Benzo-(1,2,3)-thiadiazole-7-carbothioic S-methyl ester (BTH) stimulates defense reactions in <Emphasis Type="Italic">Xanthosoma sagittifolium</Emphasis>

The root rot disease caused by Pythium myriotylum is responsible for about 70% of cocoyam production loss in Cameroon. The potential of benzo-(1,2,3)-thiadiazole-7-carbothioic S-methyl ester (BTH) to trigger resistance in cocoyam (Xanthosoma sagittifolium) plants against P. myriotylum was investigated. Under controlled conditions, BTH was an efficient elicitor of some defense reactions in cocoyam. Application of 0.2 mg ml⁻¹ of BTH on leaves 7 days before inoculation of roots with P. myriotylum enhanced the activities of peroxidase (Pox) and polyphenoloxidase (PPO) as well as the total phenolic content. This resistance was noted as a decrease in disease incidence and severity in BTH-treated plants. This increase in Pox activities was correlated with two new isoforms in a white (sensitive) cultivar inoculated after stimulation. In a yellow (resistant) cultivar, stimulation was characterized by the appearance of one isoform. Qualitative analysis of phenolic compounds by HPLC showed an increase of hydroxycinnamic and flavonoid derivatives after inoculation. We also observed the appearance of a new caffeoylshikimic acid derivative after stimulation followed by inoculation of both cultivars. The findings indicated that the pattern of induction is different and depends on the variety.     

Stem and root rot of scarlet runner bean (Phaseolus coccineus) caused by Pythium myriotylum

A severe rot was found on the stems and roots of scarlet runner bean (Phaseolus coccineus) in Ibaraki Prefecture (Japan) in August 2004. The causal fungus was identified as Pythium myriotylum. We propose the name of stem and root rot of scarlet runner bean (“Kuki-negusare-byo” in Japanese) for this new disease.     

<Emphasis Type="Italic">Pythium</Emphasis> and <Emphasis Type="Italic">Phytophthora</Emphasis> species associated with root and stem rots of kalanchoe

Pythium and Phytophthora species were isolated from kalanchoe plants with root and stem rots. Phytophthora isolates were identified as Phytophthora nicotianae on the basis of morphological characteristics and restriction fragment length polymorphism (RFLP) analysis of the rDNA-internal transcribed spacer regions. Similarly, the Pythium isolates were identified as Pythium myriotylum and Pythium helicoides. In pathogenicity tests, isolates of the three species caused root and stem rots. Disease severity caused by the Pythium spp. and Ph. nicotianae was the greatest at 35°–40°C and 30°–40°C, respectively. Ph. nicotianae induced stem rot at two different relative humidities (60% and >95%) at 30°C. P. myriotylum and P. helicoides caused root and stem rots at high humidity (>95%), but only root rot at low humidity (60%).     

Pathogenicity, Electrophoretic Characterisation and In planta Detection of the Cocoyam Root Rot Disease Pathogen, Pythium myriotylum

Cocoyam (Xanthosoma sagittifolium), an important staple food crop for many people in the tropics and subtropics, suffers great losses from a root rot disease which is most probably caused by Pythium myriotylum, although it has been claimed that a complex of three root pathogens is needed to cause the disease. In this study, we compared two Pythium isolates from diseased cocoyam roots, CRPm and Bokwai, with other putative P. myriotylum isolates from culture collections and from Cameroonian soil, with respect to host range and isozyme patterns. Pathogenicity was tested on tomato, bean, cowpea, tobacco and cocoyam. CRPm and Bokwai were only pathogenic to tobacco and cocoyam. On cocoyam, these isolates caused typical symptoms within 48h on 100% of the inoculated plantlets. Only two other isolates of P. myriotylum from culture collections were moderately to weakly pathogenic to cocoyam. Isolates of P. myriotylum were very variable in their pathogenicity to bean, cowpea, tomato and tobacco. Isozyme patterns of - and -esterases were used to differentiate CRPm and Bokwai from all other isolates. Unlike the other P. myriotylum strains, cocoyam isolates were unable to grow at 37°C. Malate dehydrogenase isozyme bands originating from CRPm were consistently detected in CRPm-infected cocoyam roots grown in vitro and in vivo. These findings indicate that CRPm can penetrate cocoyam roots and cause disease in the absence of other root pathogens. This study also indicates that P. myriotylum from cocoyam developed a certain degree of host specialisation.     

