Population dynamics of soil microorganisms associated with fungicide-dusted caladium seedpieces

The effects of three fungicidal dusts (captan ; a mixture of benomyl, thiram and streptomycin sulfate; and a mixture of chloroneb, thiram and streptomycin sulfate) on the short-term populations dynamics of fungi and bacteria associated with caladium seedpieces planted in raw muck soil were investigated. Both germinating seedpieces and seedpieces which were decomposing after the removal of eyes were used. To determine microbial populations, dilutions of a comminuted suspension of a seed-piece and surrounding soil were plated on selective media at 0,2,4, 8 and 12 weeks after seedpieces were planted. Addition of seedpieces to soil resulted in increases in populations in the following approximate chronological order: fluorescent Pseudomonas spp, Pythium spp, total bacteria, Fusarium spp and other genera of fungi. Most organisms assayed reached higher populations on decomposing than on germinating seedpieces. The effects of the fungicidal dusts on populations of microorganisms associated with seedpieces were not related to changes in populations that followed incorporation of the dusts into soil without seedpieces. The fungicidal dusts reduced total fungal population increases on germinating, but not on decomposing, seedpieces. Bacterial population increases were similar for all treatments of germinating seedpieces, but were prolonged on decomposing, fungicide-dusted seedpieces, as compared to controls.