关键词: 黄龙病, Cadidatus Liberibacter asiaticus（Las）, 土霉素, 淀粉, 韧皮部蛋白2

Abstract:

【Objective】The objective of this study is to evaluate the control efficacy of oxytetracycline (OTC) on sweet orange Huanglongbing (HLB), detect the expression of phloem protein 2 (PP2) gene, and to provide a scientific basis for the effective prevention and control of HLB as well as a reference for OTC mechanism research. 【Method】OTC, which can effectively inhibit and kill pathogenic bacteria, was injected with 0.1 g/tree of 4-year-old Valencia sweet orange with different severity of HLB (newly infected, mild infected and severely infected plants), and then the contents of Cadidatus Liberibacter asiaticus (Las), starch and PP2 gene of leaves were evaluated at 7, 30, 60, 90 days post injection, respectively. Furthermore, 90 days after injection, the young and mature tissues of the plants were observed by using starch staining light microscopy (LM). The extraction of tender leaves was investigated 80 days after OTC injection. 【Result】Trunk injection of OTC 0.1 g/tree had the most obvious therapeutic effect on newly infected Valencia sweet orange. Seven days after injection, Las could not be detected and it maintained for 90 days. The starch content in mature leaves decreased obviously, but starch grains were still enriched in stems. The Las content of mild infected Valencia leaves decreased from (1.68×10 ⁶±858884) cells/g leaf to (7.21×10 ⁴±30981) cells/g leaf, the descending range was obvious, and the starch content in mature leaves showed a decreasing trend within 90 days. The Las content of severely infected Valencia leaves decreased from (4.10×10 ⁸±3.04×10 ⁸) cells/g leaf to (2.80×10 ⁷±2.70×10 ⁷) cells/g leaf, but the starch content in mature tissues of severely infected plants was still high, except the newly autumn shoots. The results indicated that 0.1 g/tree OTC was not enough to cure 4-year-old severely infected Valencia. The expression of PP2 gene in Valencia significantly decreased 30 days after OTC injection, and remained stable in the subsequent 90 days, which was consistent with the expression level at 30 days after injection.【Conclusion】OTC can be used in the prevention and control of HLB, and has better therapeutic effect on newly infected Valencia (Las content is less than 9.00×10 ⁵ cells/g leaf) and mild infected Valencia (Las content is 9.00×10 ⁵-9.00×10 ⁷ cells/g leaf). It was not suitable for the treatment of severely infected plants (Las content is more than 9.00×10 ⁷ cells/g leaf). After injection of OTC, the expression of PP2 gene decreased obviously, suggesting that OTC can effectively reduce the stress of phloem pathogens.

Key words: Huanglongbing (HLB), Cadidatus Liberibacter asiaticus (Las), oxytetracycline (OTC), starch, PP2