[1] [1] GRAY E J, SMITH D L. Intracellular and extracellular PGPR: commonalities and distinctions in the plant-bacterium signaling processes[J]. Soil Biology & Biochemistry, 2005, 37(3): 395-412.

[2] [2] BENEDUZI A, AMBROSINI A, PASSAGLIA L, et al. Plant growth-promoting rhizobacteria (PGPR): their potential as antagonists and biocontrol agents[J]. Genetics and Molecular Biology, 2012, 35(4): 1044-1051.

[3] [3] BAIS H P, FALL R, VIVANCO J M, et al. Biocontrol of Baci- llus subtilis against infection of Arabidopsis roots by Pseudomo- nas syringae is facilitated by biofilm formation and surfactin production[J]. Plant Physiology, 2004, 134(1): 307-319.

[5] [5] TIMMUSK S, GRANTCHAROVA N, WAGNER E G, et al. Paenibacillus polymyxa invades plant roots and forms bio- films[J]. Applied and Environmental Microbiology, 2005, 71(11): 7292-7300.

[6] [6] YUAN J, ZHANG N, HUANG Q W, et al. Organic acids from root exudates of banana help root colonization of PGPR strain Bacillus amyloliquefaciens NJN-6[J]. Scientific Reports, 2015, 5: 13438-13447.

[7] [7] JIN Y, ZHU H, LUO S, et al. Role of maize root exudates in promotion of colonization of Bacillus velezensis strain S3-1 in rhizosphere soil and root tissue[J]. Current Microbiology, 2019, 76(7): 855-862.

[8] [8] YARYURA P M, LEON M, CORREA O S. et al. Assessment of the role of chemotaxis and biofilm formation as requirements for colonization of roots and seeds of soybean plants by Bacillus amyloliquefaciens BNM339[J]. Current Microbiology, 2008, 56(6): 625-632.

[9] [9] SUO B, CHEN Q, WU W, et al. Chemotactic responses of phytophthora sojae zoospores to amino acids and sugars in root exudates[J]. Journal of General Plant Pahtology, 2016, 82(3): 142-148.

[10] [10] WU K, YUAN S, XUN G, et al. Root exudates from two tobacco cultivars affect colonization of ralstonia solanacearum and the disease index[J]. European Journal of Plant Pathology, 2015, 141(4): 667-677.

[11] [11] ZHANG F, MENG X, YANG X, et al. Quantification and role of organic acids in cucumber root exudates in Tricho- derma harzianum T-E5 colonization[J]. Plant Physiology and Biochemistry, 2014, 83: 250-257.

[12] [12] TAN S, YANG C, MEI X, et al. The effect of organic acids from tomato root exudates on rhizosphere colonization of Bacillus amyloliquefaciens T-5[J]. Applied Soil Ecology, 2013, 64: 15-22.

[13] [13] ANKATI S, RANI T S, PODILE A R, et al. Changes in root exudates and root proteins in groundnut-Pseudomonas sp. interaction contribute to root colonization by bacteria and defense response of the host[J]. Journal of Plant Growth Regulation, 2019, 38: 523-538.

[16] [16] CHANEY R L, REEVES P G, PHILIP P G, et al. An improved understanding of soil Cd risk to humans and low cost methods to phytoextract Cd from contaminated soils to prevent soil Cd risks[J]. Biometals, 2004, 17(5): 549-553.

[20] [20] GRIMM A C, HARWOOD C S. Chemotaxis of Pseudomonas spp. to the polyaromatic hydrocarbon naphthalene[J]. Applied and Environmental Microbiology, 1997, 63(10): 4111-4115.

[21] [21] ADLER J. A method for measuring chemotaxis and use of the method to determine optimum conditions for chemotaxis by Escherichia coli[J]. Journal of General Microbiology, 1973, 74(1): 77-91.

[23] [23] SUSANA B, GERMAN A, EVELIN C, et al. Root colonization and growth promotion of wheat and maize by Pseudomonas aurantiaca SR1[J]. Soil Biology and Biochemistry, 2009, 41(9): 1802-1806.

[24] [24] CAO Y, ZHANG Z, LING N, et al. Bacillus subtilis SQR 9 can control Fusarium wilt in cucumber by colonizing plant roots[J]. Biology and Fertility of Soils, 2011, 47(5): 495-506.

[26] [26] THIMMARAJU R, KIRK J C, PAUL W P, et al. Root-secreted malic acid recruits beneficial soil bacteria[J]. Plant Physiology, 2008, 148(3): 1547-1556.

[27] [27] SHAN S P, GUO Z H, LEI P, et al. Increased biomass and reduced tissue cadmium accumulation in rice via indigenous Citrobacter sp. XT1-2-2 and its mechanisms[J]. Science of the Total Environment, 2020, 708(1): 135224-135234.