Waterlogging tolerance in the tribe Triticeae:: the adventitious roots of Critesion marinum have a relatively high porosity and a barrier to radial oxygen loss

Nine species from the tribe Triticeae-three crop, three pasture and three 'wild' wetland species-were evaluated for tolerance to growth in stagnant deoxygenated nutrient solution and also for traits that enhance longitudinal O-2 movement within the roots. Critesion marinum (syn, Hordeum marinum) was the only species evaluated that had a strong barrier to radial O-2 loss (ROL) in the basal regions of its adventitious roots, Barriers to ROL have previously been documented in roots of several wetland species, although not in any close relatives of dryland crop species. Moreover, the porosity in adventitious roots of C. marinum was relatively high: 14% and 25% in plants grown in aerated and stagnant solutions, respectively. The porosity of C, marinum roots in the aerated solution was 1.8-5.4-fold greater, and in the stagnant solution 1.2-2.8-fold greater, than in the eight other species when grown under the same conditions. These traits presumably contributed to C, marinum having a 1.4-3 times greater adventitious root length than the other species when grown in deoxygenated stagnant nutrient solution or in waterlogged soil. The length of the adventitious roots and ROL profiles of C, marinum grown in waterlogged soil were comparable to those of the extremely waterlogging-tolerant species Echinochloa crus-galli L. (P. Beauv.). The superior tolerance of C, marinum, as compared to Hordeum vulgare (the closest cultivated relative), was confirmed in pots of soil waterlogged for 21 d; H. vulgare suffered severe reductions in shoot and adventitious root dry mass (81% and 67%, respectively), whereas C, marinum shoot mass was only reduced by 38% and adventitious root mass was not affected.