Bioorganic Fertilizer Enhances Soil Suppressive Capacity against Bacterial Wilt of Tomato

<div><p>Tomato bacterial wilt caused by <i>Ralstonia solanacearum</i> is one of the most destructive soil-borne diseases. Many strategies have been taken to improve soil suppressiveness against this destructive disease, but limited success has been achieved. In this study, a novel bioorganic fertilizer revealed a higher suppressive ability against bacterial wilt compared with several soil management methods in the field over four growing seasons from March 2011 to July 2013. The application of the bioorganic fertilizer significantly (<i>P</i><0.05) reduced disease incidence of tomato and increased fruit yields in four independent trials. The association among the level of disease incidence, soil physicochemical and biological properties was investigated. The soil treated with the bioorganic fertilizer increased soil pH value, electric conductivity, organic carbon, NH₄⁺-N, NO₃^--N and available K content, microbial activities and microbial biomass carbon content, which were positively related with soil suppressiveness. Bacterial and actinomycete populations assessed using classical plate counts were highest, whereas <i>R</i>. <i>solanacearum</i> and fungal populations were lowest in soil applied with the bioorganic fertilizer. Microbial community diversity and richness were assessed using denaturing gel gradient electrophoresis profile analysis. The soil treated with the bioorganic fertilizer exhibited higher bacterial community diversity but lower fungal community diversity. Redundancy analysis showed that bacterial community diversity and richness negatively related with bacterial wilt suppressiveness, while fungal community richness positively correlated with <i>R</i>. <i>solanacearum</i> population. We concluded that the alteration of soil physicochemical and biological properties in soil treated with the bioorganic fertilizer induced the soil suppressiveness against tomato bacterial wilt.</p></div

Population of <i>Ralstonia solanacearum</i> in soil and disease incidence over time in Test 1 (a and c) and Test 2 (b and d).

<p>The dotted lines and ◇ represent the mean max temperature in the above time periods in different trials. CK: NPK fertilizer; O: NPK fertilizer + organic fertilizer; B: NPK fertilizer + bioorganic fertilizer; S: NPK fertilizer + soil disinfection; S+B: soil disinfection + NPK fertilizer + bioorganic fertilizer. * indicates the significant difference between the treatments at the 0.05 probability level according to the Duncan’s test.</p

The population of bacteria (a and b), fungi (c and d), and actinomycetes (e and f) in soils from different treatments in Test 1 (a, c and e) and Test 2 (b, d and f).

<p>CK: NPK fertilizer; O: NPK fertilizer + organic fertilizer; B: NPK fertilizer + bioorganic fertilizer; S: NPK fertilizer + soil disinfection; S+B: soil disinfection + NPK fertilizer + bioorganic fertilizer. Bars with different letters indicate a significant difference between the treatments, as defined by Duncan’s test (<i>P</i><0.05).</p

Effect of different treatments on tomato yields.

<p>CK: NPK fertilizer; O: NPK fertilizer + organic fertilizer; B: NPK fertilizer + bioorganic fertilizer; S: NPK fertilizer + soil disinfection; S+B: soil disinfection + NPK fertilizer + bioorganic fertilizer. Bars with different letters indicate a significant difference between the treatments, as defined by Duncan’s test (<i>P</i><0.05).</p