Abstract
Among several studied strains, Streptomyces rochei IT20 and S. vinaceusdrappus SS14 showed a high level of inhibitory effect against Phytophthora capsici, the causal agent of pepper blight. The effect of two mentioned superior antagonists, as single or combination treatments, on suppression of stem and fruit blight diseases and reproductive growth promotion was investigated in pepper. To explore the induced plant defense reactions, ROS generation and transcriptional changes of selected genes in leaf and fruit tissues of the plant were evaluated. The plants exposed to the combination of two species responded differently in terms of H2O2 accumulation and expression ratio of GST gene compared to single treatments upon pathogen inoculation. Besides, the increment of shoot length, flowering, and fruit weight were observed in healthy plants compared to control. Likely, these changes depended on the coordinated relationships between PR1, ACCO genes and transcription factors WRKY40 enhanced after pathogen challenge. Our findings indicate that appropriate tissue of the host plant is required for inducing Streptomyces-based priming and relied on the up-regulation of SUS and differential regulation of ethylene-dependent genes.
Highlights
Phytophthora blight caused by Phytophthora capsici Leonian is one of the devastating soilborne diseases of pepper (Capsicum annuum L.) and several important crops throughout the world [1, 2]
In vitro data showed that IT20 and SS14 did not antagonize growth and P-solubilizing activity of each other (S1 Fig)
There was no significant difference in the number of fruits among bacterial treated plants
Summary
Phytophthora blight caused by Phytophthora capsici Leonian is one of the devastating soilborne diseases of pepper (Capsicum annuum L.) and several important crops throughout the world [1, 2]. This fungus-like pathogen can display numerous symptoms depending on a host, including foliar blighting, damping-off, wilting, stem, and fruit blight [3]. Biological control programs have become an eco-friendly manner to manage soil-borne diseases and reduce chemical treatments [4, 5]. Some species of Streptomyces, gram-positive filamentous bacteria, are considered as plant growth-promoting rhizobacteria (PGPR) colonizing rhizosphere/plant root, and improving plant health and growth.
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