| The homoeologous group 4 in the Triticinae
P. K. GUPTA Cytogenetics Laboratory, Division of Plant Sciences, Meerut University, Meerut, India In the recent months, important work in wheat has been done using the techniques of molecular biology. The compensating nullisomic-tetrasomic lines were used by SHEPHERD (1968), BREWER et al. (1969) and HART (1970) in order to find out the variability in proteins or enzyme products of the genes located on the homoeologous chromosomes. While definite differences were recorded in the seed proteins (SHEPHERD 1968), remarkable homogeneity was observed in the isozymes tested (BREWER et al. 1969). Out of the 12 isozyme systems, for which the tests were conducted, variability was observed only in case of alkaline phosphatase. The genes for this enzyme could thus be located on the wheat chromosomes 4B and 4D. In another recent report (HART 1970), 40 strains of wheat, including 38 of the 42 possible combinations of compensating nullisomic-tetrasomic lines, were tested for alcohol dehydrogenase. It was concluded that the genes for alcohol dehydrogenase should be located on the chromosomes of the homoeologous group 4. It can perhaps be inferred, therefore, that the chromosomes of the homoeologous group 4 have differentiated to a greater degree than those of other groups. However, BELFIELD and RILEY (1969) concluded on the basis of meiotic pairing, that there was no evidence of any appreciable difference in the closeness of the chromosomes in the different homoeologous groups. SEARS (1966) on the basis of phenotypes, did find such differences and in his study, homoeologous group 4 was one such group where differences were rather prominent. With this information available about wheat chromosomes, we can perhaps have a look on the chromosomes of the alien species from the sub-tribe Triticinae. Relationships of some of the chromosomes from three of the four alien genera in the Triticinae, have been established with wheat chromosomes. One chromosome from Aegilops comosa, was found to belong to homoeologous group 2 and was consequently designated as 2M (RILEY et al. 1966). Recently another chromosome from Aegilops umbellulata was shown to belong to homoeologous group 5 and was designated as 5Cu (CHAPMAN and RILEY 1970). Three chromosomes from Agropyron elongatum were shown to belong to homoeologous groups 3, 6 and 7 (BAKSHI and SCHLEHUBER 1959, JOHNSON 1966, QUINN and DRISCOLL 1967). Similarly chromosomes from Secale cereale could be shown to belong to homoeologous groups 1, 2, 3, 5 and 6 (See GUPTA 1971). Out of these alien chromosomes, whose homoeologous relationships are known, only one (3R, BARBER 1969) was studied using biochemical techniques and it was shown that the biochemical techniques were useful in establishing homoeologous relationships. |
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