Epistatic interaction of QTLs controlling leaf bronzing in rice (Oryza sativa L.) grown in a saline paddy field

We analyzed quantitative trait loci (QTLs) in rice (Oryza sativa L.) for leaf bronzing induced by growing plants in a saline paddy field. The mapping population comprised 98 backcross-inbred lines (BILs) derived from crosses between Nipponbare, the recurrent parent, and Kasalath varieties. Fifteen of the BILs showed obvious leaf bronzing, unlike the parent varieties. We identified two QTLs for leaf bronzing: one (qLb-3) was located close to the R1925 marker on the long-arm of chromosome 3, the other (qLb-11) lay in the interval between the C1350 and C477 markers on the short-arm of chromosome 11. The Kasalath allele of qLb-3 and the Nipponbare allele of qLb-11 were found to promote leaf bronzing. Moreover, it was observed that the two QTLs were epistatic, the Kasalath qLb-3 allele causing obvious leaf bronzing in the presence of the Nipponbare qLb-11 allele. To confirm this interaction, we investigated leaf bronzing in three chromosome segment substitution lines: two of these lines, SL2 and SL61, carried an introgressed Kasalath qLb-3 allele in a Nipponbare background while the third line, SL47, carried introgressed Kasalath alleles of both qLb-3 and qLb-11. Leaf bronzing occurred in the SL2 and SL61 plants, but not in the SL47 plants. We further investigated the interaction between the two QTLs using F₂ plants derived from crosses between the SL47 and SL61. In the F₂ plants, segregants harboring both the Kasalath qLb-3 allele and the Nipponbare qLb-11 allele showed leaf bronzing. These results indicate that leaf bronzing required the epistatic interaction of the Kasalath qLb-3 allele on chromosome 3 and the Nipponbare qLb-11 allele on chromosome 11.