Bacterial and actinomycetes isolates were obtained from the rhizosphere of cotton plants (Giza 70). These isolates were tested for their potency in antagonizing Rhizoctonia solani and Sclerotium rolfsii. The following results were obtained:
Out of 722 bacterial isolates investigated, 160 isolates showed antagonism against R. solani. Out of these antagonistic isolates, 83 isolates were weak, 43 moderate, and 34 isolates were potent antagonists. S. rolfsii was antagonized by 171 bacterial isolates which consisted of 66 weak, 51 moderate and 54 potent antagonists. The majority of the potent antagonists against both pathogens were found to belong to genera Pseudomonas and Bacillus.
The most potent bacterial antagonists were investigated for their sensitivity to the fungicides Vitavax Captan and Topsin M 70 in vitro. The results showed that most of the investigated isolates were sensitive to Vitavax Captan, but Topsin M 70 showed lower toxicity. Results also showed that the potent antagonists belonging to the same genus differed in their tolerance to the same fungicide; and the same bacterial isolate differed in it's sensitivity to different fungicides.
Out of 627 actinomycetes isolates tested, 281 isolates showed antagonism against R. solani. These antagonists were found to be, 81 isolates weak, 78 moderate and 122 isolates were potent antagonists. S. rolfsii was antagonized by 279 actinomycetes isolates out of which 87 isolates were weak, 93 moderate and 99 isolates were potent antagonists. The potent actinomycetes antagonists against both fungi were found to belong to genus Streptomyces.
Investigating the most potent antagonistic actinomycetes isolates for their sensitivity to fungicides, in vitro, showed that Vitavax Captan was more toxic than Topsin M70. |
