| The synthetic AABBD pentaploid was highly fertile and set seeds in 83.2%
of florets on the bagged heads. It produced plump and viable seeds in the
majority of florets in the reciprocal crosses with T. durum (Table
2). On the other hand, the other pentaploids did not show the natural
anther dehiscence in general, resulting in low selfed seed-set, because
of the low proportion of mature pollen grains in the anthers (Table
2). Less than 50% of seed-sets were observed in these two pentaploids
when they were reciprocally crossed with T. durum. And the majority
of the seeds produced were shrivelled and inviable, except in the case of
the cross AABBM x AABB. By considering the misscrossing rate in the control
crosses, the male and female fertility are 70.8 and 64.3% for AABBD, 28.3
and 37.4% for AABBM, and only 4.1 and 18.5% for AABBMu, respectively. Being
different from the case in the crosses between AABB (female) and hexaploid
amphiploids (male) having M or Mu genomes, some plump seeds were obtained
in the crosses between AABB (female) and AABBM or AABBMu (male). The cytological
observation revealed that the plants from the plump seeds had 28, 29 or
33 chromosomes, suggesting a few critical chromosomes of M or Mu genomes
may be responsible for seed shrivelness in these crosses. Fig. 1 shows the chromosome transmission of D, M, and Mu genomes in pentaploids, where only female side could be figured because of small sample size in each reciprocal cross. Since the AABB background in pentaploid crosses were genetically identical, this system employed in the experiment can reveal the direct comparison of chromosome transmission among three genomes of Aegilops species. The result showed that the chromosomes of D. M, and Mu genomes were not randomly transmitted through female gametes, but the progenies tended to possess the smaller number of chromosomes. This phenomenon may be mainly due to the elimination of univalent chromosomes through female gametogenesis. Since the transmission figures of AABBD and AABBM pentaploids did not deviate from the cruve drawn with the equation of (.75+.25)7, the elimination rate of univalent chromosomes in D or M genomes could be estimated about 25%. MURAMATSU (1939) and KIHARA and WAKAKUWA (1935) reported 20-25% of univalent elimination in D genome chromosomes in the pentaploids between T. polonicum and T. Spelta, or T. durum and T. vulgare. The present investigation used the artifical amphiploids as the hexaploid parents, and the results indicated that D and M genomes diploid species did not differ significantly from the D genome of common wheat in refference to the pentaploid transmission. On the other hand, the pattern of pentaploid transmission in AABBMu was different from those of the other two. No 28-chromosome plants was obtained in the backcross of AABBMu x AABB. The result indicated that there must be an essential chromosome of Mu genome involved to obtain viable progeny in this cross. This can be explained by the fact of incompatible interaction between the cytoplasm of Ae. uniaristata and AABB genome reported by MAAN (1977). Probably, some of non-germinating seeds produced in the cross may involve 28-chromosome embryos. The present experiment showed some sirnilarities and differences among D, M, and Mu genomes of Aegilops species. The progenies obtained in the experiment will be used for further genetic analysis of these three genomes. Acknowledgment The experiment was conducted partly in Agronomy Department of North Dakota State University, and lately in Kihara Institute for Biological Research. Heads and friends in both institutes are acknowledged. Literature Cited KIHARA, H. 1924. Cytologische und genetische Studien bei wichtigen Getreidearten mit besonderer Ruecksicht auf das Verhalten der Chromosomen und die Steriltaet in den Bastarden. Mem. Coll. Coll. Sci. Kyoto Imp. Univ., Ser. B.1 KIHARA, H. 1949. Genomanalyse bei Triticum und Aegilops. IX. Systematischer Aufbau der Gatung Aegilops auf genomanalytischer Grundlage. Cytologia 14: 135-144 KIHARA, H. and S. WAKAKUWA. 1935. Weitere Untersuchungen ueber die pentaploiden Triticum- Bastarde. IV. Japan J. Bot. 7: 18-25 MAAN, S.S. 1977. Cytoplasmic control of cross-incompatiability, and zygotic and sporophytic sterility in interspecific hybrids. Proc. 8th Congress of Eucarpia, Madrid Spain. pp. 201-214 MAAN, S.S. and T. SASAKUMA. 1978. Chromosome pairing relationship among the D and M genomes of Triticum and Aegilops species. Proc. 5th Wheat Genet. Symp., New Delhi, India MATSUMURA, S. 1939. Weitere Untersuchungen uber die pentaploiden Triticum-Bastarde IX. Aequations und Zertationskreuzungen des Bastards T. durum x T. vulgare. Japan. J. Bot. 9: 21-29 SASAKUMA, T. and S.S. MAAN. 1978. Cross-incompatibility and -inviability involving M and Mu genome species and their cytoplasm of Triticinae. Japan. J Genet. 53: 446 |
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