Production of Kestoses (Fructosylsucroses) by Phytophthora parasitica var. nicotianae

The synthesis of kestoses (trisaccharides composed of two fructose units and one glucose unit) by races 0 and 1 of Phytophthora parasitica var. nicotianae is shown. The trisaccharide is found in culture filtrates of isolates grown in liquid media containing 3% sucrose. The utilization of sucrose and trisaccharide formation by the organisms over a 16-day period is described. The kestoses were identified by chemical and enzymatic analysis, and two of three possible isomers were found.     

RAPD PCR for Diagnosis of Phytophthora parasitica var. nicotianae Isolates which Cause Black Shank on Tobacco

Phytophthora parasitica var . nicotianae is the fungal pathotype of tobacco black shank (TBS, Disease severity ≥ 2.0). Random amplified polymorphic DNA (RAPD) analysis was used to differentiate isolates which cause TBS from those which do not. Greenhouse assays combined with zoospore inoculation were performed to assess the virulence of the fungal isolates, and the results were compared with the RAPD pattern analysis. The RAPD results exhibited total correlation with the virulence assay results. Amplification patterns generated by RAPD reactions were used to generate a phenogram depicting the genetically distinct nature of the cluster defined by the TBS isolates. This cluster was exclusive and distinct from P. parasitica var . nicotianae isolates which do not cause TBS. Thus, RAPD proved to be a sensitive and highly reliable method for quickly identifying fungal pathotypes which cause TBS.     

An Extracellular Protein from Phytophthora parasitica var nicotianae Is Associated with Stress Metabolite Accumulation in Tobacco Callus

The most abundant extracellular protein produced by Phytophthora parasitica var nicotianae at early stages of rapid growth in culture has a molecular weight of 46 kilodaltons and has been designated Ppn 46e. Culture conditions for the production of this protein have been optimized and the protein has been purified by gel filtration and ion-exchange chromatography. Ppn 46e is a soluble, acidic protein (pI 4.67). The amino acids Asx (aspartic acid or asparagine), alanine, glycine, Glx (glutamic acid or glutamine), and serine are the most abundant at 13.4%, 12.3%, 12.1%, 9.3%, and 9.3% of the residues, respectively. The purified protein is, by weight, 1.8% glucose, 1.6% mannose, and 0.5% galactose. A bioassay for Ppn 46e based on tobacco callus has been developed. In this assay as little as 20 nanograms (4.3 × 10⁻¹³ mole) Ppn 46e causes the accumulation of the sesquiterpenoid phytoalexin, capsidiol, as estimated by gas chromatography. Levels of capsidiol of 25 micrograms per gram fresh weight were elicited by 80 nanograms Ppn 46e per callus piece. Pretreatment of the protein with either pronase or by boiling resulted in a loss of elicitor activity. Periodate treatment, which inactivates glucan elicitors, did not affect the ability of Ppn 46e to cause capsidiol accumulation. Monospecific antibodies to Ppn 46e were raised in mice. Western blotting experiments employing these antibodies showed that Ppn 46e was present in infected tobacco plants. Dot blotting experiments revealed the presence of the Ppn 46e epitope(s) in Phytophthora megasperma, P. cactorum, P. cinnamomi, and P. infestans but not in Fusarium.     

龙舌兰麻种质资源抗斑马纹病鉴定研究

通过分离培养斑马纹病病原菌,人工接种鉴定不同龙舌兰麻种质的抗斑马纹病的特性.结果表明,番麻、东368、墨引6、墨引12、墨引7、墨引5、假7、马盖麻、东109、金边孤叶龙舌和兰墨引4号11份种质为高抗种质,病斑扩展速度和病情严重度可作为龙舌兰麻抗病性快速鉴定技术手段.     

Genetic and Pathogenic Variation Among Tobacco Black Shank Strains of Phytophthora parasitica var. nicotianae from the Main Tobacco Growing in China

Pathogenic and genetic variability among seven populations of Phytophthora parasitica var. nicotianae from individual tobacco fields (Yunnan, Shandong, Henan, Heilongjiang, Shanxi, Fujian and Sichuan provinces) were investigated using pathogenicity and randomly amplified polymorphic DNA (RAPD) analyses; 63 strains were isolated from different fields of seven tobacco growing regions, using tobacco cv. Hongda as a baiting host. Pathogenic variability was evaluated in greenhouse studies using five tobacco cultivars that have different levels of resistance to tobacco black shank; 75 and 73% of the strains were pathogenic on M3 and M4, 29 and 33% on M1 and M2, and 94% were pathogenic on M5, respectively. Disease severity incited by different strains varied significantly on individual tobacco cultivars. The percentage of strains pathogenic on different cultivars varied among locations. Genotypic variation among 63 strains was evaluated by RAPD analysis. Ten primers detected 89 polymorphic bands. Cluster and principal coordinates analysed cluster groups. the minor group contained 26 strains, and major group contained 37 strains. Estimates of genetic diversity based on RAPD analysis ranged from 0.24 to 0.34 within populations to 0.36 among all strains from all populations. Phytophthora parasitica var. nicotianae populations were genotypically and phenotypically variable, but no distinct genotypic differences were identified among populations from the seven locations.     

