Effects of temperature on germination of sporangia,infection and protein secretion by Phytophthora kernoviae

Phytophthora kernoviae is a pathogen on a wide range of plants, but little is known of optimal infection conditions. Rhododendron ponticum leaves were inoculated with six different isolates of P. kernoviae sporangia and incubated at different temperatures from 10 to 28 °C. After 1 week, lesion development and pathogen recovery were only observed from all isolates at 15 and 20 °C and a few isolates at 10 °C. In an experiment with temperatures ranging from 20 to 25 °C, lesion development and pathogen recovery on R. ponticum, Magnolia stellata and Viburnum tinus occurred consistently at 20 and 21 °C, was limited at 22 °C, and did not occur at 23 °C and above. There was no difference in sporangia and zoospore germination at 20–25 °C. In a temperature fluctuation experiment, the necrotic area of inoculated R. ponticum leaves increased with longer incubation at 20 °C and decreased with longer incubation at 24 °C. Crude extracts of secreted proteins from P. kernoviae cultures grown at 20 and 24 °C were compared to determine any effects of temperature on pathogenicity. When spot tested on R. ponticum leaves, crude protein suspensions from cultures grown at 20 °C induced necrosis, while proteins from cultures grown at 24 °C did not. Proteomic analysis confirmed that a 10 kDa protein secreted at both 20 and 24 °C shared sequence homology to the conserved domains of known elicitins of other Phytophthora spp. The protein secreted at 20 °C that was responsible for necrosis has not been identified.     

Development of detection systems for the sporangia of <Emphasis Type="Italic">Peronospora destructor</Emphasis>

A monoclonal antibody that recognises components of the wall of sporangia of Peronospora destructor was raised. Tests using spores of higher fungi and other species of mildew demonstrated the specificity of the monoclonal. The antibody was used to develop lateral flow devices for sporangia of P. destructor. A competitive lateral flow format was developed which could detect onion downy mildew sporangia. Five-microliter gold anti-mouse IgM solution pre-mixed with 10 μl of P. destructor monoclonal antibody (EMA 242) proved the optimal concentration for detection of sporangia of P. destructor when applied to sample pads of lateral flow devices. Limits of approximately 500 sporangia of P. destructor could be detected by the absence of a test line on the lateral flow device within test samples. Using a scanning densitometer improved the sensitivity of detection. Further development and validation of the test is required if it is to be used for risk assessments of onion downy mildew in the field.     

Suppressed germination and early death of Phytophthora infestans sporangia caused by pectin, inorganic phosphate, ion chelators and calcium-modulating treatments

In laboratory experiments, chemical treatments were applied to sporangia of Phytophthora infestans incubated at 12 °C, conducive to cytoplasmic cleavage and release of zoospores (indirect germination), and at 20 °C, conducive to germination by hyphal outgrowth (direct germination). Both types of germination were suppressed by applying increasing concentrations (1–5 mM) of CaCl₂ or MgCl₂, or by low concentrations of pectin, inorganic phosphate, chelators (EGTA, BAPTA), calcium channel-blockers (lanthanum, gadolinium, verapamil) or compounds that interfere with intracellular calcium-mediated processes (trifluoperazine, caffeine). The suppression by some treatments was partly overcome by adding Ca²⁺ or Mg²⁺ in the early stages of incubation, but Ca²⁺ was usually more effective than Mg²⁺, and suppression at 20 °C was more easily overcome than at 12 °C. Pectin (0.1%) or BAPTA (5 mM) caused rapid death of sporangia at both 12 ° and 20 °, whereas EGTA (5 mM) or Na₂HPO₄ (5 mM) caused rapid death only at 12 °. The findings indicate that germinability and viability of P. infestans sporangia are strongly affected by the external availability of Ca²⁺ or other divalent cations, especially during zoosporogenesis.     

