Abstract
Green mold disease, a common citrus post-harvest disease caused by Penicillium digitatum, has an unresolved initial infection mechanism. Understanding the infection mechanism leads to the development of potential controls and preventive measures against the disease. The present study aimed to delineate the infection mechanism by investigating spore germination, changes of organic molecules and enzyme activity, and differential expression of genes in the P. digitatum infection. P. digitatum spore germination was observed by a pathology section scanner and it was found that in vivo germination was 3 h behind the in vitro germination. In addition, cell wall degrading enzymes and soluble sugar and titratable acid content during the infection process measured dynamically. The level of pectinase reached its maximum of 6067 U/g before 48 hpi, while cellulase increased rapidly after 48 hpi. The soluble sugar and organic acid content increased considerably with the progression of the infection. The transcriptomic profile of P. digitatum before and after infection was analyzed by RNA-seq. The genes related to cell wall degrading enzymes were significantly up-regulated and annotated to participate in two major carbon source synthesis pathways. The study delineated the initial infection mechanism of P. digitatum which eventually opened the gate way for the development of new control strategies in the future.
Highlights
Citrus fruits grow on flowering trees and shrubs, and are known as one of the four big fruits of the world
This study provides a good knowledge of elucidation about infection mechanism of P. digitatum on postharvest citrus during initial infection process
In the observation of the surface morphology of citrus fruits, inoculation of P. digitatum into wounds resulted in tissue maceration after 48 hpi and the tissue maceration nearly spread to the whole fruit at 96 hpi
Summary
Citrus fruits grow on flowering trees and shrubs, and are known as one of the four big fruits of the world. Post-harvest green mold disease caused by P. digitatum, is the most serious infection of citrus [3]. According to Kubicek et al [11], most pathogens invade host tissues by secreting cell wall degrading enzymes (CWDEs). The exploration of the pathogen infection process into plant tissue through microscopic observations can give a deeper understanding of pathogen infection mechanisms. In the present study: (1) The early infection process of P. digitatum in citrus wound tissues was investigated by sectioning the tissues pathology section scanner. (2) The activity of the main cell wall degrading enzymes, soluble sugar and titratable acid contents of citrus fruits during the process of infection was measured dynamically. This study provides a good knowledge of elucidation about infection mechanism of P. digitatum on postharvest citrus during initial infection process
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