柑橘黄龙病菌在染病贡柑枝条和果实橘络内的分布规律

 柑橘黄龙病是柑橘生产上最具毁灭性的病害之一,由目前还无法分离培养的候选韧皮部杆菌亚洲种(“Candidatus Liberibacter asiaticus”, CLas)引起的。早期研究表明CLas在染病柑橘植株内的分布并不均匀。为进一步探究CLas在染病枝条及果实内的空间分布规律,本研究以感染黄龙病的贡柑(带果实)枝条为材料,利用定量PCR(quantitative PCR, qPCR)分析同一枝条不同部位及果实橘络中的CLas浓度。结果表明,带果贡柑枝条不同部位的CLas分布不均匀且以果实橘络部位的CLas浓度最高(15 487.6 CLas cells/ng总DNA)。通过对同一橘络不同片段长度(每1.5 cm)中的CLas进行定量分析发现,同一橘络中的CLas同样呈不均匀分布(CLas个数范围:12 407~10 271 089)。此外,定量分析发现黄龙病引起的畸形果大小两侧橘络中的CLas浓度差异不显著。该结果可为探究CLas在柑橘枝条及果实中的转运规律提供参考。

Distribution of “Candidatus Liberibacter asiaticus” in Huanglongbing-affected Citrus reticulata Blanco cv. Gongkan branches and the fruit pith

Citrus Huanglongbing (HLB), one of the most destructive diseases for citrus industry, is caused by the currently unculturable bacterium “Candidatus Liberibacter asiaticus” (CLas). Previous study has revealed the uneven distribution of CLas in infected trees. To further understand the spatial distribution of CLas in infected citrus branches and within fruit, in this study, the HLB-affected citrus Gongkan (Citrus reticulata Blanco var. Gongkan) fruiting branches were collected. The quantitative PCR was performed to systematically quantify the concentrations of CLas in 8 different parts of infected branches and fruit pithes. The highest concentration of CLas was found in fruit pith (15487.6 CLas cells/ng total DNA). The qPCR detection also revealed the uneven distribution of CLas in the infected citrus branches and in individual fruit pith (12 407 ~ 10 271 089 CLas cells/1.5 cm pith segment). No significant difference of CLas concentrations was found in the pith from two parts (with different sizes) of the malformed fruit caused by CLas infection. Our results provide a reference for further study of the CLas transportation in infected citrus branches and fruits.