The zinc violet and its colonization by arbuscular mycorrhizal fungi

Among the plants growing on several heavy metal soils, the zinc violets (the yellow Viola calaminaria (DC.) Lej. s. str. of the Aachen/Liege area and the blue Viola guestphalica Nauenburg of Blankenrode/Paderborn) were consistently colonized by arbuscular mycorrhizal (AM) fungi. The degree of AM-colonization ion apparently correlated with the heavy metal content in soils as indicated by the composition of the plant community. Among diverse violets examined from various non-polluted areas, Viola lutea (DC.) Lej. and some other alpine violets showed high mycorrhizal colonizations of the roots. A specific Glomus Brl isolate was obtained from the roots of the yellow zinc violet (V. calaminaria s. str.) of the Breinigerberg area near Aachen. RFLP-analysis indicated the uniformity of this isolate. Incubation with Glomus Brl allowed plants like maize, barley, alfalfa and zinc violets to grow until flower and seed formation in two different heavy metal soils supplemented with nutrient solutions in greenhouse experiments. Controls (sterilized heavy metal soils not inoculated with Glomus Brl or yellow lupins as non-mycorrhizal plants) did not grow. The Glomus Brl isolate from the zinc violet more efficiently supported growth of maize or alfalfa in heavy metal soils than a commonly used Glomus intraradices Schenck and Smith isolate. The potential applications of these findings are discussed.