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Citrus medica is an older cultivated varieties of the genus Citrus and the parent or ancestor of Citrus fruits with significant commercial value. Due to its nutritional and medicinal values, C. medica occupies an important position in the citrus industry. The southwestern part of China is an important center for the origin and diversity of C. medica, and its cultivation has reached a certain scale. Citrus Huanglongbing (HLB) has been spreading for hundreds of years in the major citrus-producing areas in China. C. medica infected with HLB and healthy C. medica were used as the materials. Firstly, the symptoms of the leaves and fruits of C. medica infected with HLB were observed. Secondly, the distribution pattern of HLB in different tissue parts of C. medica was explored. Meanwhile, the tissue anatomical structures and multiple physiological indicators of C. medica infected with HLB and healthy C. medica were analyzed and measured through comparison. Through comparative observation, it was found that the leaves of C. medica infected with HLB showed typical symptoms such as yellowing, mottling and mosaic, and some branches presented symptoms of witches broom and abnormal flowering, but no “red nose fruit” was observed. The distribution of HLB in different parts of the same C. medica was uneven, with the highest content in the fruit pith, followed by the midrib of the old leaves, and HLB was not detected in the fibrous roots. In C. medica infected with HLB, the cells in the phloem, xylem, parenchyma and root were arranged irregularly, the phloem tissue was deformed and collapsed, and the thickness of the phloem of the taproot was significantly decreased compared with that of the healthy C. medica at the same period (P<0.05). No obvious starch grain accumulation was observed in each tissue section of C. medica infected with HLB, but when the starch content was measured, it was found that the starch contents in the old leaves, new leaves, taproot, fibrous roots and fruit pith of C. medica infected with HLB were all higher than those of the corresponding healthy tissues. The hydrogen peroxide content in each tissue of the diseased C. medica increased significantly (P<0.5), especially significantly accumulated in the young tissues (new leaves, fibrous roots) infected with HLB. Compared with healthy C. medica, the callose deposition phenomenon in the tissues of C. medica infected with HLB, especially in the main root and the midrib of the old leaves, was more obvious. The research results of this study could provide a theoretical basis for the relevant studies on exploring the characteristics of damage caused by HLB and the defense mechanism of citrus against HLB in the future.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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