Abstract：
Citrus blue and green molds caused by Penicillium digitatum, P. italicum, and P. polonicum, are the major postharvest diseases of citrus fruit. In the present study, Actinomycin X2 (Act-X2), a naturally occurring antibiotic produced by Streptomyces species, was found to show excellent antifungal effect against these three pathogens with a minimum inhibitory concentration (MIC) value of 62.5 μg/mL for them all, which was better than the positive control thiophanate-methyl. Act-X2 significantly reduced the percentage of spore germination, and highly inhibited the mycelial growth of P. italicum, P. digitatum, and P. polonicum with EC50 values being 34.34, 13.76, and 37.48 μg/mL, respectively. In addition, Act-X2 greatly decreased the intracellular protein content while increasing the reactive oxygen species (ROS) level and superoxide anion (O2-) content in the mycelia of pathogens. In vivo test indicated that Act-X2 strongly inhibited the infection of navel oranges by these three Penicillium species, with an inhibition percentage of >50% for them all at the concentration of 10 MIC. Transcriptome analysis suggested that Act-X2 might highly influence the ribosomal functions of P. polonicum, which was supported as well by the molecular docking analysis of Act-X2 with some key functional proteins and RNAs of the ribosome. Furthermore, Act-X2 significantly reduced the decay percentage and improved the firmness, color, and sugar-acid ratio of navel oranges spray-inoculated with P. polonicum during the postharvest storage at 4 °C for 60 d.
摘要：
由指状青霉引起的柑橘蓝色和绿色霉菌，P.italicum,和Polonicum,是柑橘类水果的主要采后病害。在本研究中,放线菌素X2（Act-X2），一种由链霉菌产生的天然抗生素，发现对这三种病原体表现出优异的抗真菌作用，它们的最小抑制浓度（MIC）值为62.5μg/mL，优于阳性对照甲基托布津。Act-X2显着降低了孢子萌发的百分比，并高度抑制意大利毕赤酵母的菌丝生长，P.digitum,EC50值为34.34、13.76和37.48μg/mL，分别。此外,Act-X2大大降低了病原体菌丝体中的细胞内蛋白质含量，同时增加了活性氧（ROS）水平和超氧阴离子（O2-）含量。体内试验表明，Act-X2强烈抑制了这三种青霉菌对脐橙的感染，在10MIC的浓度下，它们的抑制百分比均>50％。转录组分析表明，Act-X2可能高度影响Polonicum的核糖体功能，Act-X2与核糖体的一些关键功能蛋白和RNA的分子对接分析也支持了这一点。此外，Act-X2显著降低了衰减率，提高了硬度，颜色,在采后4°C下贮藏60d时，接种了紫菜的脐橙的糖酸比。
