In vitro somatic growth and reproduction of phenylamide-resistant and -sensitive isolates of Phytophthora erythroseptica from infected potato tubers in Idaho

Pink rot of potato, most commonly caused by Phytophthora erythroseptica , is a major field and post-harvest problem in southern Idaho, USA, particularly since 1998 when isolates resistant to the phenylamide fungicide metalaxyl-M (mefenoxam) were detected. Isolates of P. erythroseptica were collected from infected tubers in 2001 and 2002 from six Idaho counties and tested for resistance to metalaxyl-M on amended agar. Metalaxyl-M resistant (MR) and metalaxyl-M-sensitive (MS) isolates were identified in six counties; 160 isolates were highly resistant, seven moderately resistant and 57 sensitive to metalaxyl-M with mean EC₅₀ values of 182, 23 and 0·5 mg L⁻¹ ai metalaxyl-M, respectively. Mycelial growth rates and oospore production in agar were assessed for 20 MS and 20 MR isolates at 10, 15, 20, 25 and 30°C. Growth rates of MR isolates were between 2·5 and 3·1 times greater ( P  < 0·05) than those of MS isolates at 10, 15, 20 and 25°C, and oospore production was between 6·8 and 20·5 times greater ( P  < 0·0001) for MR than for MS isolates at the same temperatures. Colony growth in V8 broth at 18°C was greater for MR than MS isolates ( P  < 0·0032). However, zoospore production at 18°C was greater for MS than for MR isolates ( P  < 0·0109), and zoospore production m m ⁻¹ of colony circumference was also greater for MS than for MR isolates, 14 191 and 9959, respectively ( P  = 0·0109). Sexual reproduction of MR isolates in nature may be greater than MS isolates, but MS isolates may be more asexually fit based on the fitness parameters studied.     

Trichoderma harzianum T39 and T. virens DAR 74290 as Potential Biological Control Agents for Phytophthora erythroseptica

Trichoderma harzianum isolate T39 and T. virens isolate DAR 74290 were evaluated as potential biological agents for control of pink rot of potato and root and stem rot of tomato caused by Phytophthora erythroseptica. Cell-free metabolites of T. virens DAR 74290 completely inhibited growth of P. erythroseptica in vitro and appeared to be fungicidal. T. virens DAR 74290 and Trichodex, a commercial formulation of T. harzianum T39, were tested for their ability to protect potato and tomato plants from disease caused by P. erythroseptica in glasshouse experiments. Trichodex and T. virens DAR 74290, alone and combined, reduced disease severity in shoots and roots of potatoes 10 weeks after inoculation with the pathogen. The yield of potatoes from plants treated with P. erythroseptica and T. virens DAR 74290 (mean of 12.9g fresh weight/pot) was significantly greater than in controls inoculated with the pathogen alone (mean of 2.1g/pot). Treatment with Trichodex alone increased the yield of tubers compared to the uninoculated controls. T. virens DAR 74290 increased the survival of tomato seedlings inoculated with the pathogen, and both this isolate and Trichodex decreased the severity of disease on tomato.     

Sensitivity of Phytophthora infestans to flumorph: in vitro determination of baseline sensitivity and the risk of resistance

The sensitivity of 127 Phytophthora infestans isolates to flumorph was determined in 2003 and 2004. The isolates originated from two geographical regions and showed similar levels of sensitivity in both years. Baseline sensitivities were distributed as a unimodal curve with EC₅₀ values for growth of mycelia ranging from 0·1016 to 0·3228  µ g mL⁻¹, with a mean of 0·1813 (± 0·0405) µ g mL⁻¹. There was no cross-resistance between flumorph and metalaxyl. Laboratory studies were conducted to evaluate the risk of P. infestans developing resistance to flumorph. Mutants resistant to metalaxyl or flumorph were obtained by treating mycelium of wild-type isolates with ultraviolet radiation. Metalaxyl-resistant mutants were obtained with a high frequency and exhibited resistance factor values (EC₅₀ resistant/EC₅₀ sensitive phenotypes) of more than 100, while flumorph-resistant mutants were obtained at much lower frequencies and had very small resistance factors (1·5–3·2). There was cross-resistance between flumorph and dimethomorph, but not with azoxystrobin or cymoxanil. Most flumorph-resistant mutants showed decreases in hyphal growth in vitro and in sporulation both in vitro and on detached leaf tissues. These studies suggested that the risk of resistance developing was much lower for flumorph than metalaxyl. However, as P. infestans is a high-risk pathogen, appropriate precautions against resistance development should be taken.     

