The Time of Flooding Occurrence is Critical for Yield Production in Rice and Vary in a Genotype-Dependent Manner

Flash floods occur in rainfed lowland and flood-prone areas and have a profound incidence on crop yield, which is tightly linked to worldwide food insecurity. The most flooding-threatened crop is rice. Under this condition, rice undergoes anoxic and post-anoxic shock that affects its growth, development capacity and ultimately causes an important grain yield loss. Therefore, the introduction of submergence-tolerant varieties in a flood-prone area was proposed as a preventive solution to limit these effects. Such a solution presents room for improvement and would benefit from a post-submergence management to ensure a better rice yield, yet remains to be defined. In this study, we assessed the effect of flooding on growth and yield of different rice varieties submerged at a different time of their developmental stage. We compared three rice varieties, namely Prachinburi 2 (PCR2), Kao Samer 1 (KSM1) and Neang Guang 5 (NG5), for their tolerance to 14 days of 50 cm depth submergence at 30, 60 and 90 Days After Germination (DAG). At 30 DAG, the recovery ability of KSM1 was restricted, showing decreased shoot dry mass and grain yield, whereas photo assimilate transport of PCR2 and NG5 was altered, resulting in high leaf nitrogen (N) concentration but low grain yield. Our data revealed that rice varieties were more tolerant to submergence at 60 and 90 DAG. In opposition to KSM1 and NG5 grain yield, PCR2 showed rapid recovery with a marked increase of shoot dry mass and grain yield. Taken together, our result indicates that de-submergence at late developmental stage promotes rice recovery and yield of tolerant variety. Gene discovery work is required to identify molecular players and pathways that are involved in submergence stress recovery in rice.