A Possible Role for Ferrous Complexes in Fungal Disease Suppression: Glume Blotch and Net Blotch of Cereals

Germination of spores of Septoria nodorum and Pyrenophora teres was inhibited and germ-tube growth in germinated spores was reduced b y ferrous ions complexed with a number of cheiating agents. No such inhibition was observed with ferric complexes and none of the chelating agents in the desferri form was toxic to the fungi. The germination mechanism in spores suspended in ferrous-2,3-dihydroxybenzoic acid (Fe¹¹-DHBA) for 24 h could not subsequently be released to any great extent by incubation with ethylenediamjne-di (o-hydroxyphenyl-acetic acid) (EDDHA). Lesion development by the fungi in the presence of ferrous complexes on detached leaves of host plants was almost totally suppressed, but compounds which preferentially chelate ferric ions, used in the desferri form significantly stimulated lesion development by S. nodorum on wheat leaves. Cermination, appressorium formation and lesion development on leaves of host plants were also significantly reduced by Fe¹¹-DHBA when plants were sprayed to run-off up to 5 days prior to inoculation. Disease development and subsequent 1000 grain weight loss were reduced by approximately 50 percent in wheat and barley plants when the flag leaves were treated with Fe¹¹-DHBA (5 × 10^?4 M) prior to inoculation with S. nodorum and P. teres respectively, compared with inoculated, untreated plants.