II. 49. Geographical differentiation of the genes for compact head character in barley.
R. Takahashi, J. Hayashi and I. Moriya. The Ohara Institute for Agricultural Biology, Okayama University, Kurashiki, Japan.
In Japan and Korea a large number of cultivars of compact head type are grown widely, and genetic studies hitherto made using these varieties have suggested that they may have in common a recessive gene l on chromosome 1 for the character in question. It is unknown, however, whether the compact head cultivars, sometimes found among barleys in the regions other than East Asia, are of the same genic constitution.
In order to approach this problem, allelism tests were made using the following two testers: one is a dense var, called Honen (Abbrev. H) which is known to have a gene l, and the other Natsudaikon Mugi (N) having the allelic gene L for lax spike. So far, 92 cultivars (P) with compact head (less than 2.5 mm in rachis internode length) were selected among our world barley collection and crossed to each of the above-mentioned testers. Two kinds of F1's thus obtained and their parental varieties (P) were grown together and the length of rachis internodes was determined.
The summarized results, shown in Table 1, indicate that East Asian varieties (from Japan, Korea and China) have given F1(H) (derived from the cross with Honen) having spikes as compact as those of their parents. This indicates that all of them have in common the same gene l as in Honen. However, F1's from the crosses of Honen with varieties originated from west of India, inclusive, were much more lax, in general, in spike density than their parents. This suggests that these varieties consisted of those which have some different gene or genes for compact head, besides those with the gene l. This is visualized by Figure 1B showing the correlation between spike densities of F1(H) and F1(N), in which two different groups of varieties, say A and B, are easily discernible. The varieties of group A have given F1(H) with spikes as dense as their parents, almost the same as the East Asiatic compact varieties as seen in Table 1 and Figure 1A. On the other hand, F1(H) from the crosses with varieties of group B were by far more lax than their parents, which suggests that these varieties contain a semidominant gene for compact head character. It is noted here that the varieties of group B are those originating from the regions west of Pakistan, while those of group A are of Nepalese, Pakistani and Ethiopian origins. In order to accumulate further data we are now growing in our field a much larger number of Fl's and their parents of these kinds.
