Physiological Studies on Nodule Formation. The Characteristics and Inheritance of Abnormal Nodulation of Trifolium pratense by Rhizobium leguminosarum

Five to 7 per cent of plants of Trifolium repens L. and T.pratense L. and 100 per cent of plants of T. subterraneum L. were nodulated by Rhizobium leguminosarum but none of T. hybridum L., T. glomeratum L. or T parvifirum Ehrh. The frequency of nodulation of T. pratense by R. leguminosarum was much increased by breeding from susceptible plants. Such plants were not nodulated by bacteria isolated from any other cross-inoculation group, but remained fully susceptible to R. trifolii. The nodules formed by R. leguminosarum are generally associated with lateral roots and are ineffective.