Identification of alternate dwarfing gene sources to widely used Dee-Gee-Woo-Gen allele of sd1 gene by molecular and biochemical assays in rice ( Oryza sativa   L.)

After the success of IR8 and TN1, breeders depended heavily on these two rice cultivars for source of short stature led to the narrow genetic base to majority of present day rice varieties, as far as sd1 (semi-dwarf1) gene is concerned. In addition, analysis of genetic lineage of the majority of the cultivated rice varieties in tropical Asia reveals that sd1 from DGWG (Dee-Gee-Woo-Gen) is the source of dwarfing gene. Such high amount of genetic homogeneity renders rice plants vulnerable to epidemic of diseases and insect pests. In the current study, we made an attempt to identify the alternate sources of DGWG allele of sd1 gene by characterizing 29 induced and 3 spontaneous dwarf accessions employing marker for DGWG allele of sd1 gene and exogenous application of gibberellic acid (GA3). When occurrence of DGWG allele of sd1 gene and GA3 response were analyzed together, existence of two kinds of dwarfs was noticed viz., dwarf accessions with DGWG allele and dwarf accessions without DGWG allele of sd1 allele exhibiting varying responses to GA3. As many as 22 of 32 dwarf accessions showed absence of DGWG allele of sd1 gene with varying response to GA3 could be used as excellent alternate sources for DGWG allele of sd1 gene. These dwarf accessions could be used for broadening the genetic base for the plant height and thereby minimize the risk of genetic vulnerability. Our strategy of combining molecular and biochemical assays can be efficiently used for identifying alternate dwarfing gene sources to the Green Revolution gene sd1.

Keywords
Dee-Gee-Woo-Gen, dwarfing gene, gibberellic acid assay, molecular marker, rice, sd1 gene.