Rice variety, Improved White Ponni is a medium duration crop, but highly susceptible to lodging impacting maximum yield losses. The present investigation aimed to identify early and early semi-dwarf mutants in Improved White Ponni by inducing variations using gamma rays without altering its native grain quality traits. Seeds were treated with various doses of after fixation of the LD50 value of gamma radiation and reported that most of the traits exhibit variations in the mutants at various

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... ls of irradiation. The selection for earliness and dwarf plant height was imposed in M2 and it was confirmed by evaluation of M3 generation. Apart from semi-dwarf early mutants, high tillering habit, narrow rolled leaf, upper albino leaf and grassy stunt and extreme dwarf mutants were also identified. Characterization of mutants using already reported genic and linked microsatellite markers associated with semi-dwarfism and earliness resulted that PIC value ranges between 0.037 and 0.949 with an average of 0.382. Single marker analysis revealed that RM302 and RM310 on chromosome 1 and 8 had exhibited an association with the traits plant height, culm and internodal lengths. Of these gene-specific markers, GA20Oxi_1 and GA20Oxi_2 have shown polymorphism among mutants. GA20Oxi_2 showed null alleles in the dwarf mutants and this clearly emphasized that there are some base deletions exists in the region of exon 2 of sd1 region. GA3 response study shown that identified mutants were GA3 responsive except IWP 11-2, IWP 48-2, IWP 50-11 and IWP 33-2 which showed very low responsive. Agar plate assay revealed that, IWP 50-11, IWP 33-2, IWP 43-1, IWP 47-2 and IWP 18-1 had low production of α- amylase. Scanning electron microscope examination on confirmed mutants exhibited larger cell size and a lesser number of cells per unit area than the wild-type which shows that these mutants are defective in GA mediated pathway