Effects of temperature onPhytophthora porri in vitro,in planta,and in soil

Cardinal temperatures for mycelial growth ofPhytophthora porri on corn-meal agar were <5 (minimum), 15–20 (optimum) and just above 25 °C (maximum). The number of infections after zoospore inoculation of young leaf plants was relatively low at supra-optimal temperatures, but was not affected by sub-optimal temperatures. Even at 0 °C plants were infected. The incubation periods needed for symptom formation were 36–57 d at 0 °C, 13–18 d at 5 °C, and 4–11 d at > 11 °C, and were fitted to temperature between 0 and 24 °C with a hyperbolical model (1/p=0.00812^*T+0.0243). Oospore germination, reported for the first time forP. porri, was strongly reduced after 5 h at 45 °C, and totally absent after 5 h at 55 °C. Soil solarization for six weeks during an exceptionally warm period in May–June 1992 in The Netherlands raised the soil temperature at 5 cm depth for 17 h above 45 °C, but did not reduce the initial level of disease in August significantly.     

On the specificity of the in vitro and in vivo antifungal activity of benomyl

With respect to sensitivity to benomyl in vitro four categories of fungi were distinguished; taxonomically related fungi usually proved to belong to the same category. Within the form-class Deuteromycetes a correlation appeared to exist between sensitivity to this fungicide and morphogenesis of conidia.Phoma betae, in contrast to all otherPhoma spp., was shown to be highly resistant to benomyl. This, however, may be expected on account of its perfect state. The data on the in vitro antifungal activity of benomyl conformed to those on the effectiveness of benomyl against plant diseases.     

Imidazolinone inhibition of acetohydroxyacid synthase in vitro and in vivo

Imidazolinone herbicides inhibit the first enzyme of branched-chain amino acid biosynthesis, acetohydroxyacid synthase. The inhibition of the enzyme in vitro by these herbicides increases with incubation time, but is not irreversible, as deduced by reaction progress curves. In contrast to this result is the apparent irreversible inhibition of the enzyme by these imidazolinones that occurs when the herbicide is applied to intact corn plants. Plants treated with imidazolinone herbicide and then extracted showed dramatically reduced enzyme activity. This effect on extractable enzyme level occurred with several different imidazolinone herbicides in either foliar or soil application. The decrease in extractable enzyme activity could be observed within four hours after treatment. Herbicides other than imidazolinones did not reduce the extractable enzyme level. These findings suggest that the enzyme- imidazolinone interaction in vivo may be different from the interaction observed in vitro.     

In vitro and in vivo analyses of the mechanism of action of SWEP

In vitro experiments with intact chloroplasts from hydroponically grown spinach (Spinacia oleracea L. var. Winter Giant) plants, have shown an I₅₀ value for SWEP (methyl N-3,4-dichlorophenyl) carbamate) of 0.1 μM in PS I and II-linked electron transport H₂0 → NADP⁺. With thylakoid membranes the I₅₀ values for PS II-linked Hill reactions H₂O → [Fe(CN)₆]³⁻ and H₂O → dichlorophenolindophenol are in the range 0.05-0.1 μM, whereas the I₅₀ shifts to 0.45 μM in short PS II-linked transport chain diphenylcarbazide → dichlorophenolindophenol. Trypsination of PS II-enriched particles produces a negligible increase of the I₅₀ value in diphenylcarbazide → dichlorophenolindophenol electron transport, a much smaller increase than occurs with diuron- or atrazine-type inhibitors. All these data show SWEP as a strong inhibitor of electron transport in the Q-B region of the PS II-reducing side. However, it appears to have a different binding site than that of urea and triazine herbicides, either on a trypsin resistant or on a non-surface cluster. As a consequence of the NADPH shortage, SWEP brings about a strong inhibition of CO₂ assimilation, with an I₅₀ of 0.04 μM, and a lower percentage of trioses-P among the intermediates of the Calvin cycle. In vivo experiments have shown a three to five times higher inhibition of PS II-linked electron transport, when SWEP was supplied through the roots than when it was applied to the leaves. We have found I₅₀ values of CO₂ assimilation by isolated chloroplasts of foliar disks of 3 and 5 μM, respectively, when the herbicide was root supplied, as opposed to 10 and 25 μM after leaf application.     