Chemical and Physical Factors Influencing Growth of Phytophthora parasitica var. nicotianae on Vegetable Oils

Factors influencing the growth of Phytophthora parasition var. nicotiona on vegetable oil liquid media were studied. This fungus grew poorly on oleic acid, triolein, and tristearin. Cholesterol and α-tocopherol reversed the toxicity of oleic acid. Growth was often stimulated by addition of mineral oil to a glucose medium, and sterols dissolved in mineral oil frequently stimulated grwoth. Shaking produced a 5-fold or more increase in growth on either glucose or cottonseed oil media. Cholesterol (20 μ/ml further increased growth on glucose meidum in shake culture by at least 100%. Growth was usually better at pH 6.7 than at 5.4 or 7.7. Growth in shake culture on a glucose medium supplemented with cholesterol and α-tocopherol approached that occuring on vegetable oil media.     

Constitutive expression of an inducible lipoxygenase in transgenic tobacco decreases susceptibility to Phytophthora parasitica var. nicotianae

Plant lipoxygenases (LOXs) are key enzymes involved in the generation of fatty acid derivatives, called oxylipins. In tobacco, LOX gene expression and activity are very low in healthy tissues and are highly enhanced in response to infection by Phytophthora parasitica nicotianae and to elicitor treatment. We previously showed, using antisense-LOX1 plants, that expression of the tobacco LOX1 gene is required for the race-cultivar specific resistance of tobacco to Phytophthora parasitica nicotianae. In order to investigate the effect of over-expressing a LOX gene on plant resistance, we transformed tobacco plants with the LOX1 coding sequence fused to the CaMV 35S promoter. Four transgenic lines with enhanced levels of LOX protein and specific activity over control plants were selected for further analysis. These plants were macroscopically indistinguishable from WT plants. Upon stem inoculation, the sense-LOX1 plants displayed a significantly decreased susceptibility to virulent races of Phytophthora parasitica nicotianae, stem lesions being 2- to 3-fold shorter in the transgenic lines than in WT plants. Using a root inoculation assay, the survival rate of sense-LOX1 seedlings was increased about 4-fold compared to their WT counterparts, with 60 to 80% of transgenic plants vs 15 to 20% of WT controls remaining healthy following inoculation with Phytophthora parasitica nicotianae. This is the first demonstration that the over-expression of a LOX gene is sufficient to reduce the susceptibility of a host plant to an oomycete pathogen.     

Retraction of flagella by Phytophthora parasitica var. nicotiana zoospores

Summary Light and electron microscope evidence is presented to show that retraction of flagella may occur in Phytophthora parasitica zoospores during encystment.     

In vitro and in vivo antimicrobial efficacy of essential oils and individual compounds against Phytophthora parasitica var. nicotianae

Aim

To evaluate the antimicrobial effects of essential oils (EOs) from cassia, basil, geranium, lemongrass, cumin and thyme, as well as their major components, against Phytophthora parasitica var. nicotianae; to investigate morphological changes in hyphae and sporangia in response to treatment with cinnamaldehyde; and to further evaluate potential biocontrol capacities against tobacco black shank under greenhouse conditions.

Methods and Results

The results revealed that the extent of mycelial growth inhibition was primarily dependent on the composition and concentration of the EOs and the structure of individual compounds. Cinnamaldehyde had a significantly higher inhibitory effect on mycelial growth, formation of sporangia, and production and germination of zoospores in P. parasitica var. nicotianae in vitro, achieving complete inhibition of these phenotypes at 72, 36, 36 and 18 mg l^?1, respectively. Scanning electron microscopic observations revealed that cinnamaldehyde can cause considerable morphological degenerations of hyphae and sporangia such as cytoplasmic coagulation, shrivelled mycelia and sporangia aggregates and swelling and lysis of mycelia and sporangia walls. In vivo assays with cinnamaldehyde demonstrated that this compound afforded protective effect against tobacco black shank under greenhouse conditions in susceptible tobacco plants.

Conclusions

The results of in vitro and in vivo bioassays, together with SEM imaging of the microstructure of P. parasitica var. nicotianae supported the possibility of using cinnamaldehyde as a potent natural biofungicide in the greenhouse.