北方五省(区)马铃薯晚疫病菌对甲霜灵和精甲霜灵的敏感性检测

为了明确我国不同地区马铃薯晚疫病菌对甲霜灵和精甲霜灵的抗性状况,2007-2009年从河北、黑龙江、吉林、辽宁和内蒙古马铃薯主产区采集马铃薯晚疫病菌,采用菌丝生长速率法和叶盘漂浮法测定其对甲霜灵的敏感性,采用叶盘漂浮法测定其对精甲霜灵的敏感性.结果表明:以菌丝生长速率法检测的380株晚疫病菌中和以叶盘漂浮法检测的222株晚疫病菌中对甲霜灵的抗性菌株分别占80％和73.5％;菌丝生长速率法检测结果显示,河北省对甲霜灵的抗性菌株所占频率从2007年的100％降为2008年的66.4％,2009年又回升至74.2％,而吉林和黑龙江两省对甲霜灵的抗性菌株分布频率呈上升趋势.叶盘漂浮法检测的95个菌株中对精甲霜灵的抗性菌株占54.5％,其中河北省40个菌株对精甲霜灵的中间型菌株占优势(62.5％),抗性菌株仅占34.9％,而其他4省55个菌株对精甲霜灵的抗性菌株占优势(69.1％).受检测的北方五省(区)马铃薯晚疫病菌群体中对甲霜灵和精甲霜灵的抗性菌株已占优势,马铃薯晚疫病菌已普遍对甲霜灵及精甲霜灵产生抗性.在对甲霜灵和精甲霜灵普遍产生抗性的地区,应优先选用与甲霜灵、精甲霜灵作用机理不同的药剂防治马铃薯晚疫病.     

Characterization of some Asian isolates of Phytophthora infestans

A total of 401 isolates of Phytophthora infestans were collected from eight Asian regions (Korea, India, Taiwan, Indonesia, Thailand, Nepal, China and Japan) between 1992 and 2000 – 318 from potato and 83 from tomato. The isolates were analysed for mating type, metalaxyl resistance, RG57 fingerprinting, mitochondrial DNA (mtDNA) haplotype and the polymorphism of three allozyme loci, i.e. glucose-6-phosphate isomerase ( Gpi ), peptidase ( Pep ) and malic enzyme ( Me ). The isolates were multilocus-genotyped based on RFLP (RG57) fingerprint, dilocus allozyme genotype, mtDNA haplotype and mating type. Twenty multilocus genotypes were identified among 125 isolates. Of these genotypes, 14 had not been previously reported. Some of the multilocus genotypes were common to isolates from several geographical regions, suggesting migration. The metalaxyl-resistant isolates belonged to the multilocus genotypes JP-1, JP-2, and JP-3. Multilocus genotypes coexisting in a single field were found in following regions: Thailand (1994), central China (1996), Nepal (1997) and Japan (1998 and 2000). The possible origins of certain genotypes are discussed, including the possibility of sexual recombination within the P. infestans populations in Nepal and perhaps Thailand.     

