江苏省稻瘟病菌对稻瘟灵的抗药性监测及特性分析

 近几年我国山东省、黑龙江省、辽宁省等多地稻瘟病菌(Magnaporthe oryzae)已对稻瘟灵杀菌剂产生了抗药性。江苏省是我国水稻生产大省,为明确江苏省稻瘟病菌对稻瘟灵的敏感性,本研究分离了2019年采自江苏省6个地区的稻瘟病菌单孢菌株101株,监测到13株稻瘟病菌为稻瘟灵的抗药性菌株,全省稻瘟病菌对稻瘟灵的抗性频率为12.9%。除仪征市未监测到抗药性菌株外,其他5个地区徐州市、淮安市、连云港市、东台市以及宜兴市稻瘟病菌对稻瘟灵的抗性频率分别为40.0%、33.3%、11.5%、5.0%和5.9%。利用菌丝生长速率法对其进行了敏感性测定,结果表明,这13株抗药性菌株的EC₅₀值为15.0~20.6 mg·L^-1,其抗性水平在3.6~5.0之间,均表现为低抗水平。进一步对筛选到的稻瘟灵抗性菌株适合度分析发现,只有2株抗性菌株2019-33和2019-45适合度降低,其余抗性菌株均无明显变化。这13株抗性菌株与嘧菌酯、咪鲜胺以及稻瘟酰胺均不存在交互抗性,且抗性相关基因MoIRR未发生任何位点突变。     

辽宁省稻瘟病菌对肟菌酯敏感性监测

 为了明确稻瘟病菌对肟菌酯的敏感性,利用菌丝生长速率法测定了2018~2019年辽宁省11个水稻产区分离的220株稻瘟病菌对肟菌酯的敏感性,并在此基础上对供试菌株的抗药性水平进行了分析。结果表明:稻瘟病菌对肟菌酯的EC₅₀值分布范围为0.011 1～0.498 3 μg·mL^-1,敏感性差异达44.89倍。220株稻瘟病菌对肟菌酯的敏感性分布频率不符合正态分布,说明已经出现对肟菌酯敏感性降低的分化群体,根据野生敏感型病原群体对药剂敏感性呈正态分布的原理,将供试群体中91.82%符合正态分布菌株的平均EC₅₀值(0.043 0±0.017 9) μg·mL^-1作为稻瘟病菌对肟菌酯的敏感性基线。辽宁省稻瘟病菌对肟菌酯的抗性倍数分布范围为0.256 9~11.493 8,平均抗性指数为0.27,抗性菌株出现频率为6.82%。目前菌群以敏感性群体为主,肟菌酯可作为防治稻瘟病的主要药剂,但在多地发现抗性菌株,应注意与不同作用机制药剂轮换使用。     

禾谷镰孢菌对氰烯菌酯的敏感性基线及室内抗药性风险初步评估

 本文报道了禾谷镰孢菌(Fusarium graminearum)对氰烯菌酯(2-氰基-3-氨基-3-苯基丙烯酸乙酯,JS399-19)的敏感性基线及其抗药性风险。离体条件下氰烯菌酯对51个禾谷镰孢菌菌株的平均EC₅₀和MIC值分别为(0.153±0.050)μg/mL和小于4.0μg/mL;通过紫外线照射和药剂驯化的方法获得了14个禾谷镰孢菌对氰烯菌酯的抗药性突变体,紫外光诱变抗药性突变频率为1.67×10^-7。这些突变体的抗性水平可分为低、中、高3种类型,其EC₅₀分别为1.5~15.0μg/mL、15.1~75.0μg/mL和75.0μg/mL以上。与亲本菌株2021相比,抗药突变体间的菌丝生长量和产生子囊壳能力发生不同程度的增加或下降,而分生孢子繁殖量则显著下降。在无药培养基上菌丝体转代培养8次后,抗药水平保持不变,且与亲本菌株有相同的致病性。所测定的突变体在含1%葡萄糖的PDA上菌丝生长除UV-2021-4显著下降外,其余都表现生长速率比亲本显著增加。在含3%和4%葡萄糖的PDA上2021生长优于亲本菌株。氰烯菌酯与苯并咪唑类、麦角甾醇生物合成抑制剂类、甲氧基丙烯酸酯类、二硫代氨基甲酸盐类和取代芳烃类杀菌剂没有交互抗性。     

