Exploring sheath blight quantitative trait loci in a Lemont/O. meridionalis advanced backcross population

Oryza meridionalis is the wild Oryza species endemic to Australia. There are eight AA-genome Oryza species, one of which is cultivated rice, O. sativa, and O. meridionalis is the most genetically distant one. An O. meridionalis (IRGC105608) accession, previously identified as being moderately resistant to rice sheath blight (ShB) disease, was used as the donor parent to develop an advanced backcross population with the US semidwarf rice cultivar, Lemont, as the recurrent parent. The population was genotyped with 113 DNA markers and a linkage map constructed that spanned 1234.5 cM. ShB disease was evaluated in both greenhouse and field conditions. Days to heading (DH), plant height (PH) and culm angle (CA) were recorded because they can confound ShB disease ratings under field conditions. Multiple interval mapping identified qShB9-2 as the ShB-QTL most consistently effective across the generations and variable evaluation environments, with resistance to ShB disease attributed to the O. meridionalis allele in all cases. No QTL for any of the potentially confounding traits was identified in this region of chromosome9 of this cross. Lemont was found to contribute the desirable alleles that decreased the DH on chromosome 8 and PH on chromosome 1, in part due to the semidwarf gene, sd1, for short plant stature. No CA-QTL was identified due to the lack of segregation for this trait, especially in the advanced backcross generations. Further studies will be undertaken to fine map the qShB9-2 region and identify linked markers for use in cultivar development.