Figure 1 shows the phenol reactions for grains and glumes of several cultivars. Grain reactions ranged in coloration as follows:
Reaction 0: no change in colour, e.g. Dural.
Reaction 1: light brown, e.g. Chinese Spring, Heron.
Reaction 2: medium brown, e.g. Halberd, Red Egyptian.
Reaction 3: dark brown, e.g. Cheyenne, Eagle, Hope, Holdfast, Kenya Farmer, Marquis, Thatcher, Timgalen, Timstein.
Chromosome substitution lines
Table 1 shows the phenol reactions for grain of chromosome substitution lines of homoeolgous group 2, in which nearly all reactions darker than Chinese Spring were observed. Samples for each series were obtained from several sources. Of the Thatcher series, only the 2A, 2B and 2D lines were examined. Lines 1D and 2B of the Cheyenne series were not available. All lines involving chromosomes of groups 1, 3, 4, 5 and 6 gave reactions indistinguishable from that of Chinese Spring. Darkening was obtained for a few lines involving group 7 chromosomes of the Cheyenne and Red Egyptian series, but usually only for some grains of the samples. Unequivocal grain colorations were obtained for chromosomes 2A and 2D as shown.
Rye
Further involvement of group 2 chromosomes was found by examining Chinese Spring addition and substitution lines involving Imperial Rye chromosomes. Grain of SEARS' Chinese Spring-Imperial Rye triticale gave a phenol reaction of 2. (The original Imperial Rye was not available). The 2R (2A) substitution line (probably a translocation 2R-2AL (SEARS 1968)) and the 2R addition line both gave grain reactions of 3. Other rye substitution lines were not tested, but the remaining six addition lines reacted the same as Chinese Spring. Rye addition lines based on Holdfast would not be suited to this approach, since the wheat parent itself reacts strongly with phenol.
The grain reaction of Chinese Spring
Of 34 available nullisomic-tetrasomic lines of Chinese Spring, only those nullisomic for 2D gave a O reaction. Nulli-2B tetra-2D produced a 2 reaction, considerably darker than grain of Chinese Spring. (Nulli-2A tetra-2D was not available). All other lines reacted similarly to Chinese Spring. Further evidence that chromosome 2D is involved was provided by the 2 reaction of tetrasomic 2D. Chinese Spring ditelo-2DAlpha reacted identically to Chinese Spring. (Ditelo-2DBeta is not fertile and hence cannot be tested by this method). Thus the gene regulating the pale brown phenol reaction of Chinese Spring grain appears to be located on the Alpha arm of chromosome 2D.
Genetic studies on the grain reaction of Timstein
The Timstein 2A substitution line was crossed to the respective ditelomonotelosomic 2A lines of Chinese Spring. The appropriate cytologically selected plants with 2n=42t (42 chromosomes including one telocentric) in each cross were test-crossed as female with Chinese Spring. Chromosome numbers of progenies were determined by root-tip mitotic analyses. These plants were grown to maturity and the grains harvested from them were tested for phenol colour reaction.
In the case of the 2AL telosomic test-cross, 68 individuals were analysed as being positive (+ve) (significantly darker than Chinese Spring) or negative (-ve):
The approximate 1:1 ratio of positive: negative phenol colour reactions suggests that a single gene for reaction was involved, and based on that interpretation a linkage value of 36.8+ or -5.8% between the locus involved and the 2A centromere was estimated.
In the test-cross involving the 2AS telosome, only 18 plants were examined: 15 with 2n=42 all reacted positively whereas 3 with 2n=42t reacted negatively. Although the number of plants is small, the results are as expected if the locus under test is located in 2AL.