马铃薯晚疫病菌对烯酰吗啉的敏感性基线及其室内抗药突变体的研究

 2003-2004年在内蒙古和黑龙江省共分离获得100株马铃薯晚疫病菌,并测定了这些菌株对烯酰吗啉和甲霜灵的敏感性。结果表明,不同地区、不同年份的马铃薯晚疫病菌对烯酰吗啉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0.0631-0.2206μg/mL之间,最不敏感菌株是最敏感菌株的3.1倍,平均为(0.1153±0.0308)μg/mL,未出现敏感性下降的抗药性亚群体,因此可作为马铃薯晚疫病菌对烯酰吗啉的敏感性基线;64%的供试菌株对甲霜灵的敏感性下降,甲霜灵与烯酰吗啉之间不存在交互抗药性。采用紫外线诱变菌丝的方法仅从3个菌株中的1个菌株获得了3%突变频率的抗烯酰吗啉突变体,抗性倍数为1.5-1.9,没有获得高抗药水平的突变体。这些突变体与氟吗啉之间具有正交互抗药性,而与霜脲氰或嘧菌酯之间无交互抗药性;与野生亲本菌株相比,抗药突变体的生长速率和产孢子囊能力显著下降,不利于抗药群体的发展。但由于马铃薯晚疫病菌被杀菌剂抗性行动委员会认为是高抗药性风险病原菌,建议生产上应将烯酰吗啉与其它无交互抗性的药剂交替使用或混合使用,以避免或延缓抗药性的产生。     

江西省番茄绵疫病菌对嘧菌酯的敏感性检测及抗性风险分析

为明确番茄绵疫病菌对嘧菌酯的敏感性，采用菌丝生长速率法测定了2018—2019年从江西省番茄主产区采集分离得到的58株绵疫病菌Phytophthora capsici对嘧菌酯的敏感性，并以敏感菌株YD5为亲本，通过紫外线诱导获得了4株抗性突变体，研究了突变体的生物学性状；进而采用菌丝生长速率法测定了敏感菌株YD5及其4个抗性突变体对烯酰吗啉和甲霜灵的EC₅₀值，分析嘧菌酯与烯酰吗啉和甲霜灵是否存在交互抗性。结果表明:嘧菌酯对绵疫病菌菌丝生长有较强的抑制作用，其对58个绵疫病菌的EC₅₀值介于0.1867~1.6239 μg/mL之间，平均EC₅₀值为 (0.8606±0.3318) μg/mL，58个菌株对嘧菌酯的敏感性频率分布呈正态分布，表明番茄绵疫病菌对嘧菌酯仍然较为敏感。通过紫外线诱导获得4个抗性突变体，突变体的抗药性能够稳定遗传，且在致病力与游动孢子萌发率方面与亲本菌株无显著差异，产孢量较亲本菌株显著下降。嘧菌酯与烯酰吗啉和甲霜灵之间均不存在交互抗药性。研究表明，番茄绵疫病菌对嘧菌酯具有中等抗性风险，一旦田间出现抗性菌株，应立即采取措施控制菌群的转移扩散。同时，需加强番茄绵疫病菌对嘧菌酯的田间抗性监测，在生产过程中轮用或混用不同作用机制的药剂，以避免或延缓抗药性的发展。     

