Dissection of root behavior to abiotic stimuli for breeding of climate-resilient crops

In the last century, the “Green Revolution” using modern agricultural techniques, has achieved a dramatic increase in crop production to support a growing world’s population. By the middle of this century, a further increase in crop production will be required because the world’s population is on track to reach 10 billion. However, in addition to the decrease in water resources and land degradation, climate changes such as global warming have in recent years resulted in the frequent occurrence of extreme droughts and floods around the world, threatening stable crop production. Under this situation, the development of climate-resilient crops is a global challenge. Conventional breeding, which achieved the “Green Revolution”, has conducted predominantly phenotypic selection for above-ground architecture. However, can we achieve the “Second Green Revolution” against the unstable agricultural ecosystem by improving only the above-ground architecture?

When we look at the ground, we notice a root, which has not been substantially improved so far. The root is an essential organ for absorbing water and nutrients from the soil, and it is the first to respond to excess or deficient water and nutrients. In other words, differences in root behavior in response to edaphic stress have a significant impact on plant growth. Therefore, we cannot avoid improving the root for the “Second Green Revolution”. However, is the root that is difficult to evaluate and select in the field really useful as a breeding target? If so, what traits and genes should we try to genetically improve? To answer these questions, we need a better understanding of root behavior in response to edaphic stress.

This special issue of Breeding Science consists of ten review articles focused on root behavior under specific abiotic stress based on various perspectives (e.g., morphology, physiology, agronomy, and molecular biology). The first article summarizes the benefits and challenges of root traits as breeding targets. The second article comprehensively introduces the role of roots in plant growth. In the following articles, root behavior to specific abiotic stress is examined, focusing on water stress (drought and waterlogging), deficiency and excess of nutrients (e.g., nitrogen and phosphorus), and salinity stress. The final article introduces high-throughput phenotyping for assessing roots in the fields to more easily understand root behavior. We hope that this special issue will help readers who are not yet familiar with plant roots to better understand the importance of roots, and to include them in research and breeding of plant roots.