Control Of Tobacco Bacterial Wilt By BIO-Organic Fertilizer And Soil Amendments

Tobacco bacterial wilt caused by soilborne pathogen of Ralstonia solanacearum is one of the most prevalent diseases. Bio-control has become an important way to overcome the soil-borne plant disease at present, and the use of antagonistic bacteria against Tobacco bacterial wilt is drawing more and more attention. In this study, an antagonistic strain was isolated from the rhizosphere soil of health tobacco plants in the field severely diseased by tobacco bacterial wilt and was named as SQR-7. The organic fertilizer (OF) used in this study consisted of amino acid fertilizer and mature composts. The BOF used was made through a second solid fermentation by inoculating SQR-7into organic fertilizer. Pot and field experiments were carried out to investigate effects of the BOF and the BOF plus soil amendments against on tobacco bacterial wilt and the influences on bacterial microflora, the relationship between the homology of Ralstonia solanacearum phcA and their biochemical classification.Pot and field experiments were designed to have same five treatments, such as:T1, the control; T2, the soil was applied with common organic fertilizer; T3, the soil was applied with the BOF; T4, the soil was treated with lime before the application of the BOF; T5, the soil was treated with lime and bicarbonate before the application of the BOF. DGGE and plate counting were used to investigate microflora in the rhizosphere soils.Pot experiment results showed that application of common organic fertilizer (T2) had no control effect against tobacco bacterial wilt, while all other three treatments(T3,T4and T5) showed significant control effects against tobacco bacterial wilt and the controlling percentages varied in the range of66.7%-87.9%. Applocation of BOF had some influence on microflora in the rhizosphere, increasing the number of bacteria by3.5and6.1times and the number of actinomycetes by3.7and3.5times, but decreasing the number of fungi by70.1%and66.2%, respectively in T3and T4, and increasing the number of bacteria and actinomycetes by13.6times and5.1times, respectively, but decreasing the number of fungi by75.0%in T5. The combined treatment of the soil with lime and bicarbonate before application of the BOF could control tobacco bacterial wilt effectively by altering composition of the microflora in tobacco rhizosphere, and decreasing the number of pathogens.Field experiment results showed the controlling percentages of T2, T3, T4, T5were4.55%,15.80%,30.25%,50.25%, respectively at80days after transplanting while the disease index of control was82.64%. PCR-DGGE showed that the bacterial microflora of T3, T4, T5were richer than T1and T2, and T5was the richest. The results above indicated that OF cannot control the tobacco bacterial wilt, while the SQR-7containing bio-organic fertilizer could effectively control the disease by increse the diversity of bacterial microflora. The controlling effect is even better when the soil was treated with lime and bicarbonate before the application of the BOF; Application of the BOF could also significantly promote the growth of tobacco plants in field, and the effect is more significant in the soils pretreated with lime and bicarbonate; Plant heigh, stem circle and maxium leaf area in T3were1.38,1.08,1.33times,1.50,1.09,1.34times in T4and1.66,1.11,1.44times in T5when compared with the T1, respectively.phc A is a key regulating the expression of pathogenic factor in R. solanacearum. We compared homology of phcA sequences of6strains R. solanacearum isolated from different regions in GuiZhou province with the known phcA sequences in NCBI and malyzed the relationship between the phcA homologies of R. solanacearum and their biochemical types. The results indicated that in general, biovars based on traditional biochemical classification coincided with genotype based on homologues of phcA, but not always the same. The result was helpful to the classification of R. solanacearum by two or more conserved and virulent genes.