甘薯形态结构对茎线虫病的抗性机制

 甘薯抗茎线虫病品种鲁薯-78066和胜利百号块根周皮的木栓层细胞有4 ～ 5层，并在细胞壁上沉积有较多的木栓质。表皮接种线虫结果表明，这种形态结构可有效阻止马铃薯腐烂线虫侵入。感病品种粟子香和徐薯18的周皮不发达，只有1 ～ 2层木栓层细胞，而且木栓质极少，线虫能在24h内从表皮直接侵入。甘薯抗病和感病品种的地上茎和地下茎髓部均可受到该线虫危害。抗病品种鲁薯-78066和胜利百号在地下茎和块根顶端连接部位与感病品种粟子香和徐薯18相比较，抗病品种木质部薄壁细胞的壁厚，木质化程度高，导管数量多，线虫不能够穿过这种结构进一步扩展。抗、感品种薯块表皮的伤口有利于线虫侵入，表皮和皮层变成黑褐色，呈糠皮状，但线虫不能进入木栓形成层危害块根皮层以内的组织。

Mechanism of Morphological Structure of Sweet Potato Resistance to Potato Rot Nematode (Ditylenchus destructor)

The phellem was found to consist of four to five layers of cell in the root tuber periderm of resistant varieties of sweet potato Lushu-78066 and Shengli-100. There was more suberin in the cell wall of phellem of resistant varieties than that in susceptible varieties. The experiment showed that the morphological structure of the sweet potato can prohibit invasion of potato rot nematode effectively. The periderm of susceptible varieties was poorly developed consisting of 1 to 2 layers of cell of phellem with few suberin. The nematodes may invade the epidermis of susceptible varieties within 24 hours. The pith of stem and subterraneous stem in resistant and susceptible varieties of sweet potato may be invaded by the nematodes. But the cell wall of xylem parenchyma was thicker, more ligni-fied, with more vessels at the top of root tuber linking the subterraneous stem in resistant varieties Lushu-78066 and Shengli-100 than those in susceptible varieties Li Zixiang and Xushu-18. The structure can limit invasion and spread of the nematodes further. Wound of epidermis was of great advantage to invasion in resistant and susceptible varieties. The invasion may cause peridermis and cortex to become black, brown and spongy. But the nematode can not invade tissue inside phellogen of the root tuber, indicating that phellogen played the role of a barrier to the spread of nematodes.