Nodulation response of woody Papilionoid species after inoculation with rhizobia and soil from Hawaii, Asia and North America

Among subfamilies in the Fabaceae, the capacity to form root nodules is mos t common in the Papilionoideae. Yet nodules have never been observed on spe cies of Cladrastis, and there are conflicting reports of the capacity of sp ecies in the genus Styphnolobium to nodulate. Our objectives were to evalua te Styphnolobium japonicum (formerly Sophora japonica) and Cladrastis kentu kea for the capacity to nodulate and to characterize any isolated rhizobia. N-deficient plants were inoculated with rhizobia chosen for their low host specificity or for their symbiotic potential with indigenous and introduce d trees and shrubs of Sophora species in Hawaii, Japan and China. Soil samp les from the root zones of mature S. japonicum, C. kentukea and other woody legumes, introduced or indigenous to Hawaii, Japan, China and the continen tal USA, also were used as inocula. Inoculation did not elicit nodulation o f C. kentukea or S. japonicum, despite that N concentrations of shoots of S . japonicum (1.6%) and C. kentukea (1.5%) fell below the highest shoot N pe rcentage that previously was associated with well-nodulated plants of Maack ia amurensis (1.8%). In addition to these analyses, rhizobia were isolated from nodules on the roots of a tree reported to us as S. japonicum. Nine of the 10 isolates selected as representatives of similarity groups were capa ble of nodulating M. amurensis, which led to the identification of the puta tive S. japonicum as Maackia floribunda. We also found that broad-range Bra dyrhizobium USDA 6, USDA 3384 and USDA 3456 induce nodules on R. pseudoacac ia and M, amurensis, which were used as control species during inoculation trials with S. japonicum and C. kentukea. Our conclusion that S. japonicum and C. kentukea lack the capacity to nodulate is based on the most thorough analysis of the nodulation capacity of these species to date. Previous rep orts of nodulation of S. japonicum may have been due to inaccurate plant or nodule identification.