SPECIFICITY OF ARROWLEAF CLOVER FOR RHIZOBIA AND ITS ESTABLISHMENT ON SOIL FROM CRIMSON CLOVER PASTURES

Successful establishment of clover (Trifolium spp.) on soil requires that the appropriate rhizobia are present to establish an N2 fixing association. Experiments were undertaken in the laboratory to determine if the rhizobial requirements of arrowleaf clover (Trifolium vesiculosum Savi) were different from those of crimson clover (Trifolium incarnatum L.) because arrowleaf clover is often being sown in pastures that have previously grown crimson clover. Generally, rhizobia capable of nodulating crimson clover were also able to nodulate arrowleaf clover but fixed little N2. Soil collected from nine pastures that were growing crimson clover and had never been planted to arrowleaf clover contained rhizobia capable of effectively (nodules fixed N2) nodulating arrowleaf clover. Protein profiles of rhizobia isolated from nodules of arrowleaf and crimson clover grown on soil from one of the nine locations indicated that at least 12 rhizobial strains were present, and those that selectively nodulated crimson clover generally were not able to fix N2 or showed delayed nodulation on arrowleaf clover. When arrowleaf clover was grown on the same soil, four of the five strains that formed nodules on its roots were effective. It appears that arrowleaf clover was able to select effective rhizobia from a mixed population and that it may be successfully established on fields that have grown crimson clover, even though the rhizobial requirements for the two hosts are different. © 1989 Soil Science Society of America.