抗氟吡菌胺辣椒疫霉菌株的诱导及其生物学特性的研究

 采用菌丝生长速率法, 测定了采自泰安、平谷、杭州和昆明4个地区的42株辣椒疫霉病菌对氟吡菌胺的敏感性, 结果表明, 其EC₅₀值在0.618 ~0.927 μg·mL^-1之间, 平均EC₅₀ =(0.743±0.067 7) μg·mL^-1。 42个菌株对氟吡菌胺的敏感性分布呈单峰曲线, 未出现抗性的病原菌亚群体, 可将其单峰曲线作为辣椒疫霉对氟吡菌胺的敏感性基线。采用药剂驯化和紫外照射对辣椒疫霉敏感菌株TA进行诱变处理, 获得了2株辣椒疫霉抗氟吡菌胺菌株;利用菌落直径法测定抗氟吡菌胺菌株的遗传稳定性、菌丝生长速率及对其它杀菌剂的交互抗性;通过活体叶盘法测定抗氟吡菌胺菌株和敏感菌株的致病力及产孢子囊能力, 分析抗性和敏感菌株之间生物学特性差异。结果表明, 敏感菌株TA经过氟吡菌胺 48代连续汰选, 其抗性达58.0倍, 获得中抗菌株TA-R;紫外照射获得了抗性达260.6倍的高抗菌株TA-UV, 且其抗性均能稳定遗传;TA-R和TA-UV对甲霜灵、霜脲氰表现出正交互抗性, 对烯酰吗啉、百菌清、代森锰锌和丙森锌无交互抗性;抗氟吡菌胺菌株TA-R、TA-UV与敏感菌株在活体叶盘上的致病力、离体产孢能力均差异不显著(P＜0.05), 但其菌丝生长速率、菌丝干重均低于敏感菌株。     

重庆地区辣椒疫霉对氟吡菌胺的敏感性及抗性突变体的生物学性状

为明确重庆地区辣椒疫霉对氟吡菌胺的抗性风险，采用菌丝生长速率法测定了采自重庆未使用过氟吡菌胺地区的110株辣椒疫霉菌株对氟吡菌胺的敏感性，并对辣椒疫霉抗氟吡菌胺突变体的诱导方法及抗性突变体的主要生物学性状进行了研究。结果表明:110株辣椒疫霉对氟吡菌胺的EC₅₀平均值为(0.32 ± 0.11) μg/mL，不同菌株的敏感性频率呈连续单峰曲线分布，未出现敏感性明显下降的亚群体，因此可将该EC₅₀平均值作为重庆地区辣椒疫霉对氟吡菌胺田间抗性监测的敏感基线。通过紫外诱导菌丝体的方法，共获得3株可稳定遗传的抗氟吡菌胺突变体，抗性倍数介于69.5~98.5之间，突变频率为0.86%；抗性突变体BS11-5-1与亲本菌株BS11-5在菌丝生长速率、温度适应性、产孢子囊能力及致病力方面均无显著差异，而抗性突变体JLP11-4-2和JLP11-4-3在菌丝生长速率、温度适应性、产孢子囊能力及致病力方面均显著低于亲本菌株JLP11-4；不同抗性突变体对渗透压的敏感性与亲本菌株之间均存在不同程度差异；3个抗性突变体对Biolog PM1中95种碳源的利用情况与亲本菌株基本相似。交互抗性测定表明，辣椒疫霉抗氟吡菌胺突变体对甲霜灵、霜脲氰、烯酰吗啉、丁吡吗啉及嘧菌酯之间均不存在交互抗性，建议可将氟吡菌胺与上述几种杀菌剂交替或混合使用。     

辣椒疫霉对烯酰吗啉的敏感性基线及室内抗药突变体研究

 采用菌丝生长速率法测定了125株采自河北、内蒙古、陕西、安徽和北京等地区的辣椒疫霉病菌对烯酰吗啉的敏感性,结果表明,其EC₅₀值分布于0.126~0.318μg/mL之间,最不敏感菌株是最敏感菌株的2.5倍,平均EC₅₀=(0.218±0.0368)μg/mL。125个菌株对烯酰吗啉的敏感性分布呈单峰曲线,未出现抗性的病原菌亚群体,可将该单峰曲线作为辣椒疫霉对烯酰吗啉的敏感性基线,将烯酰吗啉对该病原群体的平均EC₅₀值作为田间抗药性监测的参考标准。通过紫外诱变敏感菌株N-7的菌丝获得了12株抗烯酰吗啉的突变体,抗性指数在16.38~132.15之间;通过紫外诱变敏感菌株DZ-16的游动孢子获得1株抗性指数为680倍的高抗药水平的突变体。突变体的部分生物学性状研究表明,其致病力与敏感菌株相当;大部分突变体产生孢子囊的能力与亲本菌株相比均有不同程度的提高;离体条件下,突变体和亲本菌株释放游动孢子的能力相当;突变体的菌丝生长速率与亲本菌株相比具有不同程度的差异。测定了敏感亲本菌株和突变体的交配型,均为A1型菌株,经紫外诱变后交配型没有发生改变。综合分析表明,抗性突变体的产生有利于抗药性群体的发展。为避免和延缓抗药性的产生,生产上应将烯酰吗啉与其它无交互抗药性的杀菌剂交替使用。     

