Wheat (Triticum aestivum) faces flooding on an estimated 15-20% of its cropping area each year, resulting in average 43% grain yield loss due to soil flooding. Moreover, global warming is expected to increase in major wheat-producing areas. In contrast, rice (Oryza sativa and Oryza glaberrima) is tolerant to soil flooding, but a few days of complete submergence can lead to severe damage and even plant death.
Our aim is to identify traits that can improve wheat and rice flood tolerance. For this, we examine the physiology of wheat and rice germplasm with contrasting flood tolerance. This includes sourcing wheat genotypes from CIMMYT Germplasm Bank and collaborators in Norway, Japan, and Australia. In addition, seeds of wild relatives to wheat (emmer, einkorn) have been supplied by NordGen, and wild relatives to rice (e.g., O. barthii, O. granulata) by the International Rice Gene Bank. We focus on root traits enhancing O2 supply to the metabolically active root tip and shoot traits that improving leaf gas exchange under water.
Gas exchange during submergence is enhanced by the formation of a leaf gas film on submerged, superhydrophobic leaves. However, genetic diversity for leaf gas film formation among predominately Danish wheat cultivars was low, and contrasting submergence tolerance between two wheat cultivars (Frument and Jackson) could not be attributed to leaf gas film thickness or retention time. Interestingly, shoot carbohydrate levels in flood tolerant Jackson and intolerant Frument were similar, contrasting with known tolerance mechanisms of carbohydrate conservation in submergence tolerant rice cultivars.
To identify genetic variation in roots traits conferring flood tolerance, we screened eight wild relatives of rice and three rice cultivars for key root traits known to confer flood tolerance. Key root traits included a barrier to Radial Oxygen Loss (ROL), aerenchyma and root anatomical traits which were analysed using a plasticity index when mimicking soil flooding. We found that dryland Oryza species showed lower plasticity in flooding related root traits, but that O. sativa genotypes displayed similar plasticity as wild relatives.
Current efforts also include field screening of >300 African rice accessions, including undescribed African landraces and O. glaberrima genotypes, in order to breed for flood and salinity tolerance. Work is conducted with Sokoine University of Agriculture and the International Rice Research Institute, funded by DANIDA.