Abstract:In order to determine the colonization ability of Bacillus subtilis L1-21 in Citrus leaves and fruits and its control effect on fruit green mold,the colonization dynamics and downwardconduction of B. subtilis in citrus leaves were investigated by foliar spraying with 106 cfu/mL green fluorescent labelled strain (L1-21GFP),colonization in citrus fruits was checked through spraying and soaking with 108 cfu/mL L1-21GFP,and control effect on green mold was evaluated by spore injection with Penicillium digitatum and incidence investigation. After treatment for 10 min,the colonization of B. subtilis L1-21GFP in leaf surface and mesophyll reached 1.36×103 and 8.08×102 cfu/cm2,respectively,and displayed a continuous increasing trend. At 1 h after treatment,the GFPtagged endophyte was stable in leaf surface with 1.51×102 cfu/cm2. The bacterial concentration reached 5.67 cfu/cm2 in mesophyll at 2 h after treatment,which gradually increased to 1.15×103 cfu/cm2 after 30 h. Endophyte L1-21GFP could easily colonize in fruits,and bacterial concentration in pulp and peel after 1 h was 9.51×103 cfu/g and 3.51×104 cfu/g,respectively. However,there was significant difference in the colonization ability in fruits among different citrus varieties,and Citrus reticulata cv Ponkan had the highest colonization. In addition,after soaking for 30 min,the control effect of L1-21 on fruit green mood was 100% on the third day,and 80.36% on the fifth day. Taken together,B. subtilis L121 could colonize in citrus leaves and fruits effectively,providing a theoretical basis for further application of this strain to control citrus diseases.