Short growing seasons and late season heavy rains are the main challenge of rice cultivation in North of Iran. Thus, the isolation of novel mutants with higher yield, a shorter growing period (earlier maturity date), and high grain quality is necessary. Chemical agents can be beneficial since they provide high mutation rates to produce variants for tolerance to biotic/abiotic stress conditions (Jain, 2010). The dose assessment for chemicals is characterized by altering the duration and concentration of treatment, the solvent used (e.g. dimethyl sulfoxide), or the pH of the solution (Jain, 2005). Gohar is a high yielding variety with slender grains and good cooking quality. The variety is late in maturing, requiring a growing period of 135 to 140 days (seed to seed) under local conditions. Therefore, it is of particular importance to improve the variety in order to
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