感染黄龙病茶枝柑的症状表现及其病原在枝条与果实橘络中的分布规律

Symptoms of Citrus reticulata cv.chachiensis Infected with Huang longbing and Candidatus liberibacter asiaticus Distribution in Branches and Fruit Pith

茶枝柑(Citrus reticulata cv.chachiensis)在广东新会地区有悠久的栽培历史,其果皮可制作陈皮,具有一定的药用价值。茶枝柑黄龙病(Citrus Huanglongbing,HLB)发生历史悠久,危害严重,而目前尚无对感染黄龙病的茶枝柑症状描述及病菌Candidatus Liberibacter asiaticus(CLas)分布的相关研究。本研究通过采集广东新会感染CLas茶枝柑枝条和果实,对感病的茶枝柑叶片及果实的典型症状进行观察,同时通过实时荧光定量PCR(real-timequantitative PCR,qPCR)分析CLas在茶枝柑枝条不同部位及果实橘络中的分布规律,为筛选高浓度CLas材料提供依据。观察发现感染CLas的茶枝柑叶片呈现斑驳黄化症状,新叶尤为严重;感染CLas的茶枝柑果实表现出典型的“红鼻子”果症状,果实畸形形状不对称,种子败育。病原定量分析表明,CLas在同一染病茶枝柑枝条中呈不均匀分布:果实中轴组织中的CLas含量最高,为(2770162.87±544972.11)个,其次为橘络(2721335.84±528771.21)个,二者均显著高于其他部位。进一步对同一橘络不同片段中的CLas进行定量分析发现,CLas在同一橘络中亦呈不均匀分布,其中位于1~3 cm的片段组织中的CLas含量显著高于其他部位(P<0.05),CLas在橘络及果实中轴中的浓度显著高于其他部位。研究结果可为茶枝柑黄龙病的鉴定、CLas在柑橘枝条及果实中的转运规律探究及后续筛选高浓度CLas材料提供参考依据。

Citrus reticulata cv.chachiensis,also known as Xinhui Mandarin Orange,has a long history of cultivation in Guangdong(Xinhui)and is a local agricultural product in Guangdong.There are no relevant studies on the symptoms description and distribution of Candidatus Liberibacter asiaticus(CLas)in C.reticulata cv.chachiensis infected with Citrus Huanglongbing(HLB).Through this study,it can provide a basis for the study of the movement of CLas in citrus plant branches and fruit pith and can also provide ideal plant materials for the subsequent acquisition of high concentra-tion of CLas.In this study,C.reticulata cv.chachiensis branches and fruit pith infected with CLas were used as plant material to identify symptoms and analyze the distribution of CLas in different parts of citrus branches and different length fragments of the fruit pith based on real-time quantitative PCR(qPCR).Through the observation of the leaves and fruits from the infected citrus plants,the upper leaves of the branches infected with CLas showed mottled and ele-ment-deficient yellowing,especially the symptoms of the new leaves of the branches were more obvious,while the color of the lower old leaves was dark green and the texture was hard.Compared with the healthy fruit,the fruit infected with CLas showed uneven coloring,showing typical symptoms of“red nose fruit”.Meanwhile,compared with the healthy fruit,the fruit infected with CLas showed uneven size,abnormal body and asymmetrical shape,the seed was small and the seed aborted.The concentration of CLas in the central axis of the fruit was close to that in the fruit pith,and sig-nificantly higher than that in other parts of the branches(P<0.05).CLas was also unevenly distributed in different length segments of the same fruit pith,and the concentration of CLas was the highest in the middle of fruit pith(1-3 cm frag-ment),the concentration of CLas in the central axis and fruit pith of HLB-infected C.reticulata cv.chachiensis fruits is significantly higher than that of other parts.The study could be a reference for the identification of HLB,a basis for the study of the movement of CLas in citrus plant branches and fruit pith,and used to select ideal plant materials for the subsequent acquisition of high concentration of CLas.