QTLs for constitutive aerenchyma from Zea nicaraguensis improve tolerance of maize to root-zone oxygen deficiency

Zea nicaraguensis is a wild relative of Zea mays subsp. mays (maize) that has high waterlogging tolerance. One of its traits is constitutive aerenchyma formation (CAF) in roots and this may be one of the reasons for the tolerance, but it has not yet been proven by comparing plants that differ only in CAF in the same genetic background. We therefore produced an introgression line AE24-50-44-91 (IL-AE91) possessing four quantitative trait loci for CAF from Z. nicaraguensis in the background of maize (inbred line Mi29). The degree of root CAF in IL-AE91 was intermediate between that of Mi29 and Z. nicaraguensis. Seedlings of IL-AE91 grown aerobically were more tolerant to transfer to oxygen-deficient conditions than were Mi29 seedlings. On day 2 of oxygen deficiency, the root extension rate and viability of root-tip cells in IL-AE91 were ~2.7 and ~1.3 times greater, respectively, than they were in Mi29. On day 4, the area of aerenchyma at 80 mm from the root tips was ~1.5 times greater in IL-AE91 and radial oxygen loss from the apical parts of roots was ~3.4 times higher than in Mi29. These results demonstrate that CAF reduces the stress from low external oxygen levels caused by soil waterlogging.