By means of a modified agar‐ring method, the antibiotic efficacy of 300 isolates of actinomycetes, obtained from soil samples from Turkey, against six different test fungi was investigated. A wide range in their degree of sensitivity was evident. Whereas Sclerotinia sclerotiorum was completely inhibited by more than 90 % of the tested isolates, Rhizoctonia solani and Alternaria alternata were suppressed by only 17 and 14 %, respectively; Pythium debaryanum, Cochliobulus sativ, us and Macrophomina phaseolina held an intermediate position. Isolates which completely prevented the growth of Rhizoctonia solani and Alternaria alternata, were usually also highly effective against the other test fungi. Possible conclusions which may be drawn from these results are discussed.
In studies conducted to gain information on the antagonistic potential of Acrophialophora levis, an isolate obtained from the rhizosphere of olive trees in Aegean Region (Turkey) was assayed in vitro for its antibiotic activity against 16 important soil-borne plant pathogenic fungi belonging to Mastigomycotina, Ascomycotina, Basidiomycotina and Deuterornycotina, and six bacteria by using the streak method. The results of this study clearly demonstrated that A. levis exhibited an antagonistic activity against all of the test fungi and three of the test bacteria through antibiosis.As evidenced by the respective zones of inhibition, Botrytis cinerea and Sclerotinia sclerotiorum proved to be extremely susceptible; Pythium debaryanum, Rhizoctonia solani and Phytophthora capsici appeared to be the most resistant among the fungi tested.Among the test bacteria, Corynebacterium michiganense pv. michiganense, Bacillus subtilis and Xanthomonas campestris pv. vesicatoria showed some sensitivity to the antibiotic effect of this antagonist.
An isolate of Neocosmospora vasinfecta var. afncana (F-2) was assayed for its antagonistic activity against 15 soil-borne fungi; 14 of them were important plant pathogens. The fungus exhibited a strong antibiotic effect against most of the fungi under test. While Pythium debaryanum, Macrophomina phaseolina, Phytophthora capsici, Scierotmia sclerotiorum, Cochliobolus sativus and Aiternaria alternata showed a very high degree of sensitivity as evidenced by the respective zones of mhibition caused by the antagonist, Phoma betae, Rhizoctonia solant and VertidUium dahliae proved to be the most resistant. A mutual antibiosis existed between A', vasinfecta var. africana and five of the test fungi.The culture filtrate of the antagonist, diluted ten times with PDA, suppressed the mycelial growth of P. debaryanum and P. capsici completely. Whereas m this test R. solani proved to be the least sensitive, the remaining test fungi showed some differences in their susceptibility, but in any case their growth was inhibited significantly as cotnpared to the controls.
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