Aerenchyma, gas exchange, growth, leaf and root anatomical traits of drought and flooding-tolerant rice genotypes under water stress

Rice is one of the most important cereals and is consumed by more than 50% of the human population being a key crop for food security and agriculture. Climate change models indicate that it may cause abrupt alterations in water availability promoting events of drought and flooding in some environments leading to the necessity of tolerant crops. This work investigated the drought effect in rice genotypes contrasting for water availability recommendation. Rice genotypes recommended for drained soils (A502, CMG1590, Douradão, and Soberana) and flooding (Pampa) were submitted to field capacity and 50% of the field capacity conditions. Growth, gas exchange, photochemical parameters, and anatomical traits from roots and leaves were evaluated. The tolerance index and cluster analysis were used to classify tolerant and sensitive groups, data was submitted to two-way ANOVA, and means were compared by the Scott-Knott test. Results showed that A502 and Pampa genotypes were grouped in a drought-tolerant clade and other genotypes were grouped as drought-sensitive. Pampa showed increased root cortical aerenchyma, root dry mass, and photosynthesis that seem to help in drought tolerance while A502 showed increased aerenchyma and root dry mass, other genotypes have different responses to these variables. Results suggest that the capacity for increasing root cortical aerenchyma presented by Pampa, which is a flooding-tolerant genotype improved the development of the root system and photosynthesis is an important model for drought and flooding cross-tolerance in rice.