Dose-response relationships between phytopathogenic bacteria and their hosts

Theories on the relationships between the challenge dose of phytopathogenic bacteria and the quantal response of the host plant are discussed and applied to experimental results. In a number of cases the extent of disease was directly proportional to the dose, which is an indication of independent action. Departures from linearity in the relationships were ascribed tointer alia a shortage of multiplication sites, antagonism amongst the cells of the pathogen and heterogeneity of the tested host plants with respect to susceptibility. In a few host-pathogen combinations, dose-response relationships showing an upward curve were found; this is probably an indication of facultative synergism. The relationships found in homologous and heterologous host-pathogen combinations were similar. The implications of the above findings for the quantitative study of factors affecting the susceptibility of plants to bacterial infection are discussed.Samenvatting Na een bespreking van de theorieën over de relatie tussen het aantal fytopathogene bacteriën per inoculatie en de al-of-niet respons — waarbij dus de grootte van de individuele respons niet in acht genomen wordt — worden deze theorieën getoetst aan de resultaten van proeven die in de literatuur beschreven zijn. Onderschied wordt gemaakt tussen proeven waarin de proporties en die waarin de aantallen geslaagde inoculaties bepaald zijn. Verder is een vergelijking gemaakt tussen homologe en heterologe combinaties van waardplant en pathogeen.Waar de proporties geslaagde inoculaties werden gemeten, vond ik in een aantal gevallen evenredigheid tussen dosis en respons, mits een transformatie werd toegepast voor veelvoudige infectie. Dit is een aanduiding dat de cellen van het pathogeen elkaar niet beïnvloeden. Afwijkingen van dit rechtlijnig verband kunnen o.a. worden toegeschreven aan antagonisme tussen de cellen van het pathogeen, aan heterogeniteit in vatbaarheid van de waardplanten of aan een beperkt aantal vermeerderingsloci.In drie gevallen werd een naar boven gekromde lijn gevonden, hetgeen waarschijnlijk wijst op facultatief synergisme.In proeven waarin de aantallen geslaagde inoculaties gemeten werden, vond ik in de literatuur evenredige en dus rechtlijnige verbanden met afbuigingen naar rechts voor responses tot te hogere doses. De afwijkingen van rechtlijnigheid kunnen hier worden toegeschreven aan een beperkt aantal vermeerderingsloci of aan antagonisme tussen de cellen van het pathogeen.Geen essentieel verschil in dosis-respons verhoudingen werd gevonden tussen homologen en heterologe waardplant-pathogeen combinaties.De implicaties van bovengenoemde resultaten voor de kwantitatieve studie van factoren die de vatbaarheid van planten voor infectie door bacteriën bepalen, worden besproken.     

European collaborative studies for the validation of PCR-based detection tests targeting regulated fungi and oomycetes

In 2007, the mycology unit of the French plant protection laboratory (LNPV-UMAF) organized and launched four collaborative studies for the validation of detection protocols targeting the regulated oomycetes Phytophthora ramorum , P. fragariae / P . rubi , Plasmopara halstedii and the fungus Monilia fructicola . The participants were recruited through the European Mycological Network (EMN). All four protocols were based on species-specific PCR tests already published in the scientific literature and, except for Pl. halstedii , combined a detection test and a confirmation of detection test. For each target organism, we evaluated the performance of protocols, i.e. accuracy, qualitative repeatability and qualitative reproducibility, by a statistical analysis of the results obtained by the 16 participant laboratories with a series of 10 blinded samples. As demonstrated by the collaborative trials results, all four detection protocols were shown to be fit for the purpose of regulatory compliance. The collaborative trial appears a powerful tool to evaluate the performance of a detection method, and is of special interest to laboratories employing a quality assurance system.     

卵菌与真菌Argonaute家族基因的生物信息学分析

 Argonaute蛋白广泛存在于真核生物与原核生物中,可在非编码小RNA或DNA的引导下,对完全匹配或部分匹配的靶标进行切割、翻译抑制或染色体修饰。本研究利用生物信息学对127种卵菌与真菌的基因组进行分析,旨在了解各个物种中AGO家族基因的数量、蛋白结构域、进化关系及转录模式等。结果发现,大部分卵菌与真菌的基因组中(51%)含有2个AGO基因,而疫霉菌和壶菌等平均含有4个以上。卵菌与真菌的AGO基因在进化上相互独立,多拷贝AGO基因可能是通过基因复制形成;大部分AGO基因具有6个可预测的功能域(即:N端、Linker 1、PAZ、Linker 2、MID和PIWI),并且在PAZ和PIWI功能域上,与核酸5'和3'端结合及与催化活性相关的氨基酸位点整体相对保守,仅个别位点存在一定的差异。侵染大豆过程中,大豆疫霉和终极腐霉的两对同源AGO基因具有保守的表达模式,且基因表达水平相对较高,可能具有相似的生物学功能。上述结果将为深入解析AGO介导的RNA干扰机制及生物学功能奠定基础。     