辣椒疫霉对双炔酰菌胺敏感性及对其它杀菌剂的交互抗性

采用菌丝生长速率法测定了不同地区115个辣椒疫霉菌株对双炔酰菌胺的敏感性,同时测定了紫外诱导和药剂驯化的10个抗性突变体及其4个亲本菌株对双炔酰菌胺、烯酰吗啉、甲霜灵、嘧菌酯和霜脲氰的敏感性。山东青州、寿光和河北定兴、藁城4地辣椒疫霉菌株均对双炔酰菌胺较敏感,且敏感性差异不显著。不同抗性水平菌株对5种药剂的敏感性测定和相关性分析结果显示,双炔酰菌胺与其它几类药剂之间均不存在交互抗性。10个抗性突变体继代培养11代后,8个抗性突变体抗药性不能稳定遗传;2个抗性突变体抗药性不仅能够稳定遗传,且EC₅₀值维持在很高水平,分别为1 429.524 μg/mL和6 872.476 μg/mL,因此,双炔酰菌胺的连续使用有利于抗药群体的发展。     

辽宁省稻瘟病菌对稻瘟灵的抗性监测及其对稻瘟病的田间防治效果

为明确辽宁省水稻稻瘟病菌Magnaporthe oryzae对稻瘟灵的抗性水平及变化动态，本研究于2017—2019年自辽宁省6个市的6个稻区采集并分离获得187株稻瘟病菌，利用菌丝生长速率法测定这187株稻瘟病菌菌株对稻瘟灵的敏感性及抗性，并采用茎叶喷雾法测定稻瘟灵对水稻稻瘟病的田间防治效果以及该药剂与其它药剂的交互抗性。结果表明：供试187株稻瘟病菌菌株对稻瘟灵的EC₅₀范围为0.94~34.96 μg/mL，左侧正态分布峰内EC₅₀平均值为5.05 μg/mL，稻瘟病菌对稻瘟灵的敏感性分布频率不符合正态分布，表明菌群中已经出现对稻瘟灵敏感性下降的亚群体。187株稻瘟病菌菌株对稻瘟灵的平均抗性倍数为3.70，抗性菌株出现频率为55.61%，平均抗性指数为0.40，抗性水平呈逐年增加趋势。2017—2019年稻瘟灵对水稻叶瘟病的防治效果分别为82.97%、78.86%和81.36%，对水稻穗颈瘟的防治效果分别为79.81%、77.68%和80.20%，说明在现有防控手段下未产生高水平抗性群体。稻瘟灵与肟菌酯、戊唑醇之间无交互抗性。与不同药剂轮换使用的前提下，稻瘟灵仍可作为主要药剂防治稻瘟病。     

Identification of the G143A mutation associated with QoI resistance in Cercospora beticola field isolates from Michigan,United States

