Marker assisted introgression of multiple genes for bacterial blight resistance into aromatic Myanmar rice MK-75

- Pyramiding of bacterial blight resistance genes into Myanmar mega and improved variety, aromatic Manawthukha using marker assisted backcross breeding method.
- Broad-spectrum resistance that can be useful in different areas in Myanmar which is vulnerable to bacterial blight infection.
- Development of aromatic Manawthukha lines with bacterial blight resistance while maintaining grain and cooking qualities.

Bacterial blight disease (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major threat to rice yield in rainfed and irrigated lowland ecosystems in Myanmar. Large-scale and long-term cultivation of released Myanmar rice varieties have continuously caused the outbreak of BB since 1983. In this study, a high yielding Manawthukha rice line 'Yn 3248-2-128-76-4-3-75' (MK-75) with fragrance and intermediate amylose content was used as a recipient parent to improve its resistance to BB. RGDU-07097-1-8M-9 (RG-9), an improved line carrying xa5, Xa21 and xa33 was used as the donor parent. Resistant alleles of xa5, Xa21 and xa33 from RG-9 were successfully transferred into MK-75 by using marker-assisted backcrossing (MAB) method while maintaining the cooking quality of MK-75. Twenty eight selected BC3F2 introgression lines (MK-75 ILs) carrying different combinations of these three loci were tested for BB resistance at seedling and maximum tillering stages against ten Thai and five Myanmar Xoo strains. The triple and double resistance gene-introgressed lines (xa5Xa21xa33 or xa5Xa21 or xa5xa33 or Xa21xa33) had higher level of resistance and wider resistance spectrum than MK-75 against both Thai and Myanmar Xoo strains. The single resistance gene-introgressed lines carrying xa5 had higher resistance against Thai Xoo strains, while lines carrying Xa21 showed higher level of resistance to Myanmar Xoo strains. These results clearly indicated that pyramiding of multiple genes is a useful approach for improving BB resistance in MK-75. All ILs had physical grain quality, fragrance and amylose content similar to MK-75. Thus the improvement of BB resistance in MK-75 may have a wide range of benefits in breeding program and should be immediately useful in areas where original Manawthukha, the progenitor or MK-75 is widely grown.