Abstract

Gamma (γ) ionizing ray is a physical mutagen, producing variation in crop improvement and employing such as a complementary tool in breeding process. The γ-ray dosages are a critical issue, so it should be optimized. In this research, various doses of gamma radiation including 150, 250, 350 and 450 Gy applied on three rice varieties (Tarom-hashemi, Sange-tarom and Nemat), and their effects were evaluated on 50% lethal dose (LD₅₀), rate and percent of germination, radicle and plumule length at in vitro, including cluster analysis of dosage quantities at genotypes, range of variation (R), variation coefficient of treatment regarding to control dosage (CVt/CVnt). Euclidean similarity coefficient including UPGMA (Unweighted Pair Group Method with Arithmetic Mean) algorithm was used for cluster analysis. The results indicated that 250 and 350 Gy γ-rays have much more better effects to create variation rather than other doses and also clearly showed that γ-ray made novel variation in panicle sterility percentage, plant height, 1000 grain weight and fertile tillers on the studied varieties. Meanwhile the dendrogram of clustering classified into 3 groups on the base of gamma effects and control doses were placed in different groups. The LD₅₀ values related to seed germination computed 350, 310 and 170 at Sange-tarom, Tarom-hashemi and Nemat respectively.

Key words: Gamma ray, rice, mutation, morpho-physiological characteristics.