Host specificity in the Rhizobium symbioses of two Aspalathus species and an invasive alien legume, Acacia saligna

Abstract

The symbiotic specificity of Aspalathus capensis and A. carnosa in relation to their geographical distribution, was investigated by growing plants in soil and in tubes containing soil solutions plus nitrogen-free nutrient solutions. Soila were collected from three sites within their distribution and two from 90km outside. Both species formed nodules in all three soils from within their distribution and A. capensis in one from outside. A. carnosa did not survive in tube culture. The possible role of hostspecificity in the distribution of A. capensis and A. carnosa is discussed. A widespread invasive alien legume, Acacia saligna . was grown in the same soils and soil solutions. It formed nodules only in the three soils from within the distribution of Aspalathus capensis. The degree of nodulation varied between these soils. The possible importance of host-strain specificity in the invasive ability of alien legumes is discussed.