Impacts of barley root cortical aerenchyma on growth, physiology, yield components, and grain quality under field waterlogging conditions

Waterlogging is a major ecological threat that restricts crop growth and yield in high rainfall zones across the globe. Waterlogging tolerance is conferred by several complimentary mechanisms, with root cortical aerenchyma (RCA) formation being one of the major ones. In this study, three pairs of near-isogenic lines (NILs) of commercial barley varieties which we introgressed a quantitative trait locus (QTL) for RCA formation, and eight other genotypes contrasting in waterlogging tolerance were subjected to growth under waterlogged and control (non-waterlogged) conditions. Field trials were conducted in 2019 and 2020. The waterlogging treatment began at the two-three leaf stage and continued for two months. The water was subsequently drained, and the crops allowed to recover for final grain yield. Under waterlogging conditions, genotypes with RCA-QTL had significantly higher aerenchyma, white adventitious roots, leaf normalised difference vegetation index (NDVI), higher shoot biomass, tiller number, compared with genotypes without RCA-QTL. Across the three commercial varieties in waterlogged conditions, the average boost to yields from the introgression was 1.8 t/ha. The genotype YF225 showed a degree of waterlogging tolerance but had no RCA-QTL. This appears to be an alternate waterlogging tolerance mechanism that is not yet understood. Importantly, the addition of the RCA-QTL to three commercial varieties showed no significant negative effects on plant growth, yield, and grain quality attributes under control conditions. We conclude that the introgression of an RCA-QTL into other varieties is a promising breeding target for mitigating losses caused by waterlogging.