The interaction of some phytopathogenic fungi with plant tissue

The phytoalexin test of Müller was applied to various host/parasite combinations. The highest production was obtained when spores ofSclerotinia fructicola were on slices of potato tuber, and spores ofColletotrichum lindemuthianum in contact with bean pod tissue. During the period of incubation of the fungus on the host plant tissue substances were formed or excreted by the plant tissue. Several amino acids and carbohydrates (saccharose, glucose and fructose) could be demonstrated by paper chromatography. Most of these substances were found at much higher concentrations in the controls (i.e. drops of double distilled water incubated upon host tissue), than in the supernatant of the spore suspension after the incubation period. Drops of spore suspension and drops of double distilled water on glass cavity slides never contained these substances, or they were in such low concentrations as to be undetectable by paper chromatography. Inhibition of spore germination by a phenolic compound was not confirmed in the used test objects and host/parasite combinations.     

卵菌与真菌Argonaute家族基因的生物信息学分析

Argonaute蛋白广泛存在于真核生物与原核生物中,可在非编码小RNA或DNA的引导下,对完全匹配或部分匹配的靶标进行切割、翻译抑制或染色体修饰。本研究利用生物信息学对127种卵菌与真菌的基因组进行分析,旨在了解各个物种中AGO家族基因的数量、蛋白结构域、进化关系及转录模式等。结果发现,大部分卵菌与真菌的基因组中(51%)含有2个AGO基因,而疫霉菌和壶菌等平均含有4个以上。卵菌与真菌的AGO基因在进化上相互独立,多拷贝AGO基因可能是通过基因复制形成;大部分AGO基因具有6个可预测的功能域(即:N端、Linker 1、PAZ、Linker 2、MID和PIWI),并且在PAZ和PIWI功能域上,与核酸5’和3’端结合及与催化活性相关的氨基酸位点整体相对保守,仅个别位点存在一定的差异。侵染大豆过程中,大豆疫霉和终极腐霉的两对同源AGO基因具有保守的表达模式,且基因表达水平相对较高,可能具有相似的生物学功能。上述结果将为深入解析AGO介导的RNA干扰机制及生物学功能奠定基础。     

Identification,pathogenicity and community dynamics of fungi and oomycetes associated with pea root rot in northern France

The pea root rot complex is a major concern for green pea production worldwide. This study aimed at characterizing its composition and dynamics throughout a cropping season in northern France. To this end, fungi and oomycetes were isolated from green pea plant roots with symptoms sampled at the flowering stage in 22 fields in 2017, and at the pea emergence, elongation and flowering stages in two fields in 2018. Out of 646 isolates collected, 317 were identified using molecular markers. Fusarium oxysporum, F. solani and F. redolens were highly predominant. Pathogenicity tests separated the isolates into four aggressiveness groups. F. solani isolates were the most aggressive. Phylogenetic analysis of their TEF1 sequences showed that they mainly belonged to the F. pisi lineage, and that F. oxysporum isolates were genetically close to isolates from the UK that did not belong to the forma specialis pisi. In addition, several Clonostachys rhizophaga isolates are reported for the first time to cause pea root rot. The oomycetes were rarely found and were represented by a few Pythium spp. isolates. Lastly, this study shows that the fungal and oomycete communities associated with pea root rot change during the cropping season. The level of dissimilarity of the root-rot-associated communities decreased throughout the cropping season towards a more similar composition at the flowering stage, dominated by F. solani, F. oxysporum and F. redolens. The proportion of nonpathogenic to weakly pathogenic isolates decreased progressively during the growing season in favour of moderately to highly pathogenic isolates.     

Synthesis of some acetylenic and halovinyl heterocyclic carbonyl compounds and their activity against some phytopathogenic fungi

Twenty-three acetylenic or halovinyl carbonyl compounds with heterocyclic substituents were synthesised and tested in vivo against eight phytopathogenic fungi of different taxonomic classes. Some of them were fungicidal against Uromyces appendiculatus on Phaseolus vulgaris, though none showed a wide spectrum of activity.     

斑蝥素及去甲斑蝥素对七种植物病原真菌的抑制作用

采用菌丝生长速率法研究斑蝥素和去甲斑蝥素对苹果树腐烂病菌等7种植物病原真菌的抑菌活性.斑蝥素25～200mg/L对7种病原真菌的菌丝生长均有抑制作用,对苹果树腐烂病菌和苹果轮纹病菌EC50分别为0.1 mg/L和8.2 ms/L.去甲斑蝥素50～200 ms/L对苹果树腐烂病菌、苹果轮纹病菌、白菜黑斑病菌、黄瓜菌核病菌的菌丝生长有明显的抑制作用,对苹果树腐烂病菌和苹果轮纹病菌菌丝生长EC50分别为13.6mg/L和80.2mg/L.两种药剂EC卯处理5天后,在扫描电镜中发现两种供试菌菌丝加粗、皱缩,在透射电镜下观察到细胞膜畸形、细胞内空腔增多,出现电子致密物、囊泡等亚细胞结构变化.     

