Photosynthetic Chromosome Segment Substitution Line with a ‘KDML 105’ Genetic Background under Drought Conditions

Drought is a major abiotic stress that decreases plant growth and yield.Quantitative trait loci for drought tolerance (DT-QTLs) in rice were identified and chromosome segment substitution lines (CSSLs) containing diverse DT-QTL segments in a 'KDML105' genetic background were generated.In this study, CSSL1 and CSSL4 were evaluated and compared with their parental lines, 'KDML105' and DH212, under drought conditions, which were simulated by withholding water for 12 days at the booting stage.Plants were subsequently re-watered and their biomass was determined 60 days later.The CSSL4 and DH212 flag leaves tended to maintain relatively stable gas exchange parameters compared with 'KDML105' and CSSL1 during the early water-withholding period.Moreover, the chlorophyll a and b contents were the same between the droughtstressed CSSL4 plants and the non-stressed plants.Interestingly, the total carotenoid content of CSSL4 increased after the drought treatment, suggesting a role for carotenoids in the non-enzymatic defense mechanism that maintains the PSII efficiency under drought conditions.For both analyzed CSSLs, the total dry mass, shoot dry mass and root dry mass increased after re-watering, particularly for CSSL4, in which the biomass increased by 20.73%, with increases in the root biomass resulting in a lower shoot:root ratio.Thus, the CSSLs increased their biomass during the recovery period likely because of the DT-QTLs from DH212.Moreover, CSSL4 plants were able to maintain photosynthetic pigment contents, which contributed to the enhanced growth during the recovery period.Therefore, CSSL4 represents a valuable genetic resource for breeding new drought-tolerant rice cultivars.