| Tomato(Solanum lycopersicum) is one of the most important vegetables in the world, bacterial wilt caused by Ralstonia solanacearum is a serious soil-borne diseases. Traditional controlling methods, such as crop rotation, chemical control and resistant varieties have lots of limitations. Biochar is a product made from agricultural wastes. As a new type of soil amendment, recent studies show that biochar has significant effect on soil-borne plant diseases prevention and control. Taiwan red cherry which is susceptible to R. solanacearum was used as materials to study the effects of wheat biochar addition on disease-resistance of tomato through pot experiment. Soil microbial biomass and activity, contents of organic acids and amino acids in soil and its effects on R. solanacearum were the focuses to investigate soil microbial effects mediated by biochar treatment. The main results were as follows:(1) After tomato plants are infected by R. solanacearum, plant biomass were decreased, while wheat biochar addition can reduce the disease index of tomato and enhance the ability of disease resistance. Disease index was decreased by 61.11% 12 days after inoculation by wheat biochar addition, while the fresh weight, dry weight and total carbon content of plants were significantly increased by 39.04%, 22.26%and 15.92%, respectively. There was no significant effect on available silicon and total nitrogen content of plants.(2) After tomato plants are infected by R. solanacearum, the amount of R.solanacearum in stem and soil were significantly increased, while wheat biochar addition can significantly decrease the amount of R. solanacearum in stem and soil by49.15% and 40.24%, respectively. Soil respiration and nitrification, soil microbial biomass nitrogen(MBN) and phosphorus(MBP) were significantly increased, while the microbial biomass C:N and C:P ratios were significantly decreased by wheatbiochar application. There was no effect on soil microbial biomass carbon(MBC).Correlation analysis showed that soil microbial activity, MBN and MBP had significant negative correlation with the amount of soil R. solanacearum, while significant positive correlation with the total C, total N and available silicon content of soil. This suggested that wheat biochar can enhance the availability of nutrient source for microorganisms, which potentially leads to increase in microbial biomass and activity.(3) Bacteriostatic test in vitro showed that citric acid, salicylic acid, succinic acid, fumaric acid, tartaric acid and methionine had inhibitory rolet against R.solanacearum, while threonine promoted the growth of R. solanacearum. After wheat biochar was used, the content of citric acid, fumaric acid and methionine in soil were significantly increased by 20.38%, 37.82% and 63.43%, respectively, while the content of threonine was significantly decreased by 39.04%. Correlation analysis showed that soil microbial activity, MBN and MBP had significant positive correlation with the content of citric acid, fumaric acid, lysine, methionine, arginine and phenylalanine, while significant negative correlation with the content of tartaric acid and salicylic acid. This suggested that wheat biochar can regulate the content of organic and amino acids in soil, enhance abundance and activities of beneficial microbes and suppress the growth of R. solanacearum.In conclusion, two different mechanisms have been proposed to explain the effects of wheat biochar on disease suppression:(i) improving soil quality in terms of nutrient availability and physico-chemical properties;(ii) regulating the content of organic and amino acids in soil to improve the microecological environment, which leads to enhanced abundance and activities of beneficial microbes. |
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