Genotypic adaptation to soil water deficit in rice - a comparison of desirable traits for aerobic production and lowland drought resistance

Abstract

Rainfed lowland rice and aerobic rice are two contrasting cropping systems that differ greatly in their growing environment, water management, and yield level. Rainfed lowland rice is a common cropping system in tropical Asia and the crop is grown in a paddy field with standing water during some of the growing season producing a grain yield of up to 3–6 ​t ​ha⁻¹. In contrast, aerobic rice is commonly irrigated, has no standing water in the field, and is being developed as a water-saving technology in temperate and subtropical areas with yield of up to 6–10 ​t ​ha⁻¹. However, both rainfed lowland and aerobic rice commonly experience soil water deficit during growth, and genotypic adaptation to water deficit is required to produce high yield. This review describes how soil water deficit affects rice growth and yield and aims to identify traits required for lowland and aerobic rice in their adaptation to soil water deficit and ways to achieve yield improvement. Some common traits are found to be desirable in both cropping systems, including low canopy temperature and well-developed root systems at soil depth. While aerobic rice is shown to require high stomatal conductance with high stomatal density to minimise potential photosynthetic losses due to CO₂ transport limitation, it appears desirable for rainfed lowland rice to adopt conservative water use and not consume soil water too quickly with adaptation mechanisms such as reduced stomatal density. This review concludes with several suggestions to improve grain yield in both rainfed lowland and aerobic rice.