farkhondeh ommati

Fire blight of pome fruits caused by Erwinia amylovora is one of the most devastating disease especially on pear and quince in Semnan province. A total of eighty strains were isolated from different localities and hosts including apple, pear, quince and rose during 2006-2007. Fifty strains were studied for their phenotypic characteristics, genotypic variability, pathogenicity and also resistance to streptomycin and cupper oxychloride. On the basis of physiological, biochemical and morphological features, tested strains were identified as E. amylovora. They were Gram negative, formed levan, facultative anaerobic and induced hypersensitivity reaction in tobacco leaves. They did not produce fluorescent pigment on King`s B medium. On the basis of Phenotypic features, host rang and geographical distribution, eight representatives were selected for evaluating the genetic diversity among them, by rep-PCR using ERIC and BOX primers. All strains were identical to ATCC 49946 strain. On the basis of these experiments no resistance to antibiotics and copper oxychloride was found among the E. amylovora strains causing fire blight of pome fruit trees in Semnan province, therefore chemical bactericides can be safely used in an integrated management program of the disease in Semnan province orchards and this similarity may help to follow a similar method in selecting resistant varieties and forecasting of the disease management.

Pythium root rot of sugar beet caused by Pythium aphanidermatum is an important yield reducing disease in Iran and so far its chemical control has not been achieved successfully, therefore, alternative control measures including biological control might be effective in managing this disease. A green house study was conducted to investigate the efficacy of some native Trichoderma isolates in controlling this disease in Agricultural Research Center, Shahrood, Iran during 2007- 2008. Out of 22 Trichoderma isolates collected from sugar beet fields, seven isolates belonging to four species (Trichoderma harzianum, T. longibrachatum, T. erinaceum and T. koningii), among which T. erinaceum is a new species for Iran mycoflora and had previously performed effective in inhibiting mycelial growth of the pathogen through dual culture and production of volatile and non-volatile metabolites were selected for green house evaluations using seed and soil treatment methods. Results of green house experiments during two years evaluations indicated significant reduction in seedling damping-off in potted plants treated with Trichoderma isolates either as seed or soil treatment (compared with untreated control). Plant growth promotion was also observed in plants treated with Trichoderma isolates in comparison with untreated control. Based on the overall results of this study, T. harzianum 2736 demonstrated the highest disease reduction (70%) in both methods.

Biological efficacy of Trichoderma species may differ due to variations in ecosystems. This study was conducted to assess the biocontrol efficacy of some native Trichoderma isolates against Fusarium oxysporum، an important causal agent of potato wilt disease under lab. and green house conditions in Shahrood Agricultural Research Center، Shahrood، Iran during 2006-2007. Fourteen isolates were collected among which eight showed promising ability in inhibiting the growth of the pathogen through dual culture and production of volatile and non-volatile inhibitors but T. asperellum (T2) and T. atroviride (T3) were almost more efficient than other isolates in inhibiting the mycelial growth of the pathogen in comparison to control (P ≤ 0. 01). Eight isolates were evaluated against the disease under green house condition. Potted plants treated with Trichoderma isolates + F. oxysporum showed lower disease incidence in comparison to Fusarium infested control (P ≤ 0. 05). Best disease control was observed in potted plants treated with F. oxysporum + T. asperellum (T2) showing 2. 5 % disease incidence in comparison to Fusarium infested control، in which disease incidence was 73 %.

Application of botanical and biological methods in plant disease controls are unique techniques in reducing environmental pollutions. Trichoderma species are effective agents in biocontrol strategies and identifying their useful isolates for further studies seems to be helpful. The purpose of this study was to assess the in-vitro biocontrol efficacy of some native Trichoderma isolates against Pythium aphanidermatum an important causal agent of sugar beet root rot disease in North Iran. Evaluations were conducted in Shahrood Agricultural Research Center, North Iran during 2007. Collected Isolates of Trichoderma belonging to four species (T. harzianum,. longibrachatum, T. erinaceum and T. koningii), among which T. erinaceum is a new fungus for Irans'' mycoflora. Results of lab tests including dual culture technique, assessment of volatile and non-volatile effects on pathogen'' colony growth indicated the effectiveness of all ten isolates against P. aphanidermatum. In dual culture T. harzianum-2733 and T. longibrachatum-2734 were best in reducing the colony growth of P. aphanidermatum by 57% compared to control. Volatile antibiotic compounds of T. longibrachiatum-2737 and non-volatile antibiotic compounds of T. harzianum-2739 were best among Trichoderma isolates and controlled the colony growth of the pathogen by 66 and 87% respectively.