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This work is supported with a grant from FONTAGRO: “Desarrollo de genotipos de Brachiaria adaptados a suelos con drenaje deficiente para aumentar producción bovina y adaptar sistemas de pastoreo al cambio climático en América Latina”. Roots of plant species adapted to waterlogging usually display characteristics that enable them to withstand the adverse conditions in water-saturated soils, of which aerenchyma is the most obvious adaptive one. Aerenchyma are cortical airspaces that provide a low resistance internal pathway for the movement of O 2 from the shoots to the roots, where it is consumed in respiration and could also partially oxidize the rhizosphere. The present work explores the extent to which aerenchyma formation occur under well drained and waterlogged conditions in Brachiaria genotypes with contrasting levels of tolerance to poorly drained soils. • All genotypes responded to waterlogging by increasing the formation of root aerenchyma. • The higher percentage of aerenchyma in two accessions of the tolerant B. humidicola (CIAT 6133 and CIAT 679) should be of adaptive advantage at the offset of and during waterlogging. • The moderate level of waterlogging tolerance observed for CIAT 26110 and CIAT 606 may not be related to aerenchyma formation. A pot experiment was performed in January, 2009 at the Forages patio area (CIAT, Cali, Colombia). Genotypes used: B. humidicola CIAT 6133, B. humidicola CIAT 679 (tolerant); B. brizantha CIAT 26110, B. decumbens CIAT 606 (moderately tolerant); B. brizantha CIAT 6294, B. ruziziensis Bruz 44-02, B. hybrid Mulato 2 CIAT 36087 (sensitive). Two stem cuttings per pot were sown and allowed to grow for 50 days in 3,1kg of a fertilized top oxisoil from Santander de Quilichao. The experiment was a Randomized complete block with 4 replications. Waterlogging treatment was imposed by applying excessive water to the pots (5 cm over soil surface) for 21 days. Plants without waterlogged soils and maintained at field capacity were used as a control Root anatomy: Freehand sections were taken every 5cm and photographed with a digital camera connected to a Leitz Orholux II microscope. Cross sectional area and aerenchyma within each capture were measured using ImageJ software. • For all genotypes, a 21 day waterlogging treatment increased the area of aerenchyma when compared to the control (Figures 1 and 2). • Differences in aerenchyma formation between two moderately tolerant ( C I A T 2 6 1 1 0 a n d C I A T 6 0 6 ) a n d t h r e e s e n s i t i v e (Bruz 44-02, CIAT 6294 and CIAT 36087) were not significant. Fig. 1. Root anatomy of contrasting Brachiaria genotypes grown under field capacity (CONTROL) and waterlogged conditions. Sections were taken at the distance of 150 mm from the root tip. Fig. 2. Percentage of aerenchyma of roots grown in an oxisoil maintained at field capacity or waterlogged for 21 days. * denotes a statistically significant difference at 95% confidence level (LSD) between columns of a same genotype. • Although moderately tolerant and sensitive genotypes genotypes had significant increase of aerenchyma formation under waterlogged conditions, it was not possible to establish the role of aerenchyma in their differential tolerance to waterlogging. % Aerenchyma * * * * * Sensi&ve Moderately tolerant Tolerant CIAT 679 CIAT 26110 Bruz 44-02
