Spreading Culm Locus Discovered While Dissecting a Sheath Blight Resistance QTL Within a Set of TeQing-into-Lemont Introgression Lines.

A new gene-mapping population comprised of 123 TeQing-into-Lemont backcross introgression lines (TILs) was developed for the purpose of providing a uniquely efficient avenue for verifying, molecularly tagging, and incorporating desired TeQing QTL into improved U.S. rice varieties.  The TILs were being studied in order to fine map some of the previously reported sheath blight resistance QTL (SBR-QTL).  One of the targeted SBR-QTL, qSB9b, was known to reside in the bottom 37 cM of chromosome 9. Data on 145 SSRs allowed identification of a subset of 31 TILs containing TeQing introgressions in and around the qSB9b region. Seven additional SSRs were evaluated to tag this telomeric region every 0.5 Mbp, or approximately every 2 cM. Recombination in one or more TILs was found to be already fixed for all but two of these nine marker intervals.  While the 31 TILs selected as containing all/part of qSB9b were being grown for the sheath blight effort, segregation for erect versus spreading culms was noted. Because each TIL contains more than one introgressed region, it was not clear if this was due to a spreading culm gene (Spr) residing near the qSB9b QTL, or due instead to a common introgression elsewhere in the genome. Three replications of the 31 TILs were grown one plant per 10 x 10 cm pot, and observed twice weekly for tiller angle and number. Correlation between tiller angles and marker data indicates that a Spr gene resides in the upper half of the qSB9b region, in the 0.6 Mbp region between RM3808 and RM215. Marker-trait correlations were not perfect in that the two most erect TILs contained TeQing alleles throughout the entire end of chromosome 9. We are now investigating if these TILs contain another erectness gene over-riding the effect of this apparent Spr locus.