贵州省烟草黑胫病菌对甲霜灵的抗药性

为了明确贵州地区烟草黑胫病菌对甲霜灵的抗药性水平, 从贵州省12个市、县采集黑胫病病株, 经分离纯化鉴定, 获得98株黑胫病菌株, 采用生长速率法测定其对甲霜灵的敏感性。结果表明, 采自不同地区的菌株对甲霜灵的敏感性差异较大, 各供试菌株的EC50 值分布范围为0.419 2～20.486 1 μg/mL; 各地区平均EC50 在0.551 9～10.986 0 μg/mL之间; 最低抗药性水平为1.00, 最高抗药性水平为48.87, 相差48.87倍, 各地区平均抗药性水平在1.32～26.21之间。遵义、兴仁、贵定、赫章和兴义有抗甲霜灵菌株出现, 除遵义部分菌株的抗性水平表现为高抗外, 其余菌株对甲霜灵产生的抗性均处于中抗水平。     

Genetic diversity,sensitivity to phenylamide fungicides and aggressiveness of Phytophthora ramorum on Camellia,Rhododendron and Viburnum plants in Spain

Phytophthora ramorum has been detected in official plant health surveys on Rhododendron, Viburnum and Camellia in ornamental nurseries in northern Spain since 2003. A collection of 94 isolates of P. ramorum was obtained from 2003 to 2008 from plants with symptoms at different geographical locations. Isolates were identified based on morphology and sequence of the rDNA ITS region. Mating type, genetic variation, sensitivity to phenylamide fungicides and aggressiveness of these isolates were determined. All isolates belonged to the A1 mating type, ruling out the possibility of genetic recombination. Seven microsatellite markers were used to study genetic diversity; three out of the seven microsatellite markers were polymorphic within the Spanish population of P. ramorum. This study confirms that all Spanish isolates of P. ramorum belonged to the EU1 lineage. Twelve intralineage genotypes were detected, five that are unique to Spain (EU1MG38, EU1MG41, EU1MG37, EU1MG39 and EU1MG40) and seven that are also present in at least one other European country (EU1MG1, EU1MG29, EU1MG22, EU1MG13, EU1MG2, EU1MG18 and EU1MG26). Genotypes EU1MG37, EU1MG39 and EU1MG40 were isolated from Rhododendron from one region; EU1MG38 and EU1MG41 were isolated from Camellia from two different regions. Isolates of genotype EU1MG38 were resistant to metalaxyl and mefenoxam. The level of genetic diversity within the Spanish population of P. ramorum is limited and indicates a relatively recent clonal expansion.     

Phenotypic variation in Nordic populations of Phytophthora infestans in 2003

A total of 743 single-lesion isolates of Phytophthora infestans were collected in summer 2003 from Denmark, Finland, Norway and Sweden. Most of the isolates were tested for mating type, and subsets were tested for sensitivity to fungicides and virulence (host specific pathogenicity). Approximately 60% of the isolates were A1 mating type in each country. Both mating types were present in 40% of the fields where more than one isolate was tested, indicating strong potential for sexual reproduction. The proportion of metalaxyl-resistant isolates dropped to under 15% from the 60% observed in the early 1990s in Norway and Finland, possibly due to lower selection pressure because of decreased use of metalaxyl. Propamocarb-HCl sensitivity remained unchanged in the Nordic countries compared to the situation in 1997–2000 in Finland. Four isolates collected from Finland and Sweden were able to sporulate in the presence of this fungicide at a concentration of 1000 mg L⁻¹. In Norway and Finland the frequencies of virulence factors and pathotypes remained nearly unchanged since the 1990s, but the mean number of virulence factors per isolate increased from 5·6 to 6·3. In Denmark and Sweden virulence factors 2 and especially 6 were more common than in Norway and Finland. In addition, in the Swedish population the frequencies of pathotypes were quite even while in other countries pathotype 1,3,4,7,10,11 was most prevalent.     

疫霉菌对霜脲氰抗性遗传及对霜脲氰和甲霜灵的交互抗性

就疫霉菌对霜脲氰抗性的产生和遗传，以及疫霉菌对霜脲氰和甲霜灵的交互抗性进行了研究。结果表明，苎麻疫霉容易对霜脲氰产生抗药性突变，但抗性在连续３代单游动孢子分离过程中逐渐丧失。大雄疫霉对霜脲氰不易产生抗性突变，恶疫霉、大雄疫霉和苎麻疫霉对甲霜灵和霜脲氰不存在交互抗性     

Mefenoxam sensitivity and fitness analysis of Phytophthora nicotianae isolates from nurseries in Virginia, USA

