Abstract:
Herbicide resistant (HR)of rice has the potential to improve efficiency of weed management practices, reduction in
rice production cost, increase productivity and reduce usage of herbicides. However, HR in Sri Lankan rice varieties
has so far not been evaluated or developed. Sri Lankan rice varieties may harbor HR for possible incorporation in rice-breeding programs and mutagenesis may activate new genes conferring HR. The chemical mutagen, Sodium azide
(NaN3) (1.5 mmol/1, 3.0 mmol/1 and 6.0 mmol/1 concentrations) was used to induce HR in eighteen cultivated rice
varieties against pre-emergent broad-spectrum herbicide, Glyphosate. Randomized Complete Block Design (RCBD)
was used in the experiment and there were five replicates and three blocks in each treatment. For each rice variety,
percentage resistance for Glyphosate concentrations (0.25 g/1 and 0.5 g/1) was noted. The plants with > 40%
resistance were considered as resistant to Glyphosate. Morphological characters, Days to seed germination, Days
taken to flower, Plant height at 12 weeks after sowing (WAS), number of leaves at 12 WAS, leaf length, width, length of
panicle and number of seeds/panicle of the herbicide-treated resistant plants and un-treated resistant plants were
recorded. Statistical analyses were carried out using SAS 6.12. Five cultivated rice varieties, Bg406, Bg352, Bg379-2,
Bg300, Bw364 showed resistance against Glyphosate at 0.25 g /1 concentration. The results showed that NaN3 could
be used to produce Glyphosate resistant rice varieties from existing cultivated rice varieties (or new improved
varieties). The mutant rice varieties were greatly differ from their parental varieties having increased days taken to
flower and seed germination, reduced plant height, number of leaves/plant, leaf-length, leaf-width panicle-length
and number of seeds/panicle., and imposing a mutagenic penalty on the yield of the crop as whole. The higher the
NaN3 concentration used for mutagenesis, the greater the Glyphosate resistance. However, further studies are being
carried out to confirm the stability of Glyphosate resistance among these mutated rice varieties.