白藜芦醇及其衍生物对植物病原真菌的抑菌活性

为了明确植物源活性成分芪类化合物在农业病害防治中的前景,在离体条件下分别测定了白藜芦醇(Ⅰ)及其衍生物(Ⅱ~Ⅴ)对植物病原真菌菌丝生长的抑制作用以及对菌丝形态和孢子萌发的影响,采用叶片法和温室盆栽法研究了白藜芦醇的防病作用原理。结果表明:5个供试化合物对6种供试病原菌的菌丝生长均有不同程度的抑制作用,但均对番茄早疫病菌 Alternaria solani 的抑制活性最高,其中又以3,5-二羟基-4'-甲氧基二苯乙烯(Ⅲ)的抑制活性最高;白藜芦醇可造成番茄早疫病菌菌丝体畸形,并可抑制该病菌孢子的萌发,但未引起孢子形态改变。叶片法和温室盆栽法试验的结论一致,即白藜芦醇能够抑制病原菌的侵染,对植株起到一定的保护作用。     

植物病原真菌寄生性与分泌蛋白组CAZymes的比较分析

 通过信息学方法对植物病原真菌分泌蛋白组进行预测以及对碳水化合物酶类ＣＡＺｙｍｅｓ 注释和比较?分析病原真菌寄 生性与ＣＡＺｙｍｅｓ 家族功能的关系? 结果显示非专性寄生(半活体营养型和死体营养型)真菌编码的分泌蛋白占基因组编码 基因的比例较专性寄生真菌(活体营养型)的偏高?ＣＡＺｙｍｅｓ 家族中?非专性寄生真菌的糖基水解酶家族ＧＨ 和多糖裂解酶家 族ＰＬ 较专性寄生真菌显著扩增?功能聚类分析发现?非专性寄生真菌参与纤维素、果胶、木聚糖等植物细胞壁组分降解相关 的基因较专性寄生真菌明显增多? 结果表明了ＣＡＺｙｍｅｓ 与寄生类型的高度关联性?揭示了其在非专性寄生真菌致病过程中 可能的关键作用?     

竹醋液对几种植物病原真菌的抑制活性

 新制竹醋液抑制6种作物8种病原真菌菌丝生长的活性大小序为:苹果霉心病菌 > 小麦赤霉病菌 > 黄瓜炭疽病菌 > 番茄灰霉病菌 > 葡萄炭疽病菌 > 番茄早疫病菌 > 草莓灰霉病菌 > 苹果腐烂病菌 > 苹果轮纹病菌 > 黄瓜灰霉病菌,有效抑制中浓度(EC₅₀)介于0.1185%-0.8035%(g/mL,干重/体积)之间。室温下保存1年的竹醋液抑制7种作物8种病菌菌丝生长的EC₅₀在0.0832%-0.3334%之间,对苹果霉心病菌的抑制活性下降,对6种作物的6种病菌的抑制活性均高于新制竹醋液。在2%水琼脂培养基上测定发现竹醋液明显抑制草莓灰霉菌分生孢子萌发,对该菌7个菌株的EC₅₀在0.0365%-0.1311%之间,平均为0.0673±0.0332%。叶盘漂浮法测定发现0.0125%、0.025%和0.05%的竹醋液对葡萄霜霉病的防效分别为23.5%、38.8%和78.4%,对葡萄霜霉病菌5个菌株EC₅₀在0.0191%-0.0464%之间,平均为0.0317 ±0.0109%。     

不同分子量壳多糖对植物病菌的拮抗作用及其诱导提高寄主植物抗病性

采用固体培养基体外抑菌法研究了分子量为1002、2350、5060的三种壳多糖对22种植物病原菌的拮抗作用.结果表明:三种壳多糖对供试植物病原菌有不同程度的抑制作用,随壳多糖浓度的增加对不同病原菌的抑制作用增强,壳多糖的分子量对植物病菌的抑制作用没有显著影响.壳多糖对活体植株染病的防治效果与壳多糖的使用次数呈正相关,水溶性壳多糖(分子量为2350)对活体植株染病的防治效果最好.壳多糖可诱导植物产生与抗病有关的过氧化物酶和β-1,3葡聚糖酶,而这些酶的产生随着处理次数的增加依次增加,分子量为2350的壳多糖诱导作用最佳,可使过氧化物酶活性增加4倍以上,β-1,3葡聚糖酶活性增加2倍以上.     