Inhibition of seed germination and early stem elongation of Cuscuta australis by ethofumesate

Hmergence of dodder (Cuseuta australis R. Br.) was unexpecledly prevented in plois of a sugarbeet field where ethofumesate had been applied at 1.6 Kg/ha. Appropriate laboratory tesls have shown that ethofumesate is a potent inhibitor of dodder seed germination (I D₅₀= 10 μg/ml) and of early stem elongalion (ID₅₀= 73μg/ ml). Wheat. a standard susceptible species to field applications of ethofumesate, is equally susceptible to inhibition of stem elongation (ID₅₀=68 μg/ml), but it is far less susceptible to inhibition of germination (I D₅₀=188 μg/ml). Compared to propyzamide. ethofiimesate is a stronger inhibitor of germination. Metolachlor and Hercules 22234 [eihyl N-chloroacetyl-N-(2,6-diethylphenyl) aminoacetate] are also active in inhibiting dodder germination and stem elongation, but at higher concentrations than ethofumesate. Current methods of controlling dodder in sugarheets may be improved with inclusion of pre-emergence use of ethofumesate.     

Inhibition by aluminum of mycelial growth and of sporangial production and germination inPhytophthora infestans

Mycelial growth on clarified V8 agar of the potato late blight pathogenPhytophthora infestans was inhibited when either aluminum chloride (AlCl₃, 6 H₂O) or aluminum sulfate (Al₂(SO₄)₃, 18 H₂O) was added to the culture medium at concentrations of 2.5–100 mg.l^–1 Al³⁺. Toxicity of Al³⁺ varied among the fiveP. infestans isolates tested, but toxicity of sulfate and chloride salts was similar for a given isolate. Overall sporangial production was affected in all five isolates by both Al³⁺ forms. Al³⁺ also decreased sporangial germination at concentrations equal to or greater than 10 mg.l^–1 in two isolates. These data support the hypothesis of aluminum toxicity as a major factor in soil suppressiveness toP. infestans.     

3种外来入侵植物提取液对3种病原真菌孢子萌发的抑制作用初探

以三裂叶蟛蜞菊(Wedelia trilobata)、水葫芦(Eichhornia crassipes)和薇甘菊(Mikania micrantha)3种常见外来入侵物种为试验材料,研究了其水提取液对黄瓜枯萎病病菌(Fusarium wilt)、黄瓜灰霉病病菌(Botrytis cinerea)和番茄早疫病病菌(Alternaria solani)3种病原真菌孢子萌发的抑制作用。结果表明,3种外来入侵植物提取液均对3种病原菌孢子萌发都有抑制作用。其中,番茄早疫病病菌孢子萌发的抑制作用随3种入侵植物提取液浓度的升高逐渐升高;黄瓜灰霉病病菌孢子萌发的抑制作用随三裂叶蟛蜞菊和薇甘菊提取液浓度的升高也逐渐升高,但却随水葫芦提取液浓度的升高逐渐降低;而黄瓜枯萎病病菌孢子萌发的抑制作用并未随3种入侵植物提取液浓度的升高而呈规律性变化。水葫芦提取液对3种供试病原菌的孢子萌发抑制作用较三裂叶蟛蜞菊和薇甘菊要强,其提取液浓度为0.10 g/m L时对黄瓜枯萎病病菌和番茄早疫病病菌孢子萌发的抑制作用最高,其抑制率分别为83.80%和88.51%。     

Inhibition of seed germination and seedling growth by hound's-tongue (Cynoglossum officinale L.) seed leachate

The leaching of phenolics from decoated seeds, seed coats and pericarps of hound's-tongue ( Cynoglossum officinale L.), factors affecting leaching, and seed germination and seedling growth inhibitory activities of the leachate were investigated. Embryonic axes and cotyledons contained a large amount of methanol-soluble phenolic substances. Decoated seeds released phenolics into an aqueous incubation medium and this solution was capable of inhibiting root elongation of several grassy and broadleaf species, but not of hound's-tongue. The leachate and the phenolic fraction of the leachate inhibited germination of bluebunch wheatgrass ( Pseudoroegnaria spicata (Pursh) A. Löve [syn. Agropyron spicatum (Pursh) Scribn. and J. G. Sm.]). The non-phenolic fraction of the leachate did not inhibit seed germination or root and shoot elongation of bluebunch wheatgrass. Low oxygen and an increasing temperature significantly increased the amount of phenolic substances leached from decoated seeds. Increased leaching of phenolic substances related to an increasing temperature was associated with the loss of seed viability. Further investigation of the role of water-extractable hound's-tongue seed phenolics in the interaction of this species with its biotic environment under field conditions is needed to determine the ecological significance of these findings.     

