*2.1. Plant Materials*

We used CSSLs with the genetic background of KDML105 rice and containing a putative drought-tolerance segmen<sup>t</sup> of chromosome 8 from DH103 between markers RM5353 and RM3480 [11]. These are CSSL97, CSSL104, CSSL106, CSSL107, and parental lines (KDML105 and DH103). They were used to study drought-stress responses. All rice seeds were provided by the Innovative Plant Biotechnology and Precision Agriculture Research Team (APBT) at the National Center for Genetic Engineering and Biotechnology (BIOTEC), Thailand.

### *2.2. Evaluation of Physiological Responses at Vegetative Stage under Drought-Stress Conditions*
