A Database for Triticeae and Avena
*Present address: Tohoku Seed Co., Ltd., Utsunomiya 321, Japan.
Tabata (1961) first reported a gametophytic factor, Ga, which was linked with the waxy locus, wx, on chromosome 1. Takahashi and Hayashi (1966) found the di-storted segregation ratios of the cu-2 segregants in several F2 populations 'Cheshiro-hen', due to the certation between pollens of different genotypes. In our study of linkage between two loci for the BaYMV resistance and esterase isozymes, the distorted segregation ratio was observed in a F2 hybrid between 'Ko A' and 'Mokusekko 3'. As shown in Table 1, the frequency of genotype of 'Mokusekko 3' (P2:/Ca-null-Nz for allelic combination at esterase isozyme loci, Est-1, Est-2 and Est-4) was markedly lower than the theoretical one T~5%), while that of the other parent, 'Ko A'I (P1:Af-null-Su) was higher. A similar result was obtained in the same hybrid population grown in the next year.
Furthermore, using reciprocal B1F1 hybrids, the segregation ratio of esterase isozyme genotypes was examined. As is apparent in Table 2, the distortion occurred in B1F1 hybrids, only when F1 hybrids of the single cross (P1 x P1) were used as the male and either of the parents as the female. Namely, in B1F1 hybrids of P1 × F1 combination, the frequency of P1 genotype was significantly higher than the theoretical one (50%), while that of F1 genotype (heterozygote) was lower. On the contrary, P2 genotype was remarkably less frequent than F1 genotype in B1F1 hybrids of P2 × F1. These results indicate that the certation occurred between the pollens having different genotypes, although indifferently of the female genotype.
For estimating the recombination value between two loci for the certation and esterase isozymes, the segregation ratio of esterase isozyme genotypes was examined in each of the F3 progenies derived from heterozygotes in F2 population of the single cross (P1 × P2)- As seen in Fig. 1, the progenies were divided into two groups based on the segregation ratio. One of the groups consists of F3 progenies showing the distorted segregation ratio (open circle), and the other progenies exhibit the normal segregation ratio (P1 = P2 = 25%; closed circle).
From the numbers of the two groups of F3 progenies, the recombination value between two loci for the certation and esterase isozymes were estimated to be 11.7 + 4.14%, using the formula proposed by Nakagahra et al. (1972).
As the three loci for esterase isozymes (Est-1), Est-2 and Est-4.) linked closely each others are located at the terminal of the long arm of chromosome 3 (Konishi and Matsuura, 1987), the locus for the certation (Ga-2) is thought to be on the long arm of chromosome 3. Furthermore, the certation observed in hybrid populations of 'Choshiro-hen' (Takahashi and Hayashi, 1966) might also be controlled by the same gene (Ga-2, because the two loci for curly-2 (cu-2) and esterae isozyme-4 (Est-4) are linked with 23.75 + 1.9% recombination value (Konishi and Matsuura, 1987).
References:
Konishi, T. and Matsuura, S. 1987. Linkage analysis of Est-4 locus for esterase isozyme-4 in barley. BGN 17:68-70.
Nakagahra, M., Omura, T. and Iwata, N. 1972. Gemetophytic genes and their loci on the eleventh linkage group of cultivated rice. Japan. J. Bred. 22:305-312.
Tabata, M. 1961. Studies of a gametophyte factor in barley. Jpn. J. Genet. 36:157-167.
Takahashi, R. and Hayashi, J. 1966. Inheritance and linkage studies in barley. II. Assignment of several new mutant genes to their respective linkage groups by the trisomic method of analysis. Ber. Ohara Inst. Landw. Biol., Okayama Univ. 13:185-198.