Bacterial Panicle Blight Resistance QTLs in Rice and Their Association with Other Disease Resistance Loci and Heading Date

Bacterial panicle blight (BPB) of rice (Oryza sativa L.) occurs when the bacterium Burkholderia glumae Kurita and Tabei infects emerging and flowering panicles, causing kernels to abort. To identify quantitative trait loci (QTLs) for BPB resistance, a population of 300 recombinant inbred lines (RILs) derived from a cross between 'Lemont' and 'TeQing' were evaluated in 2001 and 2002 in field plots spray-inoculated with B. glumae at the time of flowering. Because this RIL population had been previously used to map QTLs for three other diseases, present use of this population allowed direct comparison between the various disease resistance QTLs. Multiple interval mapping using QTL Cartographer v2.5 putatively identified 12 BPB QTLs, three of which were statistically significant in both years and found to have epistatic effects in 2002. TeQing was the source of resistance for eight QTLs; Lemont for four. Four BPB QTLs colocated with QTLs previously identified as providing resistance to one or multiple other diseases. Three BPB QTLs were also associated with late flowering. Because late flowering panicles are subjected to cooler temperatures that are less conducive to disease development during grain fill, it is possible that the genetic effects of the heading-related QTLs were biased. The present data could not distinguish between pleiotropy and close linkage of the BPB QTLs with the previously identified heading and disease resistance QTLs.