Euphytica 45 : 223-227, 1990 .©1990 Kluwer Academic Publishers. Printed in the Netherlands .

Chromosome pairing in hybrids of Trilicum aestivum and the amphiploidHordeum chilense X T. turgidum cony . durum

Jose Antonio Fernandez and Nicolas JouveDepartment of Cell Biology and Genetics, University of Alcala de Henares, Apdo. 20,Alcald de Henares (Madrid), Spain

Received 28 September 1988; accepted in revised form 20 February 1989

Key words: Triticum aestivum, Hordeum chilense, Triticum turgidum, Triticum durum, durum, C-banding,meiosis

Summary

The meiotic behaviour of a hybrid between Triticum aestivum and the amphiploid Hordeum chilense x T.turgidum cony . durum, was studied using a C-banding staining method . This hybrid has the genome formulaof AA BB D Hch with 2n = 6x = 42 chromosomes . The durum wheat chromosomes (genomes A and B)were easily recognized, whereas the D and Hch chromosomes were recognized as a whole . Meiotic pairingwas homologous, as expected (14 bivalents from A and B genomes + 14 univalents from D and Hchgenomes). However, some pollen mother cells at metaphase-I presented pseudobivalents that could havebeen caused by either homoeologous or autosyndetic pairing amongst D and Hch chromosomes .

Introduction

The synthetic amphiploid between Hordeum chi-lense and Triticum turgidum cony . durum was ob-tained by Martin & Sanchez-Monge Laguna(1982) . This amphiploid was called Tritordeum andhas the genome formula AA BB Hch Hch .

The C-banding pattern ofH. chilense and Tritor-deum somatic chromosomes was reported by Fer-ndndez & Jouve (1984), who also investigated themeiotic pairing in the amphiploid and the hybrid6x-triticale x Tritordeum (1985), using a Giemsastaining technique . These studies provide usefulinformation dealing with the use of both the wildbarley H. chilense and the amphiploid Tritordeumas a new source of germplasm in wheat and triticalebreeding programmes .This paper describes the chromosome pairing,observed

in the hybrid T aestivum x Tritordeum

(2n = 42, genomes AA BB D Hch) using a C-banding method to distinguish the nature of chro-mosome associations.

Materials and methods

The hybrid T. aestivum x Tritordeum was ob-tained by Dr . A. Martin (E .T.S .I .) Agr6nomos,C6rdoba, Spain) and has the intergenotypic formu-la [T aestivum cv. `Chinese Spring'] x [Tritor-deum line `(H. chilense x T. turgidum cony . durumcv 'Cocorit')'] .

Anthers containing pollen mother cells (PMCs)at metaphase-I were fixed in 3 :1 alcohol: acetic acidand subsequently stained following the techniquedescribed by Jouve et al . (1980). Wheat chromo-some pairs identification were made in accordancewith our previous descriptions (Fernandez &

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Jouve, 1984; Ferrer et al ., 1985; Fernandez et al .,1985) .

Results and discussion

The Giemsa staining technique herein applied inmeiotic cells has permitted the genomic assignmentof durum wheat chromosomes, and the unequiv-ocal identification of nine pairs (4A, 7A and theseven of the B genome) . Similarities in C-banddistribution and chromosomal length masked theindividual distinction between D and Hch chromo-somes, with the exception of chromosome 6Hch .However, it has been possible to recognize bothgenomes as a whole with respect to A and B ge-nomes (Fig . 1) .

The meiotic behaviour at first metaphase is sum-marized in Table 1 . The expected pairing in thehybrid would be of 14 bivalents (7 bivalents AA+ 7 bivalents BB) plus 14 univalents (7 univalentsD and 7 univalents Hch), assuming that only homo-logous pairing would occur . A mean number nearof 14 bivalents and 14 univalents was recorded andthe maximum pairing observed was of 15 bivalents .Some PMCs, which presented either 14 or 15 biva-lents, showed 'pseudobivalents' (stickiness ratherthan by chiasmata) in an average of 0 .10. They canbe caused by either homoeologous or autosyndeticpairing amongst D and Hch chromosomes . Theaverage of bivalents between non-homologous

Table 1 . Average of chromosome associations in 100 PMCs at metaphase-I (ranges in parenthesis) in an hybrid T aesdvum xTritordeum studied by C-banding

* Pseudobivalents .

chromosomes per PMC (0 .10) was lower than theobserved in meiosis of the hybrid between 6x-trit-icale and Tritordeum (0.15) previously reported(Ferndndez & Jouve, 1985) .