Fungicide seed treatment efficacy against Microdochium nivale and M. majus in vitro and in vivo

BACKGROUND: Seed-borne Microdochium majus (Wollenweber) and M. nivale Fries are the primary pathogens responsible for Fusarium seedling blight in the UK. The two species show differences in pathogenicity, host preference and sensitivities to temperature, but their relative sensitivities to fungicide seed treatments are unknown. The aim was firstly to determine the efficacy of fungicide seed treatments towards single-spore isolates of M. majus and M. nivale using in vitro experiments, and subsequently to determine efficacy in vivo over a range of temperatures. RESULTS: Differences in EC(50) values between all seed treatments were evident from the in vitro experiments and ranged from 0.028 mg L(-1) for fludioxonil to 22.8 mg L(-1) for carboxin + thiram. The two seed treatments that showed best performance in vitro were used to examine efficacy towards seed-borne infection in vivo at 4, 8, 12 and 16 degrees C. Generally, seedling emergence improved and the severity of stem-base disease symptoms on emerged seedlings was reduced for both species through the use of the fungicides. The combination of fludioxonil + difenconazole showed improved performance compared with fludioxonil alone. Significantly less severe symptoms were observed through the use of fludioxonil and fludioxonil + difenconazole compared with bitertanol + fuberidazole at 12 degrees C and for all except one M. nivale infected seed lot at 8 degrees C. CONCLUSIONS: Differences in fungicide sensitivity between the two species in vitro were not evident in vivo. This is the first report of the effect of fungicide seed treatments on the control of seedling blight caused by M. majus and M. nivale.     

温度和湿度对南方根结线虫存活的影响

在实验室条件下,测试了不同温度处理对离体南方根结线虫存活的影响,结果表明,在25、30、35℃和40℃下,杀死90%以上离体南方根结线虫分别需要30d(100%)、26d(96.6%)、24d(94.1%)和9d(99.6%),而45、50℃下则需要15min和2.3min。同时测试了不同温湿度处理对土壤中南方根结线虫存活的影响,结果表明,25、30℃是土壤中根结线虫的适宜温度,当土壤含水量为14%时,40d死亡率分别为91.1%、90.4%;35℃线虫处于抑制状态,40d死亡率为85.3%;而线虫对40℃以上的高温敏感,随着处理温度升高,杀死线虫所需时间缩短。根结线虫在不同温湿度下的死亡情况不同,土壤温度为25～35℃,土壤含水量为6%是线虫的适宜湿度;土壤温度达到40℃且含水量为6%和14%时,杀死100%根结线虫仅需4d,不利于其存活;而50℃的高温和含水量达18%的高湿更不利于其存活。     

温度对益蝽生长发育的影响

为明确温度对益蝽生长发育和繁殖的影响, 在室内设置18?20?22?25℃和28℃温度条件, 开展了以草地贪夜蛾为食物的益蝽若虫存活率?发育历期以及成虫寿命的研究?结果表明:在18~28℃范围内, 益蝽若虫在25℃条件下存活率最高(92.20%), 生长速度最快, 18℃下存活率最低(49.60%)?28℃条件下, 卵发育历期为5.5 d, 而18℃条件下, 卵发育历期为15.5 d?18℃条件下, 益蝽从卵发育至成虫需要85.0 d, 而在28℃条件下, 益蝽卵发育至成虫只需要29.8 d?22~28℃为益蝽适生温区, 在18~28℃条件下, 益蝽发育速率随着温度的升高而加快, 各虫态的发育历期?成虫寿命均随温度的升高而缩短?在18~28℃内, 益蝽各个虫态的发育速率与温度符合线性函数模型?益蝽卵?成虫的发育起点温度分别为14.20℃和13.13℃, 有效积温分别为74.90日·度和427.57日·度?在18?20?22?25?28℃条件下, 雄虫和雌虫的寿命分别为10.0 d和12.8 d?27.2 d和31.8 d?41.8 d和56.8 d?35.2 d和50.0 d?28.8 d和31.8 d?其中在22℃条件下, 雄虫和雌虫寿命最长, 分别为41.8 d和56.8 d?该研究结果为益蝽的生长发育和群体饲养提供了科学依据?     

