Comparison of strains of Lysobacter enzymogenes and PGPR for induction of resistance against Bipolaris sorokiniana in tall fescue

Lysobacter enzymogenes C3, the only biocontrol agent previously known to induce resistance in tall fescue against Bipolaris sorokiniana, was compared in growth chamber experiments with other strains of L. enzymogenes, strains of plant growth promoting rhizobacteria (PGPR) that induce systemic resistance in dicot plants, and the synthetic elicitor 1,2,3-benzothiadiazole-7-thiocarboxylic acid-S-methyl-ester (BTH). The treatments were evaluated for induction of localized or systemic resistance against B. sorokiniana when applied to leaves and roots. In addition, the effects of induced resistance on pathogen conidial germination on the phylloplane were assessed. None of the bacterial or chemical treatments induced systemic resistance when applied to a leaf. Strains of L. enzymogenes differed in their ability to cause localized disease inhibition following foliage treatment and to induce systemic resistance in leaves when applied to roots. In contrast to C3, two other strains of L. enzymogenes were ineffective in inducing systemic resistance. PGPR strains varied in effectiveness in causing localized disease inhibition when applied to leaves. Most of the bacterial strains increased peroxidase activity in the treated leaves, providing evidence that localized disease inhibition may have been plant mediated. The involvement of localized induced resistance was confirmed in P. fluorescens WCS417r, which did inhibit B. sorokiniana conidial germination or hyphal growth in vitro. Soil drenches with nearly all PGPR strains resulted in systemic resistance in leaves, but the treatments varied as to the timing and strength of induced systemic resistance. BTH induced localized resistance when applied to leaves but did not activate resistance in leaves when applied to roots. All cases of induced resistance were associated with an inhibition of conidial germination on leaf surfaces and, thus, this reaction appears to be a hallmark of induced resistance in the B. sorokiniana-tall fescue pathosystem. (C) 2004 Elsevier Inc. All rights reserved.