Yahan Zhou

Effects of postharvest oligochitosan treatment on anthracnose disease in citrus (Citrus sinensis L. Osbeck) fruit

Citrus fruit (Citrus sinensis L. Osbeck) is susceptible to infection by Colletotrichum gloeosporioides during poststorage, which rapidly decreases sensory and nutritional quality of the fruit. The ability of oligochitosan treatment to control C. gloeosporioides of citrus fruit during storage was examined, and possible underlying mechanisms were discussed. Disease incidence and lesion diameter were lower in oligochitosan-treated fruits compared with their respective controls. The fruits dipped in oligochitosan showed increased contents of lignin, hydroxyproline-rich glycoprotein (HRGP), hydrogen peroxide (H2O2), ascorbate, glutathione, total phenol, and flavonoid compounds. In addition, enzymatic activities of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7), polyphenoloxidase (PPO, EC 1.14.18.1), ascorbate peroxidase (APX, EC 1.11.1.11), and β-1, 3-glucanase (GLU, EC 3.2.1.39) also increased in citrus fruit peels, all of which were correlated with the onset of induced disease resistance. These results indicated that oligochitosan treatment can induce disease resistance of citrus fruit to C.gloeosporioides Penz. Oligochitosan can be a potential alternative to conventional control methods of postharvest anthracnose in citrus fruit.

Analysis of changes in volatile constituents and expression of genes involved in terpenoid metabolism in oleocellosis peel

Oleocellosis is a serious physiological disorder in citrus fruit that mainly results in appearance and quality deterioration. It has been well established that the occurrence of oleocellosis is highly correlated with the release of peel oil from citrus fruit, while there is little information on the dynamic changes in the content of the volatile constituents and the expression of genes involved in terpenoid metabolism during oleocellosis development. In the present research, large changes in the volatile profiles and gene expression in terpenoid metabolism were observed in oleocellosis peels compared to healthy ones. Among volatiles, the decreased contents of α-pinene, d-limonene, β-myrcene, linalool, β-caryophyllene, α-terpineol, nonanal, neryl acetate and (-)-carvone played a major role in these changes. For gene expressions in terpenoid metabolism, the up-regulated genes aldehyde dehydrogenase (NAD+) (ALDH) and the down-regulated genes β-caryophyllene synthase 1 (BCS1), α-terpineol synthase 2 (TES2) and myrcene synthase (MS) were the main differences in oleocellosis peels.

Optimization of a protective medium for freeze‐dried Pichia membranifaciens and application of this biocontrol agent on citrus fruit

To optimize a protective medium for freeze‐dried Pichia membranifaciens and to evaluate biocontrol efficacies of agents against blue and green mould and anthracnose in citrus fruit.