**5. Future outlook and conclusions**

Among the essential nutrient elements, nitrogen has a paramount importance for rice growth and development in natural ecosystems. To promote optimum N nutrition for the higher rice yield, it is important to explore the possible variability in NUE in rice genotypes. Understanding the molecular mechanisms of variable NUE in rice genotypes would help to develop NUE in the elite rice variety under abiotic stressful conditions using traditional and molecular plant breeding methods, including genome editing. Global climate change plunges world rice production toward various abiotic stress. Flooding, drought and salinity are correlated to cause problems in rice production. If rice seedlings experience flooding during the vegetative stage, they may suffer from terminal drought during the reproductive stage, depending on the ecosystems. Likewise, periodic drought conditions may upregulate the existing salinity stress through intensification of a high amount of salt layer on the upper surface soil. Therefore, there is a dire need to adopt a holistic approach to address the problems of abiotic stresses for future rice breeding. Genomics and post-genomics approaches have high potentials for dissecting underlying molecular mechanisms in differential NUE in rice genotypes. With the help of molecular mapping, fine-tuning of target QTLs, genome editing of a number of major and minor QTLs associated with abiotic stress tolerance in rice have been detected in recent years. Further enhanced research endeavors are now underway toward the development of more tolerant rice varieties to abiotic stresses. The identified QTLs are valuable resources for marker-assisted selection (MAS) to develop elite rice genotypes tolerant to flood, drought and salinity. Novel approaches are needed to apply for accelerating the mitigation of the problems of abiotic stresses in rice such as marker-assisted breeding (MAB), rapid generation advance (RGA), gene editing and transgenic technology. Attempts should be taken to develop abiotic stresstolerant rice varieties, which can perform in a sustainable manner in a wide range of environmental conditions. Identified QTLs and rice germplasms tolerant to abiotic stresses could be explored to understand the molecular genetics of flooding, drought and salt tolerance in rice. New genes involved in abiotic stress tolerance are needed to be identified. There is a need for strategic research on molecular breeding and agronomic aspects to enhance the resilience of global rice production. To achieve these goals, capacity building of rice scientists, farmers and other stakeholders involved in developing abiotic stress-tolerant rice variety might help to increase the desired NUE in rice.
