Litchi (Litchi chinensis Sonn.) is a commercially important fruit but its production and quality are restricted by litchi downy blight, caused by the oomycete pathogen Peronophythora litchii Chen. Volatile substances produced by a biocontrol antinomycetes Streptomyces fimicarius BWL-H1 could inhibited P. litchii growth and development both in vitro and in detached litchi leaf and fruit infection assay. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) analyses indicated that volatile organic compounds (VOCs) from BWL-H1 resulted in severe damage to the endomembrane system and cell wall of P. litchii cells in vitro and abnormal morphology of appressoria, as well as deformed new hyphae in infection process. VOCs could suppress mycelial growth, sporulation, while with no obvious effect on sporangia germination. Based on gas chromatography-mass spectrophotometric analyses, 32 VOCs were identified from S. fimicarius BWL-H1, the most abundant of which was phenylethyl alcohol. Eight VOCs, including phenylethyl alcohol, ethyl phenylacetate, methyl anthranilate, α-copaene, caryophyllene, humulene, methyl salicylate and 4-ethylphenol, that are commercially available, were purchased and their bioactivity was tested individually. Except for humulene, the other seven tested volatile compounds shown strong inhibitory activity against mycelial growth, sporulation, sporangia germination and germ-tube growth of P. litchii. Especially, 4-ethylphenol showed the highest inhibitory effect on sporulation at a very low concentration of 2 µL/L. Overall, our results provided a better understanding of the mode of action of volatiles from BWL-H1 on P. litchii, and showed that volatiles from BWL-H1 have the potential for control of postharvest litchi downy blight.

Botrytis cinerea is the pathogen of gray mold disease affecting a wide range of plant hosts, with consequential economic losses worldwide. The increased frequency of fungicide resistance of the pathogen challenges its disease management, and thus the development of alternative control strategies are urgently required. In this study, we showed excellent synergistic interactions between resveratrol and pyrimethanil. Significant synergistic values were recorded by the two-drug combination on the suppression of mycelial growth and conidia germination of B. cinerea. The combination of resveratrol and pyrimethanil caused malformation of mycelia. Moreover, the inoculation assay was conducted on table grape and consistent synergistic suppression of the two-drug combination was found in vivo. Our findings first revealed that the combination of resveratrol and pyrimethanil has synergistic effects against resistant B. cinerea and support the potential use of resveratrol as a promising adjuvant on the control of gray mold.

Pericarp browning and fruit decay severely reduce the postharvest quality of litchi. Improving the antioxidant capacity of the fruit is an effective way to solve these problems. In our study, the appropriate zinc oxide nanoparticles (ZnO NPs) treatment and its mechanism of action on the storability of litchi was investigated. Litchi fruit was soaked in a 100 mg·L⁻¹ ZnO NPs suspension, water, and 500 mg·L⁻¹ prochloraz for 2 min, respectively. The results showed that the ZnO NPs treatment delayed pericarp browning and decay in litchi fruit and was more effective than prochloraz treatment. The ZnO NPs-treated fruit showed significantly increased contents of total anthocyanin, total phenols, and activities of DPPH scavenging, superoxide dismutase, and glutathione peroxidase, as well as the lowest activities of polyphenol oxidase and laccase. ZnO NPs generated hydrogen peroxide and superoxide anion radicals, which were beneficial in slowing down the decay and inducing antioxidant capacity. However, these reactive oxygen species also consumed catalase, peroxidase, glutathione, and glutathione peroxidase. This means that litchi should be treated with an appropriate concentration of ZnO NPs. We concluded that treatment with a 100 mg·L⁻¹ ZnO NPs suspension could induce antioxidant capacity, which is a promising and effective method to maintain the postharvest quality of litchi.

Excoecaria cochinchinensis Lour., a small evergreen shrub in the family Euphorbiaceae, is usually grown as a native ornamental plant in South China. In April 2019, severe powdery mildew infection w...

The cultivation and overall quality of Litchi, a fruit of significant commercial value in China, are hindered by the presence of the oomycetes pathogen Peronophythora litchii. This pathogen is responsible for the occurrence of litchi downy blight, resulting in substantial economic losses during the storage and transportation of the fruit, and affects nutritional growth. Effective and environmentally safe methods to control litchi downy blight are urgently needed. The application of biocontrol agents such as Streptomyces bacteria has proven effective for controlling plant diseases. Our present study isolated the Streptomyces strain TJGA-19, identified as S. abikoensis, with potent inhibitory activity against P. litchii. The antifungal active substances are mainly in the aqueous phase of TJGA-19 fermentation filtrate extraction. The fermentation filtrate of TJGA-19 not only suppressed the pathogen growth, sporulation, and sporangia germination, but also delayed the disease development of litchi downy blight. In addition, the stability of the TJGA-19 fermentation filtrate was not sensitive to the proteinase K, temperature, white-flourescence light, or ultraviolet treatment. Furthermore, the morphology and ultrastructure of P. litchii treated with fermentation filtrate was characterized by marked shrinking and deformation, with serious disruption of plasma membrane permeabilization and the organelles. Hence, S. abikoensis TJGA-19 and its metabolites demonstrated marked efficiency against the phytopathogenic pathogen P. litchii and provide a potential candidate for controlling litchi downy blight.