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Peronophythora litchii , the oomycete pathogen of litchi downy blight, infects leaves, flowers and fruits of litchi at pre-harvest stage, while the greatest economic loss was caused at postharvest stage, due to infection occurring during fruit storage and transportation. Therefore, litchi downy blight is considered as an important postharvest disease in litchi fruit, and effective, environment-friendly fungicide(s) is urgently required. In this study, the effectiveness of pterostilbene on the control of litchi downy blight and its action mechanism were investigated. Pterostilbene substantially suppressed sporangia germination of P. litchii , with inhibition rate of 100% in the treatment of pterostilbene at 32 mg L −1 , and its IC 50 value on zoospore release was evaluated to be 6.8 mg L −1 . Similarly, pterostilbene inhibited the mycelial growth of P. litchii and induced deleterious morphological modifications and ultrastructural alteration, including deformation and shrinking of mycelia and sporangia, the damage of cell wall, plasma membrane and organelles. Pterostilbene application significantly reduced the decay of litchi fruit and leaf caused by P. litchii , with the decay index reduction up to 48.6% and 88.0%, respectively. Moreover, peel browning of litchi caused by P. litchii reduced from 3.5 to 1.8 after treated with 1600 mg L −1 pterostilbene. Our study showed that pterostilbene could be a potential candidate on the control of litchi downy blight. [ABSTRACT FROM AUTHOR]

As the natural antimicrobial metabolites, phenolic compounds were reported to be effective in the inhibition of phytopathogenic fungi, including the postharvest decay agents. However, comprehensive study on the biological activity of phenolic compounds and their application on controlling postharvest gray mold of table grapes is lacking. In this study, the antifungal effect of 18 natural or synthetic phenolic compounds purchased from commercial suppliers, including simple phenolic, phenolic acids, stilbenes and flavonoids, were determined on four gray mold strains by an in vitro agar dilution assay. Overall, seven phenolic compounds were effective on inhibiting B. cinerea growth and were selected to test their activity on conidial germination as well as in vivo application on grape berries. Pterostilbene showed the highest antifungal activity and greatly reduced the growth of the mycelia, caused hyphae deformation, suppressed conidial germination of B. cinerea , and completely inhibited the germination of conidia at the concentration of 50 mg L −1 . Furthermore, treatment of grape berries with pterostilbene and piceatannol significantly reduced the disease incidence and severity. Our results demonstrate the antifungal activity of phenolic compounds and highlight their potentials as an alternative strategy in the control of postharvest gray mold of table grapes. [ABSTRACT FROM AUTHOR]

• Pterostilbene (PTE) delayed postharvest gray mold on postharvest table grapes. • PTE caused obvious destruction on the plasma membrane and organelles. • PTE induced significant deformation on hyphae and conidiophore. • PTE induced up-regulation of gene Bclcc1 and Bclcc2 and enzyme activity of laccase. • PTE induced overexpression of genes related with cellular damage. Botrytis cinerea is an economically devastating necrotrophic fungus that is responsible for gray mold infection of table grapes. Fungicides application remains the most common approach in its control. However, in consideration of food and environmental safety, safe and eco-friendly alternatives are desirable to manage gray mold. Pterostilbene is a natural antimicrobial metabolite that inhibits growth of several phytopathogenic fungi. Moreover, pterostilbene has been widely used as a food additive on the basis of its safety and oxidation properties. However, the specific inhibitory effects of pterostilbene for pathogen control of postharvest fruit and its precise mechanism of action remain to be defined. Here, 0.25 g L−1 pterostilbene could suppress the development of gray mold in table grapes. Fluorescent staining indicated that pterostilbene-mediated disease suppression is mediated through loss of plasma membrane integrity. Electron microscopy revealed that pterostilbene inhibits B. cinerea by altering the morphology of the hyphae and conidiophores, with destruction of the plasma membrane and organelles. Furthermore, quantitative real-time PCR highlighted pterostilbene-mediated gene modulation and overexpression of genes associated with laccase production and cellular damage on B. cinerea , together with increased laccase activity. These data better define the mechanisms through which pterostilbene inhibits B. cinerea growth, thus making pterostilbene an attractive candidate in postharvest fruit disease management strategies. [ABSTRACT FROM AUTHOR]

