Interactions between PGPR and cucumber during induced systemic resistance: Recognition and early host defense responses.

摘要

This dissertation involves the study of interactions between plant growth promoting rhizobacteria (PGPR) which induce systemic resistance in cucumber against anthracnose disease (caused by Colletotrichum orbiculare) and the study of early plant defense responses associated with the reduction of fungal disease development. To examine early bacterial/plant cell to cell interactions between PGPR and cucumber, a stem-injection method was first developed for applying PGPR. Eight PGPR strains which previously demonstrated some ISR activity were assessed for induction of systemic resistance in cucumber against C. orbiculare following PGPR application as seed treatment or stem-injection. Six of eight PGPR strains significantly ;Three PGPR strains (Bacillus pumilus strain SE34, B. pumilus strain SE49, and Pseudomonas fluorescens strain 89B-61) were used to determine if inducing PGPR are recognized by the plant, as determined by the hypersensitive reaction (HR). HR was visualized by confluent or individual cell death at one or more concentrations with all 3 PGPR strains, confirming that plants recognized inducing PGPR strains.;PGPR strain SE49 was selected for determining specific host defense responses associated with PGPR-mediated ISR. Among the various physiological and chemical changes, PGPR treatment increased lignification, total peroxidase activity and specific activity of an anodic isozyme (pI 4.2), and total superoxide dismutase (SOD) as well as a particular type of SOD (CuZn-SOD) activity, but not chitinase activity when compared to the control treatment.