BIOLOGICAL CONTROL OF SIX SOIL-BORNE FUNGI OF COTTON USING ANTAGONISTIC STREPTOMYCES ISOLATES

Abstract

In this study, antagonistic activity of fifteen isolates of Streptomyces, in vitro or in vivo,
was determined against six fungi causing cotton seedling diseases. Data showed that all Streptomyces
isolates were highly antagonistic in-vitro studies, isolate Sc-2 was the most effective against
Fusarium solani (antagonism distance (AD) was 1.72 mm), on the other hand, isolates Qa-53, Ps-12
showed the lowest antagonism against F. solani (AD were 0.80, 0.83 mm, respectively). Rhizoctonia
solani was the most sensitive fungus in vitro to the antagonism of most Streptomyces isolates (Qa-84,
Qa-51, Is-10, Ps-12, Si-1, Si-4, Si-6, Si-8 and Si-9) with their AD ranged from 2.27 to 2.70 mm.
However, Sc-2 was the least effective with AD as low as 0.93 mm. F. moniliforme was the least
sensitive fungus to the antagonism of Streptomyces isolates. Antagonisms of Streptomyces isolates
against F. solani; Sclerotium rolfsii and R. solani were positively correlated with their antagonisms
against F. oxysporum (P0.01), R. solani (P0.05) and Macrophomina phasulina (P.0.01),
respectively, but negatively correlated against F. moniforme. Treated fuzzy seeds with Streptomyces
significantly reduced seedling disease in Sc-11, Ma-13, Ps-12, Si-1 and Si-6. All Streptomyces
isolates were ineffective in controlling the disease when the seeds were acid delinted. Some
Streptomyces isolates showed no efficiency on reducing the seedling disease wheather the seeds were
fuzzy or acid delinted such as Sc-2, Qa-44, Qa-51, Qa-53, Qa-84, Da-3, Is-10, Si-4, Si-8 and Si-9.