Root contribution to stay-green in rice (Oryza sativa L.) subjected to desiccated soils in the post-anthesis period

The stay-green trait as a maintenance capacity of green leaves assimilating under des- iccated soils in the post-anthesis period is known in several crop plants. Our objectives were to clarify if the capacity to stay green in the terminal growth stage is related to root performance in Vietnam rain-fed rice cultivars. Three Vietnam cultivars were grown under flood conditions in 130-L volume pots. Irrigation was withheld from half of the pots at the anthesis period, while the flood condition was maintained in the remaining pots. The SPAD value as an indicator of green color, green leaf area (GLA) and leaf conductance (CL) decreased after heading, but trends of the decrease by soil desicca- tion differed among cultivars. The cultivar, which showed higher maintenance of the SPAD value, GLA and CL under desiccated soils, had significantly denser roots in the surface soil layer at harvest. The water absorption rate per soil volume and per root length of almost all soil layers in the cultivar was maintained longer and higher in desiccated soils. The SPAD value and GLA of detached leaves in the cultivar incubated under dark and humid conditions were maintained significantly longer. This showed that the leaf properties contribute to the maintenance of green leaves. These results suggest that in stay-green rice cultivars the properties that keep the leaves green contribute to a delay in the suppression of assimilate processes and maintain the water absorption function of the roots by maintaining the assimilate supply to roots.