Contribution of Different Genomes to Adaptability in Wheat

A number of diploid and polyploid species of wheat have been analysed for the sensitivity of their chromosomes to conditions of high temperature. This has been done as part of a study on the adaptation of the wheat plant and the role of the interaction between the A, B and D genomes in relation to such adaptability.

It has been found that the chromosomes in the polyploid species are less sensitive to conditions of high temperature than those in the diploid species. It has been further observed that among the different polyploid species, chromosomes in the hexaploid species are less sensitive than those in the tetraploids, Thus, it has been found that, in general, the diploid species are temperature sensitive, the hexaploid species are relatively resistant, while the tetraploids show an intermediate type of behaviour. Moreover, the different tetraploid species show significant differences in the temperature sensitivity of their chromosomes.

Apart from the differential response of the species, it has been observed that there are significant intraspecific intervarietal differences with regard to the effect of high temperature on chromosomal structure.

These and other observations have been interpreted to indicate that an interaction between the chromosomes of the A and B genomes has contributed to a wider adaptation of the wheat plant. In addition, an interaction between chromosomes of the D genome on the one hand, and those of the A and B genomes on the other, has made a further contribution to adaptability.

An attempt has been made to understand the mechanisms responsible for the greater environmental stability of the chromosomes of the polyploid species. It has been suggested that polyploid wheat species with their different genomes simulate, in a sense, the behaviour of genetically heterozygous organisms, which according to some authors show greater developmental stability. It has, however, been emphasized that in the case of wheat, heterozygosity occurs only at the level of genomes, and not for individual gene loci. It has been concluded that the greater environmental stability of the polyploid wheat species is genotypically controlled, and the wide range of recombinant genotypes produced through the combined effect of hybridization and chromosome doubling has helped to achieve it.