Mutagenesis
The rice (O. sativa L.) grains of cultivar IR64 were soaked in
distilled water for 24 h initially, and then were soaked in a
phosphate buffer (pH 3.0) for 4 h. These rice grains were then
divided into four groups and further soaked in 1, 2, 5 and 10 mM of
NaN3 solution (dissolved in the same phosphate buffer) for 24 h,
respectively. Afterwards, the treated grains were rinsed with deionized
water and then planted in nursery trays. The calculated
rates of seedling emergence of those rice grains that had been
subjected to various NaN3 treatments were generally above 76%
(Table 1). Through randomized selection 500 three-leaf-stage
seedlings from each treatment group were transplanted in the
experimental farm field of Taiwan Agricultural Research Institute
(Wufeng, Taichung). Only the M1 generation plants with
morphological characteristics distinctly different from the wild
type IR64 were marked and collected (only one panicle was
harvested from each plant) to produce the M2 generation plants.
The produced M2 plants were advanced to the M8 generation
through the single-seed-descent method (two generations were
grown per year) (Grafius, 1965). A total of 254 mutants of the M8
generation were grown and maintained in the field for quantitative
analyses.