The Effect of Water Level in Rice Cropping System on Phosphorus Uptake Activity of in a + Breeding Line.

Pyramiding useful QTLs into an elite variety is a promising strategy to develop tolerant varieties against multiple abiotic stresses. However, some QTLs may not be functionally compatible when they are introgressed into the same variety. Here, we tested the functional compatibility of and , major QTLs for tolerance to phosphorus (P)-deficiency and submergence conditions, respectively. Phenotypic analysis revealed that IR64-Pup1+Sub1 (IPS) plants harboring both and QTLs show significant tolerance to submerged conditions, similarly to IR64-Sub1, while IPS failed to tolerate P deficiency and mild drought conditions; only IR64-Pup1 showed P deficiency tolerance. In submerged conditions, and , major genes for and QTLs, respectively, were expressed at the same levels as in IPS and IR64-Sub1 and in IPS and IR64-Pup1, respectively. On the other hand, in P-non-supplied condition, crown root number, root length, and expression level were significantly lower in IPS compared to those of IR64-Pup1. However, there was no significant difference in P content between IPS and IR64-Pup1. These results imply that does not compromise function in submerged condition, while suppresses function in P-non-supplied condition, possibly by regulating the transcript level of . In conclusion, and are regarded as functionally compatible under submergence condition but not under P-non-supplied condition. Further study is needed to elucidate the functional incompatibility of and QTLs in IPS under P-non-supplied condition.