Abstract

Fusarium head blight (FHB) caused by Fusarium graminearum leads to significant yield losses of wheat (Triticum aestivum L.) in many provinces of Iran, especially in the northern provinces in the margin of Caspian Sea. One strategy for the control of FHB is to use antagonistic bacteria that are plant growth promoting. In order to assess the potential of phyllospheric microorganisms in biological control of FHB, one hundred and ninety isolates of  Pseudomonas, Erwinia and Bacillus spp. were collected from phyllosphere of healthy and infected wheats. Among them, eight isolates were selected and purified with the most antagonistic ability against the growth of pathogenic fungal species (F. graminearum) using the dual culture method. According to the results of biochemical and physiological tests, they were identified as three biovar of Pseudomonas fluorescens, one isolate of them was Erwinia herbicola and two species of Bacillus such as Bacillus subtilis and Bacillus cereus. Production of antifungal substances and volatile metabolites, siderophores and secretion of lytic enzymes such as protease and cellulase were evaluated as the inhibitory mechanisms in vitro. Furthermore, the effects of antagonistic bacteria were studied on severity and incidence of disease caused by F. graminearum in greenhouse conditions. Statistical analysis of data indicated that wheat spikes treatment with antagonistic bacteria not only reduced the severity and incidence of disease compared with the control but also showed positive influence on growth and yield of wheat cultivars. In general, multiple isolates such as B. subtilis 1 and P. fluorescens bv. 1 and 4 together were determined as the most effective strains in reducing incidence of disease. It can be concluded that multiple antagonistic isolates have better effects of control than single isolate.

Key words: Biological control, Fusarium head blight, Fusarium graminearum,Pseudomonas fluorescens, Erwinia herbicola and Bacillus subtilis.