三种葱属作物挥发物和提取液对植物病原真菌和卵菌的抑菌活性

采用菌丝生长速率法测定了大蒜、洋葱和葱茎挥发物及提取液对26种主要植物病原真菌和卵菌的抑制活性,以期为利用葱属作物轮作或间作控制病害提供指导。试验结果表明,3种葱属作物挥发物和浸提液具有广谱抗植物病原真菌和卵菌活性,但不同葱属作物对不同种类的病原菌抑菌效果有差异。洋葱和葱茎挥发物和浸提液的抑菌能力比大蒜弱,但对部分疫霉菌、腐霉菌、丝核菌等土传病原菌仍具有与蒜瓣相似的抑菌活性。另外,小麦赤霉病菌、辣椒早疫病菌等部分病原菌对3种葱属作物挥发物和浸提液具有耐性。因此,生产上利用葱属作物轮作或间作防治病害时需要根据不同葱属作物对不同病原菌抑制效果的差异进行合理选择,同时需避免葱属作物长期连作引起病原菌敏感性降低。     

10种香料植物挥发油的抑菌活性研究

为了研究香料植物的抑菌活性,为进一步开发植物源杀菌剂提供理论参考,采用生长速率法及悬滴法测定10种香料植物挥发油对茄镰孢(Fusarium solani)、链格孢(Alternaria alternata)、核盘菌[Sclerotinia sclerotiorum (Lib.) de Bary]、齐整小核菌(Sclerotium rolfsii Sacc.)、束状炭疽菌[Colletotrichum dematium( Pers.) Grove]的抑制活性.结果表明,肉桂、草果、香茅具有较强的抑菌活性,在浓度为0.5 g/L时对供试的5种植物病原菌菌丝抑制率均达100％,对茄镰孢、链格孢、束状炭疽菌的孢子萌发抑制率均高于90％.0.5 g/L浓度的香茅挥发油对5种目标菌的抑制作用达到100％,与30％苯甲·丙环唑乳油杀菌剂作用等同,且高于75％百菌清可湿性粉剂、50％多菌灵可湿性粉剂、70％甲基硫菌灵可湿性粉剂等常规杀菌剂.本研究结果表明,香茅值得进一步研究开发.     

Antifungal activity and mode of action of Galla rhois-derived phenolics against phytopathogenic fungi

Antifungal activity and target sites of methanolic extract and its constituents from the gall (Galla rhois) caused by the Chinese sumac aphid, Schlechtendalia chinensis, on the nutgall sumac tree, Rhus javanica, were examined. In tests with six phytopathogenic fungi using a whole plant bioassay, the gall extract exhibited good antifungal activity. The biologically active constituents isolated from Galla rhois were characterized as the phenolics methyl gallate and gallic acid by spectroscopic analyses. Methyl gallate was highly suppressive to Magnaporthe grisea, Botrytis cinerea, and Puccinia recondita, whereas gallic acid exhibited good antifungal activity against M. grisea and Erysiphe graminis. These two compounds were ineffective against rice sheath blight caused by Rhizoctonia solani. Methyl gallate did not adversely affect conidial germination (94%) but significantly inhibited appressorium formation (7%) of M. grisea. Moderate and significant inhibition of conidial germination (64%) and appressorium formation (5%) of M. grisea, respectively, were observed with gallic acid. In complementation tests with M. grisea, cAMP and 1,16-hexadecanediol restored significantly and slightly appressorium formation inhibited by methyl gallate and gallic acid, respectively. These results indicate that methyl gallate and gallic acid acted on a cAMP-related signaling pathway regulating appressorium formation in M. grisea.     

Effect of sulfite-hydrosulfite and nitrite on thiol redox state, oxidative stress and sclerotial differentiation of filamentous phytopathogenic fungi

This study shows that Na₂S₂O₄, Na₂SO₃ and NaNO₂ decreased differentiation of filamentous phytopathogenic fungi representing the four main types of sclerotia at maximum growth non-inhibiting concentrations, and also increased and decreased the oxidized and the reduced components of their thiol redox state, respectively. Na₂S₂O₄, Na₂SO₃ and NaNO₂ also severely inhibited fungal growth at certain concentrations. These effects concurred by the increase of the high oxidative stress indicator lipid peroxidation and could be attributed to the oxidative cytotoxicity of sulfites and nitrite. The cytotoxic mechanism of the latter may be related to the acidic pH. Sulfites and nitrite can be used as potent fungicides against sclerotiogenic phytopathogenic fungi by acting as growth inhibiting cytotoxic oxidants and by sustaining fungi in their undifferentiated hyphal stage, in which they are more vulnerable to degradation by soil microorganisms.