The hybrid presented secondary associations ofunivalents, side to side, side to end, and end to end(Fig . 1) . One cell with two trivalents and eight cellswith one trivalent out of 100 PMCs studied wererecorded. In some cases, nature of the involvedchromosomes (7A and 4B) has been proved. Theformation of this multivalents demonstrates thatreciprocal interchanges between wheat chromo-somes from different parentals put together in thehybrids exist .

An individual pairing analysis (univalents, openbivalents, ring bivalents and trivalents) of the nineidentified wheat chromosomes was carried out(Fig . 2) . When the meiotic behaviour of the nineidentified wheat chromosomes were compared bymeans of a contingency chi-square test, highly sig-nificant differences were found (x2 = 125 .7; 24 df;P < 0.001). Chromosomes of genome A, whichexhibit less heterochromatin than the B genomeones, also show a significant higher level of pairing(x2 = 43 .64; 2 df; P < 0 .001) .

Meiotic pairing between AA BB genomes waslower in this hybrid (average of univalents = 0 .99 ;Xata/PMC = 23 .29) than in 6x-triticale x Tritor-deum (average of univalents = 0 .68; Xata/PMC= 24.20) (Fernandez & Jouve, 1985) . This resultcould be explained on the basis of the differences in

Genomes Univalents Bivalents Trivalents Xata/PMC

Open Ring Total

AA BB 0.99 ± 1 .5 3 .76 ± 1 .5 9 .65 ± 1 .5 13 .41 ± 1 .0 0 .04 ± 0 .2 23 .29 ± 1 .9(0-6) (0-8) (6-13) (10-14) (0-2) (18-28)

H`° & D 13.84± 0 .5 0 .10 ± 0 .3* 0 .10 ± 0.3*(12-14) (0-1) (0-1)

AA BB HC°D 14 .83 ± 1 .7 3 .86 ± 1 .5 9 .65 ± 1 .5 13.51±1 .0 0 .08 ± 0.3 23 .29 ± 1 .9(12-20) (0-8) (6-13) (10-15) (0-2) (18-28)

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specific source of A and B genomes between the parentals in each hybrid. Thus, the hybrid T. aesti- vum x Tritordeum presents the genomes A and B of two different ploidic species of wheat, whereas these genomes have arisen from &rum wheat in the hybrid 6x-triticale x Tritordeum.

A higher level of open bivalents in most of the identified chromosome pairs in the hybrid 7Y aesfi- vum x Tritordeum with respect to 6x-triticale x Tritordeum was recorded. Thus, chromosomes 4A, 2B, and 5B appear as open bivalents with a percentage of 15%) 11% and 29%) respectively, in the hybrid 6x-triticale x Tritordeum (Fernandez & Jouve, 1985), and 31%) 24% and 60% in the hybrid T. aestivum x Tritordeum (Fig. 2). The pair SB showed interparental differences in the pattern of distribution and amount of constitutive hetero- chromatin (Fig. 1). This can explain the lower level of pairing of this chromosome. Our results confirm the different tendencies to pair of each wheat chro- mosome pair previously reported in wheat (Ferrer et al., 1984; Jouve et al., 1985). The assumption that differences in physical length and heterochro- matin patterns influence the intensity of pairing is deemed reasonable.

Genome A chromosomes, which have less heter- ochromatin than those of genome B, also showed significantly higher level of pairing in both hybrids. Chromosome 4B presented, exceptionally, level of pairing similar to those of genome A. Elsewhere, chromosome pair 4A showed a particularly low level of pairing in the amphiploid Tritordeum (Fer- nandez et al., 1985), and in both 6x-triticale x Tritordeum (Fermindez & Jouve, 1985) and i? aes- tivum x Tritordeum hybrids (Fig. 2). These results support the intergenome reallocation of chromo- somes 4A and 4B which was previously proposed by other authors (Dvorak, 1983; Rayburn & Gill, 1985) and recently approved at the 7th Intemation- al Wheat Genetics Symposium (1988).

