The influence of host and non-host crops on the rhizobial population of the root rhizosphere

Abstract

Field pea (Pisum sativum), a new crop to the Dark Brown and Black Chernozemic Soil Zones of Saskatchewan, forms a symbiosis with Rhizobium leguminosarum biovar viceae. This rhizobium is not native to the region, yet numbers in excess of 10^4 g-1 soil have been observed several years after a single inoculated field pea crop was grown. Modified immunoblot and ELISA techniques utilizing strain-specific polyclonal antibodies were used to monitor the environmental effect of host and non-host crop on rhizobial populations. The proportion of soil rhizobia able to nodulate pea differed between a competitive and poorly competitive isolate. Numbers of rhizobia declined over time in non-rhizosphere soil and increased in the presence of host plant. Both isolates maintained or increased soil populations from the initial level in the presence of certain non-host plants. The proportion of rhizobia available to nodulate a pea root increased more for the poorly competitive isolate in the presence of host and non-host root systems but did not reach the level of the highly competitive isolate.