Mefenoxam is one of the most commonly used fungicides for managing diseases caused by Phytophthora spp. on ornamentals. The objectives of this study were to determine whether Phytophthora nicotianae, a destructive pathogen of numerous herbaceous annual and perennial plant species in nurseries, has developed resistance to mefenoxam, and to evaluate the fitness of mefenoxam‐resistant isolates. Ninety‐five isolates of P. nicotianae were screened for sensitivity to mefenoxam on 20% clarified V8 agar at 100 a.i. µg mL^?1. Twenty‐five isolates were highly resistant to this compound with EC₅₀ values ranging from 235·2 to 466·3 µg mL^?1 and four were intermediately resistant with EC₅₀ values ranging from 1·6 to 2·9 µg mL^?1. Sixty‐six isolates were sensitive with EC₅₀ values less than 0·04 µg mL^?1. Nine resistant and seven sensitive isolates were tested for mefenoxam sensitivity on Pelargonium × hortorum cv. White Orbit. Mefenoxam provided good protection of pelargonium seedlings from colonization by sensitive isolates, but not by any resistant isolates. Four resistant and four sensitive isolates were compared for fitness components and their relative competitive ability on Lupinus Russell Hybrids in the absence of mefenoxam. Resistant isolates outcompeted sensitive ones within 3 to 6 sporulation cycles on lupin seedlings, regardless of their initial proportions in mixed zoospore inoculum. Resistant isolates exhibited greater infection rate and higher sporulation ability than sensitive ones when they were applied separately onto lupins. These results suggest that fungicide resistance may pose a serious challenge to the continued effectiveness of mefenoxam as a control option for nursery growers.     

Phenotypic and genotypic variation in Michigan populations of Phytophthora infestans from 2008 to 2010

Severe potato and tomato late blight epidemics in Michigan since 2008 prompted characterization of Phytophthora infestans isolates from the region. From eight counties in Michigan, 124 isolates were collected from infected potato and tomato plants from 2008 to 2010 and characterized using ‘classical’ markers and microsatellites. The classical markers included mating type, Gpi allozyme, mitochondrial DNA haplotype, sensitivity to metalaxyl‐M and tuber pathogenicity. All isolates from 2008 to 2010 were A2 mating type and Ia mtDNA haplotype (124 isolates), 105 isolates had Gpi profile 100/122, 17 isolates had the profile 100/100/111 and the remaining two isolates had 100/111/122. Sensitivity to metalaxyl‐M, expressed as EC₅₀ for mycelial growth in vitro, ranged from <0·1 to 91 μg mL^?1, where 95 and 96% of isolates were classified as either sensitive or intermediate in 2008–2009 and 2010 respectively. The metalaxyl‐M sensitivity and dominant Gpi profile were typical of clonal lineage US‐22, first isolated in 2008 in North America from tomato plants. Tuber pathogenicity, characterized as severity of tuber late blight, was also variable among isolates; however, isolates were less aggressive than previous genotypes present in Michigan, such as US‐8. Microsatellites (simple sequence repeats; SSRs) revealed a shift in the population, characterized by two clusters differentiated over time. These results suggested displacement of the US‐8 genotype by US‐22 from 2008 to 2010 in Michigan. Continuous tracking of changes within P. infestans populations provides evidence of genetic shifts due to migration, prompting modification of management strategies based on the phenotypic characteristics of causal genotypes.     

马铃薯晚疫病菌对甲霜灵抗性机制的初步研究

 选取对甲霜灵敏感、中抗和高抗的马铃薯晚疫病菌(Phytophthora infestans)菌株各2株,采用电导率法和同位素掺入法,研究了甲霜灵对马铃薯晚疫病菌不同抗药性水平菌株细胞膜通透性和RNA聚合酶活性的影响,借助液相色谱分析方法检测了不同抗药性水平菌株对甲霜灵的降解作用。结果表明:甲霜灵对马铃薯晚疫病菌不同抗药性水平菌株的细胞膜通透性没有明显影响;随着甲霜灵浓度提高,敏感菌株的RNA聚合酶活性受到显著抑制,10μg/mL甲霜灵对敏感菌株RNA聚合酶活性的抑制率达到40%以上,而10和100μg/mL甲霜灵对高抗菌株的RNA聚合酶活性只表现轻微的抑制作用,抑制作用分别小于8%和21%,甲霜灵对中抗菌株RNA聚合酶活性的抑制作用介于对敏感菌株和高抗菌株的抑制作用之间。抗性菌株对甲霜灵有一定的降解作用,培养30d后高抗菌株HL105和SC1的降解率分别达到13.46%和16.14%。     