Clear intergeneric pairing D/Hch or R/Hch has not been observed (chromosomes are only associ- ated as pseudobivalents). This result seems to pre- vent the possibility of genetic interchange between such genomes. Moreover, it should be taken into account that homoeologous pairing detected at metaphase-I not always implied chiasmata forma-

Fig. 1. Chromosome pairing at metaphase I in pollen mother cells of the hybrid Z aestivum X Tritordeum. A) 1 chilense univalents (the unidentified are indicated by arrows) + 7 wheat univalents (D genome, indicated by w) + 14 wheat bivalents (A and B genomes). B) 7 chileme univalents + 7 wheat univalents (D genome) + 2 wheat univalents (lB’, 1B’) + 13 wheat biva- lents. One chifense-chilense-wheat end to end secondary associ- ation is observed. C) heteropicnotic ring bivalent SB. The most heterochromatic chromosome 5B (low position) corresponds to common wheat set.

tion (Orellana, 1985). Genetic recombination seems not to be an efficient way to introduce genes of H. chilense to common wheat or 6x-triticale. The partial diploid constitution in the hybrids could influence the lack of wheat-chilense chromosome

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4A

82

4B

7B

Fig. 2 . Diagrams showing the frequencies of tivalents (T), ring bivalents (RB), open bivalents (OB) and univalents (U) of the nineidentified wheat chromosome pairs (4A, 7A and the seven of genome B) and overall pairing of the remaining A genome chromosomes(IA, 2A, 3A, 5A and 6A) .

7A

2B

5B

UAjss' O B

RB

Tl llllllitl

3B

6B

pairing which could be higher in polyhaploids .Thus, rod bivalents were found in the intergenerichybrid of T turgidum with H. bulbosum (2n =3x = 21; A B Hb) (Blanco et al ., 1986). Never-theless, the fact that R, D and Hch chromosomesappear mainly as univalents brings on the possibil-ity of substitute chromosomes of the third genomeof 6x-triticale (R/Hch), T aestivum (D/Hch) andTritordeum (Hch/R and Hch/D) using the hybridsin selfing and backcrossing programmes . Thiscould be a way to obtain `secondary' lines of Tritor-deum and 6x-triticale .

Phenotypically, hybrids T aestivum x Tritor-deum grew vigorously, tillered profusely andreached a great height but were completely sterile(Fernandez,1986) . However, 6x-triticale x Tritor-deum hybrids were low fertile (2 or 3 seeds perspike) and could be of interest to obtain durumwheat/H. chilense or durum wheat/Secale cerealeaddition lines .

References

Blanco, A ., V . Fracciolla & B . Greco ., 1986 . Intergenericwheat x barley hybrid . J . Hered 77 : 98-100.

Dvorak, J . 1983. The origin of wheat chromosomes 4A and 4Band their genome reallocation . Can . J . Genet . Cytol . 25 :210-214 .

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Fernandez, J .A. 1986 . Caracteristicas gen6ticas y citogen6ticasde Hordeum chilense y de su anfiploide x Triticum turgidumcony . durum . PhD dissertation . University of Alcala de He-nares (Madrid) .

Fernandez, J .A. & N. Jouve. 1984 . Giemsa C-banding of thechromosomes of Hordeum chilense and its amphiploid x Trit-icum turgidum cony . durum. Z . Pflanzenzucht . 93 : 212-221 .

FernSndez, J .A. & N . Jouve, 1985. Meiotic pairing of 6x-Trit-icale and the amphiploid Hordeum chilense x Triticum turgi-dum cony. durum . J. Hered. 76 : 63-64 .

Fernandez,, J.A ., J .M. Gonzalez & N . Jouve, 1985 . Meioticpairing of the amphiploid Hordeum chilense x Triticum turgi-dum cony . durum studied by means of Giemsa C-bandingtechnique . TAG 70 : 85-91 . 1985 .

Ferrer, E ., J.M. Gonzalez & N. Jouve, 1984 . Identification ofC-banded chromosomes in meiosis of common wheat, Trit-icum aestivum L . TAG 67: 257-261 .

Jouve, N ., N. Diez & M . Rodrfguez, 1980 . C-banding in 6x-Triticale x Secale cereale L . hybrid cytogenetics TAG 57 :75-79 .

Jouve, N ., J .M. Gonzalez, A. Fominaya, & E . Ferrer, 1985 .The analysis of meiosis of the B genome in common wheat .Can. J . Genet. Cytol . 27 : 17-22 .

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Orellana, J . 1985 . Most of the homoeologus pairing at meta-phase I in wheat-rye hybrids is not chiasmatic . Genetics 111 :917-931 .

Rayburn, A .L. & B .S . Gill, 1985 . Molecular evidence for theorigin and evolution of chromosome 4A in polyploid wheats .Can . J . Genet. Cytol . 27 : 246-250 .