Two introgressed quantitative trait loci confer a broad-spectrum resistance to blast disease in the genetic background of the cultivar RD6 a Thai glutinous jasmine rice

Two quantitative trait loci (QTL) that confer a broad-spectrum resistance to blast disease identified in the rice cultivar Jao Horn Nin (JHN) were transferred to the Thai glutinous jasmine rice cultivar RD6 by marker-assisted backcrossing (MAB). Four backcrosses and one selling were conducted in which the derived introgression lines (ILs) that carried homozygous JHN alleles at the QTL recovered up to 98% of the RD6 genome. Ninety-eight BC4F2 introgression lines that consisted of four combinations of the two QTL were evaluated for their resistance to eight single spore isolates and natural isolates at three research locations. Introgression lines were examined for their agronomic performance by comparing them to the original RD6 in multi-location trials across five locations. All ILs that carried the QTL (either one or two QTL) showed lower disease scores than ILs without any QTL and lower scores than the recipient cultivar RD6, whereas their agronomic performances were not significantly different from the original RD6. All ILs that carried at least one QTL showed a broad-spectrum blast resistance that was similar to the donor cultivar JHN. The success in improving the blast resistance in RD6 by MAB was shown. In this study, MAB accelerated the development of broad-spectrum blast resistance in the genetic background of the Thai glutinous rice cultivar RD6 within 4 years. The improved RD6 has now been tested in cultivation for several years. Two of the ILs were released in 2008. Currently, farmers in the north and northeast regions of Thailand (areas that are particularly vulnerable to blast disease) benefit from growing these two varieties. (C) 2010 Elsevier B.V. All rights reserved.