Abstract: [Objective] In rice breeding community, drought tolerance (DT) is becoming one of the most important target traits for variety improvement under ever-increasing severe drought situation all over the world. Identification of the root character QTLs which are directly related to DT will provide useful marker information for development of DT rice variety via marker-assisted selection against root QTL. [Method] The 55 chromosome segment substitution lines (CSSL) derived from Lemont/Teqing with Teqing genetic background was planted in PVC pipes and phenotyped for root characters and grain yield under irrigation and drought stress conditions.QTLs affecting root length (RL), root number (RN), root weight (RW), grain yield (GY) and their stability of expression between drought and water conditions were identified. [Result] A total of 25 main-effect QTL for four traits were identified, which can be grouped into three types based on their behaviors. TypeⅠincluded 4 QTLs which were detected both in the two conditions, type Ⅱ consisted of 12 QTLs which were mapped only in the control condition, and type Ⅲ comprised 9 QTLs which were induced by drought and detected only under the stress. In addition, eleven QTLs (QGy6,QGy8,QGy1, QRl8a, QRl12, QRn11, QRn12, QRw1a，QRw1b, QRw7 and QRw12a) affecting trait differences between stress and control were identified. [Conclusion]There were three QTLs (QRl2b, QRl8b and QRn12) which expressed both in the two conditions with same direction and magnitude of gene effect. These three root-QTLs and other eleven QTLs affecting trait differences were considered to directly contribute to DT. The results would facilitate fine-mapping of DT-related root QTL and DT rice breeding by MAS.

Key words: Rice, Chromosome segment substitution lines (CSSL), Drought, Root, Marker-assisted selection