Significance and Impact of the Study

This study provides a theoretical basis for the potential use of cinnamaldehyde as commercial agents or lead compounds that can be exploited as commercial biofungicides in the protection of tobacco plants from P. parasitica var. nicotianae infection.     

前体、诱导子及抑制剂对紫杉烷生物合成的促进作用研究

研究了前体、诱导子和抑制剂对中国红豆杉细胞培养生产紫杉烷的促进作用。结果表明,向培养基中加入30mg/L 3-甲基－2－丁烯－1－醇,2mmol/L苯甲酸钠,10mg/L矮壮素,100μmol/L茉莉酸甲酯,0.1mmol/L丝氨酸,可以使紫杉醇含量增加1141.1%;加入0.1mmol/L苯甲酸钠,80μmol/L茉莉酸甲酯,0.1mmol/L丝氨酸可以使2α,5α,10β,14β－四乙酰氧基－紫杉－4（20）,11－二烯含量增加134.6%;25mg/L矮壮素,100μmol/L茉莉酸甲酯,0.5mmol/L丝氨酸可以使1β－羟基巴卡亭I含量增加95.2%;5mg/L3－甲基－2－丁烯－1－醇,10mg/L矮壮纱,40μmol/L茉莉酸甲酯,可以使14β-(2-甲基丁酰氧基）－2α,5α,10β－三乙酰氧基－紫杉－4（20）,11－二烯的含量增加76.4%。     

Effects of Elicitors on the Accumulation of Proteinase Inhibitors in Injured Potato Tubers

The time course of accumulation and the composition of proteinase-inhibiting proteins in diffusates from potato tubers treated with elicitors such as salicylic, jasmonic, and arachidonic acids were studied. The 40-kDa reserve protein patatin and the chymotrypsin inhibitors, among which proteins of 24.6, 22.0, and 16.0 kDa were prevalent, accumulated in diffusates from potato tubers. Jasmonic and arachidonic acids activated the accumulation of the chymotrypsin inhibitors in tubers in response to the injury stress, whereas salicylic acid inhibited this process. The effects of jasmonic and arachidonic acids increased when their concentrations decreased to 10^–6M. Salicylic acid inhibited this process. The data suggest an important role of the lipoxygenase metabolism in signal transduction of the anti-injury defense system in dormant potato tubers.     

Microassay for biological and chemical control of infection of tobacco byPhytophthora parasitica var.nicotianae

We developed a simple, rapid, small-scale assay for infection of tobacco seedlings byPhytophthora parasitica var.nicotianae. One 7-day-old tobacco seedling was placed in each well of a 96-well microtiter plate and inoculated with 500 zoospores ofP. parasitica var.nicotianae. After 72 h all of the inoculated seedlings of the susceptible cultivar, KY14, were infected, and the pathogen had produced sporangia that were visible on the surfaces of the seedlings. Sporangia did not develop on seedlings that were inoculated simultaneously with zoospores and either 1 µg/mL of the chemical fungicide metalaxyl or 5 µL of filtrate of a sporulated culture of the biocontrol agent,Bacillus cereus UW85. Seedlings of tobacco cultivar KY17 were infected byP. parasitica var.nicotianae, although mature plants of this variety are resistant to the pathogen. This microassay may facilitate the rapid screening of potential biological and chemical control agents and may be useful for studying mechanisms of infection and control ofPhytophthora spp. under hydroponic conditions.     

Early season root production and zoospore infection of cultivars of flue-cured tobacco that differ in level of partial resistance to Phytophthora parasitica var. nicotianae

Root production of four cultivars of flue-cured tobacco was quantified in the field, greenhouse and phytotron. The cultivars ranged in level of partial resistance to the black shank pathogen, Phytophthora parasitica var. nicotianae, from susceptible to highly resistant. In the field, root-observation plates were installed approximately 10 cm from plants, and in greenhouse and phytotron studies, plants were grown in 4-liter containers with one sloping transparent side for root observation. Root growth was determined weekly for four weeks after transplanting in the field and daily up to 14 days after transplanting in the greenhouse and phytotron. Root tracings were made on acetate sheets placed against the sloping transparent side of the containers or against the transparent observation plates in the field following removal of soil from the outside of the observation plate. Root growth was quantified by retracing the root pattern on the acetate sheets over a digitizing tablet attached to a personal computer. Numbers of roots, root length, and mean and maximum rate of root growth were determined. Cultivars Hicks (susceptible) and K-326 (low level of resistance) had significantly larger root systems than moderately resistant G-28 or highly resistant NC 82. Differences in total root length were due to increased branching that resulted in development of significantly greater numbers of roots in Hicks and K-326. For example, between day 21 and 28, Hicks produced more than three times the number of new roots as NC 82 in the field. The mean rate of root extension observed (2.17 mm hr^–1) was similar in all four cultivars. Infection efficiency on the different cultivars was determined in the field by inoculating roots with zoospores of P. p. nicotianae. Lesions were visible as water soaked areas within 24 hr of inoculation. At 48 hr after inoculation, percentages of inoculations that resulted in lesion formation were 57, 46, 23, and 16% for Hicks, K-326, G-28 and NC 82, respectively. The possible role of rooting intensity as a mechanism of avoidance to P. p. nicotianae in tobacco cultivars is discussed.     

