Geum amphiploid and chromosome pairing was regular. Since the induced amphiploid should be homo- zygous, the cause of variation in fertility is not apparent. If an amphidiploid is produced by the fusion of unreduced gametes from both parents, the gametes may be heterozygous, and segregation for some characters can be expected in the later generations. Such an explanation is not applicableeither to the Geumor the T.aegilopoides X Ae. squarrosa, AADD, amphiploid.

STEBBINS and VAARAMA ( I 954) studied the segregation in the progeny of the induced allo- octoploids involving two genera in the Hordeae, Elymus and Sitanion. There was very little segregation of morphological characters, but there was wide segregation for pollen and seed set. Meiosis in the allopolyploids was irregular and the mean number of multivalents ranged from 4 to 5.4. The uniformity of morphological characters and the considerable but independent variation in pollen and seed fertility was ascribed to an un-

usual combination of auto- and allopolyploidy. There is, however, no cytological or genetic evidence for this suggestion which appears to be mainly based on the assumption that genes for morphology and fertility are not located on the same sets of chromosomes.

The fertility of an amphiploid can be improved by selection. A good example is provided by Trificale, an amphiploid between Triticum and Secale. In the earlier generations the yield of this amphiploid was about half that of standard varieties of wheat and most of the difference was attributable to seed sterility. After 15 generations of selection the yield increased to about 90% of the wheat standard (MUNTZING 1957), and pri- marily because the percentage of seed set in the amphiploid increased. In tetraploid rice (produced either by crossing induced autotetraploids of particular varieties or by artificial doubling of sterile intervarietal hybrids), selection from F2 to F5 carried out by MASHIMA and UCHIYA- MADA (1955) increased the fertility from about 10% to 25%. Similarly, gradual improvement in the fertility of the amphiploid, T. aestivo-timopheevi, has also been reported (BELEA 1970).

Selection is not always effective in increasing fertility. OKA (1955) also selected tetraploid rice from F2 to F7. He found that plants with different fertilities were produced and that despite selection the mean fertilities tended to decline in later generations. The present selection for fertility in the synthetic amphiploid (T. aegilopoides X Ae. squarrosa) was carried out on a much smaller scale, but the results appear to be similar to those reported by OKA. He explained his results in terms of ‘genic changes’. Recently, KAO et a]. (1970) have reported the effect of four to nine generations of selection for increased fertility in hybrid populations of autotetraploid barley. Selection was ineffective in increasing the percentage seed set. Selection was also carried out for reduced seed set and this was also ineffective.

It is difficult to cross the synthetic tetraploid AADD with varieties of T. aestivum or with the synthetic hexaploid, T. durum var. Carleton X Ae. squarrosu. The main difficulty was that most plants of the synthetic AADD were completely male sterile and the majority of the crosses therefore had to be made using the tetraploid as female parent. Crosses in this direction, however, were much less successful than when the tetra-

Hereditas 68, 1971


ploid was used as a pollen parent. There was no sign of somatoplastic sterility in either case.

A similar problem may have affected the success of the backcrosses. Two AADDB pentaploids obtained from two varieties of T. aestivurn, Chinese Spring and A. T. 38, were available for backcrossing. Both pentaploids were almost male sterile and therefore were used as female parent but no seed was obtained. There was no sign of seed breakdown. These crosses were made during the winter under artificial conditions which were not ideal for crossing but the hexaploid pollen was viable, and the failure of seed set indicates some female sterility in the pentaploids. This may be an effect of the tetraploid parent.

Some fertile pollen was produced by both pentaploids, and the crosses using this pollen may be more successful whether or not the pentaploids are also female sterile. But this will require more pollen than was available from the present pentaploids.

The following suggestions are made to increase the success of the future attempts to extract the AADD component from T. uestivum. The main problem in the present work has been the low fertility both male and female, of the synthetic AADD. The first improvement must be the production of synthetic AADD plants that have a high fertility. There are three ways in which this can be attempted.

( I ) Selection for fertility of the present synthetic tetraploid may be continued. It is possible that selection involving larger numbers of indi- viduals in each generation may be more effective.

(2) One selfed seed was obtained from one of the pentaploids (AADDB). Such seeds might provide new fertile tetraploids or pentaploids, which can be used in the extraction work.

(3) It is important that new synthetic AADD tetraploids involving several different strains of Triticum aegilopoides (AA) or T. monococcum (AA) and Aegilops squurrosa (DD) should be produced. Some of these tetraploids might be more fertile and more stable than the present tetraploid, and if so it should be easier to obtain a large number of pentaploid hybrids from different combinations. It is possible that some of these pentaploid hybrids will be more fertile and therefore more useful in the extraction of the AADD component. Also, further studies of a number of different synthetic AADD tetraploids will increase the understanding of the

segregation that occurs in these synthetic allopolyploids.

