Comparison of transgenic plant production for bacterial blight resistance in Pakistani local rice (Oryza sativa L.) cultivars

Abstract

The study was carried out to improve bacterial leaf blight resistance in three rice cultivars (Basmati - 370, DR - 82 and IR - 6) by Agrobacterium mediated transformation system. Three week-old scutellum derived calli were infected with Agrobacterium strain EHA101, containing binary vector pTCL5 which has Xa 21 gene. Different levels of acetosyringone were tested to enhance transformation efficiency. Acetosyringone at 300 ìM showed 56.6% GUS expression with 100 and 200 ìM acetosyringone showing 13.3 and 30.0% GUS expression, respectively. Maximum transformation efficiency was obtained using DR - 82 with calli exposed to 300 ìM acetosyringone for 2 min. Direct hygromycin selection with 48 h of
co-cultivation was superior to pre-selection in all three cultivars. Transient GUS expression was 51.4% while stable GUS expression in calli was 18.8%. PCR analysis confirmed the presence of the Xa 21 gene in transformed regenerated plants. Stable varietal transformation efficiency was DR - 82 > Basmati-370 > IR - 6. Resistance of transgenic plants against Xanthomonas oryzae pathovar oryzae was evaluated with various strains/isolates at the seedling stage. All PCR positive transgenic plants of DR - 82 and Basmati - 370 were resistant with lesion areas less than 5% of the inoculated leaf area. The tested transgenic plants were resistant to all the indigenous and exotic strains tested due to the broad spectrum protection provided by the Xa 21 gene.