微生物源农药申嗪霉素的研制与应用

申嗪霉素是中国自主研发的一种新型微生物源农药,具有高效、安全、广谱等特点,其主要成分是甜瓜根际促生菌M18产生的次级代谢产物吩嗪-1-羧酸。文章重点就申嗪霉素产生菌M18的分离及其代谢产物的鉴定、申嗪霉素生物合成及调控机理最新研究进展、申嗪霉素高产工程菌株的构建和产业化、以及申嗪霉素大田防病试验结果及推广应用情况等进行详细综述,并对其抗菌作用机理进行探讨,旨在为申嗪霉素的生物合成机理研究、遗传和代谢改造以及推广应用提供参考。     

Pythium rot of chingensai ( Brassica campestris L. chinensis group) caused by Pythium ultimum var. ultimum and Pythium aphanidermatum

Severe rot was found at the base of leaves and stems of chingensai (Brassica campestris L. chinensis group) in Okayama Prefecture in 2000. The causal fungi were morphologically identified as Pythium ultimum Trow var. ultimum and P. aphanidermatum (Edson) Fitzpatrick. This is the first report of rot caused by Pythium species on chingensai. We named this disease Pythium rot of chingensai.     

Pythium rot of Chinese cabbage (Brassica rapa L. subsp. pekinensis) caused by Pythium aphanidermatum

Severe rot was found at the base of leaves and stems of Chinese cabbage (Brassica rapa L. subsp. pekinensis) in Ibaraki Prefecture every year in early September from 2002 through 2004. The causal fungus was identified as Pythium aphanidermatum (Edson) Fitzpatrick. This is the first report of P. aphanidermatum on Chinese cabbage. A similar disease of Chinese cabbage caused by P. ultimum Trow var. ultimum is known as Pythium rot. We propose adding P. aphanidermatum as a new pathogen of this disease.     

Identification and pathogenicity of Pythium species causing damping-off of kidney bean

Five Pythium species (Pythium irregulare, P. mamillatum, P. myriotylum, P. spinosum and P. ultimum var. ultimum) were isolated from the hypocotyls and roots of kidney bean plants with damping-off from a commercial field and from experimental plots that have undergone either continuous cropping with kidney bean or rotational cropping with arable crops. In inoculation tests, all five Pythium species were pathogenic to kidney bean. This is the first report of damping-off of kidney bean caused by Pythium species; we named this disease damping-off of kidney bean. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession numbers AB291811, AB291944 and AB291945.     

Pythium rot of figmarigold (<Emphasis Type="Italic">Lampranthus spectabile</Emphasis>) caused by <Emphasis Type="Italic">Pythium aphanidermatum</Emphasis>

A new leaf rot disease was found on the leaves of figmarigold (Lampranthus spectabile). The causal organism, identified as Pythium aphanidermatum was found to cause the same symptoms after artificial inoculation and was then reisolated from the inoculated plants. We propose to name the disease Pythium rot of figmarigold.     

Evaluation of plant growth-promoting rhizobacteria for biological control of pythium root rot of cucumbers grown in rockwool and effects on yield

Three strains ofPseudomonas fluorescens (63-49, 63-28, and 15), one strain ofPseudomonas corrugata (13) and one strain ofSerratia plymuthica (R1GC4) were tested on rockwool-grown cucumbers for their ability to reduce Pythium root-rot caused byPythium aphanidermatum. These strains were previously selected for biocontrol ability from collections of >4000 bacteria. Strains 63-49 and 63-28 were tested on cucumber plants grown in rockwool in two replicatedPythium-inoculated trials conducted in British Columbia (B.C). Another inoculated, replicated trial was conducted in Quebec with all five strains. Cucumber yields (fruit number and weight) were measured over a ten-week harvest period. Strain 63-49 caused an early promotion of plant growth and increased cucumber yields at early harvests. No measurable effect ofPythium inoculation on disease development was observed in the Quebec trial, due to unfavourable cool weather. However, 63-49 significantly increased the total number of cucumbers (12%) and cucumber weight (18%), compared to the non-treated control. Strains 13, 15 and R1GC4 slightly increased the cumulative cucumber yields, but strain 63-28 had no effect. In the B.C. trial, inoculation withP. aphanidermatum reduced the number and weight of cucumbers by 27%. Treatments ofPythium-inoculated cucumbers with 63-49 significantly increased fruit number and weight by 18%, compared to thePythium-inoculated control. Strain 63-28 increased the cumulative number of cucumbers over time, compared to thePythium-inoculated control, but the increase was less than with 63-49. The use ofPseudomonas spp. in rockwool-grown cucumbers can increase yields, both in the presence and absence of Pythium root rot, and with variable seasonal conditions and disease pressures.     