Acknowledgments. - I am grateful to Professor A. H. Bunting and Dr. J. K. Jones for supervision and to Pro- fessor A. Muntzing and Professor A. Lundqvist for helpful discussions.

Literature cited BELEA, A. 1970. Contribution to the genetic analysis of the amphidiploid Triticum aestivo-timopheevi. - Acta Agron. Acad. Sci. Hung. 19: 127-135.

GAIEWSKI, W., 1953. A fertile amphipolyploid hybrid of Geum rivale with G . macrophyllum. - Acta Soc. Bot.

GERSTEL, D. U. and PHILLIPS, L. L. 1958. Segregation of synthetic amphiploids in Gossypium and Nicotiana. - Cold. Spring Harbor Symp. Quant. B id . 23: 225-237.

GRANT, V. 1954. Genetic and taxonomic studies in Gilia. - El AIiso 3 : 19-34.

KALTSIKES, P. J., EVANS, L. E. and BUSHUK, W. 1968. Durum-type wheat with high bread-making quality. - Science 159: 21 1-213.

KAO, K. N., REINBERGS, E. and HARVEY, B. L. 1970. Selection for seed setting in hybrid populations of autotetraploid barley, Hordeum vulgare L. emend. LAM. - Crop Sci. 10: 491-492.

KERBER, E. R. 1964. Wheat: Reconstitution of the tetraploid component (AABB) of hexaploids. - Science 143: 253-255.

MASHIMA, I. and UCHIYAMADA, H. 1955. Studies on the breeding of fertile tetraploid plants of rice. - Bull. Nut. Inst. Agr. Sci. Ser. D, p. 104-136.

MUNTZING, A. 1957. Cytogenetic studies in ryewheat (Triticale). - Cytologia (Suppl.), Proc. Int . Genet. Symp. 1956, p. 51-56.

OKA, H. 1955. Studies on tetraploid rice. VI. Fertility variation and segregation ratios for several characters in tetraploid hybrids of rice, Oryza sativa L. - Cytologia 20: 258-266.

OKAMOTO, M. 1957. Asynaptic effects of chromosome V. - Wheat Inform. Serv. 5 : 6.

RILEY, R . and CHAPMAN, V. 1957. The comparison of wheat-rye and wheat-Aegilops amphidiploids. - J. Agr. Sci. 49: 246-250.

SEARS, E. R. 1941. Chromosome pairing and fertility in hybrids and amphidiploids in the Triticinae. - Res. Bull. Missouri Agr. Exp. Sta. 337, 20 p.

SIDDIQUI, K. A. 1964. Cytogenetic studies in the tribe Triticeae. - Ph. D. Thesis, Univ. Reading, England,

- 1969a. Extraction of ancestral constituents of natural polyploids. I. Production of pentaploids (AABBD) for extracting the tetraploid (AABB) component of the hexaploid Triticum aestivum. - - Pakistan J . Bot. I : 67-76. - 1969b. Extraction of ancestral constituents of natural

polyploids. 11. Study of the first backcross of the pentaploids (AABBD) and 34-chromosome plants to the hexaploid, Triticum aestivum. Ibid. 1: 149-1 59.

SIDDIQUI, K. A. and JONES, J. K. 1969. Genetic necrosis in Triticum x Aegilops pentaploid hybrids. - Euphytica 18: 71-78.

POI. 22: 41 1-439.

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SISODIA, N. S., LARTER, E. N. and BOYD, W. J. R. 1970. Effect of planting date on the meiotic and reproductive behaviour of hexaploid Triticale (Tritirale hexaploide LART). - Crop. Sci. 10: 543-545.

STEBBINS, G. L. and VAARAMA, A. 1954. Artificial and natural hybrids in the Gramineae, Tribe Hordeae. VII. Hybrids and allopolyploids between Elymus glaucus and Sitanion spp. - Genetics 39: 378-395.

WAGENAAR, E. B. 1969. Meiotic restitution and the origin of polyploidy. I l l . The cytology and fertility of

eight generations of the offspring of a spontaneously produced amphipolyploid of Tritirum rru.wum x T . rurgidum. - Can. J . Genet. Cytol. 11: 729-738.

K. A. Siddiqui Danish Atomic Energy Commission Research Establishment Riso Agricultural Research Department 4000 Roskilde, Denmark

Hereditas 68. 1971

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Extraction of AADD component of Triticum aestivum (AABBDD)