黑龙江省和吉林省马铃薯晚疫病菌对氟啶胺和甲霜灵的敏感性变化

2006-2008年在黑龙江省和吉林省共分离获得61株马铃薯晚疫病菌,测定了这些菌株对交配型、氟啶胺和甲霜灵的敏感性。交配型测定结果显示所有菌株都显示A1交配型。甲霜灵测定结果显示10个菌株(16.4%)显示为敏感性,11个菌株(18.0%)显示为中抗,40个菌株(65.6%)显示为抗性。这说明吉林省和黑龙江省发生的晚疫病菌已对甲霜灵产生抗性。氟啶胺敏感性测定结果表明,不同地区、不同年份分离的马铃薯晚疫病菌对氟啶胺的敏感性无显著差异, 其敏感性呈连续的单峰曲线分布, EC50在0.203 3~0.783 7 μg/mL之间, 最不敏感菌株是最敏感菌株的3.85倍, 平均值为(0.4781±0.0163)μg/mL, 未出现敏感性下降的抗药性群体, 因此可作为马铃薯晚疫病菌对氟啶胺的敏感性基线;83.6%的供试菌株对甲霜灵的敏感性下降, 甲霜灵与氟啶胺之间不存在交互抗药性。测定氟啶胺对马铃薯晚疫病的盆栽防治试验结果表明,氟啶胺可湿性粉剂、氟啶胺悬浮剂和烯酰吗啉能很好地控制晚疫病,防治效果分别为85.71%、87.00%、82.19%,而甲霜灵的为23.92%。     

Near‐field air concentrations of pesticides in potato agriculture in Prince Edward Island

BACKGROUND: Pesticides in air have become of increasing concern in recent years. This study examined downwind air concentrations of carbofuran, methamidophos, mancozeb and diquat dibromide resulting from spray drift within 24 h of application, within 100 m of potato fields. RESULTS: Concentrations ranged from less than 0.05 µg m^?3 in prespray samples to 6.37 µg m^?3 for methamidophos at 3 h post‐spray. For most applications, air concentrations decreased with distance from the field and with time after application. Methamidophos concentrations in the air downwind continued to increase up to 3 h after spray. Air concentrations during spray were positively correlated with application rate (r = 0.904), and air concentrations at 1 h and 3 h post‐spray were positively correlated with vapour pressure (r = 1.000 and r = 0.999 respectively). Carbofuran, methamidophos and diquat dibromide concentrations during spray were above some Canadian and international health protection guidelines. CONCLUSION: Although pesticide air concentrations measured in this study are generally consistent with other studies, maximum concentrations are greater than those that have been measured elsewhere, and some are above published air quality guidelines. An evaluation of the degree of risk posed by these and other pest control products to human and wildlife receptors is recommended. Copyright © 2009 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.     

Concentrations and environmental risk of chlorothalonil in air near potato fields in Prince Edward Island, Canada

