Thai jasmine rice cultivar KDML105 carrying Saltol QTL exhibiting salinity tolerance at seedling stage

Saltol, the major salinity tolerance quantitative trait loci (QTL) in rice, was introgressed from IR66946-3R-230-1-1 (FL530) into Khao Dawk Mali 105 (KDMl105) by two rounds of marker-assisted backcrossing (MAB). Twenty-eight BC₂F₂ introgression lines (BILs) with positive Saltol allele (BIL^+Saltol) and 19 BILs with negative Saltol allele (BIL^?Saltol) were validated for the effect of Saltol as key salinity tolerant trait at seedling stage. A hydrophonic system with salt stress of 12 dS m^?1 (130 mM Na⁺) was conducted, and significant differences between BILs^+Saltol and BILs^?Saltol were observed for the period of plant survival (PPS), total K⁺ (T-K⁺) and Na⁺ (T-Na⁺) concentration, whole plant Na⁺-K⁺ ratio (T-Na⁺/K⁺), shoot Na⁺ (S-Na⁺) and K⁺ (S-K⁺) concentration, and shoot Na⁺-K⁺ ratio (S-Na⁺/K⁺). BILs^+Saltol displayed higher PPS, uptake less Na⁺ (T-Na⁺; 43.4 ppm), and more K⁺ (T-K⁺; 30.9 ppm), while the BILs^?Saltol uptake more Na⁺ (T-Na⁺; 45.7 ppm) and less K⁺ (T-K⁺; 28.2 ppm). Direct effects on PPS and salt injury score (SIS) were observed, indicating Na⁺/K⁺ homeostasis mechanism by the Saltol under hydrophonic salt stress. All BILs^+Saltol recovered KDML105 cooking quality profile such as low apparent amylose content (AAC), high score of alkaline spreading value (ASV), intermediate gel consistency (GC), and strong fragrance. However, variation in agronomic traits was observed. The possibility of lowering S-Na⁺/K⁺ ratio under salt stress at seedling stage in KDML105 by introgression of the Saltol was demonstrated. Currently, BC₂F₇ of the BIL^+Saltol selected lines are being tested for salinity tolerance in the salt-affected areas in the northeast of Thailand.