Pre-infection events in non-nodulating species of African Acacia

Non-nodulation occurs sporadically throughout the family Leguminosae, the g enus Acacia is unusual as there are a range of species which are consistent ly non-nodulating, but which are closely related to species able to form no dules. A comparative study of these and coexisting related nodulating speci es has been made to establish whether the non-nodulating species exhibited any pre-infection characteristics which are typical of their nodulating cou nterparts. The non-nodulating species did not form any nodule-like structur es, but exhibited pre-infection characteristics such as rhizobial attachmen t similar to that of their nodulating counterparts. The root exudate of nod ulating A. polyacantha contained stimulatory compounds which aided binding of rhizobia to the roots of the non-nodulating species and nodulation was c ompletely inhibited when A. polyacantha was co-cultured with a non-nodulati ng species.