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Results and discussion

The statistical analysis of the data had revealed that the mean values of two and three years old seeds were significantly lower than those of the freshly harvested seeds. It was therefore thought proper to consider percentages in reduction over the disomic lines to suggest the involvement of the chromosome(s).

Coleoptile length
The one year old seeds of all the monosomic lines were affected at almost same degree. Storage effect became more conspicuous in two years old seeds (
Table 1). In monosomic line 5A, the coleoptile length was found only 47% compared to the fresh seeds. In other monosomic lines for chromosomes 1B, 2B, 3A, 4A and 7D, the reduction was over 35%. Monosomic line 7B showed only 10% reduction which was much lower than disomic line (25%). The reduction in coleoptile length in the seeds stored for three years was more than 50% in the monosomic lines for chromosomes 1B, 4A, 5A, 6A, 6B, 7A and 7D. The disomic line showed 29% reduction. Interestingly enough, monosomic line 7B again showed less reduction (20%) compared to disomic line.

These observations suggest that the factors for coleoptile length promoter are located on at least nine chromosomes, 1B, 2B, 3A, 4A, 5A, 6A, 6B, 7A and 7D in variety Pb. C591. The involvement of chromosomes 1B, 2B, 3A, 6A, 6B, 7A, and 7D in this character was demonstrated by Gale and Spencer (1974). Allan and Vogel (1964) observed the involvement of at least eleven chromosomes for the development of normal coleoptile length. Logically the progress in improving the length of coleoptile will be slow, because of the involvement of so many chromosomes. Besides these chromosomes which possess genes for length promotion, chromosome 7B was found to carry a gene or gene complex which inhibits the length of coleoptile (hemizygous ineffective). It leaves an opportunity to modify the effect of the gene or gene complex located on chromosome 7B through mutation, recombination or both and increase the length of coleoptile.

Seedling height
Freshly harvested monosomic and disomic seeds did not show much differences in their seedling height (
Table 2). Monosomic line 7A showed 20% reduction while the reduction in disomic line was 6% in one year old seeds. The reduction in seedling height became more apparent in the seeds stored for two years. Monosomic lines 1B, 5A and 5D showed reduction in the seedling height to the tune of 59%, 53%, and 50%, respectively, while disomic line showed only 35% reduction. In the monosomic line 6D and 7B, the reduction were 18% and 16%, respectively. The reduction in seedling height was much more in three years old seeds. Monosomic line for chromosomes 1B, 4A, 5A, and 6A showed more than 63% reduction, while it was 53% in disomic line. The maximum reduction of 70% was observed in monosomic line 4A. Based on these observations it is presumed that chromosomes 1B, 4A, 5A and 6A carry genes for promoting the seedling height in an Indian tall variety Pb. C591. Chromosome 4A has been reported to carry dwarfing genes Rht1 (Gale and Marshall 1976) and Rht3 (Gale et al 1975). Similarly chromosome 5A has been reported to carry dwarfing gene Rht12 (Sutka and Kovacs 1987). It is therefore likely that variety Pb. C591 may be carrying alleles of the dwarfing genes Rht1, Rht3 and Rht12. Since many chromosomes are common in promoting coleoptile length and seedling height, it will appear as if these traits are positively correlated.

The reduction in seedling height in the monosomic line 7B was much lower than disomic line, suggesting that the chromosome 7B may be carrying gene or gene complex which inhibits the seedling height. Chromosome 7B has been reported to carry Rht9 by Law and Worland (1985).

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