Phomopsis longanae Chi-Induced Changes in Activities of Cell Wall-Degrading Enzymes and Contents of Cell Wall Components in Pericarp of Harvested Longan Fruit and Its Relation to Disease Development.

Yihui Chen,Shen Zhang,Mengshi Lin,Hui Wang,Junzheng Sun,Hetong Lin,Yifen Lin,John Shi

doi:10.3389/fmicb.2018.01051

Abstract

The main goal of this study was to investigate the influences of Phomopsis longanae Chi infection on activities of cell wall-degrading enzymes (CWDEs), and contents of cell wall components in pericarp of harvested “Fuyan” longan (Dimocarpus longan Lour. cv. Fuyan) fruit and its relation to disease development. The results showed that, compared with the control samples, P. longanae-inoculated longans showed higher fruit disease index, lower content of pericarp cell wall materials (CWMs), as well as lower contents of pericarp cell wall components (chelate-soluble pectin (CSP), sodium carbonate-soluble pectin, hemicelluloses, and cellulose), but higher content of pericarp water-soluble pectin (WSP). In addition, the inoculation treatment with P. longanae significantly promoted the activities of CWDEs including pectinesterase, polygalacturonase, β-galactosidase, and cellulase. The results suggested that the P. longanae stimulated-disease development of harvested longans was due to increase in activities of pericarp CWDEs, which might accelerate the disassembly of pericarp cell wall components. In turn, resulting in the degradation of pericarp cell wall, reduction of pericarp mechanical strength, and subsequently leading to the breakdown of longan pericarp tissues. Eventually resulting in development of disease development and fruit decay in harvested longans during storage at 28°C.

Highlights

In developed countries, fruit decay caused by pathogens affects 20–25% of the harvested fruits during post-harvest handling and storage
There is a diverse array of Cell walldegrading enzymes (CWDEs), including polygalacturonase (PG), pectin methylgalacturonase (PMG), pectinesterase (PE), pectin lyase (PL), pectate lyase (PNL), cellulase (CX), β-glucosidase, and xylanases (Al-Hindi et al, 2011; Li et al, 2012; Kubicek et al, 2014)
Ramos et al (2016) found that Macrophomina phaseolina induced the cell wall degradation of maize and sunflower, which was initiated by the pectinase that was the first CWDE secreted by M. phaseolina

Summary

Introduction

Fruit decay caused by pathogens affects 20–25% of the harvested fruits during post-harvest handling and storage. The activities of PG and PMG were higher than CX that appeared in the later stage of the degradation process (Ramos et al, 2016) This sequence promoted the initial tissue maceration before the degradation of cell wall materials (CWMs). It was reported that Fusarium culmorum was able to secrete CWDEs including cellulases, xylanases, and pectinases These CWDEs degraded the wheat spike plant tissues (cellulose, xylan, and pectin) and enabled the invasion to the tissues by F. culmorum (Kang and Buchenauer, 2000). Kang and Buchenauer (2000) reported that in the cell wall, the degree of pectin degradation was higher compared with cellulose and xylan at the early stage of infection, which implied that there might be earlier secretion or higher activity of pectinases over cellulases or xylanases. It can be concluded that the secretion of CWDEs plays an important role in the degradation of plant cell wall during pathogenesis

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Conclusion