RiceCAP: Comparison of Sheath Blight QTLs in Two Bengal / O. Nivara Advanced Backcross Mapping Populations.

Two advanced backcross populations were developed between a popular southern US tropical japonica rice (Oryza sativa L.) cultivar Bengal and two different Oryza nivara (IRGC100898; IRGC104705) accessions to identify quantitative trait loci (QTLs) related to sheath blight (SB) disease resistance. Both populations were genotyped with approximately 125 SSR markers distributed throughout the 12 rice chromosomes. The linkage map for the population with IRGC100898 covered a 1742 cM distance with an average interval size of 13.8 cM. Sheath blight disease was evaluated under both inoculated greenhouse and field conditions. Days to heading, plant height and plant type, confounding factors for rice SB disease, also were recorded. Five SB QTLs were identified via multiple interval mapping with three being in regions where rice SB QTLs previously were not reported. These are potential novel QTLs. Three (qSB2, qSB3 and qSB6) of the five SB QTLs were common in both SB screening methods. The O. nivara parent contributed three SB QTLs (qSB2, qSB6 and qSB11) with two of them (qSB2 and qSB11) being novel QTLs. The fact that SB QTLs were found in approximately the same region as previously reported QTLs from O. sativa cultivars indicates these QTLs are conserved across the Oryza genus. Three SB QTLs (qSB3, qSB6 and qSB11) were located in the same region as either days to heading or plant height QTLs, suggesting these morphological traits may influence SB response. QTL mapping results from the second Bengal/O. nivara mapping population are being analyzed and will be compared with the reported results as a validation of SB QTLs. Through additional backcrossing of lines containing the putative SB QTLs from O. nivara with Bengal and subsequent selection using molecular markers, we are developing germplasm with improved SB resistance.