温度对阿维菌素(Avermectin)杀螨活性的影响

研究了不同恒温条件下阿维菌素(Avermectin)对朱砂叶螨[Tetranychus cinnabarinus(Boisduval)]和二斑叶螨(T.urticae Koch)的致死作用,拟合了阿维菌素对两种叶螨的毒力与温度之间的关系。结果表明:阿维菌素分别在16、21、26、31℃和36℃的恒温条件下,对两种叶螨的毒力与温度呈正相关关系,即温度越高毒力越强;朱砂叶螨对阿维菌素的敏感性高于二斑叶螨。     

温度对美洲斑潜蝇生长发育的影响

经测定明确,美洲斑潜蝇卵的发育起点为（８.５４±１.６６）℃,有效积温为（６２.４０±５.７９）日度;幼虫的发育起点为（８.０２±２.９９）℃,有效积温为（７２.２１±１１.８９）日度;蛹的发育起点为（１０.５１±１.３７）℃,有效积温为（１４１.２０±１４.１１）日度;卵至蛹的发育起点为（９.７８±１.０５）℃,有效积温为（２７０.７４±１９.７７）日度;成虫羽化适宜温度为２０～３０℃。     

Effects of temperature and leaf wetness on Pyrenophora teres growing on barley cv. Sonja

Conidia of Pyrenophora teres germinated only in the presence of liquid water and at temperatures above 2°C. The speed with which germination occurred was inversely proportional to temperature measured from a base of 2°C, up to the maximum temperature tested of 21°C. Once conidia on leaves had been wetted, about 40% of all infections that would eventually occur were established within 100°C-hours. Subsequent lesion extension was rapid, with area doubling times of about 1 day between 10 and 20°C.
If conidia germinated, up to 80% formed successful infections on young, susceptible leaves. On older leaves fewer spores germinated and the proportion that then infected was smaller.
The latent period, defined as the time before which sporulation did not occur under any wetness conditions, ranged from about 25 days at 5°C to 11 days at 20°C under dry conditions. Under continuously wet conditions it was about 20% shorter at all temperatures. Its inverse had a curvilinear relation to temperature.
Spores were produced after one to several days of humidity above 95%. The precise period decreased with increasing temperature, but at 25°C spores never appeared. The drier a dead leaf was, the longer the pathogen in it look to produce spores.     

In vitro antimicrobial and in vivo antioomycete activities of the novel antibiotic thiobutacin

BACKGROUND: A number of synthetic fungicides are not effective when confronted by oomycete pathogens because many fungicide targets are absent from oomycetes. Moreover, resistance to fungicides has already arisen in oomycete species, and thus development of new, effective and safe compounds for use in oomycete disease control is necessary.RESULTS: Zoospore lysis began at 10 microg mL(-1) of thiobutacin, and most of the zoospores were collapsed at 50 microg mL(-1). Thiobutacin also revealed inhibitory activity against the cyst germination and hyphal growth of Phytophthora capsici at 50 microg mL(-1). Treatment with thiobutacin exhibited protective activity against development of Phytophthora disease on pepper plants.CONCLUSION: The authors verified in vitro antioomycete activity of thiobutacin against P. capsici and its control efficacy against Phytophthora blight in vivo. This is the first report to demonstrate in vivo antioomycete activity of the novel antibiotic thiobutacin against P. capsici infection.     

Plant-pathogen interactions of sunflower and Macrophomina phaseolina in vitro and in vivo

The relative pathogenicity of isolates of Macrophomina phaseolina was comparable both on sunflower tissue cultures and on mature plants and seedlings. The relative susceptibility of the different sunflower lines in vitro showed a similar pattern for cotyledon callus cultures, but not for immature embryo cultures. Although these protocols appear to be unsuitable for the selection of novel disease resistance, they do offer the potential for a rapid, non-destructive screen for resistant material.     

小麦白粉病与温度的定量关系研究

温度对小麦白粉病影响试验的结果表明,此病害适宜发生的温度为15～20℃,低于10℃或高于25℃对该病有明显抑制作用。当温度高于26℃时,试验显示随着温度的升高,终止小麦白粉病病程的时间缩短,据此建立了不同温度(x)与相应终止病程的时间(y)的关系模型为y=21 900e^{-0.303 5x}(χ²=1.65<χ²_0.05,7=14.07)。同时,根据高温区病害的严重度(y)与温度(x)的试验数据,建立了其关系模型为:y=-3.00x+76.60(r²=0.922 1^**),由此计算获得了连续10 d(一个病程时间)温度为25.53℃即可终止此病害的病程。该试验结果将为小麦白粉病的越夏区划提供基础数据。     

