Inhibition effects of vermicomposting products and activated sludge extraction on strains of pathogenic bacteria of potato

Abstract: Potato is one of the most important cash crops in China. Nevertheless, serious soilborne diseases have posed a great threat to potato production in recent years, due mainly to the deteriorated soil environment during the commonly-used continuous cropping practice with the expansion of planting areas. Alternatively, organic waste is widely expected to effectively control soilborne diseases, due to its richness in nutrients, bioactive substances, and living microorganisms. Specifically, two typical organic wastes are the vermicomposting product and activated sludge from the gourmet powder factory. Therefore, the objective of this study was to investigate the suppressive effects of the vermicomposting product and activated sludge on two representative pathogenic bacteria of Rhizoctonia solani and Fusarium oxysporum. The growth rate in the culture dish was adopted to determine the suppressive effects of extracts from two materials on the pathogens. A bioassay experiment in a pot was used to treat the canker disease of potato stem, particularly for the stable promotion of seedling growth. The results showed that the extracts of the vermicomposting product and activated sludge presented significantly suppressive effects on the pathogens, where the inhibition rate increased dramatically with the decrease of dilution ratio. The inhibition rate in the 100 times diluent of the vermicomposting product and activated sludge extracts were 78.3% and 98.8% on R. solani, while 60.1% and 75.8% on F. oxysporum, respectively. The specific synergistic effects of 1 000 times dilution in two extracts were 98.6% and 72.6% for R. solani and F. oxysporum, respectively. But the inhibitory effect on pathogenic bacteria decreased rapidly after high-temperature sterilization of the vermicomposting product and activated sludge, indicating a relatively minor difference, compared with the control. Additionally, suppressive effects in the 100 times diluent in the mixing extracts were 18.4% and 20.3% on R. solani, while 5.3% and 9.2% on F. oxysporum, respectively. It proved that the vermicomposting product and activated sludge extracts can be used to effectively control canker diseases of potato stem caused by F. oxysporum. Correspondingly, the combined application can be expected to synergically prevent and control the stem canker of potatoes. The control effect was up to 69.0%, 38.0%, 21.1% higher than that of the vermicomposting product and activated sludge alone, while the high of potato seedlings increased by 56.8%, compared with the control, where the extracts from two materials were 1:1 mixed and diluted 200 times. It infers that the significant synergistic effect can greatly contribute to disease prevention and growth promotion, when the vermicomposting product and activated sludge were used concurrently. Therefore, the organic wastes, including the vermicomposting product and activated sludge, can be expected to control the potato soilborne diseases in modern sustainable agriculture.