II. 18. Geographical distribution of the two dominant complementary genes for hybrid weakness in barley.
T. Konishi, Institute for Agricultural and Biological Sciences, Okayama University, Kurashiki 710, Japan.
The present author found that a Turkey 193 x Col-orange cross gave weak F1 plants, which were characterized by only a few spikes on the short stems with remarkably shrivelled, yellowish leaves after the boot stage. And, in the F2 generation of this cross, segregation of weak and normal plants was confirmed to occur in a 9:7 ratio, which suggested that the hybrid weakness was due to two dominant complementary genes Wek-a and Wek-t, tentatively called here A and T.
This experiment aimed to survey the geographical distribution of the complementary genes, A and T. A total of 1,106 cultivars originated from various parts of the world, together with 82 strains of wild barleys, were crossed each with two tester stocks, Col-orange and Turkey 193 with the gene A and T, respectively, and occurrence of hybrid weakness in their F1 generation was examined. If F1(A) is weak and F1(T) is normal, the variety must have the gene T, and if the relation is the reverse, it must have the gene A. When the hybrids, F1(A) and F1(T), with either of the tester stocks are normal, the variety must have doubly recessive genes, a and t.
Table 1. Geographical distribution of barley varieties with AA tt genotype.
The results of the test crosses clearly indicated that Turkey 193 was unique in having genotype aa TT, while those varieties with genotype AA tt were abundant in the world. It is interesting to note that the frequency of varieties with genotype AA tt was considerably different with geographical regions. As is apparent in Table 1, the frequency of this genotype is very high among the varieties of Asian regions, including Japan, Korea, China, Nepal and S.W. Asia, but it becomes extremely low among Turkish and Ethiopian varieties. In Europe, it is only one third of the varieties there. Such a geographical regularity of distribution of AA tt genotype is well recognized for the six-rowed barley, and it is especially conspicuous for the naked forms.
As for the two-rowed barley, such a geographical regularity is no longer recognizable, however. Generally speaking, only about one third of the two-rowed, covered varieties from S.W. Asia, Turkey and Europe have the AA tt genotype, but Japanese two-rowed varieties are somewhat higher in the frequency of this genotype. This may be due to the fact that about four fifths of them consist of the selection from or hybrid derivatives from Golden Melon or Svanhals which are of AA tt genotype.
Among the wild relatives crossed with two tester stocks, three strains
of Hordeum agriocrithon from Tibet and most of the strains of H.
spontaneum are of AA tt genotype.
