Some Accessions of Amazonian Wild Rice (Oryza glumaepatula) Constitutively Form a Barrier to Radial Oxygen Loss along Adventitious Roots under Aerated Conditions

A barrier to radial oxygen loss (ROL), which reduces the loss of oxygen transported via the aerenchyma to the root tips, enables the roots of wetland plants to grow into anoxic/hypoxic waterlogged soil. However, little is known about its genetic regulation. Quantitative trait loci (QTLs) mapping can help to understand the factors that regulate barrier formation. Rice (Oryza sativa)induciblyforms an ROL barrier under stagnant conditions, while a few wetland plantsconstitutivelyform one under aerated conditions. Here, we evaluated the formation of a constitutive ROL barrier in a total of four accessions from two wild rice species. Three of the accessions were wetland accessions ofO. glumaepatula, and the fourth was a non-wetland species ofO. rufipogon. These species have an AA type genome, which allows them to be crossed with cultivated rice. The threeO. glumaepatulaaccessions (W2165, W2149, and W1183) formed an ROL barrier under aerated conditions. TheO. rufipogonaccession (W1962) did not form a constitutive ROL barrier, but it formed an inducible ROL barrier under stagnant conditions. The threeO. glumaepatulaaccessions should be useful for QTL mapping to understand how a constitutive ROL barrier forms. The constitutive barrier of W2165 was closely associated with suberization and resistance to penetration by an apoplastic tracer (periodic acid) at the exodermis but did not include lignin at the sclerenchyma.