Walnut green husk extract enhances the effect of chlorine dioxide on kernel quality and antioxidant properties of fresh-eating walnuts during their shelf life.

Fresh-eating walnuts are perishable and become mildewed during shelf life, limiting their sales span. The effects of chlorine dioxide (ClO2) alone and its combination with walnut green husk extract (WGHE) on shelf stored fresh walnuts were investigated to develop a pollution-free preservative for the produce. The initial development of mildew incidence was delayed by both treatments under 25 °C, whereas, WGHE + ClO2 acted more effectively than ClO2 under 5 °C. The WGHE + ClO2 treatment presented superior effects on improving moisture, soluble sugar and total phenol content, alleviating loss of oil and unsaturated fatty acid and delaying peroxide value increase of walnut kernels at both temperatures. Both treatments inhibited the activities of three lipolytic enzymes and two oxidases at 25 °C and 5 °C, WGHE + ClO2 acted more effectively at 5 °C. The results guide the combined application of WGHE with ClO2 on shelf preservation of fresh walnut.

An Efficient Virus-Induced Gene Silencing System for Functional Genomics Research in Walnut (Juglans regia L.) Fruits.

The Persian walnut (Juglans regia L.) is a leading source of woody oil in warm temperate regions and has high nutritional and medicinal values. It also provides both tree nuts and woody products. Nevertheless, incomplete characterization of the walnut genetic system limits the walnut gene function analysis. This study used the tobacco rattle virus (TRV) vector to construct an infectious pTRV-JrPDS recombinant clone. A co-culture inoculation method utilizing Agrobacterium was screened out from four inoculation methods and optimized to set up an efficient virus-induced gene silencing (VIGS) system for J. regia fruit. The optimized VIGS-TRV system induced complete photobleaching phenotype on the walnut fruits of four cultivars, and the JrPDS transcript levels decreased by up to 88% at 8 days post-inoculation (dpi). While those of browning-related J. regia polyphenol oxidase (PPO) genes JrPPO1 and JrPPO2 decreased by 67 and 80% at 8 dpi, respectively, accompanied by a significant reduction in fruit browning phenotype. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis screening and Western Blot showed that the PPO protein levels were significantly reduced. Moreover, a model of TRV-mediated VIGS system for inoculating J. regia fruit with efficient silence efficiency via co-culture was developed. These results indicate that the VIGS-TRV system is an efficient tool for rapid gene function analysis in J. regia fruits.