Antimicrosporidial activity of (fluoro)quinolones in vitro and in vivo

Microsporidia are a cause of emerging and opportunistic infections in humans and animals. Although two drugs are currently being used to treat microsporidiosis, concerns exist that albendazole is only selective for inhibiting some species of microsporidia that infect mammals, and fumagillin appears to have been found to be toxic. During a limited sequence survey of the Vittaforma corneae genome, a partial gene encoding for the ParC topoisomerase IV subunit was identified. The purpose of this set of studies was to determine if fluoroquinolones, which target topoisomerase IV, exert activity against Encephalitozoon intestinalis and V. corneae in vitro, and whether these compounds could prolong survival of V. corneae-infected athymic mice. Fifteen fluoroquinolones were tested. Of these, norfloxacin and ofloxacin inhibited E. intestinalis replication by more than 70% compared with non-treated control cultures, while gatifloxacin, lomefloxacin, moxifloxacin, and nalidixic acid (sodium salt) inhibited both E. intestinalis and V. corneae by at least 60% at concentrations not toxic to the host cells. These drugs were tested in vivo also, where gatifloxacin, lomefloxacin, norfloxacin, and ofloxacin prolonged survival of V. corneae-infected athymic mice (P < 0.05), whereas moxifloxacin and nalidixic acid failed to prolong survival. Therefore, these results support continued studies for evaluating the efficacy of the fluoroquinolones for treating microsporidiosis and for characterizing the target(s) of these fluoroquinolones in the microsporidia.     

Effect of some substituted benzonitriles on photosynthetic activity of spinach and wheat in vivo and in vitro

The inhibitory effects of nine nitro and/or bromo-substituted benzonitrile compounds on the photosynthetic electron flow in isolated chloroplasts and on the in vivo CO₂ fixation of spinach (Spinacia oteracea L.) and wheat (Triticum aesticum L. cv. Bezoslaya) were investigated. Bromoxynil and 3-nitro-5-hromo-4-hydroxy-bcnzonitrile were the strongest and equally effective inhibitors of Ihe in vivo CO₂ fixation of spinach, hut in wheat the nitro-bromo-compound is ineffective and 3-nitro-benzonitrile is even more inhibitory than bromoxynil. None of the substances affected DCPIPH → methylviologen reduction. In the inhibition of the DCPIP reduction only the 3,5-disuhstituted 4-hydroxy-derivatives were effective. The fact that these compounds affect only the PS II reaction with both H₂O and DPC as electron donors suggests a site of inhibition on the reducing side of PS II, between Ihe PS II reaction centre and ihe DCPIP Site. It is suggested that in the inhibition of the DCPIP reduction only steric factors are important and the different electron configuration of the sterieally similar molecules may be involved only in the absorption and translocation processes of the compounds.     

不同光温条件对马铃薯繁殖根结线虫效果的影响

在沙培马铃薯条件下,分别比较不同温度、光照条件对根结线虫(Meloidogyne spp.)在马铃薯上培养效果的影响。结果表明,温度对根结线虫的培养效果有较大的影响,南方根结线虫在马铃薯上繁殖的最适温度为24～28℃,12℃时,线虫仍可侵染,但发育十分缓慢,接种后49d调查还未能观察到线虫产卵;光照条件对根结线虫的培养效果影响无明显规律性。     

不同湿润持续时间及叶片温度对温室黄瓜霜霉病发生的影响

为探明不同湿润持续时间及叶片温度与黄瓜霜霉病发生的关系,通过观察不同湿润条件下黄瓜霜霉病的初显症时间,计算逐日显症率及累积显症率,并利用热红外成像仪对显症后叶片温度进行连续监测。结果显示,不同湿润持续时间对黄瓜霜霉病的初显症时间、逐日显症率产生影响。叶片湿润持续4 h,黄瓜霜霉病在接种后7.00 d显症;叶片湿润持续12 h,黄瓜霜霉病初显症时间最早,仅为3.25 d。叶片湿润持续时间不同,黄瓜霜霉病初显症时的叶片温度存在显著差异。回归分析表明,初显症时间与最大温差呈显著正相关,与平均温度呈显著负相关。叶片湿润持续4、6 h的病斑出现高峰在显症后第2、3天,逐日显症率分别是37.50%和41.18%,比叶片湿润持续10、12 h的早。显症后期,湿润持续时间4、6、8、10、12 h的病斑累积显症率分别是87.94%、93.71%、90.25%、84.24%和88.36%,差异不显著。表明接种黄瓜霜霉菌Pseudoperonospora cubensis后叶片湿润持续时间越长,潜育期越短,叶片最大温差越小,叶片平均温度越大。