Phomopsis longanae Chi-induced longan pulp breakdown and softening in relation to cell wall polysaccharides disassembly

Cell wall polysaccharides are crucial contributors to the structural properties of plants and perform as a barrier against fungal invasion. Phomopsis longanae Chi, a principal devastating pathogenic fungus, can induce a severe pulp breakdown and softening of postharvest longan. P. longanae-induced longan pulp breakdown and softening in relation to the disassembly of cell wall polysaccharides were explicated. Results suggested that a higher pulp breakdown index and a lower pulp firmness were obtained in P. longanae-infected fruit. More importantly, P. longanae infection promoted gene expression levels and activities of cell wall-disassembling enzymes (pectin methylesterase, polygalacturonase, β-galactosidase, cellulase, and xyloglucan endotransglycosylase), and facilitated the disassembly of polysaccharides like ionic-soluble pectin, covalent-soluble pectin, cellulose, and hemicellulose, which were closely relevant to pulp breakdown and softening. Given these results, the aggravated pulp breakdown and softening of longan after P. longanae inoculation were attributed to cell wall polysaccharides modification regulated by enzyme and related genes.