Characterization of QTLs for grain weight from New Plant Type rice cultivars through the development of near-isogenic lines with an IR 64 background

Grain weight (GW), one of the yield components of rice ( Oryza sativa L.), is an important trait for improving rice productivity. In the 1990s, New Plant Type (NPT) rice breeding focused on improving the yield potential of rice varieties by introducing unique traits from Tropical Japonica Group cultivars. To reveal the genetic factors responsible for yield-related traits of NPT varieties, we previously developed 334 introgression lines with variations in traits inherited from NPT varieties in the genetic background of an Indica Group cultivar, ‘IR 64’. Three of the NPT varieties—‘IR65600-87-2-2-3’, ‘IR69093-41-2-3-2’, and ‘IR71195-AC1’—had heavier GW than ‘IR 64’. To identify the genetic basis for the heavier GW in these lines, here we performed QTL analysis in F 2 (BC 4 F 2 equivalent) populations. We detected one each QTL for GW on chromosome 5 in the three populations, and developed three near-isogenic lines (NILs) with a QTL for GW, qGW5 ( qGW5.1-YP1 , qGW5.2 - YP5 , and qGW5.3 - YP10 ), through marker-assisted selection. These three NILs were confirmed to have heavier GW than ‘IR 64’. These NILs are useful materials in research and breeding for improvement of rice productivity.