BACKGROUND: Chlorothalonil is used extensively in Prince Edward Island for the control of blight on potatoes, and has been measured throughout summer months in ambient air monitoring studies. This study was designed to characterize near-field drift of chlorothalonil, and to evaluate how exposure to measured air concentrations might impact upon local wildlife species. RESULTS: Air samples were collected using high-volume samplers at three distances downwind of sprayed potato fields, and at four different time intervals. Chlorothalonil was detected in 73% of prespray samples (from < 0.013 to 0.440 µg m⁻³). The mean air concentration 0 m away from the field edge during spray was 5.8 µg m⁻³, which was 7–41 times higher than concentrations measured in similar studies. Air concentrations were found to decline exponentially both with distance and time, although 0 m and 30 m concentrations at 2 h post-spray remained significantly (3 times) higher than prespray (P < 0.05). Wind speed was not found to be significantly correlated with air concentration; however, increases in temperature were found to be significantly correlated with increases in air concentrations at all sample times, at 0 m and 30 m distances. CONCLUSION: Frequent prespray detections and high post-spray concentrations suggest that both chronic and acute exposures to non-target species are occurring; however, risk calculations suggest a relatively low risk of effects to representative species. One measurement showed that a human-health-based short-term guideline had been exceeded, indicating that potential impacts to humans from chlorothalonil under current application conditions cannot be discounted. Copyright © 2011 Crown in the right of Canada. Published by JohnWiley & Sons, Ltd     

Ambient air concentrations of pesticides used in potato cultivation in Prince Edward Island, Canada

Ambient air concentrations of nine selected pesticides used in potato cultivation were investigated on Prince Edward Island by collecting samples during the summer of 1998 at three potato farm sites and one non-agricultural site. In 1999, air samples were collected at a single potato farm site during local application of pesticides. The fungicide chlorothalonil was the only pesticide detected in every sample in both years, even in samples with a duration as little as 5 h. In 1998, maximum (45-458 ng m(-3)) and mean (22-193 ng m(-3)) concentrations of chlorothalonil from composite 42 h samples were one to two orders of magnitude greater at agricultural sites than at the non-agricultural site (3.9 and 2.5 ng m(-3), respectively). Maximum and mean concentrations of chlorothalonil from combined 24 h samples at the farm site in 1999 were higher than those measured in 1998 (636 and 284 ng m(-3), respectively). The ubiquitous presence in air of relatively high concentrations of chlorothalonil in agricultural areas on Prince Edward Island is likely related to its repeated use on potato farms where fungicides account for 80-90% of pesticides applied. Eight of nine pesticides were detected at farm sites in 1998 and they are ranked by mean concentration from highest to lowest as follows: chlorothalonil, methamidophos, azinphos-methyl, alpha-endosulfan, beta-endosulfan, pirimicarb, metobromuron, metribuzin, metalaxyl and fluazifop-P-butyl. Concentrations of metalaxyl, pirimicarb, metobromuron and fluazifop-P-butyl in air are among the first reported values for these pesticides. Five pesticides were detected at the Summerside farm in 1999, but only two fungicides (chlorothalonil and metalaxyl) were used locally, while the presence of metribuzin, alpha-endosulfan and methamidophos in air was not associated with local application. Evidence of pesticide drift was observed for chlorothalonil, alpha-endosulfan and methamidophos, and these pesticides were identified as being of high concern in terms of potential wildlife exposure on the Island.     

Genetic diversity and host differentiation among isolates of Phytophthora infestans from cultivated potato and wild solanaceous hosts in Peru

To test the hypothesis that isolates of Phytophthora infestans attacking wild Solanaceae exhibit specialization for particular host species, 115 isolates of P. infestans were collected from cultivated potatoes, nontuber-bearing Solanum spp. of the Basarthrum section and wild tomatoes from five departments in the northern and central highlands of Peru, and characterized using several neutral markers. All isolates belonged to one of four clonal lineages described previously in Peru: EC-1, US-1, PE-3 and PE-7. There was a strong association of three lineages with host species: PE-3 was only isolated from cultivated potato, while PE-7 and US-1 were only isolated from nontuber-bearing Solanum spp. ( Basarthrum section and wild tomatoes). EC-1 was isolated from all host groups sampled. A subset ( n  = 74) of the isolates was evaluated for metalaxyl resistance. High levels of resistance were found almost exclusively in EC-1 and PE-3, while US-1 and PE-7 isolates were generally sensitive. In a detached-leaf assay for lesion diameter using five EC-1 isolates from S. caripense and seven EC-1 isolates from cultivated potato, there was a significant interaction between isolate origin and inoculated host, caused by higher aggressiveness of EC-1 from cultivated potato on its host of origin. In a comparison of EC-1 (seven isolates from cultivated potato) and US-1 (three isolates from S. caripense ), each pathogen lineage was more aggressive on its original host species, causing a highly significant interaction between isolate origin and inoculated host. Wild tomatoes and nontuber-bearing Solanum spp. harbour several pathogen lineages in Peru and could serve as reservoirs of inoculum that might contribute to epidemics on potato or tomato. Potential risks associated with the use of wild Solanum hosts as sources of resistance to P. infestans are discussed .     

