Dosage Response of the Vesicular-Arbuscular Mycorrhizal Fungi Glomus fasciculatus and G. constrictus to Methyl Bromide

Abstract

Propagules of the vesicular-arbuscular mycorrhizal fungus G. fasciculatus were fumigated with 3000, 6000 and 12,000 .mu.l methyl bromide (MB)/l of air for periods of 1.5-48 h. Propagules fumigated with MB at a CT (concentration .times. time) less than 84,000 remained viable and were capable of infecting sudangrass [Sorghum vulgare]. G. fasciculatus did not reproduce on the roots of sudangrass if inoculum was fumigated with 12,000 .mu.l MB/l air for 7, 12 and 15 h (CT = 84,000, 144,000 and 180,000, respectively or 6000 .mu.l MB/l air for 24 h (CT = 144,000). G. fasciculatus remained viable when fumigated at 3000 .mu.l MB/l air for 48 h CT = 144,000). Dry wt of sudangrass was significantly P = 0.05) reduced when seedlings were inoculated with G. fasciculatus inoculum which had been subjected to 12,000 .mu.l MB/l air for 3 h or longer (CT = 36,000) when compared to dry wt of sudangrass which received nonfumigated inoculum. Ninety percent of the chlamydospores of G. fasciculatus and G. constrictus failed to germinate when subjected to 12,000 .mu./l MB/l air for 6 h or more (CT = 72,000). No chlamydospores of either mycorrhizal fungus germinated when subjected to 12,000 .mu.l Mb/l air for longer than 8 h (CT = 96,000). G. fasciculatus and G. constrictus are more sensitive to MB fumigation than most soil-borne plant pathogens. Furthermore, mycorrhizal fungi can readily be destroyed by MB fumigation in the top 45-cm of soil by most commercial MB fumigations.