Abstract:

Citrus greening or Huanglongbing（HLB）is one of the most destructive diseases of citrus and causes significant economic losses worldwide. HLB can cause phloem necrosis and blockage in citrus，resulting in poor transport of photosynthetic assimilates and large accumulation of starch. In this study，0.1 g · tree-1 and 0.2 g · tree -1 oxytetracycline（OTC）were injected into the 4 year old Valencia （Citrus sinensis）infected with HLB. The qPCR detection showed that the abundance of Las（Candidatus Liberibacter asiaticus）in leaves was reduced effectively in 90 d. There was no difference of the OTC treatment effect between 0.1 g · tree-1 and 0.2 g · tree-1 OTC. I2/KI coloration and LM observation showed that the content of starch in the treated group of 0.2 g · tree-1 decreased from 18.58 μg · mm-2 to 5.24 μg · mm-2 after injection. But 0.1 g · tree-1 treatment had no significant effect on reducing starch content. The results of high performance liquid chromatography（HPLC）showed that OTC gradually degraded in the plant over time. Expression analysis showed that AGPase，GPT2，β-amylase and GBSS expressed in leaves decreased after 0.2 g · tree-1 OTC injection. Among them，AGPase has the highest decreased expression. This is consistent with the results of starch content in leaves 30 and 90 days after OTC injection.

Key words: citrus, HLB, oxytetracycline, starch synthase enzyme, starch splitting enzyme, control