| For the mapping of the Ch2 gene, three strains of common wheat,
NIG 1, NIG 7, and CS ditelo-3DL, were used. Their genotypes for hybrid chlorosis
are shown as follows: CS ditelo-3DL ch1ch1Ch2Ch2 or ch1ch1 - - NIG 1 ch1ch1ch2ch2 NIG 7 Ch1Ch1ch2ch2. The breeding procedure taken for mapping the Ch2 gene is illustrated in Fig. 2. The eight F1 plants from the cross, CS ditelo-3DL x NIG 1, were pollinated by NIG 7. Because the offspring of this cross segregated two phenotypes, chlorotic and normal, it can be concluded that the Ch2 locus locates on the long arm of chromosome 3D (Fig. 2). All of the plants in this segregating generation were divided into four classes according to their chromosome constitutions and their chlorosis phenotypes (Table 2). In total, 53 recombinants were obtained among 147 plants tested. Thus, the crossing over value between the Ch2 locus and the centromere is estimated to be 53/147 or 36.1 + or - 4.0%. However, the frequency of the non-chlorotic monotelodisomics (one of the recombinant classes) was in great excess, and that of the chlorotic disomics was in shortage, comparing to their expected frequencies. Reasons for this discrepancy must be elucidated in further works. From the results described above, the first linkage map to chromosome 3D was constructed as shown in Fig. 3. It appears that the Ch2 gene locates on the distal part, while the s gene locates on the very proximal region of the long arm of chromosome 3D. To confirm this map, distance between the s and Ch2 genes must be measured, that is now under investigation. Literature Cited SEARS, E.R. 1947. The sphaerococcum gene in wheat. Genetics 32: 102-103. TSUNEWAKI, K. and H. KIHARA 1961. F1 monosomic analysis of Triticum macha. Wheat Inf. Serv. 12: 1-3. (Received Jan. 24, 1978) |
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