柑橘黄龙病病原菌Las在叶圆片嫁接接种的‘锦橙’中早期扩散研究

Early Spread Characteristics of Candidatus Liberibacter Asiaticus in Jincheng Orange(Citrus sinensis Osbeck) by Leafdisc Grafting

为了探究黄龙病(Citrus Huanglongbing,HLB)病原菌在柑橘韧皮部的早期运动情况,以柑橘黄龙病亚洲致病种CandidatusLiberibacterasiaticus(Las)为毒源,黄龙病高感品种‘锦橙’实生苗为受体材料进行叶圆片嫁接传毒。利用定量PCR技术对嫁接口处近端主脉、远端主脉、叶柄以及缘周叶组织进行了为期84d的菌量测定。结果发现,病原菌在近端主脉中积累最快,其次是远端主脉、叶柄和缘周叶组织。以近端主脉为原初侵染部位,Las在嫁接叶片中1～84 d的早期运动可分为潜伏期(1～42 d)、指数期(43～70 d)和稳定期(71～84 d)。在早期侵染过程中,Las病原菌主要沿叶主脉从原初侵染部位由近向远扩散,其扩散趋势与症状从原初侵染部位向外扩散紧密相关。证实叶圆片嫁接法可作为柑橘HLB一种有效的传毒方式。

:To understand the spread characteristics of HLB pathogen in citrus at early infection stage, the populations of the Candidatus Liberibacter asiaticus(Las)pathogen,the symptom development in the susceptible‘Jincheng’Orange(Citrus sinensis Osbeck)were investigated using leafdisc grafting during the first eighty-four days of infection. Quantitative real-time PCR(qPCR)analysis showed that the presence of Las was firstly detected in the proximal midrib 49 days after grafting,and until 77 days after grafting,the pathogen was found in the distal midrib,petiole and the marginal tissue around the leafdisc. Using the proximal midrib as the primary infection tissue,the early spread of Las pathogen in the leafdisc-grafted leaf can be grouped into three phases from one to eighty-four days after Las inoculation:lag phase(1–42 days),logarithmic phase(43–70 days)and stationary phase(71–84 days). The results showed that the pathogen spreads mainly along the midrib from the proximal tissue to the distal tissue in the grafted leaves,which was in accordance with HLB symptoms spread out from the proximal midrib. The study also displayed that leaf-disc grafting was a powerful tool for the transmission of HLB pathogen in citrus.