BACKGROUND: Cercospora leaf spot (CLS), caused by the fungus Cercospora beticola, is the most serious foliar disease of sugar beet (Beta vulgaris L.) worldwide. Disease control is mainly achieved by timely fungicide applications. In 2011, CLS control failures were reported in spite of application of quinone outside inhibitor (QoI) fungicide in several counties in Michigan, United States. The purpose of this study was to confirm the resistant phenotype and identify the molecular basis for QoI resistance of Michigan C. beticola isolates. RESULTS: Isolates collected in Michigan in 1998 and 1999 that had no previous exposure to the QoI fungicides trifloxystrobin or pyraclostrobin exhibited QoI EC₅₀ values of ?0.006 µg mL^?1. In contrast, all isolates obtained in 2011 exhibited EC₅₀ values of > 0.92 µg mL^?1 to both fungicides and harbored a mutation in cytochrome b (cytb) that led to an amino acid exchange from glycine to alanine at position 143 (G143A) compared with baseline QoI‐sensitive isolates. Microsatellite analysis of the isolates suggested that QoI resistance emerged independently in multiple genotypic backgrounds at multiple locations. A real‐time PCR assay utilizing dual‐labeled fluorogenic probes was developed to detect and differentiate QoI‐resistant isolates harboring the G143A mutation from sensitive isolates. CONCLUSION: The G143A mutation in cytb is associated with QoI resistance in C. beticola. Accurate monitoring of this mutation will be essential for fungicide resistance management in this pathosystem. Copyright © 2012 Society of Chemical Industry     

Baseline sensitivity of natural populations and resistance of mutants of Xanthomonas oryzae pv. oryzae to a novel bactericide,zinc thiazole

During 2009–2010, a total of 323 isolates of Xanthomonas oryzae pv. oryzae were obtained from rice with symptoms of bacterial leaf blight (BLB) in four provinces (Zhejiang, Jiangsu, Anhui and Hubei) in China. These isolates were tested for baseline sensitivity to zinc thiazole, a novel bactericide with strong antibacterial activity against Xanthomonas. The sampled pathogenic population had similar sensitivity to zinc thiazole (0·1–16·8 mg L^?1) in all four regions and over the whole two‐year study period. The baseline sensitivity was distributed as a unimodal curve with a mean EC₅₀ value of 6·79 ± 1·61 mg L^?1. The risk of mutation to resistance of zinc thiazole in X. oryzae pv. oryzae was further evaluated in vitro and in vivo. Twelve zinc thiazole‐resistant mutants were obtained through ultraviolet (UV) irradiation, culturing on zinc thiazole‐amended nutrient agar (NA) plates, and culturing on zinc thiazole‐treated rice plants. These zinc thiazole‐resistant mutants had resistance factors (RF = EC₅₀ value of a mutant / EC₅₀ value of the wildtype parent of this mutant) of 12·4 to 186·1 with a mean RF value of 44·1. Mutants obtained via UV irradiation, culturing on NA plates and culturing on rice plants had mean RF values of 51·8, 24·5 and 14·4, respectively. All mutants showed decreases in resistance to zinc thiazole after 20 successive transfers on bactericide‐free media or 10 successive inoculation–reisolations on bactericide‐free rice plants. No significant difference was found in bacterial growth and sensitivity to bismerthiazol between zinc thiazole‐resistant mutants and their parents. However, a significant decrease was observed in the pathogenicity of zinc thiazole‐resistant mutants compared with their parents, especially for mutants obtained via UV irradiation.     

番茄灰霉病菌对咯菌腈的抗性诱变及抗药突变体的生物学特性

为评估番茄灰霉病菌Botrytis cinerea对咯菌腈的抗性风险,就室内经紫外照射获得抗药突变体的方法及抗性突变体的生物学性状进行了研究。结果表明:番茄灰霉病菌分生孢子的紫外照射亚致死时间为90~120 s;经亚致死时间紫外照射后,4个亲本菌株中有2个菌株共产生了6个抗咯菌腈的突变体,其EC50值是亲本菌株的310倍以上,抗性突变频率为3.13×10-7;经紫外照射诱变获得的所有抗性突变体在菌丝生长速率、产孢量、产菌核能力及其在番茄果实上的致病性方面均比其亲本菌株明显降低。相关分析显示,所得抗咯菌腈突变体对氟啶胺、啶菌唑、啶酰菌胺和嘧霉胺无交互抗性。表明番茄灰霉病菌对咯菌腈的抗药性风险较低。     

Resistance to pyraclostrobin, boscalid and multiple resistance to Pristine® (pyraclostrobin + boscalid) fungicide in Alternaria alternata causing alternaria late blight of pistachios in California

