| I. Research Notes Two new awn promoter genes in bread wheat J.V. GOUD and A.R. SADANANDA Department of Agricultural Botany, college of Agriculture, Dharwar, Karnataka, India The most extensive genetic studies on inheritance of awning have been reported by WATKINS and ELLORTON (1940). They have shown that five major genes, viz., B1 b2a, B2, A, Hd determine awn development. The B genes act as awn inhibitors, A acts as awn promotors, b1a leads to half awned condition and Hd gives hooded condition. Different methods of aneuploid analysis generally have not only substantiated the above mentioned series, but have shown that additional chromosomes are also associated with some form of awn expression. WENZEL (1971) through monsomic analysis of cultivars Kurrachu and Norin-9 using Heines Koga-II monosomics, reported the presence of genes for awnedness on eight chromosomes of which 1B, 5D and 7A were reported for the first time, to carry genes responsible for this character. In the present communication presence of two new awn promotor genes has been indicated. The material for the present investigation constituted the F2 populations derived from crossing Red Bobs (Awnless), a Canadian cultivar and its monosomic lines for chromosomes 1A, 1B, 1D, 2D, 3D, 4A, 4D, 5A, 6A, 6D and 7B with Indian variety Sharbati Sonora (awned). The eleven monosomic F2 Populations were obtained by selfing the respective monosomic plants, selected after confirming the monosomic condition. The F2 plants were classified into three categories based on awn characters, viz., i) awned - all spikelets having long awns, ii) hooded - only top spikelets having long awns and iii) awnless. Awning in bread wheat is controlled by a series of awn promotor genes and three major epistatic genes Hd, B1 and B2. If any two or all the three of the genes were in homozygous condition, the plant would be awnless. If homozygous for only one dominant pair, it would be tipped or hooded and if all the three were in homozygous recessive state, it would give awned expression (WATKINS and ELLORTON 1940). Based on this hypothesis, the genotype of Red Bobs, an awnless variety was assumed to be AA Hd Hd b1b1 B2B2, while that of awned variety, Sharbati Sonora as aahdhd b1b1b2b2 where 'a' is a multiple allelic series of awn promotors. On these assumptions, the goodness of fit of frequencies of three phenotypic classes was tested against 45 awnless : 12 hooded : 7 awned ratio. The results obtained are presented in Table 1. A glance of the table would indicate significant deviations in the segregating pattern in monosomic populations for chromosomes 1A, 2D, 4D and 1% level and 4A as critical chromosome at 5% level. Red Bobs, the monosomic parent, is an awnless variety, whereas the male parent Sharbati Sonora is a fully awned variety. The F2 progenies of the eleven monosomic crosses and a disomic population segregated not only to the parental types but also to an array of intermediates. This segregation pattern showed a good fit for 45 awnless: 12 hooded: 7 awned ratio. This ratio was obtained after assuming the genotypes of Red Bobs, to be homozygous recessive to any of the two inhibitory genes i.e., either AA, HdHd, B1B1, b2b2 or AAHdHd b1b1 B2B2, whereas aahdhd b1b1b2b2 was assigned to Sharbait Sonora. The results indicated that the chromosomes, 1D, 2D, 4A and 4D as the critical chromosomes. |
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