| "Camara" a tetraploid wheat carrying a 1D disomic substitution
for chromosome 1B T. MELLO-SAMPAYO Instituto Gulbenkian de Ciencia, Oeiras, Portugal D-genome chromosome substitutions for chromosomes of A and B genomes can be produced in tetraploid wheat (2n=4x=28). CAMARA, MELLO-SAMPAYO and NORONHA-WAGNER (1966) and MELLO-SAMPAYO and RAMOS (1968) obtained monosomic substitution lines of chromosome 1D for both homoeologous 1A and 1B chromosomes at the tetraploid level. This was accomplished when both reciprocal nullisomic-tetrasomic lines of chromosomes 1A and 1B of Triticum aestivum variety, Chinese Spring, were crossed to T. durum variety, Ld 222. The hybrids were then backcrossed to the durum wheat parent. Some of the resulting tetraploid plants were double monosomic 1D and 1A or 1B and both showed a 12II+2I configuration at meiosis. It was logically expected that from those plants some individuals carrying 1D disomically substituted for its alternate homoeologous, could be obtained, by selfing. This was true in the case of disomic 1D substitution for 1B which was obtained in 1965. This combination which has only one backcrossing to Ld 222 has been continuously selfed since then and it shows a very stable phenotype. It has been given the name "Camara". The plant is about 25% shorter than its parent Ld 222, the species being more compact fully fertile and carrying shorter seed and it matures earlier than the durum wheat parent. "Camara" shows a regular configuration of 14II at metaphase I of meiosis. Both chromosomes 1B were lost when replaced by a pair of 1D chromosomes and the number of nucleolar organizers present in the cells was reduced accordingly. This could be easily detected through the counting of the maximum number of nucleoli shown by somatic cells at telophase-prophase. It was observed that this number which is four in normal tetraploid wheats was reduced to two. Tests were performed in order to identify both the substituent and substituted chromosomes. Crosses with Chinese Spring ditelosomic lines, 1DL and 1BL, were used for the purpose. When "Camara" was crossed to ditelo 1BL, the telocentric chromosome 1BL remained as univalent in the pentaploid hybrid (meiotic configuration 14II+7I). On the contrary, when ditelo 1DL was utilized, the 1DL telocentric formed a heteromorphic bivalent. This demonstrated that in the tetraploid complement of "Camara", a pair of chromosomes 1B was replaced by a pair of homoeologous 1D chromosomes. |
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