Abstract
Huanglongbing (HLB) is a devastating citrus disease that has caused massive economic losses to the citrus industry worldwide. The disease is endemic in most citrus-producing areas of southern China, especially in the sweet orange orchards where soil acidification has intensified. In this work, we used lime as soil pH amendment to optimize soil pH and enhance the endurance capacity of citrus against Candidatus Liberibacter asiaticus (CLas). The results showed that regulation of soil acidity is effective to reduce the occurrence of new infections and mitigate disease severity in the presence of HLB disease. We also studied the associated molecular mechanism and found that acid soil improvement can (i) increase the root metabolic activity and up-regulate the expression of ion transporter-related genes in HLB-infected roots, (ii) alleviate the physiological disorders of sieve tube blockage of HLB-infected leaves, (iii) strengthen the citrus immune response by increasing the expression of genes involved in SAR and activating the salicylic acid signal pathway, (iv) up-regulate 55 proteins related to stress/defence response and secondary metabolism. This study contributes to a better understanding of the correlation between environment factors and HLB disease outbreaks and also suggests that acid soil improvement is of potential value for the management of HLB disease in southern China.
Highlights
Huanglongbing (HLB) is one of most destructive citrus diseases worldwide, which is caused by the phloem-restricted bacterium Candidatus Liberibacter asiaticus (CLas) and is transmitted through the citrus psyllid (ACP) Diaphorina citri [1]
Soil pH values fluctuate slightly, most of the orchard measurement points selected in this experiment had pH values between 4.5 and 5.5 (Figure 1A)
We identified 119 differentially expressed proteins at a cutoff value of >|±1.5|-fold (p value < 0.005) (Supplementary Table S2), including 55 up-regulated and 64 down-regulated proteins, in the midribs sample in liming-amended soils compared with the midribs sample collected from untreated soils
Summary
Huanglongbing (HLB) is one of most destructive citrus diseases worldwide, which is caused by the phloem-restricted bacterium Candidatus Liberibacter asiaticus (CLas) and is transmitted through the citrus psyllid (ACP) Diaphorina citri [1]. The disease has spread to more than 11 citrus-growing regions especially in Guangdong, Hunan, Guangxi and Jiangxi provinces [5]. Since 2012, just in Ganzhou, Jiangxi province, more than 45 million infected trees have been removed, and the direct economic loss is estimated to be more than 9 billion yuan [6]. There is an urgent need to develop a sustainable solution to suppress the spread of HLB disease and enable the continued economic production of CLas-infected citrus trees
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