حمیدرضا علیزاده

Fusarium oxysporum f. sp. radices-cucumerinum , causal agent of Fusarium cucumber wilt, is one of the main soil-borne phytopathogens recently considered as the most destructive disease of cucumber in Jiroft's greenhouses. In recent decades, biological control of soil- borne phytopathogenic fungi by efficient antagonists, especially fluorescent pseudomonads , has received spectacular attentions. Therefore, in order to achieve effective biological control of the disease and organic production of cucumber, 81 strains of fluorescent pseudomonads isolated and purified from the rhizosphere of cucumber on selective S1 and KB media. Then, antagonistic effects of these isolates were screened against Fusarium oxysporum in different methods. The results of dual cultures showed that isolates 33C, 21B, 38A, 42D and 43C by creation of 5.33, 6.66, 7, 7.33 and 8.66 mm of inhibition zone, were significantly more efficient than the other strains. Biochemical identification of effective antagonists by such methods as examination of starch, levan, lecithin and casein hydrolysis, Gram staining and catalase test were performed. Also, these isolates were evaluated in terms of producing volatile compounds, hydrogen cyanide and proteases and their effects on mycelial growth of the pathogen. The results showed that volatile metabolites of isolates 21B, 38A, 43C, 33C and 42D inhibited mycelial growth by 44.1, 49.2, 52.3, 60 and 66.7%, respectively; isolates 33C, 38A, 42D and 43C were the most proteolytic ones whereas isolate 21B did not indicate any proteolytic capability. Isolates 33C, 38A, 42D and 43C were the most efficient isolates in production of Hydrogen cyanide but isolate 21B did not show any sign of HCN production. According mentioned findings, isolates 21B, 33C, 38A, 42D and 43C as the most effective antagonists, were investigated in greenhouse trails. Results of in vivo experiments showed that in comparison with control (Najafinia et al ., 2009), isolates 21B, 33C, 38A, 42D and 43