| Genetic control of factors regulating the phenol reaction
of wheat and rye grain C. W. WRIGLEY and R. A. MCINTOSH CSIRO Wheat Research Unit, North Ryde, N.S.W., 2113 and Plant Breeding Institute, University of Sydney, N.S.W., 2006. Australia The phenol test provides a ready means of checking the purity and identity of cereal grain samples (ANON 1966, WALLS 1965, WRIGLEY and SHEPHERD 1974). Its simplicity makes it attractive: coloration of the bran is assessed after incubating soaked grain on paper wetted with dilute phenol solution. The test is reported to be indicative of genotype and independent of growth conditions, provided grain ripens to less than about 30% moisture. As it is important in these applications of the test that it should be unequivocally characteristic of genotype, further investigation of its genetic regulation was warranted. Furthermore, the reaction should serve as a marker in genetic studies. JOSHI and BANERJEE (1969) have reported that in emmer wheats, the phenol reaction is monogenically controlled and that a multiple allelic series is involved. BHOWAL et al. (1969) concluded that the A genome is the source of the gene in the emmers and in bread wheat. ZEVEN (1972), using substitution lines of Chinese Spring, suggested that genes for phenol reaction of grain were located on chromosome 2A in Hope, and on 2A and 2D in Timstein. He suggested Tc (tyrosinase in caryopsis) as a gene symbol to replace earlier suggestions of Pk. F and B. The phenol reaction of the outer glumes is also useful in varietal identification. The extent of glume coloration appeared to be phenotypically independent of grain reaction for about fifty Australian wheats (WRIGLEY and SHEPHERD 1974), although some genetic linkage between the loci has been suggested (FRAZER and GFELLER 1936). ZEVEN (1972) proposed the symbol Tg for the gene for the phenol reaction of glumes. Chemically, the test is generally explained as involving the enzymic oxidation of phenol, through diphenols to quinones and finally to dark brown melanins. The enzyme system involved has variously been called monophenoloxidase or tyrosinase (ZEVEN 1972), DOPA oxidase (ABROL et al. 1971), polyphenol oxidase (TIKOO et al. 1973), or the phenolase complex (MASON 1955). Our studies indicate that the phenol reaction is mainly regulated by genes on chromosomes 2AL, 2DAlpha and 2R in the lines examined. The following results are reported in the present form because most aspects of the work are being discontinued. Materials and Methods Plant materials used were derived from various research programmes: E. R. SEARS, University of Missouri (Hope, Timstein, Red Egyptian and Thatcher substitution lines, Chinese Spring aneuploids and the Imperial Rye addition and substitution lines); L. A. SNYDER, University of Minnesota (Marquis and Kenya Farmer substitution lines); Rosalind MORRIS, University of Nebraska (Cheyenne substitution lines). For phenol testing, grains or glumes were soaked overnight in water. After blotting off excess moisture, they were spread out on filter paper (Whatman No. 1) wet with 1% aqueous phenol (10 to 20 microl per cm2), covered to prevent loss of moisture, and incubated at 40o for 2.5 hours. |
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