Identification of Sheath Blight QTL in a LaGrue x O. nivara rice advanced backcross population

Oryza nivara is considered one of the wild progenitors of cultivated Asian rice (O. sativa). An O. nivara (IRGC104443) accession, previously identified as being moderately resistant to rice sheath blight disease, was used as the donor parent to develop an advanced backcross population with the U.S. rice (O. sativa) cultivar, LaGrue, as the recurrent parent. The population was genotyped with 210 DNA markers and a linkage map constructed that spanned 1488.9 cM. Sheath blight (ShB) disease was evaluated in both greenhouse and field conditions. Days to heading (DTHD), plant height (PTHT) and culm (angle) habit (CULMHAB) were recorded because they can confound sheath blight disease ratings under field conditions. Multiple interval mapping identified qShB9 as the ShB-QTL being the source of resistance and the resistance was attributed to the O. nivara allele. The single CULMHAB QTL, qCULMHAB9, was also located in this region but had a different peak suggesting the more open tillering habit was most likely due to the tiller angle control-1 gene which was fine-mapped near the chromosome 9 sheath blight resistance in other O. sativa populations. The ShB QTL, qShB3-2, identified in the greenhouse study was not verified in field studies. None of the three DTHD QTL were colocalized with ShB QTL, while the single PTHT QTL was mapped to the region of the semi-dwarf-1 gene for short stature on chromosome 1. These results indicate that sheath blight resistance QTL can be selected that are independent of delayed heading and tall plant height ,the traits that are associated with disease escape but are undesirable in cultivated rice. Further studies will be undertaken to fine map the qShB9 region and identify linked markers for use in cultivar development.