Management of downy mildew of sweet basil (Ocimum basilicum) caused by Peronospora belbahrii by means of resistance inducers, fungicides, biocontrol agents and natural products

To control downy mildew of sweet basil (Ocimum basilicum L.), incited by Peronospora belbahrii Thines, a number of compounds were tested in 2011 and 2012 under glasshouse conditions. These included copper-based fungicides, biocontrol agents, and compounds previously reported to induce resistance in plants to pathogens. Results were compared with those provided by fungicides registered for downy mildew control in Italy. The tested compounds were used alone or applied in rotation in spray programs. In all trials, the greatest reduction in disease incidence and severity was found with treatments that included metalaxyl-M?+?copper hydroxide, a mineral fertilizer ‘Alexin’, mandipropanid, and azoxystrobin. The glucohumates activator complex and acibenzolar-S-methyl also provided significant disease control (P?<?0.05). The mineral fertilizer Alexin, the glucohumates activator complex and acibenzolar-S significantly reduced disease incidence and severity 20 days after the last treatment compared with the untreated control (P?<?0.05). Among the copper-based products, the greatest reductions in disease incidence and severity were provided by copper hydroxide with terpenic alcohols and copper oxychloride?+?copper hydroxide. The mineral fertilizer Kendal and prohexadione-Ca, as well as mustard oil, partially reduced disease incidence and severity compared with the untreated control (P?<?0.05), whereas the biocontrol agent Bacillus subtilis QST 713 and thyme oil extract were not effective in two out of three trials. When different combinations of various products used in rotation were tested, effective control was found either using a rotation of fungicides with compounds that can induce resistance, as well as by using rotation with different resistance-inducing compounds on their own.     

Selection for metalaxyl resistance in potato crops infected with Phytophthora infestans: effects of fungicides and initial frequency of resistant sporangia

Potato crops (cv. Alpha) were grown in walk-in plastic tunnels (33 m²) in winter 1987 and spring 1988. Crops were left untreated or treated (four sprays at intervals of 2 weeks) with either metalaxyl, Ridomil-MZ (metalaxyl+ mancozeb) or Ridocym (metalaxyl +mancozeb+cymoxanil). Crops were inoculated with sporangial suspensions of Phytophthora infestans containing 01, 1 or 10% metalaxyl-resistant sporangia. Disease progress and percentage resistant sporangia in tunnels were estimated for a period of 50 days. In the treated crops cumulative disease, rate of disease progress and increase in frequency of resistant phenotypes (selection coefficient) were higher in metalaxyl-treated crops than in Ridomil-MZ or Ridocym-treated crops. Cumulative disease, rate of disease progress and increase in frequency of resistant phenotypes were unaffected by the frequency of resistant sporangia in the original inoculum. Metalaxyl, Ridomil-MZ and Ridocym speeded up the selection for resistance by 92, 29 and 17%, respectively, relative to untreated crops. The time interval required for the resistant subpopulation to predominate in treated crops was inversely related to initial resistance. It was longest in crops inoculated with 0.1 % resistant sporangia and treated with Ridocym. Results indicated that metalaxyl mixtures were advantageous over metalaxyl alone, both in delaying the buildup of resistance and in improving disease control, but did not prevent resistant subpopulations increasing from 01 to 100% in a single season.     

菊花霜霉病发生特点及防治措施初步研究

菊花霜霉病是20世纪80年代,在皖南山区贡菊花上新发现的1种病害。该病具有发生面积大、发病快,为害严重的特点。每年春、秋两季发生严重。春季发病在雨水多的条件下,幼苗枯死,造成大面积缺苗;秋季现蕾前发病,叶片、花蕾、嫩茎可因病枯死,对产量影响较大。1症状病菌为害菊花叶片     

