Ten aspergilli (five each from marine and terrestrial habitats) were screened for siderophore production. All
test isolates produced siderophores as indicated by a positive reaction in the FeCl3 test, chrome azurol sulphonate assay,
and chrome azurol sulphonate agar plate test. Further, the test isolates were compared for their siderophore production
potential and chemical characteristics. Examination of the chemical nature of the siderophores revealed that all test
isolates produced hydroxamate siderophores that were trihydroxamate hexadentates. Wide-spread occurrence of
siderophores in marine isolates indicate their functional role in maintaining overall productivity of coastal waters.
Among all test aspergilli, marine Aspergillus versicolor was found to be the largest siderophore producer (182.5 μg/mL
desferrioxamine mesylate equivalent), least siderophore production was recorded in a marine strain of Aspergillus niger
(3.5 μg/mL desferrioxamine mesylate equivalent).
The entomopathogenic fungus, Metarhizium anisopliae (Metschn.) Sorokin var, anisopliae was found pathogenic to the larvae of Agrotis segetum (Schiff.), Agrotis ipsilon (Hufnagel) and Agrotis spinifera (Hubn.). It was also found pathogenic to eggs of A. segetum . Soil application of the fungus gave 45% mortality of last instar larvae of A. segetum at a concentration of 1.2 A— 10 7 spores/g of soil. The fungal spores at 10 7 /ml sprayed on A. segetum eggs gave 100% mortality. Field application of spores on the eggs proved effective in controlling the pest. The study indicates the scope of using the fungus against the pest in the field.
Antagonistic effect of seven isolates of Bacillus subtilis has been examined in dual culture tests against Rhizopus nigricans , the incitant of 'papaya' ( Carica papaya L.) frult-rot. Isolate AF 1 which caused maximum inhibition (9.6 mm) was grown in potato dextrose broth for 96 h and cell-free culture filtrate was used to study the inhibition. The concentrated extract of culture filtrate of the antagonist was diluted to indicate 0-40 per cent in potato dextrose agar and Richard's solution. There was 93% inhibition at 40 per cent in both the media. Germinated spores formed clumps in Richard's solution at and above 20 per cent concentration of the antagonistic culture filtrate, but failed to produce sporangia. Concentrated extract induced formation of bulbous structures in hyphae. Biological control of papaya fruit-rot was achieved by dipping the fruits in cell suspension of B. subtilis or in the culture filtrate, 24 h before treatment with R. nigricans .
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