EVALUATION OF GENETIC VARIABILITY INDUCED BY IRRADIATION IN WHITE ONION Cv. PHULE SAFED
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Date
2003
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MAHATMA PHULE KRISHI VIDYAPEETH, RAHURI-413 722, DIST. AHMEDNAGAR MAHARASHTRA STATE (INDIA)
Abstract
The present investigation entitled, "Evaluation of genetic variability induced by irradiation in white onion cv. Phule Safed" was undertaken with the objectives to induce novel variability in onion germplasm, especially for characters like high TSS content (16-18%), male sterility and resistance against purple blotch disease through mutation breeding. Also the effect of irradiation was studied on plant growth, bulb development and seed parameters in three crops of two generations (i.e. M1 bulb and seed crops and M2 bulb crop). The onion seeds were irradiated with four doses of gamma irradiation (10, 20, 30 and 40 kr) and M1 bulb crop was assessed during kharif, 2001. The 168 bulbs from 10 kr irradiation were selected to raise seed crop during rabi 2001-2002 and 500 plant population of M2 generation developed from 50 M, plants were evaluated as M2 bulb crop during kharif 2002. The average performance and variability between two populations (i.e. irradiated and control) was measured by t and F tests, respectively. The marked adverse effect of irradiation was noticed on seed germination, seedling development and bulb development in both M1 and M2 generations. In M1 generation, the severity of adverse effect was increased proportionately with increase in irradiation doses (i.e. 10-40 kr). Among four irradiation doses, the 10 kr irradiation was found as the most suitable irradiation dose for onion crop. In M1 bulb crop 10 kr irradiation resulted in 72.09% seed germination, 47.76% seedling mortality followed by 77.50% bulb development associated with 3-6 cm equatorial diameter. While evaluating bulb characteristics of M1 generation, it was noticed that character, equatorial diameter showed significant different average performance and variability than the control population. However, non-significant variability was noticed among irradiated and control populations for characters, polar diameter and TSS content. In M1 seed crop, an adverse effect of irradiation was noticed on most of the characters (e.g. plant height, number of umbels per bulb, pollen viability, number of seeds and seed weight per bulb), except the character, number of leaves; where more number of leaves (18.57) were observed than the control one (11.04). Thus, in M1 seed crop, significant different average performance and variability was recorded than the control population. In M1 seed crop eventhough pollen viability was reduced significantly (45.66%), complete male sterility could not be detected with 10 kr irradiation. In M2 bulb crop, an adverse effect of irradiation was continued onseed germination, seedling growth, plant height, bulb weight and bulb diameter. Thus, significant different average performance and variability was recorded by M2 generation than that of control population. More importantly, wide range variability was observed in M2 generation, particularly for characters like number of leaves, foliage colour, plant height, bulb weight and equatorial bulb diameter. This wide range variability offered by M2 generation can be exploited effectively in future crop improvement programme. Especially, vigorous plant growth coupled with bigger bulb development can be utilized to improve yield potential of Indian white onions and also for export-oriented bulb production. Nevertheless, 7.6 per cent M2 plants showed resistance against purple blotch disease under artificial epiphytotic conditions. It was associated with dark green waxy foliage containing total chlorophyll within range of 95.8 - 108 mg/100 gm, which was double than normal green foliage. Thus, eventually 10 kr irradiation was found beneficial in onion for improvement of yield potential and development of resistant source for purple blotch disease. However, to locate male sterility and higher TSS content; variability should be induced by higher irradiation doses (15-25 kr) and larger plant population (1000 plants) should be screened in M2 generation.
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