Bait method to detect Pythium species that grow at high temperatures in hydroponic solutions

Pythium helicoides, P. aphanidermatum and P. myriotylum are important pathogens that cause root rot of several crops in hydroponic culture and in ebb-and-flow irrigation systems. These species belong to a group of Pythium species that can grow at temperatures higher than 40°C. We developed a method for baiting these high-temperature Pythium species and evaluated its practicality to monitor their presence in nutrient solutions. Seeds of cucumber, tomato, radish, hemp, perilla and millet and leaves of bent grass and rose were tested as baits in hydroponic systems. Hemp, perilla and radish seeds and bent grass and rose leaves were more effective than the other baits for Pythium zoospores, and bent grass leaves were the most effective. In a sensitivity test, bent grass leaf traps (BLTs) detected three Pythium species after only a 1 day exposure to suspensions of 40 zoospores per liter of water, and the frequency of detection increased with zoospore density and with baiting period. A temperature of 38°C was optimum for the selective reisolation of the high-temperature Pythium species from the BLTs. The BLT was also tested with inoculated and noninoculated miniature roses that shared a recirculating nutrient solution. The pathogen was detected in the nutrient solution 23 days before the disease spread to the noninoculated roses. In addition, P. helicoides was detected 30 days before the disease was evident in a commercial greenhouse. The baiting method described here will be useful for monitoring high-temperature Pythium species in recirculating hydroponic culture systems.     

Root and stem rot of chrysanthemum caused by five <Emphasis Type="Italic">Pythium</Emphasis> species in Japan

Root and stem rot with wilt of above ground parts of cultivated chrysanthemums was first found in Ibaraki, Toyama and Kagawa prefectures, Japan in 2002 and 2003. Pythium species were isolated from the diseased tissues and identified as P. dissotocum, P. oedochilum, P. sylvaticum, P. ultimum var. ultimum and asexual strains of P. helicoides based on their morphologies and sequences of rDNA-ITS region. All the Pythium species were strongly pathogenic to chrysanthemums in pot conditions and were reisolated from the inoculated plants. Because Pythium root and stem rot of chrysanthemum has never been reported in Japan, we propose that this is a new disease that can be caused by the five Pythium species.     

Effect of indole-acetic acid (IAA) on the development of symptoms caused by <Emphasis Type="Italic">Pythium ultimum</Emphasis> on tomato plants

The effect of indole-acetic acid (IAA) on the development of symptoms caused by Pythium ultimum on tomato plants was investigated using different bioassays. Application of IAA (5 μg ml⁻¹) on tomato seedlings inoculated with P. ultimum did not affect their emergence suggesting that IAA did not affect the severity of Pythium damping-off. However, IAA was shown to influence the development of P. ultimum symptoms on tomato plantlets. Low concentrations of IAA (0–0.1 μg ml⁻¹) within the rhizosphere of plantlets increased the severity of the symptoms caused by P. ultimum, while higher concentrations (10 μg ml⁻¹), applied either by drenching to the growing medium or by spraying on the shoot, reduced the symptoms caused by this pathogen. In addition, the study demonstrated that P. ultimum produces IAA in liquid culture amended with L-tryptophan, tryptamine or tryptophol (200 μg ml⁻¹) and in unamended culture.     

Wilt and root rot of poinsettia caused by three high-temperature-tolerant Pythium species in ebb-and-flow irrigation systems

Poinsettia plants growing in ebb-and-flow irrigation systems developed wilting and root rot during the summer growing seasons of 2010 in Gifu Prefecture and 2011 in Aichi Prefecture. Pythium species were isolated from roots with rot symptoms. The isolates were identified as P. helicoides and P. myriotylum on the basis of morphological characteristics and sequence homologies in the rDNA internal transcribed spacer regions. In pathogenicity tests, these isolates caused severe wilting and root rot. This is the first report of poinsettia root rot disease caused by P. helicoides and P. myriotylum, although P. aphanidermatum was reported as a pathogen of poinsettia root rot. To better understand these diseases, we performed an epidemiological study of three high-temperature-tolerant Pythium species, P. aphanidermatum, P. helicoides and P. myriotylum. Disease incidence as a percentage of diseased plants was greatest at 35 °C for all three species. Disease severity using the rating scale of root rot was also highest at 35 °C, particularly with high zoospore inoculum densities (100.0 zoospores/mL). Although the disease incidence and severity were reduced at lower temperatures, the three Pythium species were able to cause disease at temperatures as low as 20 °C.     