Colonisation patterns of root tissues byPhytophthora nicotianae var.parasitica related to reduced disease in mycorrhizal tomato

Tomato plants pre-colonised by the arbuscular mycorrhizal fungusGlomus mosseae showed decreased root damage by the pathogenPhytophthora nicotianae var.parasitica. In analyses of the cellular bases of their bioprotective effect, a prerequisite for cytological investigations of tissue interactions betweenG. mosseae andP. nicotianae v.parasitica was to discriminate between the hyphae of the two fungi within root tissues. We report the use of antibodies as useful tools, in the absence of an appropriate stain for distinguishing hyphae ofP. nicotianae v.parasitica from those ofG. mosseae inside roots, and present observations on the colonisation patterns by the pathogenic fungus alone or during interactions in mycorrhizal roots. Infection intensity of the pathogen, estimated using an immunoenzyme labelling technique on whole root fragments, was lower in mycorrhizal roots. Immunogold labelling ofP. nicotianae v.parasitica on cross-sections of infected tomato roots showed that inter or intracellular hyphae developed mainly in the cortex, and their presence induced necrosis of host cells, the wall and contents of which showed a strong autofluorescence in reaction to the pathogen. In dual fungal infections of tomato root systems, hyphae of the symbiont and the pathogen were in most cases in different root regions, but they could also be observed in the same root tissues. The number ofP. nicotianae v.parasitica hyphae growing in the root cortex was greatly reduced in mycorrhizal root systems, and in mycorrhizal tissues infected by the pathogen, arbuscule-containing cells surrounded by intercellularP. nicotianae v.parasitica hyphae did not necrose and only a weak autofluorescence was associated with the host cells. Results are discussed in relation to possible processes involved in the phenomenon of bioprotection in arbuscular mycorrhizal plants.     

Protein Kinase Inhibitors Inhibit Stimulation of Inositol Phospholipid Turnover and Induction of Phenylalanine Ammonia-Lyase in Fungal Elicitor-Treated Tobacco Suspension Culture Cells

Elicitor prepared from Phytophthora nicotianae stimulated inositolphospholipid turnover and induced phenylalanine ammonia-lyaseactivity in tobacco suspension culture cells [Kamada and Muto(1994) Plant Cell Physiol. 35: 397]. Protein kinase inhibitors,K252a and staurosporine inhibited both responses. These resultssuggest that inositol phospholipid turnover plays an importantrole in PAL induction through protein kinases. In addition,their mode of inhibition were different, proposing that severaltypes of protein kinases are involved in these elicitor-inducedresponses. ¹Present address: The Johns Hopkins University School of Hygieneand Public Health, 615 N. Wolfe St., Baltimore, Maryland 21205,U.S.A. ²Present address: Nagoya University BioScience Center and GraduateSchool of Agricultural Sciences, Nagoya University, Chikusa-ku,Nagoya, 464-01 Japan.     

Comparison of Suppressiveness of Vermicomposts Produced from Animal Manures and Sewage Sludge against Phytophthora nicotianae Breda de Haan var. nicotianae

The degrees of suppression produced by vermicomposts produced from cattle manure, sheep manure or horse manure and by vermicomposts produced from sewage sludge were compared in greenhouse experiments. The effect of these vermicomposts on the growth and infection of tomato seedlings by Phytophthora nicotianae var. nicotianae was studied. The density of the pathogen and the number of micro-organisms in container media amended with vermicomposts were also analysed. The vermicomposts produced from animal manure significantly reduced the infection of tomato seedlings by the pathogen. The density of P. nicotianae in media which included these vermicomposts was similar to that in infested peat substrate (control treatment). The vermicomposts from sewage sludge did not protect tomato seedlings against P. nicotianae . They also significantly inhibited growth of the plants as well as decreasing the density of the pathogen in container media. In general the vermicomposts had no effect on total number of micro-organisms in potting media compared with control. They only had higher levels of actinomycetes but this did not appear to correspond with their ability to suppress the pathogen.