‘Okitsu’ is a mandarin cultivar showing substantial resistance to X. citri subsp. citri (X. citri). We have previously shown that this cultivar has significantly lower canker incidence and severity than ‘Clemenules’, particularly during early stages of leaf development in the field. This differential response is only seen when the leaves are inoculated by spraying, suggesting that leaf surface contributes to resistance. In this work, we have studied structural and chemical properties of leaf surface barriers of both cultivars. Ultrastructural analysis showed a thicker cuticle covering epidermal surface and guard cells in young ‘Okitsu’ leaves than in ‘Clemenules’. This thicker cuticle was associated with a smaller stomatal aperture and reduced cuticle permeability. These findings correlated with an accumulation of cuticular wax components, including primary alcohols, alkanes, and fatty acids. None of these differences were observed in mature leaves, where both cultivars are equally resistant to the bacterium. Remarkably, mechanical alteration of cuticular thickness of young ‘Okitsu’ leaves allows canker development. Furthermore, cuticular waxes extracted from young ‘Okitsu’ leaves have higher antibacterial activity against X. citri than ‘Clemenules’. Taken together, these data suggest that a faster development of epicuticular waxes in ‘Okitsu’ leaves play a central role in its resistance to X. citri.

'Okitsu'是一种普通柑桔品种，对柑橘X.citri亚种表现出明显的抗性。柠檬（X. citri）。先前我们已经表明，该品种的溃疡病发病率和严重程度均比“早熟油菜”低，尤其是在田间叶片发育的早期。仅在通过喷雾接种叶片时才能看到这种差异响应，这表明叶片表面有助于抵抗。在这项工作中，我们研究了两个品种的叶片表面屏障的结构和化学性质。超微结构分析显示，年轻的“ Okitsu”叶片的表皮表面和保卫细胞比“ Clemenules”的角质层厚。较厚的表皮与较小的气孔孔径和降低的表皮通透性有关。这些发现与表皮蜡成分（包括伯醇，烷烃和脂肪酸）的积累有关。在两个叶片对细菌均具有同等抗性的成熟叶片中，没有观察到这些差异。值得注意的是，年轻的“冲月”叶片的表皮厚度的机械改变使溃疡得以发展。此外，从年轻的“冲月”叶中提取的表皮蜡具有更高的抗菌活性。X. citri而不是“ Clemenules”。综上所述，这些数据表明，'Okitsu'叶片中表皮蜡的更快发育在其对柠檬黄杆菌的抗性中起着重要作用。