Aisan Afkhamifar - Department of Plant Protection, Science and Research Branch, Islamic Azad University, Tehran, Iran.
Cobra Moslemkhani - Seed and Plant Certification and Registration Institute, Agricultural Research, education and Extension Organization (AREEO), Tehran, Iran.
Nader Hasanzadeh - Department of Plant Protection, Science and Research Branch, Islamic Azad University, Tehran, Iran.
Javad Razmi - Department of Plant Protection, Science and Research Branch, Islamic Azad University, Tehran, Iran.
Leila Sadeghi - Seed and Plant Certification and Registration Institute, Agricultural Research, education and Extension Organization (AREEO), Tehran, Iran.

Wheat seeds harbor different microbial populations, which can be associated with each other in neutral, positive, or negative interactions. The present study investigated the interaction of fluorescent Pseudomonas and Xanthomonas translucens (Xt) as an important wheat seed-borne pathogen. In addition to P. fluorescens (A۷) and P. chloroaphis (A۴), which were previously isolated from the rhizosphere of potato as potent biocontrol agents, six more non-pathogenic Pseudomonas strains that were isolated from wheat seeds, were studied. According to the general biochemical tests and partial ۱۶S rRNA sequences alignment, the isolated strains were closely related to the species of P. gessardii, P. orientalis, P. poae, P. koreensis, and P. cedrina. The Pseudomonas strains exhibit different antagonistic activities, such as phosphate solubilization, cellulase, protease, and lipase production. Also, they have an apparent inhibition effect under in vivo conditions against X. translucens. Seed treatment by these strains led to suppressing bacterial leaf streak disease incidence in an early growth stage. However, disease progress enhanced with the seedling growth, resulting in the treated plants' complete death. Only in treated seeds by P. fluorescens (A۷), P. chloroaphis(A۴), and P. orientalis (Ais۱۱۹) decrease of AUDPC up to ۸۳%, ۷۴%, and ۶۳% was achieved, respectively, compared with the untreated controls. Our results showed that some fluorescent Pseudomonas strains could cause delay at the beginning of the disease appearance due to competition or producing antimicrobial metabolites during that time. In contrast, some may be considered a threat, enhancing disease development through synergistic effects.

Xanthomonas translucens, Pseudomonas spp, disease severity, synergy