Defining Soil Water Regimes for Screening Waterlogging Tolerance in Tropical Forage Grasses

The efficiency of screening tropical forage grass genotypes for waterlogging tolerance under controlled conditions depends on experimental protocols capable of accurately discriminating contrasting genotypes. This study evaluated morphoagronomic and physiological traits of Megathyrsus maximus and Urochloa spp. genotypes subjected to different soil water availabilities to define suitable experimental conditions for waterlogging screening. Two independent experiments were conducted in a randomized complete block design using a 5 × 4 factorial arrangement (five genotypes × four soil water regimes) with four replications, in which morphoagronomic and physiological traits were evaluated. The present study combines previously published data from the 80% and 120% pot water capacity treatments with data from the additional 60% and 100% treatments. Overall, favorable genotype performance was observed around the directly tested 80% of pot water capacity, with greater biomass production, higher numbers of green leaves, higher SPAD index values, and improved photosynthetic performance across several traits and genotypes. In contrast, 120% of pot water capacity caused the greatest reductions in plant growth and physiological activity, allowing clear discrimination between tolerant and susceptible genotypes, whereas 60% and 100% of pot water capacity produced less pronounced effects. The results indicate that approximately 80% of pot water capacity is the most suitable condition for the control treatment, whereas 120% efficiently induces waterlogging stress. This methodological approach provides an experimental basis for standardizing controlled-environment screening assays, improving the reliability of early-stage selection of tropical forage grass genotypes for waterlogging tolerance.