During a cytotaxonomical study of a Kuwaiti diploid (2n = 26) population of Diplotaxis harra (Forssk.) Boiss (Brassicaceae), cytomixis and aneuploidy were found in 1.5% and 7.8% of the pollen mother cells (PMCs), respectively. Cytomictic cells revealed wide variability as far as the number of involved PMCs and their stage of division were concerned. The cytoplasmic channels, which were of different sizes, contained migrating chromosomes in a few cases. In some PMCs, the location of some of the chromosomes was clearly indicative of an imminent migration from a donor to its attached recipient cell. At metaphase I and anaphase I, PMCs showed variable degree of chromosomal transfer. In addition to a genetic control of the phenomenon, stress factors such as high temperature or drought in certain periods of the growing season may have contributed to the incidence of cytomixis in the material. A possible relationship between cytomixis and detected aneuploid PMCs, as well as a reconsideration of an evolutionary role of cytomixis is discussed.

ATTIA, T., and G. ROBBELEN. 1986. Cytogenetic relationship within cultivated Brassica analyzed in amphihaploids from the three diploid ancestors. Can. J. Genet. Cytol. 28: 323-329. To investigate the factors controlling evolutionary differentiation within the genus Brassica, chromosome pairing in amphihaploids from crosses between the three elementary diploid species B. campestris (AA), B. oleracea (CC), and B. nigra (BB) was analyzed. The amphihaploid AC showed a high amount of pairing, while the two amphihaploids AB and BC, both including the genome of B. nigra, exhibited only low degrees of chromosome association. By the occurrence of tetra-and penta-valents, auto-as well as allo-syndetic pairing was demonstrated to exist in the AC amphihaploid. True homologous pairing between the genomes A and C was deduced from the occurrence of chromosomal interchange configurations. Although the genomes of B. oleracea and B. campestris are evolutionarily distinct, as shown by the different number and structure of their chromosomes, their close relationship is readily evident from the high level of pairing observed in the AC amphihaploids. On the other hand, the much lower pairing within the amphihaploids including the B genome is unexpected in view of the hypothesis of a common ancestor for all three of the cultivated Brassica diploids from an ancestral genome with x = 6 chromosomes. It is discussed whether B. nigra is indeed more distantly related to the two other species or whether this genome carries a suppressor of chromosome pairing.Key words: chromosome pairing, amphihaploids, evolutionary relations.ATTIA, T., et G. ROBBELEN. 1986. Cytogenetic relationship within cultivated Brassica analyzed in amphihaploids from the three diploid ancestors. Can. J. Genet. Cytol. 28: 323-329. On a fait l'analyse de l'appariement chromosomique chez les amphiplo'ides rksultants de croisements entre les trois esphces diplo'ides klkmentaires, le Brassica campestris (AA), le B. oleracea (CC) et le B. nigra (BB) afin de mieux comprendre les facteurs qui rkgissent la diffkrentiation kvolutive chez le genre Brassica. L'amphiplo'ide ac a dkmontrk un taux klevk d'appariement alors que les deux amphiplo'ides AB et BC, exprimant tous les deux le gknome du B. nigra, n'ont dkmontrk que de faibles taux d'association chromosomique. La prksence de tktravalents et de pentavalents a confirm6 l'existence de l'appariement auto et allosyndktique chez l'amphiplo'ide AC. La prksence de configurations d'interchange chromosomique a permis de conclure 21 un vkritable appariement homologue entre les gknomes A et C. Bien que les gknomes du B. oleracea et du B. campestris aient une kvolution diffkrente, c o m e le dkmontrent leurs nombres diffkrents et la diffkrence de structure de leurs chromosomes, le taux klevk d'appariement observk chez les amphiploides AC dkmontre clairement leur proche parentk. Cependant, le taux d'appariement beaucoup plus faible chez les amphiploides porteurs du gknome B est surprenant compte tenu de l'hypothhse d'un ancbe cornmun aux tro...

ATTIA, T., and G. ROBBELEN. 1986. Meiotic pairing in haploids and amphidiploids of spontaneous versus synthetic origin in rape, Brassica napus L. Can. J . Genet. Cytol. 28: 330-334. Newly resynthesized AC amphihaploids, which were characterized by high meiotic pairing and multivalent formulation, after doubling of their chromosome number showed preferential pairing and bivalent formation in the resynthesized amphidiploid Brassica napus (AACC). However, univalents as well as multivalents were also formed indicating that their chromosome behaviour was not fully diploidized. Stabilization of chromosome pairing in newly resynthesized amphidiploids can be achieved through genetic control or structural modification of the homoeologous chromosomes. A comparison of the meiotic behaviour of spontaneous haploids of natural rapeseed with that of the newly synthesized AC amphihaploids provides some evidence that both processes may be involved in the regulation of chromosome pairing in Brassica.ATTIA, T., et G. ROBBELEN. 1986. Meiotic pairing in haploids and amphidiploids of spontaneous versus synthetic origin in rape, Brassica napus L. Can. J . Genet. Cytol. 28: 330-334. Des amphihaploi'des AC nouvellement resynthktiskes, caractktiskes par un appariement klevk a la mkiose et la formation de multivalents, ont montrk apr6s le doublement de leurs chromosomes un appariement prkfkrentiel et la formation de bivalents chez les amphidiploi'des resynthktiskes de Brassica napus (AACC). Toutefois, des univalents et des multivalents ont aussi kt6 formks, ce qui indique que le comportement des chromosomes n'ktait pas entierement diploi'disk. La stabilisation de l'appariement des chromosomes peut Ctre obtenue soit par le contr6le gknktique, soit par la modification structurale des chromosomes homkologues. Une comparaison entre le comportement mkiotique des haploi'des spontankes naturelles chez le colza et celui des amphidiploi'des AC nouvellement synthktiskes procure une evidence a l'effet que les deux processus peuvent Ctre impliquks dans la rkgulation de l'appariement des chromosomes chez Brassica.

No abstract

To assess the chromosomal relationships in the cultivated diploid Brassica species, four digenomic triploid combinations were synthesized and meiotically analyzed. Two of the four digenomic combinations contained the B genome of B. nigra, one with two (BC.B) and the other with only one B genome (C.BC). In these combinations preferential pairing between the two homologous genomes with the third single genome was predominant. Since gene actions suppressing pairing between chromosomes of related genomes had not been proven to exist in Brassica, this phenomenon is assumed to be conditioned by structural chromosomal differences reflecting the distant phylogenetic relationship of B. nigra to each of B. oleracea (CC) and B. campestris (AA). On the other hand, two other digenomic triploids having two A genomes and one C genome showed a low preferential pairing of the two homologous A genomes (to form 10 II + 9 I). Moreover, a high tendency for an allosyndetic pairing between the A and C genomes was expressed by the formation of one or more trivalents in over 50% of PMCs in the two combinations A.AC and AC.A. This demonstrated a high meiotic pairing potential and a small evolutionary difference between the chromosomes of B. campestris (AA) and B. oleracea (CC). Key words: Brassica, triploid (digenomic), phylogenetics, pairing (chromosome).