一种测定大白菜霜霉病菌对甲霜灵敏感性方法的建立及应用

建立了一种新方法—离体子叶浸泡法并用于大白菜霜霉病菌对甲霜灵敏感性的检测。离体子叶在含有0.005%吐温20和0.1%丙酮的甲霜灵中浸泡3h后,接种浓度为1×104孢子囊/mL的大白菜霜霉病菌孢子囊悬浮液,保湿培养6d后观察子叶发病状况。采用离体子叶浸泡法测定了50株大白菜霜霉病菌对甲霜灵的敏感性,结果显示部分大白菜霜霉病菌菌株对甲霜灵的敏感性降低,有抗药性亚群体出现。研究表明离体子叶浸泡法重复性好,具有较高的敏感性和精密度,符合生产实际,适用于大白菜霜霉病菌对杀菌剂的敏感性检测。     

Achene germination of Parthenium hysterophorus L.: effects of light, temperature, provenance and achene size

Ray achenes of Parthenium hysterophorus L. from widely separated localities showed a positive relationship between length and weight, and those from northern India (higher latitude) were heavier than those from the south (lower latitude). The achenes germinated well in continuous light and in the dark, but maximum germination was obtained with a 10-h photoperiod. Increasing duration of light pretreatment from 6 to 48 h resulted in greater subsequent germination in the dark. The achenes germinated over a wide range of alternating temperature regimes, but achieved maximum percentage germination at 25–30°C/15–20°C. Despite significant quantitative variation, the overall germination behaviour of achenes of different sizes was similar, although large achenes always gave higher germination than small ones. Germination was significantly influenced by seed source. The north Indian populations showed higher percentage germination than those from south India. The patterns of response of achenes of different provenances to light and alternating diurnal temperatures were slightly different. Germination des akènes de Parthenium hysterophorus L.: effets de lu lumière, température et de la taille et origine des akènes Des akènes de Parthénium hysterophorus L. issus de localités très largement éloignées ont montré une corrélation positive entre la longueur et le poids; ceux du nord de l'Inde (latitude plus élevée) étaient plus lourds que ceux du sud (latitude plus basse). Les akènes ont bien germés tant en lumière continue, qu'à l'obscurité, mais le maximum de germination a été observé sous une photopériode de 10 heures. Une augmentation d'une préexposition à la lumière de 6 h à 48 h aboutit ensuite à une plus grande germination à l'obscurité. Les akènes ont germé sur un très large éventail de régimes de températures alternées mais on a obtenu le maximum de pourcentage de germination à 25–30°C/15–20°C. En dépit de variations quantitatives significatives, le comportement général de germination des akènes de tailles différentes a été comparable, même si les grands akènes germent toujours mieux que les petits. La germination est influencée de façon significative par la provenance de la graine. Les populations du nord de l'Inde expriment un pourcentage de germination plus élevé que celles du sud. Les comportements de réponse des akènes de différentes provenances à la lumière, et aux températures diurnes ont été légèrement différentes. Keimung der Achänen von Parthenium hysterophorus L.: Wirkung von Licht, Temperatur und Herkunft sowie Grösse der Achänen Die Achänen von Parthenium hysterophorus L. von weit voneinander liegenden Orten zeigten ein positives Längen-Gewicht-Verhältnis, wobei sie in Nordindien schwerer waren als im Süden. Die Achänen keimten im Dauerlicht und im Dunkeln gut, aber bei 10stündiger Lichtperiode am besten. Wenn sie zunächst einer von 6 bis auf 48 h gesteigerten Licht-Behandlung unterworfen wurden, keimten sie im Dunkeln besser. Die Achänen keimten über eine weite Spanne wechselnder Temperatur; die maximale Keimrate wurde bei 25–30/15–20°C gefunden. Trotz signifikanter Unterschiede war die Keimung verschieden grosser Achänen im grossen und ganzen ähnlich, wenn auch die grossen immer stärker als die kleinen keimten. Die Keimung war signifikant von der Herkunft beeinflusst: Die Achänen aus Nordindien hatten eine grössere Keimrate als die aus dem Süden. Das Verhalten der Achänen verschiedener Herkunft gegenüber Licht und wechselnder Tagestemperatur war wenig unterschiedlich.     

