Response of some important Iranian wheat cultivars to Fusarium culmorum under genetic diversity of indigenous bio-control agent fluorescent Pseudomonas spp.

Wheat root and crown rot caused by Fusarium culmorum is known as one of the most common diseases among wheat diseases in Iran. Recently, application of new resistant cultivars and biological control by antagonistic bacteria, such as phlD+ (a key biocontrol gene) fluorescent Pseudomonas spp. have received much attention. An important scientific gap in this strategy is the interaction between disease resistant level of cultivar and composition of beneficial soil rhizosphere bacteria. Therefore, the resistance levels of some Iranian wheat cultivars to Fusarium culmorum were assessed under diversity of naturally occurring fluorescent Pseudomonas spp. The resistance level of seven wheat cultivars and lines (Falat, Niknejad, Marvdasht, Chamran, N83, Durum and line X) to F. culmorum were tested in greenhouse conditions. Then, the rhizosphere and endorhizosphere population of bacterial isolates were evaluated. Then diversity of phlD+ isolates were assessed using restriction fragment length polymorphism (RFLP). Finally, root colonization by four phlD+ isolates in the line X (resistant) and Falat (the most susceptible) cultivars at greenhouse level were analyzed. Based on resistance analysis, the cultivars were classified in to three groups: resistant, tolerant, and susceptible. The results showed that the indigenous rhizosphere population size of fluorescent Pseudomonas spp. was significantly different among the cultivars and correlated to the level of plant resistance. The results of RFLP analysis of the phlD gene among the isolated bacteria indicated that the composition of the genotypes enriched by the individual cultivars was differed. Four distinct phlD alleles, including A, B, D and F were detected. The highest genotype diversity was observed among phlD+ strains, obtained from line X rhizosphere (resistant cultivar). Comparison of the root colonization by the inoculated strains showed that phlD+ isolates were consistently recovered from the rhizosphere of the resistant cultivar (line X), and were commonly present at populations higher than those recovered from susceptible cultivar (Falat). Based on the results, it can be concluded that amazingly, there is a positive correlation between the wheat resistance level and the population size and diversity of fluorescent Pseudomonas spp. in their rhizosphere.