Competition between three species of <i>Glomus</i> used as spatially separated introduced and indigenous mycorrhizal inocula for leek (<i>Allium porrum</i> L.)

SUMMARY The ability of three vesicular‐arbuscular (VA) mycorrhizal fungi‐Glomus caledonium (Nicol, and Gerd.) Trappe and Gerd., Glomus sp. type E3 and Glomus mosseae (Nicol. and Schenck) Gerd. and Trappe ‐ to infect leek ( Allium porrum L.), when used as spatially separated pairs of inocula was assessed by analysing the roots for the presence of diagnostic fungal enzymes alter separation of root proteins by gel electrophoresis. A difference in competitiveness was observed, such that Glomus sp. E3 was unable to infect a root system if either G. caledonium or G. mosseae were also present. When the latter two fungi were used as a pair of inocula, the one which had been placed to simulate an indigenous strain predominated in the root to the almost total exclusion of the one placed as an introduced inoculum. These results suggest that the successful establishment of VA mycorrhizal inocula in field soils will depend on the indigenous species present, the species being introduced and its placement in the soil. The use of diagnostic fungal isozyme analysis offers a method of monitoring the outcome of an inoculation programme by detecting the presence of the introduced species in the host roots.