The mechanism of disease development in pine wilt

对接种松材线虫的日本红松(Pinus Densiflora)和黑松(P.thunbergii)的组织褐变相关物质进行了鉴定，鉴定为多酚类物质。一种儿茶素类物质是与大量松材线虫相关的最丰富的多酚类物质。儿茶素是一种单宁单体，不利于松材线虫及其相关非致病种的繁殖。接种松材线虫后，接种松材线虫的田间苗木单宁明显增加，表现出抵抗松材线虫入侵的能力。测定了接种松材线虫的盆栽苗木的水分含量、单宁量、蒸腾速率和线虫分布。多元回归分析显示，两者呈负相关。木材组织含水率与特定茎节段线虫数量之间存在重要的因果关系。在接下来的实验中，线虫数量分别与接种后7、7和14天的(I)氧化油脂、(Ii)单宁和(Iii)渗滤液的量呈显著正相关。接种14d后，渗滤液的量与单宁呈显著正相关。这些结果提出如下假说：超氧阴离子的产生或单宁的过度积累，或两者兼而有之，可能会导致薄壁细胞中的异常物质渗漏，从而堵塞管胞，从而导致寄主枯萎。

Substances associated with tissue browning of Japanese red(Pinus densiflora)and black pine(P. -thunbergii)inoculated with pinewood nematode(Bursaphelenchus xylophilus)were identified to be some kind of polyphenolics. A catechin-like substance was the most abundant polyphenolic associated with large numbers of B. xylophilus. Catechin, a tannin monomer was detrimental to the reproduction of B. xylophilus and its relative non-pathogenic species, B. mucronatus. Tannin increased conspicuously in field-planted seedlings when they were inoculated with B. xylophilus, thereby they seem to resist pinewood nematode invasion.Water content, amount of tannin, transpiration rate and nematode distribution were determined for pinewood nematode-inoculated, potted seedlings of Japanese black pine which were watered daily or every-fourth day. Multiple regression analysis revealed negative correlations. between water content of wood tissue and nematode numbers in specific stem segment, suggesting an important causal relation between these two factors. In the following experiment, a significant positive correlation was observed between nematode numbers and amounts of(i)oxidized lipids, (ii)tannin and(iii)leachates at 7, 7 and 14 days after inoculation, respectively. There was also a significant positive correlation between the amounts of leachates and tannin 14 days after inoculation. The results bring us the following hypothesis that generation of super oxide anion or hyperaccumulation of tannin, or both may cause leakage of abnormal substances from parenchyma cells, and the substances plug tracheids, thereby causes host wilting.