• Benzothiadiazole (BTH) retards litchi downy blight. • BTH exhibit inhibitory activity against Peronophythora litchi in vitro. • BTH regulated enzymes activities of CAT, SOD, PPO and PAL. • BTH decreased expression levels of senescence-associated genes. • BTH induced amino acid metabolism. Benzothiadiazole (BTH) is a functional analog of salicylic acid (SA), and has been applied to delay postharvest decay in several fruit. However, the efficacy of BTH on delaying postharvest decay of litchi fruit and involved regulatory mechanisms remained unknown. Physiological, microbiological, and metabolomic analyses were applied in this study to reveal efficacy and potential mechanism of BTH on the control of postharvest litchi downy blight. Our results showed that BTH enhanced the disease resistance of litchi fruit against downy blight in vivo. The in vitro test indicated that BTH treatment markedly inhibited the mycelial growth and sporangia germination of Peronophythora litchii. Enzyme activity assay revealed that BTH treatment enhanced the activities of CAT, SOD, PPO and PAL in litchi fruit. Moreover, the expression levels of senescence-related genes were down-regulated by BTH treatment. A comparative metabonomic analysis showed that metabolites accumulation significantly affected by BTH treatment, especially amino acids contents of arginine, phenylalanine and glutamic acid increased in comparison with control group. In all, the inhibitory effect on pathogen, the blocked transcription of senescence-related genes, and the activation of defense enzymes and amino acid metabolism induced by BTH treatment might be attributed to the alleviation effect of BTH on postharvest litchi downy blight. These findings indicated that BTH might be a potential agrochemical to control postharvest litchi downy blight and extend shelf life of litchi fruit. [ABSTRACT FROM AUTHOR]

Biocontrol agents (BCAs) could be used for the control of postharvest decay of fruit. In this study, biocontrol bacteria were isolated from litchi soil, leaves and fruit tissues, and their efficacy on the control of postharvest litchi downy blight, caused by Peronophythora litchii , were determined. After evaluating the ability of 188 bacterial isolates to produce certain enzymes and metabolites, and their antagonistic activity in vitro against P. litchii , as well as preliminary identification of 82 representative isolates based on 16 S rDNA sequencing, five isolates including Bacillus amyloliquefaciens PP19 and LI24, Exiguobacterium acetylicum SI17, B. pumilus PI26, and B. licheniformis HS10 were selected for further assessments in several trials in 2016 and 2017. In comparison with control treatment, isolates PP19, SI17 and PI26 could delay the disease development of postharvest litchi downy blight. Furthermore, isolates PP19 and SI17 were able to colonize fruit pericarp without affecting fruit quality. Additionally, the colonization of PP19 changed the microbial community composition on litchi pericarp as demonstrated by pericarp microbiome sequencing. This is the first report of an E. acetylicum acted as a BCA against a phytopathogenic oomycete P. litchii. We conclude that PP19 and SI17 can be used as effective BCAs against postharvest litchi downy blight, especially applied during preharvest stage. • 188 bacteria were isolated from different microenvironments of litchi. • Exiguobacterium acetylicum is firstly found to suppress on litchi downy blight. • PP19 and SI17 were able to delayed disease development without affecting fruit quality. • Colonization of PP19 changed the microbial community composition on litchi pericarp. [ABSTRACT FROM AUTHOR]

Litchi downy blight caused by Peronophythora litchii is one of the most devastating diseases in litchi fruit, and developing safe and effective anti-pathogenic agents is required. This study aimed to investigate the inhibitory effects and related mechanisms of apple polyphenols (AP), naturally occurring products, on P. litchii in vitro and in vivo. The results showed that AP inhibited mycelial growth and sporangia germination of P. litchii in vitro in dose-dependent manner. Moreover, plasma membrane integrity of P. litchii was severely damaged by AP treatment at 5 g L−1, which could account for the leakage of reducing sugar and soluble protein during incubation of pathogen. The destruction of P. litchii due to AP exposure was further confirmed by ultrastructural observation. Microscopic image displayed that AP induced the accumulation of reactive oxygen species (ROS) in P. litchii at early stage of treatment. Proteomic results exhibited that mitochondrion-related proteins in P. litchii were down-regulated by AP, which resulted in decreases in respiration rate and ATP production, consequently contributing to compromised pathogenicity of this pathogen. In vivo test demonstrated that 5 g L−1 AP delayed the disease development of litchi downy blight in P. litchii -inoculated litchi fruit. Suppression of disease in P. litchii -inoculated litchi fruit due to AP treatment was associated with reinforcement of host resistance, as indicated by enhanced activities of phenylalanine ammonia lyase (PAL) and β-1,3-glucanase (GLU), upregulated expressions of LcPAL and LcGLU and more accumulations of total phenolics and flavonoids in AP-treated fruit. The results suggest that AP application could ameliorate the occurrence of litchi downy blight by both the direct inhibition on P. litchii and the elicitation of resistance in litchi fruit. • Apple polyphenols exert inhibitory effect in vitro / in vivo on Peronophythora litchii. • Apple polyphenols damage membrane integrity and morphostructure of P. litchii. • Apple polyphenols induce reactive oxygen species accumulation in P. litchii. • Lowered pathogenicity is linked with downregulated mitochondrion-related proteins. • Apple polyphenols induce the resistance of litchi fruit against litchi downy blight. [ABSTRACT FROM AUTHOR]