| In bread wheat awning is controlled by a set of promotor genes and three
major epistatic genes viz., Hd, B1 and B2. B1
and B2 act as awn inhibitors, while Hd confers hoodedness. If
any two or three of them are present in homozygous condition, then the plant
will be awnless. If the plant is homozygous for only one dominant pair,
it will be tip awned or hooded and if all the three are homozygous recessives,
the plants will be fully awned (WATKINS and ELLORTON 1940). The fully awned
condition is due to the recessive allele 'a' which expresses only when it
is inhibited by the partially epistatic Hd, B1 or B2
genes (HEYNE and LIVERS 1953). The awn promotor genes 'aa' have a multiple
allelic series of 13 alleles from a1 to a13, reported
to be situated on different chromosomes in different varieties (AUSEMUS
et al., 1968, BOZZINI and GIORGI 1971, BAIER et al., 1974).
The three major epiststic genes Hd, B1 and B2 have
been assigned, beyond doubt to chromosomes 4B, 5A and 6B respectively (SEARS
1953, SIKKA et al., 1965, 1959 and AUSEMUS et al., 1968).
Since the results of the present study do not show chromosome 5A as a critical line, it can be concluded that Red Bobs is homozygous recessive at B1 locus i.e., b1b1. However, it is awneless, because of the presence of the other two genes 'Hd' and B2 in dominant homozygous condition. The location of Hd and B1 could not be confirmed because these two critical lines in 4B and 6B were not available for the present study. However, one thing is certain that there should be at least two major genes for awnless condition. Since the chromosome 5A in Red Bobs does not seem to possess B1, the genotype of Red Bobs could be AAHdHdb1b1B2B2. The critical chromosomes in the present study, viz., 1A, 2D, 4A and 4D do not possess any of the major genes but still they influence the character. Hence it is assumed that these critical chromosomes carry awn promotors. According to KUSPIRA and UNRAU (1957), either hd or b2 or both together are epistatic to promotor genes and that Hd or B2 or both together are non-epistatic or partially epistatic to these promoters. This is how the promotor genes influence awn condition. There are reports that chromosomes 1A and 4A carry promotor genes designated as a12 and a7 respectively (BAIER et al., 1974). There are no reports of the presence of any promotor genes on chromosome 2D and 4D. However, in the present study, they are found to carry awn promotors on them. So the promotor genes present on chromosomes 2D and 4D are designated as a14 and a15 respectively. In brief, based on the results of the present study for awn characters, the genotype of Red Bobs with respect to awnedness has been proposed as AAHdHdb1b1B2B2, whereas that of Sharbati Sonora as aahdhdb1b1b2b2. The 'a' gene of Sharbati Sonora has at least four multiple alleles a7, a12, a14 and a15 located on chromosomes 4A, 1A, 2D and 4D respectively. Acknowledgement The authors gratefully acknowledge the supply of complete set of monosomic lines of Red Bobs by Dr. Ruby I. LARSON of Department of Agriculture, Research Station, Lethbridge, Alberta, Canada. Litirature Cited AUSEMUS, E.R., F.H. M'CNEAL and F.W. SCHMIDT 1968. Genetics and inheritance in wheat. In wheat and Whest improvement. (Ed. Quisenberry, K.S. and Reitz, L.P.) Am. Soc. Agron. Publication. pp. 225-267. BAIER, A.C., F.J. ZELLER and FISCHBECK 1974. Monosomic analysis of awning in the spring wheat cultivar Solo. Z. Pfl.zucht. 72: 283-290. BOZZINI, A. and B. GIORGI 1971. Genetic analysis of tetraploid and hexaploid wheat by utilization of monopentaploid hybrids. Theor. Appl. Genet. 41: 67-74. HEYNE, E.G. and R.W. LIVERS 1953. Monosomic analysis of leaf rust reaction, awnedness, winter injury and seed colour in Pawnee wheat. Agron. J. 45: 54-58. KUSPIRA, J and J. UNRAU 1957. Genetic analysis of certain characters in common wheat using whole chromosome substitution lines. Can. J. Plant Sci., 37: 300-326. SEARS E.R. 1953. Nullisomic analysis in common wheat. Am. Nat., 87: 245-252 SIKKA, M.S., K.K. JHA and M.S. SWAMINATHAN 1959. Monosomic analysis in bread wheat II. Identification of chromosomes carying genes for awning and glume beak shape. Indian J. Genet., 19: 56-63. SIKKA, M.S., M.S., SWAMINATHAN M.P. SINGH and B.P. PAL 1956. Monosomic analysis of some characters in wheat variety Cometaklein. Indian J. Genet., 16: 12-28. WATKINS, A.E. and S. ELLERTON 1940. Variation and genetics of awn in Triticum. J. Genet. 40: 243-270. WENZE, W.G. 1971. Monosomic analysis of some morphological characters of Heines Koga II. Z. Pflzucht, 65: 100-120. (Received Dec. 30, 1977) |
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