Pristine® (pyraclostrobin + boscalid) is a fungicide registered for the control of alternaria late blight in pistachio. A total of 95 isolates of Alternaria alternata collected from orchards with and without a prior history of Pristine® sprays were tested for their sensitivity towards pyraclostrobin, boscalid and Pristine® in conidial germination assays. The EC₅₀ values for 35 isolates from orchards without Pristine® sprays ranged from 0·09 to 3·14 µg mL^?1 and < 0·01 to 2·04 µg mL^?1 for boscalid and Pristine®, respectively. For pyraclostrobin, 27 isolates had EC₅₀ < 0·01 µg mL^?1 and six had low resistance (mean EC₅₀ value = 4·71 µg mL^?1). Only one isolate was resistant to all three fungicides tested, with EC₅₀ > 100 µg mL^?1. Among 59 isolates from the orchard with a history of Pristine® sprays, 56 were resistant to pyraclostrobin; only two were sensitive (EC₅₀ < 0·01 µg mL^?1) and one was weakly resistant (EC₅₀ = 10 µg mL^?1). For the majority of these isolates EC₅₀ values ranged from 0·06 to 4·22 µg mL^?1 for boscalid and from 0·22 to 7·74 µg mL^?1 for Pristine®. However, seven isolates resistant to pyraclostrobin were also highly resistant to boscalid and Pristine® and remained pathogenic on pistachio treated with Pristine®. Whereas strobilurin resistance is a common occurrence in Alternaria of pistachio, this is the first report of resistance to boscalid in field isolates of phytopathogenic fungi. No cross resistance between pyraclostrobin and boscalid was detected, suggesting that Pristine® resistance appears as a case of multiple resistance.     

Genetic analysis and molecular characterisation of laboratory and field mutants of Botryotinia fuckeliana (Botrytis cinerea) resistant to QoI fungicides

BACKGROUND: QoI fungicides, inhibitors of mitochondrial respiration, are considered to be at high risk of resistance development. In several phytopathogenic fungi, resistance is caused by mutations (most frequently G143A) in the mitochondrial cytochrome b (cytb) gene. The genetic and molecular basis of QoI resistance were investigated in laboratory and field mutants of Botryotinia fuckeliana (de Bary) Whetz. exhibiting in vitro reduced sensitivity to trifloxystrobin. RESULTS: B. fuckeliana mutants highly resistant to trifloxystrobin were obtained in the laboratory by spontaneous mutations in wild‐type strains, or from naturally infected plants on a medium amended with 1–3 mg L^?1 trifloxystrobin and 2 mM salicylhydroxamic acid, an inhibitor of alternative oxidase. No point mutations were detected, either in the complete nucleotide sequences of the cytb gene or in those of the aox and Rieske protein genes of laboratory mutants, whereas all field mutants carried the G143A mutation in the mitochondrial cytb gene. QoI resistance was always maternally inherited in ascospore progeny of sexual crosses of field mutants with sensitive reference strains. CONCLUSIONS: The G143A mutation in cytb gene is confirmed to be responsible for field resistance to QoIs in B. fuckeliana. Maternal inheritance of resistance to QoIs in progeny of sexual crosses confirmed that it is caused by extranuclear genetic determinants. In laboratory mutants the heteroplasmic state of mutated mitochondria could likely hamper the G143A detection, otherwise other gene(s) underlying different mechanisms of resistance could be involved. Copyright © 2012 Society of Chemical Industry     

Distribution and molecular characterization of Corynespora cassiicola isolates resistant to boscalid