拮抗性链霉菌对大丽轮枝菌微菌核形成与萌发的影响

为探索拮抗性链霉菌对棉花黄萎病病原大丽轮枝菌Verticillium dahliae Kleb.的抑菌机制,采用菌丝生长速率法、微菌核萌发法研究了6株拮抗链霉菌无菌发酵滤液对大丽轮枝菌生长、微菌核形成与萌发的影响。链霉菌无菌发酵滤液对大丽轮枝菌菌落生长、菌核形成和微菌核萌发有明显抑制作用。其中菌株B49的抑菌效果最好,5倍稀释发酵液培养14天时对菌落生长的抑菌率达69.7%;菌株B49、D184和Act12的5倍稀释发酵液对微菌核形成的抑制率达100%;将经B49、D184和Act12发酵液处理后丧失形成微菌核能力的大丽轮枝菌菌株转接至不含发酵液的PDA培养基,连续传代至第5代,其仍然不能恢复形成微菌核的能力;微菌核在含有菌株D184 5倍稀释发酵液的培养基上培养168 h时,萌发率仅为38.3%。     

两株嗜铁细菌对几种病原菌的抑制作用及对小麦种子萌发的影响

采用滤纸片法测定嗜铁菌C-12、C-13对4种病原菌的抑制作用。结果表明,嗜铁菌C-12、C-13菌悬液对小麦赤霉病菌、水稻纹枯病菌、蒜薹炭疽病菌和小麦根腐病菌生长均具有不同程度的抑制作用,达到最大抑制率的时间长短各不相同。其中C-12对水稻纹枯病菌最大抑制率为36.7%,C-13对小麦赤霉病菌最大抑制率为34.6%。嗜铁菌C-12、C-13对小麦种子发芽率和胚芽长度无明显的影响,而对胚根生长有显著促进作用,两株菌株间差异显著。     

Spatiotemporal variation in airborne sporangia of Phytophthora infestans: characterization and initiatives towards improving potato late blight risk estimation

This study investigated the value of using real‐time monitoring of Phytophthora infestans airborne inoculum as a complement to decision support systems (DSS). The experiment was conducted during the 2010, 2011 and 2012 potato production seasons in two locations in New Brunswick, Canada. Airborne sporangia concentrations (ASC) of P. infestans were monitored using 16 rotating‐arm spore samplers placed 3 m above the ground. The first cases of late blight (2010 and 2011) were detected 6–7 days after the first ASC peak, and all samplers captured their first sporangia within the same week (at 3‐ and 9‐day periods). The cumulative ASC curve and the risk curves from two DSS (PLANT‐Plus and Pameseb Late Blight) had the same shape but different magnitudes. In both locations, the negative binomial distribution fitted the data better than the Poisson distribution, which is indicative of heterogeneity, and based on Taylor's power law, the heterogeneity increased with increasing ASC. Therefore, the present results suggest that spore‐sampling network devices may be a suitable approach for early detection of incoming inoculum and, when combined with DSS, represent a potential aid for targeting the optimal time to apply a disease‐control product. In this context, cumulative ASC can be a counterweight to the DSS risk estimate: a high risk combined with significant ASC will trigger fungicide spraying. Moreover, spore sampling can be used to assess the efficiency of management strategies by means of examining the area under the inoculum progress curve.     

Inhibitory effects of aqueous extracts of black mustard on germination and growth of alfalfa

The present study investigated the allelopathic effects of various black mustard ( Brassica nigra L.) plant parts on alfalfa germination and seedling growth. Aqueous extracts of black mustard ( Brassica nigra L.) leaf, stem, flower and root plant parts were made to determine their effects on germination and dry weights of hypocotyl, and radicle length of 5-day-old alfalfa seedlings over a range of extract concentrations. All aqueous extracts significantly inhibited alfalfa seed germination and seedling growth when compared with the distilled water control. Increasing the aqueous extract concentrations of separated Brassica nigra plant parts significantly inhibited alfalfa germination, seedling length and weight. Based on significant radicle length reactions to aqueous extracts, the toxicity may be classified in the following order of decreasing inhibition: flower, leaf, mixture of all plant parts, root, and stem. Increasing the concentration of aqueous flower extracts significantly inhibited the water uptake by germinated alfalfa seeds. The greatest inhibition in water uptake occurred at a 12 g kg⁻¹ extract concentration for seeds soaked for 8 h.