从300条RAPD随机引物中筛选出扩增多态性丰富的13条引物，对寄主来源不同的29个寄生疫霉（Phytophthora parasitica）菌株进行基因组DNA遗传变异分析。用筛选出的13条引物对供试菌株进行RAPD-PCR扩增，共产生139条RAPD条带，其中133条为多态性条带，多态检测率为95.7%。利用Pop Gene Version 1.31软件对供试菌株间的遗传距离进行聚类分析并构建系统树状图，供试29个菌株被划分为5个遗传聚类组，不同菌株间具有丰富的遗传变异。其中寄主为烟草（Nicotiana spp.）、腊梅（Chimonanthus praecox）、凤尾兰（Yucca gloriosa）和西番莲（Passif lora edulis）的菌株的遗传结构与其寄主来源具有明显的相关性，而寄主为刺槐（Sophora chinensis）和番茄（L ycopersicum esculentum）的菌株与其寄主来源的相关性较小，来源于不同寄主植物的菌株之间遗传距离较远。结果提示在寄生疫霉与其不同寄主植物的长期协同进化过程中，寄主对病原菌的遗传结构具有一定的影响。

为了确定Ca2+信号途径是否参与、在哪一时期参与稻瘟病菌分生孢子萌发及附着胞形成过程的调控，用四种可从不同位点阻断Ca2+信号途径的抑制剂分别处理分生孢子，观察抑制剂对孢子萌发及附着胞形成过程的抑制作用。结果表明：Ca2+螯合剂EGTA、Ca2+通道抑制剂Verapamil、抑制磷脂酶C活性的抑制剂U-73122、影响钙调素与钙调素依赖蛋白激酶作用位点的抑制剂KN-93，随着浓度的增加，对孢子萌发和附着胞形成过程的抑制作用明显增强；同一浓度下，抑制剂对附着胞形成过程的抑制作用大于孢子萌发过程；抑制剂影响孢子萌发和附着胞形成过程在萌发早期（1～4h）最有效；在完全被抑制、不能萌发的孢子内出现了许多颗粒状囊泡；抑制剂可使附着胞形态明显变小甚至不能形成。以上结果表明钙信号途径参与了稻瘟病菌孢子萌发及疏水条件下附着胞形成过程的调控。

We examined the role of salicylic acid (SA) accumulation in the tobacco hypersensitive response (HR) and systemic acquired resistance (SAR) induced by PB90, a 90 kDa protein elicitor that is secreted by Phytophthora boehmeriae. The elicitor induced HR of a consistent shape and size on tobacco plants expressing the bacterial gene nahG. Salicylate hydroxylase is encodec by nahG and inactivates SA by converting it into catechol. The mutant NahG does not accumulate SA. In contrast, infiltration with of a wild type tobacco (cv. Xanthi nc) leaves with the elicitor caused the increase of SA levels. The same SA levels were observed in leaves not treated by the elicitor. HR appears to be mediated by a SA-independent signaling pathway. PB90 treatment resulted in enhanced resistance of wild-type plants to infection by black shank fungus, P. nicotianae, and TMV, but not in NahG plants. Moreover, the elicitor-induced expression of an SAR marker gene encoding PR-1a was suppressed in NahG plants. These results indicate that SA mediates SAR but not HR in tobacco treated with PB90. During plant-elicitor interactions, HR and SAR may be regulated by distinct signal pathways, or SA may function as an intermediate signal upstream of SAR but downstream of HR, and HR may not be a direct defense mechanism against pathogen infection.

野生型烟草Bel-W3叶片经棉疫病菌90kD蛋白激发子处理后，处理叶及其上位叶在24h内均发生2次氧化迸发产生H2O2，且第二次H2O2迸发高峰期同时出现，均出现在第12小时，处理部位细胞死亡高峰期比第二次H2O2迸发高峰期滞后8h。引起过敏反应剂量的激发子诱发反义抑制抗坏血酸过氧化物酶anti-APX烟草的过敏性坏死枯斑比野生型的大而且出现得早；不能诱发野生型烟草HR的剂量可以诱导anti-APX烟草发生HR。经激发子处理后anti-APX烟草对烟草疫霉（Phytophthora nicotianae）和TMV产生的诱导抗性比其野生型高。上述结果表明，H2O2可能是一种重要的信号分子，在棉疫病菌90kD蛋白激发子诱发烟草的HR和SAR中具有重要作用，但可能不是一种可以系统移动的信号分子。

A 90 kDa protein elicitor, PB90, was purified from the culture filtrate of Phytophthora boehmeriae. Procedures including hydrophobic interaction and ion-exchange chromatography were used to purify the protein. PB90 induced hypersensitive reaction in tobacco leaves at a concentration as low as 200 pM and induced systemic acquired resistance (SAR) to TMV, Alternaria alternata, P. parasitica and Ralstonia solanacearum. In addition, it also caused hypersensitive necrosis in leaves of Chinese cabbage and induced SAR to Collectorium higginsianum in the plant. Tobacco leaves infiltrated with 200 pM of the elicitor exhibited an enhanced phenylalanine ammonia lyase activity and peroxidase activity. The behavior on ion-exchange columns indicated that PB90 is an acidic protein. It is stable to heat, acidic and alkaline conditions, but sensitive to ProteaseK. An antiserum raised against the pure protein allowed localization of PB90 by immunogold labeling on the cell wall of the mycelia and encysting zoospores when the fungus is grown in vitro. It was implied that there is a novel protein elicitor secreted by P. boehmeriae, which has a broad activity spectrum. The characters of PB90 distinguished it clearly from the other elicitors previously identified from Phytophthora spp. The possible implications of such a novel elicitor in plant–microbe interactions are discussed.