Inhibition of Soft-RottingErwiniaspp. Strains by 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one in relation to their Pathogenicity onZea mays

Abstract

The susceptibility of 68 Erwinia strains to 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA), an inhibitory compound often found in corn, was measured with an agar diffusion assay. The strains included 34 E. chrysanthemi from corn (ECz), 25 E. chrysanthemi from hosts other than corn (ECo), and 9 E. carotovora (EC). Twenty-seven (80%) of the ECz strains were relatively resistant to DIMBOA, whereas 96% of the ECo and 89% of the EC strains were relatively susceptible. Genetically related corn plants containing (BxBx genotype) or lacking (bxbx genotype) DIMBOA were inoculated with ECz strains resistant and susceptible to DIMBOA. Significant differences generally were not noted in percentage of plants infected, proportion of resistant plants, and ED50 required to cause stalk rot symptoms in the resistant and susceptible plant populations. Furthermore, at least 7 DIMBOA-susceptible ECo strains were moderately pathogenic and produced typical stalk rot symptoms in DIMBOA-containing corn plants of the inbred line W117Ht. Therefore, DIMBOA is not the primary means of resistance of corn to E. chrysanthemi. However, since 80% of the ECz strains were resistant to DIMBOA, this compound in corn tissue probably exerts selection pressure for E. chrysamthemi strains pathogenic to corn, at some level other than that of primary host resistance.