Changes in the genetic structure through gamma radiation of the plant can produce physiologically and bio-chemically efficient plant type with respect to increase production and attractiveness. For mutation breeding, scientists use gamma radiation to produce effective plant types. Beforehand, an effective range of radiation should be identified for possible suitable mutational effect. In this context, the present study was conducted to determine the effective doses of gamma radiation for mutational breeding of sunflower (H. annuus L.) on vegetative growth performances. Sunflower seeds were exposed to different doses of gamma radiation (0 Gy, 100 Gy, 200 Gy, 300 Gy, 400 Gy and 500 Gy) as treatments. The experiment was laid out in the Complete Randomized Design (CRD) with six treatments in four replications. Each replication comprised ten plants in field. Treating the sunflower seeds with gamma radiation has a significant (p<0.05) effect on the tested parameters except on germination percentage. Untreated plants with gamma radiation and plants treated with lower doses of gamma radiation (100 and 200 Gy) showed comparable values in percentage survival as 100%, 94.5% and 92.5%, respectively. LD50 value was recorded as 440 Gy. In the first two weeks of growth, untreated plants and plants treated with 100 Gy with gamma radiation showed similar values in a number of leaves and plant height. Later in the 4 th and 6 th week highest values were found where plants were not exposed to gamma radiation. A reducing trend in values in the measured variables has been observed with the increase in gamma radiation doses. The lowest values in all observations were recorded by the seeds exposed to 500 Gy, which is the highest dosage used in this experiment. The plants treated with the dosages higher than 100 Gy exhibited misshapen, deformed and abnormalities in leaves compared to the control, but the changes were not persisted. Hence, it could be suggested that exposing the sunflower seeds to gamma radiation dose has caused the negative effects on vegetative growth performances. Further, exposing sunflower seeds close to 440 Gy may have the potential to produce the sunflower variations especially dwarf plant stature with desired characteristics and optimum survival for domestication in future studies.

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