Improvement of the submergence tolerance and the brown planthopper resistance of the Thai jasmine rice cultivar KDML105 by pyramiding Sub1 and Qbph12

• The application of marker-assisted selection (MAS) in breeding programs hastened the development of lines containing the desired trait/s. In this study, the traditional KDML105 popularly grown in rainfed lowland areas in Thailand is intolerant to flash flooding and brown planthopper damage. Two major QTL namely Sub1 and Qbph12 were incorporated into KDML105 by marker-assisted backcrossing. Homozygous lines containing Sub1 and Qbph12 were pyramided using marker-assisted selection coupled with stringent phenotypic selection in developing KDML105 breeding lines with submergence tolerance and brown planthopper resistance. The study displayed the success in combining QTL/gene into a popular rice background that is suitable in areas frequently damaged by flash flooding and brown planthopper attack. Once again, marker-assisted selection has been an indispensable tool in rice breeding program.
• The study also dealt on the maintenance of grain quality and yield stability as revealed by multi-location trials in elite lines with KDML105 background aside from the incorporation of submergence tolerance and brown planthopper resistance. Thailand has been number one exporter of premium rice and therefore quality based on physical and chemical aspects of the grain are important traits in breeding rice particularly in the rainfed lowland areas where very aromatic and palatable KDML105 is produce. Moreover, yield was improved in the elite lines as tested in three locations in the northeast Thailand. With the increase in yield and addition of new traits the elite lines while maintaining the grain cooking and eating quality has high impact to rice farmers in the area.

Shifts in weather patterns and increases in the frequency and magnitude of extreme weather events resulting from unfavorable climate change have led to frequent flooding and brown planthopper outbreaks in rice fields, particularly those in rainfed lowland areas in Thailand. The traditional jasmine rice cultivar KDML105, which is popularly grown in rainfed lowland areas in north and northeast Thailand, is intolerant to flash flooding and is very susceptible to the brown planthopper. Two major QTL, Sub1 and Qbph12, were individually introgressed from two donors into KDML105 using the marker-assisted backcrossing method. In this study, we have pyramided Sub1 and Qbph12 in the genetic background of KDML105 via marker-assisted selection coupled with stringent phenotypic selection for plant type and physical grain quality traits. In total, sixty-four pyramid lines (PLs) were developed and characterized for submergence tolerance, brown planthopper resistance, important agronomic traits and physical and chemical grain quality. Evaluation of the PLs indicated their significantly enhanced submergence tolerance and brown planthopper resistance compared with the original KDML105 line. All PLs satisfied the KDML105 grain and cooking quality standards, although their agronomic characteristics showed significant variations in days to flowering, plant height and grain yield. These variations might allow breeders to select new versions of KDML105 that are suitable for different locations in rainfed lowland environments.