II.38 Inheritance and linkage studies of the chlorotic hybrids due to complementary dominant genes.
R. Takahashi, J. Hayashi and I Moriya. The Ohara Institute for Agricultural Biology, Okayama University, Kurashiki, Okayama-ken, Japan.
Addis Ababa 12 is a strain collected in Ethiopia by Dr. T. Sakamoto of Kyoto University. This strain was found to give chlorotic F1 plants when crossed to a number of cultivars of East Asiatic origin. As apparent in Tables 1 and 2, the chlorosis can be attributed to two dominant complementary genes, denoted tentatively Ch-a and Ch-e, which are separately involved in their parental varieties.
There is a wide variation in the expression of chlorosis among the F1's derived from different crosses, but they may be classified into the following three types:
Type A or lethal, which germinates normally, but is completely stunted in growth about 10 days after sowing (Fig. 1). Two strains, N. 1386 and N. 1390, from Sama, Nepal, were identified as this type.
Type B or semi-lethal: Several pale-green spots appear on the 1st leaf about 10 days after sowing then the 2nd leaf tip comes out, and a few days after chlorosis and wilting begin from the tip of 1st leaf and expand downwards gradually. Similarly, chlorosis of 2nd leaf occurs as the tip of 3rd leaf comes out, so on. Generally, only one or two heads with slender, thin kernels are produced.
Type C: Characteristic spots and chlorosis appear somewhat later and to lesser extent than in type B. Plants more or less stunted in growth, but produce many, fertile heads. A further study was made of the genetics of differences in degree of chlorosis as above-stated by three way cross method. The cross combinations and the observed frequencies of different type plants, segregated in each hybrid population, are shown in Table 3.
The results shown in Table 3 clearly indicate differentiation of at least three alleles on Ch-a locus, which are responsible for differential chlorosis expression in the presence of Ch-e in Addis Ababa 12.
Table 1. Segregation of chlorotic and normal plants in F2 of the crosses with Addis Ababa 12.
Table 2. Segregation of chlorotic and normal
green plants in the progenies of two crosses indicated.
Table 3. Segregation of plants of different
degrees of chlorosis expression in the progenies of three different cross
combinations.
Finally, results of a linkage study on chlorotic genes will be briefly mentioned below. All the crosses were prepared so that segregation of both of the character pairs, green vs. chlorotic plants and marker character pair, may occur each in a 1:1 ratio. In Table 4 is shown the data obtained from two crosses.
Information about linkages of these two genes so far obtained are: The gene Ch-e is linked with K for hooded character with 26-35% recombination, and independent of Nn and Bb. The gene Ch-a, on the other hand, is independent of Kk and Ss. Its linkage is still unknown.
