Field evaluation on functional roles of root plastic responses on dry matter production and grain yield of rice under cycles of transient soil moisture stresses using chromosome segment substitution lines

Fluctuating soil moisture resulting from the transient occurrences of waterlogging and drought are frequently reoccurring in the rice field, which adversely affects plant growth and yield. We previously established the significant contribution of plastic development and associated physiological responses of root to shoot dry matter production under soil moisture fluctuation stresses. To evaluated the functional roles of root plastic development on yield under field condition of continuous cycle of transient soil moisture stresses. Previously selected CSSL47 and the recurrent parent Nipponbare were exposed to two soil moisture conditions; cycles of alternating waterlogging and drought condition (CAW-D) and continuous waterlogging (CWL; control). Under continuous waterlogging (CWL) conditions, the two genotypes showed no significant differences in most of the traits examined. In contrast, under continuous cycle of alternate waterlogging and drought (CAW-D) conditions, CSSL47 showed greater shoot dry matter production than Nipponbare, which was attributed to its higher stomatal conductance and photosynthetic rate, which then led to higher grain yield. The root system development of CSSL47 expressed as total root length was greater compared with Nipponbare. Before heading stage, plasticity was expressed as enhanced aerenchyma formation based on root porosity, which was associated with the promotion of lateral root production, elongation and branching and the eventual increase in total root length. Moreover, after heading, compared with Nipponbare, CSSL47 continued to produce more nodal roots from newly produced tillers, thus maintaining leaf photosynthesis and eventually resulting in heavier panicles. We provide evidences that root plasticity, which better expressed in CSSL47 than Nipponbare, under continuous cycle of transient soil moisture stresses contributed to increase in grain yield in fields. Genetic variation in plastic responses of roots could have substantial impact on yield in areas experiencing these kind of soil moisture stresses.