Further Evidence of Interchangeability Among the Groups of Rhizobium Leguminosarum

OEVERAL workers have presented data indicat\*J ing that the interchangeability of nodule bacteria so far as the nodule-forming function is concerned is not limited to the legumes within a so-called crossinoculation group. However, there is considerable difference of opinion as to the extent to which any particular nodule organism may function symbiotically with legumes in different cross-inoculation groups as well as to the extent to which the nodule organisms of several groups of legumes may nodulate any one legume. Further evidence of the nodulation of one legume, Psoralea onobrychis, by nodule bacteria from three so-called cross-inoculation groups is presented in this paper. The data reported are the result of three similar experiments conducted under -carefully controlled greenhouse conditions in three different years. Each year surface-sterilized seed of 18 different legumes, sweet clover, Melilotus alba Desv., red clover, Trifolium pratense L., garden pea, Pisum sativum L., winter vetch, Vicia villosa Roth, garden bean, Phaseolus vulgaris L., lupine, Lupinus hartwegii Lindl, soybean, Soja max L. Piper, cowpea, Vlgna sinensis Endl., Korean lespedeza, Lespedeza stipulacea Maxim., Lotus corniculatus L., Wood's clover, Dalea alopecuroides Willd., sainfoin, Onobrychis mciaefolia Scop., black locust, Robinia pseudoacacia L., false indigo, Amorpha fruticosa L., crown vetch, Coronilla varia L., pea tree, Caragana jrutex Koch, trailing wild bean, Strophostyles helvola L., and Psoralea onobrychis Nutt were inoculated with pure single cell cultures of Psoralea onobrychis isolated from nodules secured from plants found in Vermilion County, 111. The seed were then planted in i-gallon and I-quart stone-ware jars filled with sterile quartz sand. At the time of planting, the jars contained 14% by weight of sterile nitrogen-free nutrient solution. The weight of jars and contents was maintained uniformly by watering with sterile distilled water or with sterile nutrient solution, the latter being used every four weeks. At the end of 6 to 10 weeks (the length of time was not the same each year) the plants in each jar, including tops and roots, were harvested, nodulation on roots observed, and nitrogen content determined. Of these 18 legumes only Psoralea onobrychis showed nodulation, a fact which indicated that Psoralea onobrychis does not belong in any of the 15 cross-inoculation groups in which 17 of these legumes are ordinarily placed. Inasmuch as previous experiments had shown that a nonreciprocal interchangeability of the nodule organisms existed in the case of the garden bean, Phaseolus vulgaris L., and Wood's clover, Dalea alopecuroides Willd, it seemed desirable to determine whether the nodule organisms of any of the 15 groups of nodule bacteria previously mentioned would produce nodules on Psoralea onobrychis. Of the nodule bacteria used in this experiment only those isolated from false indigo, Amorpha fruticosa, Korean lespedeza, Lespedeza stipulacea, and Psoralea onobrychis produced nodules on Psoralea onobrychis, although