Field experiments were conducted during two successive seasons 2004 and 2005 to investigate the effect of various doses of gamma irradiation on growth, flowering and chemical constituents of Tagetes erecta plants cultivated under different levels of compost. The results revealed that the high compost levels had a pronounced effect on vegetative and flowering growth than the low ones. The total carotenoids, anthocyanins, total polyphenols and essential oil content of both herb and flowering

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... showed more accumulation with high compost level as compared with the low level. Gamma irradiation at various doses up to 6 K-rad, stimulated significantly the growth and flowering characters as well as different chemical constituents. The highest gamma dose (8 K-rad) in general, had a contrast effect, which inhibited most of these characters. The interaction between high compost level and gamma irradiation at the dose of 6 k-rad resulted in the maximum mean values of growth parameters,i.e. plant height, branches number, fresh and dry weight of herb and flowers. Similarly, the content of total carotenoids and total polyphenols in the herb, essential oil percentage and yield of the herb and flowers, gave the highest accumulation values with the same treatment, i.e., high compost level (7ton/Fed.) + 6 k-rad gamma irradiation.