Root responses in chromosome segment substitution lines of rice 'KDML105' under early drought stress

Drought is a major cause of potential plant stress in areas of rain fed lowland rice (Oryza sativa L.) cultivation. The characteristics of the root system are important for rice plant adaptation and acquiring water under drought conditions. This study aims to evaluate the root responses contributing the plant adaptation to drought stress of 'KDML105' chromosome segment substitution lines (CSSLs). The rice genotypes were grown in PVC tubes. At 30 d after planting (DAP), the plants were subjected to two water regimes, well-watered and early drought stress. The two experiments were different in water status shown as relative water content and soil moisture content and classified as two stress condition in particular years i.e. mild and severe stress in 2013 and 2014 respectively. Shoot dry weight (SDW) and leaf area (LA) increased by mild stress while root dry weight (RDW) and total root length were increased by severe stress. The comparison between WW and DS in the percentage of SDW, RDW and LA showed that the CSSL#6 was the great maintenance genotype in both 2013 and 2014 as well as the donor parent (DH212) while 'KDML105' showed a decreasing RDW in DS than WW. Root length density of all CSSLs was higher than 'KDML105' in the shallow soil layer (37%), but CSSL#12 was greatest in root length density at the deeper soil layers (76.7%) under mild stress. Interestingly, CSSL#1, #4, #5, #6, #12, #14 and #15 tended to produce a higher root depth (59.6%, 52.0%, 53.6%, 58.6%, 52.7%, 49.7% and 53.3%, respectively) at 30 to 90 cm of soil depth compared to 'KDML105' under severe stress. It is possible that several chromosome segments associated with root depth were introgressed from the donors (DH103 and DH212) through the breeding procedure, which can be used as a promising breeding material in Thailand.