吩嗪-1-羧酸及其类似物的合成研究进展

天然产物吩嗪-1-羧酸（PCA）作为重要的微生物代谢产物,在假单胞菌属（Pseudomonads）和链霉菌属（Streptomycetes）等微生物分泌物中广泛存在,具有医用抗肺癌活性及抗水稻纹枯病、西瓜枯萎病、辣椒疫病、小麦全蚀病、西瓜炭疽病和油菜菌核病等病原菌的广谱性农用抗菌活性,对人畜和环境无害,并具有独特的化学结构,是研发绿色农药的理想化合物。文章综述了吩嗪-1-羧酸及其类似物在微生物发酵及化学合成方面的研究进展,分析了各合成路线中的关键反应,讨论了各合成方法的优缺点。     

Pathogenicity and fungicide sensitivity of Pythium and Phytopythium spp. associated with soybean in the Huang-Huai region of China

Pythium and Phytopythium spp. cause seed decay, damping off, and root rot in soybean, wheat, and many other crops. However, their diversity and importance as pathogens, particularly in different crop rotation systems, are largely unknown. A survey was conducted in the Huang-Huai region, one of the main areas of soybean–wheat rotation farming in China. In 2016–2018, we collected 300 soybean seedlings and 150 field soil samples from several representative locations, and identified 26 Pythium and 6 Phytopythium spp. from 212 isolates, based on internal transcribed spacer 2 (ITS2) and cytochrome oxidase subunit 1 sequences. The pathogenicity of these isolates was evaluated by growing soybean and wheat seeds in dishes and pots containing oomycete cultures. We found that 12 Pythium spp. (but no Phytopythium spp.) showed high pathogenicity on soybean and/or wheat, and nine of them (75%) were highly pathogenic on both crops. Among the nine species, Pythium spinosum, Pythium ultimum, Pythium species 1 (tentatively designated as ‘Candidatus Pythium huanghuaiense’), Pythium aphanidermatum, and Pythium myriotylum were highly abundant among all isolates (15%, 10%, 9%, 8%, and 5%, respectively). Nine species were selected for testing of sensitivity to the fungicides metalaxyl and mefenoxam. The EC₅₀ values were all less than 10 μg/ml, indicating little resistance. Minimum inhibitory concentration values indicated isolates were about twice as sensitive to mefenoxam as to metalaxyl. These results provide a systematic understanding of Pythium and Phytopythium species associated with soybean in the Huang-Huai region, which is important for disease management and breeding programmes.     

Evaluation of antagonistic bacteria for suppression of bacterial ring rot of potato

Bacterial strains with potential for biological control of bacterial ring rot of potato caused byClavibacter michiganensis subsp.sepedonicus were isolated from the surface of potato tubers. Eighty-eight potential biocontrol candidates, selected on the basis ofin vitro antibiosis toC. m. sepedonicus, produced inhibition zones with radii ranging from 0.5 to 16 mm on test plates. All antagonistic isolates were screened in the greenhouse for biocontrol activity on micropropagated potato plantlets root-inoculated withC. m. sepedonicus. Eight strains consistently prevented infection of plantlets but there was no significant correlation between the width of the inhibition zone in thein vitro assay and ring rot suppression in the plant bioassay. Three strains that showed a high level of biological control potential were identified as a saprophytic enteric bacterium (strain 7G), anArthrobacter sp. (strain 16C), and a soil coryneform bacterium (strain 18A). These were tested in a field plot by co-inoculating cut seed potato tubers withC. m. sepedonicus and antagonists. Strains 7G and 18A significantly increased plant stand whereas 16C decreased disease incidence. The relative number of ostensibly ring rot-free progeny tubers was generally greater when antagonists were present.     

<Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> inhibits the plant cell wall degrading enzymes of <Emphasis Type="Italic">Sclerotium rolfsii</Emphasis> and reduces the severity of groundnut stem rot

Three hundred and ninety-three groundnut-associated bacterial strains, applied both as seed treatment and soil amendment, were evaluated for control of stem rot disease (caused by Sclerotium rolfsii) of groundnut in a controlled environment. Twelve strains significantly (P=0.01) reduced the incidence of stem, rot of which groundnut seed endophytes Pseudomonas aeruginosa GSE 18 and GSE 19 reduced the seedling mortality by 54% and 58%, compared to the control. In dual cultures, the 12 biocontrol strains reduced the mycelial growth of S. rolfsii by 32%–74% as compared to the control. Cell- free culture filtrates of P. aeruginosa GSE 18 and GSE 19 inhibited the activity in vitro of the cell wall-degrading enzymes (CWDE) polygalacturonase and cellulase by S. rolfsii up to a maximum of 55% and 50%, respectively, when measured 6 days after inoculation. Pseudomonas aeruginosa GSE 18 and GSE 19 with a known tolerance to thiram, a commonly used seed dressing fungicide, suppressed the growth of S. rolfsii, inhibited the activity of CWDE, and reduced the incidence of stem rot, suggesting the usefulness of these biocontrol strains as components in the integrated management of groundnut stem rot.     

Phylogenetic and morphological analyses of Pythium graminicola and related species

Isolates of Pythium graminicola and related species were differentiated using restriction fragment length polymorphism (RFLP) analyses of the internal transcribed spacer (ITS) regions of rDNA and the cytochrome c oxidase subunit II (COX II) gene. These sequences were used in subsequent phylogenetic analyses. Finally, the phylogenetic placement of species was compared to that determined from morphological characteristics. The 62 isolates tested were divided into seven groups, A–G, based on RFLP analysis of the rDNA-ITS region. In the RFLP analysis of the COX II gene, isolates were divided into groups similar to those based on ITS-RFLP. Groups A and B were each separated into two additional subgroups. Grouping of isolates based on RFLP analyses agreed with the morphological differentiation. Groups A, B, D, E, F, and G were identified as P. graminicola, P. arrhenomanes, P. aphanidermatum, P. myriotylum, P. torulosum, and P. vanterpoolii, respectively. Group C was closely related to group B based on phylogenetic analysis of the rDNA-ITS region and the COX II gene and is similar to P. arrhenomanes. Each of the other species occupied their own individual clades. Although P. arrhenomanes is morphologically similar to P. graminicola, our phylogenetic analyses revealed that it was evolutionarily distant from P. graminicola and more closely related to P. vanterpoolii. Our analysis also revealed that P. torulosum with smaller oogonia is more closely related to P. myriotylum with large oogonia than to P. vanterpoolii, which forms smaller oogonia and is morphologically similar to P. torulosum. P. aphanidermatum with large oogonia and aplerotic oospores was not related to the morphologically similar species P. myriotylum. Results suggest that P. graminicola and related species are phylogenetically distinct, and molecular analyses, in addition to morphological analyses, are necessary for the accurate taxonomic placement of species in this complex.     

嗜线虫致病杆菌SN313的次生代谢产物及其抑制植物病原真菌活性研究

通过化学与生物活性筛选从土壤中分离得到一株菌株,利用16S rDNA方法将其鉴定为嗜线虫致病杆菌Xenorhabdus nematophila并命名为SN313。采用微生物发酵、液相萃取、柱层析及半制备高效液相色谱等技术,对SN313的发酵液进行分离纯化,得到3个化合物。利用质谱和核磁共振等波谱技术并依据文献数据确定了这3个化合物分别是N-(2-羟基苯基乙酰) 色胺 ( 1 )、吩嗪-1-羧酸 ( 2 ) 和环(脯氨酸-色氨酸) ( 3 ),其中化合物 1 是一个新的β-吲哚基乙胺类衍生物。通过微量稀释法测定了3个化合物对4种植物病原真菌的抑制活性。结果表明:化合物 1 对辣椒疫霉Phytophthoa capsici和番茄灰霉病菌Botrytis cinerea具有明显的抑制作用 (IC₅₀值分别为11.20 μg/mL和28.94 μg/mL);化合物 2 对番茄灰霉病菌、辣椒疫霉、水稻纹枯病菌Thanatephorus cucumeris和小麦根腐病菌Bipolaris sorokiniana有明显的抑制作用 (IC₅₀ < 40 μg/mL);化合物 3 对番茄灰霉病菌具有较好的抑制效果 (IC₅₀ = 41.58 μg/mL)。从土壤微生物中获取化合物 2 ,为生物农药申嗪霉素有效成分的天然获取提供了一种新的途径。