A total of 618 isolates of corynespora leaf spot fungus (Corynespora cassiicola) collected from 24 commercial cucumber greenhouses in 12 cities in Ibaraki Prefecture, Japan, were tested for their sensitivity to boscalid. Boscalid‐resistant isolates were detected in 17 out of 19 greenhouses with a history of use of this fungicide and detection frequencies of the resistant isolates exceeded 47% in nine greenhouses. Frequencies of very highly resistant (VHR) isolates with 50% effective concentration (EC₅₀) values of boscalid exceeding 30 μg mL^?1 were higher than those of moderately resistant (MR) isolates with EC₅₀ ranging from 2·0 to 5·9 μg mL^?1 in 11 greenhouses. Additionally, highly resistant (HR) isolates with EC₅₀ from 8·9 to 10·7 μg mL^?1 were first detected. Furthermore, molecular characterization of genes encoding succinate dehydrogenase (SDH) subunits (SdhA, SdhB, SdhC and SdhD) was carried out to elucidate the amino acid substitution responsible for the resistance to boscalid. All 23 VHR isolates had the same mutation from CAC to TAC in the SdhB gene leading to the substitution of histidine with tyrosine at amino acid position 278 (B‐H278Y). At the same position, the substitution to arginine conferred by a mutation to CGC (B‐H278R) was detected in all four HR isolates. Some MR isolates showed a substitution from serine to proline at position 73 in SdhC (C‐S73P), from serine to proline or from glycine to valine at position 89 (D‐S89P) and 109 (D‐G109V), respectively, in SdhD. There was no common mutation in SDH genes of all MR isolates.     

Evaluation of the incidence of the G143A mutation and cytb intron presence in the cytochrome bc-1 gene conferring QoI resistance in Botrytis cinerea populations from several hosts

BACKGROUND: Previous studies have shown that resistance of Botrytis cinerea to QoI fungicides has been attributed to the G143A mutation in the cytochrome b (cytb) gene, while, in a part of the fungal population, an intron has been detected at codon 143 of the gene, preventing QoI resistance. During 2005–2009, 304 grey mould isolates were collected from strawberry, tomato, grape, kiwifruit, cucumber and apple in Greece and screened for resistance to pyraclostrobin and for the presence of the cytb intron, using a novel real‐time TaqMan PCR assay developed in the present study. RESULTS: QoI‐resistant phenotypes existed only within the population collected from strawberries. All resistant isolates possessed the G143A mutation. Differences were observed in the genotypic structure of cytb. Individuals possessing the intron were found at high incidence in apple fruit and greenhouse‐grown tomato and cucumber populations, whereas in the strawberry population the intron frequency was lower. Cultivation of QoI‐resistant and QoI‐sensitive isolates for ten culture cycles on artificial nutrient medium in the presence or absence of fungicide selection showed that QoI resistance was stable. CONCLUSIONS: The results of the study suggest that a high risk for selection of QoI‐resistant strains exists in crops heavily treated with QoIs, in spite of the widespread occurrence of the cytb intron in B. cinerea populations. The developed real‐time TaqMan PCR constitutes a powerful tool to streamline detection of the mutation by reducing pre‐ and post‐amplification manipulations, and can be used for rapid screening and quantification of QoI resistance. Copyright © 2011 Society of Chemical Industry     

黑龙江省水稻种质抗瘟性及稻瘟病菌致病性分析

为明确黑龙江省水稻种质抗性及稻瘟病菌的致病性,以黑龙江省8个水稻品种、24个单基因系作为供试材料,120株稻瘟病菌株作为接种体,采用喷雾接种法测定了各供试水稻的抗瘟性及稻瘟病菌的致病性。结果表明,水稻品种对2010年和2011年菌株的抗性频率分别在31.67%~68.33%和21.67%~55.00%之间,2010年最好的抗性品种为松粳12,2011年最好的抗性品种为五优稻4和东农425;松粳12东农425组合联合抗病性最好。水稻单基因系对2010年和2011年菌株的抗性频率分别在10.00%~90.00%和5.00%~86.67%之间,抗性最好的单基因系分别为IRBLzt-T(Pi-zt)和IRBLz5-CA(Pi-z5);松粳12、东农425和龙粳22的基因聚合效果最好。2010年和2011年菌株对抗瘟基因群的致病率分别在8.33%~95.83%和25.00%~95.83%之间;无毒基因总出现频率分别为461和412次。研究表明,水稻种质抗性受菌株致病性影响较大,但高抗种质相对稳定,基因聚合方式更适宜当地品种抗性改良。     

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.