Interactions between Paecilomyces formosus and Bacillus pumilus strains in occurrence and development of pistachio tree die back

Pistachio die-back is one of the most important and prevalent diseases of pistachio orchards, causing severe reduction of pistachio yield. Due to the important role of bacteria in the occurrence and development of pistachio die-back, the interaction of Bacillus spp. and Paecilomyces formosus was investigated in this research. The isolates of both groups were injected beneath of the inner bark of branches (Ohadi cultivar) using sterile syringes alone or in mixture. According to the results, Bacillus pumilus and P. formosus isolates were able to cause disease on the branches, with longitudinal developments in vascular tissue. Bacterial isolates alone caused lesions ranged 4.5-14 cm in inoculation sites. Mix inoculations, significantly, increased disease development in xylem varied 10-32 cm. Based on morphological, biochemical and molecular properties, isolation of B. pumilus strains is reported for the first time as one of the causal agents of pistachio die-back in Iran.