Control of Collar Rot Disease of Hibiscus Effect of Microorganisms in Silkworm Litter

For further information, contact Plant Pathology and Microbiology Division, Department of Agriculture, Chatuchak, Bangkok 10900, Thailand., 2003-03-01

Silkworms As Source of Bioagents

Microorganisms, a form of bioagent, are alternatively used for plant disease control for the safety of human, animals, food, and environment. These bioagents can be collected and selected from several natural sources. For this study, silkworm was selected as the natural source. Isolation and selection of antagonistic microorganisms in order to decrease collar rot disease development in roselle (Hibiscus) subdaritta L., and determination of their effect on the number of surviving Phytophthora propagules in the soil were done in this study. Laboratory and greenhouse experiments were conducted in Bangkok and in field experiments in Udonthani.

Reduced Disease When Soil Amended with Silkworm Litter

The result showed that Pseudomonas fluorescens, Bacillus #2, Actinomycetes #1, and mixed microorganisms (Pseudomonas fluorescens + Bacillus #1 + Bacillus #2 + Actinomycetes #1) could inhibit the growth of Phytophthora nicotianae var. parasitica on PDA medium and in soil. In the greenhouse, collar rot disease development in hibiscus plants decreased when infested soil (sporangia and chlamydospores) was inoculated into the amended soil with 3% silkworm litter, and a decrease in disease development was observed more on roselle plants grown in the amended soil incorporated with the antagonistic microorganisms, Pseudomonas fluorescens, Bacillus #2, and Actinomycetes #1. However, the number of surviving Phytophthora propagules was not less than that in the infested soil treatment.

Effective in Field Trials

In the field trial, disease development in roselle plants decreased when infested soil was inoculated into amended soil with 3% silkworm litter and incorporated with Pseudomonas fluorescens, Bacillus #1, Bacillus #2, Actinomycetes #1, and mixed microorganisms (Pseudomonas fluorescens + Bacillus #1 + Bacillus #2 + Actinomycetes #1). There was no difference in the number of surviving Phytophthora propagules among the soil treatments.

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