Abstract The cuticle of citrus is known to modulate fruit postharvest quality and is hypothesized to be involved in resistance against the fungal pathogen, Penicillium digitatum. However, only scarce information is available on the effect of cuticular wax on the conidial germination, germ tube elongation, and colony development of P. digitatum. Utilizing a versatile Formvar®-based in vitro system, we were able to assess the development of P. digitatum in the absence of secondary effects of its host. In vivo and in vitro, we found that the cuticular wax of mandarin (Citrus reticulata) fruit impaired P. digitatum colony expansion. Compared with the colony size of P. digitatum on intact fruit, the area of colonies on fruit supplemented with mandarin cuticular wax decreased significantly by 1.7 times, whereas it increased 1.6 times on dewaxed fruit 72 h post inoculation. Similar results were observed at 96 h post inoculation. Thus, the cuticular wax of mandarin fruit, acting as a physical barrier, impairs the colony expansion of P. digitatum, making it a viable alternative for citrus fruit coating that effectively controls green mold colony formation during postharvest storage. Interestingly, in vitro cuticular wax of mandarin fruit dramatically stimulated conidial germination and germ tube elongation of this pathogen. These results suggest that the cuticular wax might be the chemical cue for P. digitatum during host-recognition processes. Overall, our results suggest that the cuticular wax of mandarin fruit plays meaningful roles in the interaction between the citrus fruit and P. digitatum, and hence, can be considered for postharvest disease management.

中文翻译：

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柑橘表皮蜡促进分生孢子萌发和胚管伸长，并损害绿色霉菌病原体，指状青霉的菌落扩张

摘要 柑橘表皮已知可调节果实采后品质，并被假设与对真菌病原体指状青霉的抗性有关。然而，关于表皮蜡对 P. digitatum 的分生孢子萌发、胚管伸长和菌落发育的影响的信息很少。利用基于 Formvar® 的多功能体外系统，我们能够在没有宿主二次影响的情况下评估 P. digitatum 的发育。在体内和体外，我们发现柑橘 (Citrus reticulata) 果实的角质层蜡损害了 P. digitatum 菌落扩张。与完整果实上P. digitatum的菌落大小相比，添加了柑橘表皮蜡的果实上的菌落面积显着减少了1.7倍，而增加了1倍。接种后 72 小时在脱蜡果实上 6 次。在接种后 96 小时观察到类似的结果。因此，橘子的表皮蜡作为物理屏障，会削弱 P. digitatum 的菌落扩张，使其成为柑橘类水果涂层的可行替代品，可有效控制采后储存期间绿色霉菌菌落的形成。有趣的是，柑橘果实的体外角质层蜡显着刺激了该病原体的分生孢子萌发和胚管伸长。这些结果表明表皮蜡可能是指状体在宿主识别过程中的化学线索。总体而言，我们的结果表明，柑橘果实的表皮蜡在柑橘类水果和指状假单胞菌之间的相互作用中发挥着重要作用，因此可以考虑用于采后病害管理。