Changes in Microorganisms in the Rhizosphere of Mulberry Genotypes with Differing Resistance to Bacterial Wilt

Abstract

11A close relationship between soil-borne diseases, soil microbial community structure, and 12 functional diversity has been described in the mulberry plant. In the present study, microbial 13 abundance, community structure, and functional diversity in the soil rhizosphere were compared 14 in resistant (Kangqing10) and susceptible (Guisang12) mulberry genotypes using the dilution plate 15 method, micro-ecology technology, and polymerase chain reaction-denaturing gradient gel 16 electrophoresis (PCR-DGGE). The goal of this study was to develop better management methods 17 for mulberry cultivation and preventing and controlling bacterial wilt. Rhizosphere soil 18 microorganisms were more abundant in the resistant normal mulberry genotype than in the 19 susceptible normal mulberry genotype. Carbon source utilization was better in the susceptible 20 normal mulberry genotype. These properties were lower in the resistant sickly mulberry genotype 21 than in the susceptible sickly mulberry genotype. PCR-DGGE indicated that the bacterial and 22 fungal community structures of the resistant genotypes were more stable than those of the 2 23 susceptible genotypes. Correlation regression analysis implicated mulberry bacterial wilt in the 24 loss of soil nutrients, particularly organic matter and nitrogen, which can disrupt the balance of the 25 soil microbial community. Loss of soil organic matter and nitrogen had a lower impact on resistant 26 genotype plants than on susceptible genotype plants. Therefore, resistant genotype plants 27 displayed some resistance to bacterial wilt. Further insights into the soil rhizosphere microbial 28 diversities of resistant and susceptible genotypes will help in the control and prevention of 29 mulberry bacterial wilt. 30 Keywords 31 Mulberry; Bacteria Wilt; Genotypes; Microorganisms 32 42 Although this practice can increase production, in the long-term it will alter the physical and 43 chemical properties of the soil [9], reduce soil microbial diversity [10], and promote the 44 development of severe soil-borne diseases such as bacterial wilt [11, 12]. As a result, the stability 109 The total numbers of viable cultured bacteria and actinomycetes were both measured as colony 110 forming units (CFUs) on agar plates using the dilution plate method [27]. The media used to 111 separately culture bacteria and actinomycetes werebeef extract peptone medium and Gause's No.1 112 synthetic medium, respectively [28]. No antibiotics were present. The sample dilution used for 113 culture was 5g of each fresh soil sample in 45mL sterilized 0.85% NaCl. Each dilution was shaken 114 for 15 min at 150 rpm and then left standing for 30 min. The individual bacterial and actinomycete 157 PCR conditions of bacteria were 36 cycles of 94°C for 5 min, 94°C for 1min, 64°C for 1min, and 158 72°C for 1min; and a final elongation at 72°C for 7 min. PCR conditions of the fungus were 35