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Resistance

Inhibition of Soft-Rotting Erwinia spp. Strains by 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one in relation to their Pathogenicity on Zea mays. G. H. Lacy, Research associate, Department of Plant Pathology, University of Wisconsin, Madison, 53706, Present address: Department of Botany and Plant Pathology, The Connecticut Agricultural Experiment Station, New Haven, CT 06504; S. S. Hirano(2), J. I. Victoria(3), A. Kelman(4), and C. D. Upper(5). (2)(3)(4)Research associate, research assistant and professor, Department of Plant Pathology, University of Wisconsin, Madison, 53706, (3)Present address: Instituto Colombiano Agropecuario, Palmira, Colombia; (5)Research chemist, Federal Research, Science and Education Administration, U.S. Department of Agriculture, University of Wisconsin, Madison, 53706. Phytopathology 69:757-763. Accepted for publication 1 February 1979. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Association of Cereal Chemists, Inc., 1979. DOI: 10.1094/Phyto-69-757.

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 Erwinia chrysanthemi from corn (EC_z), 25 E. chrysanthemi from hosts other than corn (EC_o), and nine E. carotovora (EC). Twenty-seven (80%) of the EC_z strains were relatively resistant to DIMBOA, whereas 96% of the EC_o and 89% of the EC strains were relatively susceptible. Genetically related corn plants containing (BxBx genotype) or lacking (bxbx genotype) DIMBOA were inoculated with EC_z strains resistant and susceptible to DIMBOA. Significant differences generally were not noted in percentage of plants infected, proportion of resistant plants, and mean effective doses (ED₅₀’s) required to cause stalk rot symptoms in the resistant and susceptible plant populations. Furthermore, at least seven DIMBOA-susceptible EC_o strains were moderately pathogenic and produced typical stalk rot symptoms in DIMBOA-containing corn plants of the inbred line W117^th. Therefore, DIMBOA is not the primary means of resistance of corn to E. chrysanthemi. However, since 80% of the EC_z 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.