安徽省辣椒疫霉对甲霜灵的抗药性监测

为了明确安徽地区辣椒疫霉对甲霜灵的抗药性水平及抗性菌株的地理分布,2005-2006年从安徽省16个市、县采集辣椒疫病病株,经分离纯化鉴定,获得125株辣椒疫霉菌株,分别采用生长速率法和叶盘漂浮法测定其对甲霜灵的敏感性.结果表明,按照Parra & Ristaino(2001)标准,供试菌株中有79株对甲霜灵敏感,38株对甲霜灵敏感性处于中间状态,8株抗甲霜灵,即敏感菌株、中间菌株和抗性菌株分别占总体的63.2%、30.4%和6.4%.采自不同地区的菌株对甲霜灵的敏感性差异较大,其中以寿县的菌株最为敏感,EC50值最低为0.10μg/mL,平均为0.81±0.20μg/mL;而砀山、和县地区的菌株表现出一定的抗药性,平均EC50为8.32±0.19 μg/mL,最高达25.47μg/mL.抗性菌株的最高抗性倍数约为90倍.     

Selection for decreased sensitivity to phosphite in Phytophthora cinnamomi with prolonged use of fungicide

To test the hypothesis that resistance in Phytophthora cinnamomi to control by the fungicide phosphite (phosphonate) would arise in sites with prolonged use of phosphite, 30 P. cinnamomi isolates were collected from a range of sites with different phosphite‐use histories, including phosphite‐treated and untreated avocado orchards, and phosphite‐treated and untreated native vegetation sites. The colonizing ability of these isolates was tested by different inoculation methods against a range of host tissues, treated and untreated with phosphite, including mycelial stem inoculation on clonally propagated Leucadendron sp., mycelial root inoculation of lupin seedlings and zoospore inoculation of Eucalyptus sieberi cotyledons. Isolates from avocado orchards with a long history of phosphite use were, on average, more extensive colonizers of the phosphite‐treated Leucadendron sp., lupin seedling roots and Eucalyptus sieberi cotyledons. These isolates did not colonize untreated plant tissue (Leucadendron sp.) more extensively than isolates from sites with no history of phosphite use and no isolates were resistant to control by phosphite. Analysis of all isolates with microsatellite markers revealed the majority were from a single clonal lineage. Selection for decreased sensitivity to phosphite in planta has taken place within asexual clonal lineages of P. cinnamomi in sites with prolonged use of phosphite.     

Random amplified polymorphic DNA (RAPD) analysis of Phytophthora infestans isolates collected in Canada during 1994 to 1996

Mating type, glucose-6-phosphate isomerase ( Gpi ) allozyme banding patterns, response to the fungicide metalaxyl and random amplified polymorphic DNA (RAPD) markers were used to characterize genetic variability among 141 Canadian isolates of Phytophthora infestans collected between 1994 and 1996. Multiple correspondence analysis of RAPD profiles separated isolates into 21 groups that were not correlated to groups defined by mating type, Gpi allozyme banding patterns or response to metalaxyl. Population subdivision analysis showed that 97% of the total genetic variation was found among individuals within populations, compared with 3% among populations. The average similarity coefficient among isolates was 80%. No significant differences in haplotypic diversity were observed among the years under study, but levels of genetic diversity among local populations of P. infestans were high (0.76). All classes of response to the fungicide metalaxyl were observed, with 55% of isolates displaying moderate levels of insensitivity. The high level of genetic diversity detected within populations indicates that migration and sexual recombination probably play important roles in the population biology of P. infestans in Canada.