Relationship Between Growth and Mycotoxin Production by Fusarium species, Biocides and Environment

Fusarium head blight of cereals has, in recent years, become one of the most important pre-harvest diseases worldwide. This paper examines the in vitro efficacy of fungicides to control Fusarium species in cereals and the efficacy in the field on both Fusarium infection of ripening ears as well as their impact on mycotoxin production. Field studies suggest that fungicides such as tebuconazole and metconazole give good control of both Fusarium infection of ears and control of deoxynivalenol (DON) production. However, azoxystrobin and related fungicides are less effective, and grain from treated crops has sometimes been found to have increased concentrations of DON and nivalenol. Studies of isolates of Fusarium culmorum from different parts of Europe showed that complex interactions occur between environmental factors, fungicide type and isolate in relation to growth inhibition and DON production. These studies confirmed the ineffectiveness of azoxystrobin and suggest that environmental stress factors, particularly water availability and temperature, and low fungicide doses may stimulate mycotoxin production by Fusaria in vitro and in wheat grain.     

温度对烟草黑胫病菌致病力及代谢表型的影响

为揭示温度对烟草黑胫病菌Phytophthora nicotianae致病力及代谢表型的影响,采用菌丝生长速率法和离体叶片法分别测定不同温度下烟草黑胫病菌的生长速率和致病力,同时采用Biolog代谢表型技术测定其在20、27、30和35℃下的渗透压和pH代谢表型。结果表明,烟草黑胫病菌在21~35℃范围内生长良好且具致病力,30℃时生长速率最快,为17.72 mm/d,30℃和35℃时致病力较强,叶片接种烟草黑胫病菌后24 h内便出现病斑,随温度升高病害的潜伏期缩短。温度影响烟草黑胫病菌的渗透压和pH适应性;27℃和30℃时烟草黑胫病菌的渗透压适应范围最广,其次为21℃,35℃时烟草黑胫病菌渗透压适应范围最窄;在20、27和30℃时,烟草黑胫病菌在pH 5.0~10.0范围内可正常代谢,在35℃时pH代谢范围为5.5~10.0。     

Scab Response and Moniliformin Accumulation in Kernels of Oat Genotypes Inoculated with Fusarium avenaceum in Poland

Inoculation experiments with 14 genotypes of oats (10 cultivars and 4 lines) were performed during 1996, 1997 and 1998 in Sitaniec, South-Eastern Poland. Panicles of oats were inoculated with a conidial suspension of Fusarium avenaceum, which caused a reduction in yield by 33% and in 1000 kernel weight (TKW) by 21%. During the period between inoculation and harvest, F. avenaceum was able to accumulate moniliformin (MON) in kernels at an average level of 0.13mgkg^–1 (gg^–1). The highest reduction of yield components caused by the F. avenaceum inoculation was found for cv. Santor, followed by lines CHD 1171, STH 2795 and cvs: Kwant and Farys, while cvs Slawko, Dukat, Borys and Komes exhibited the highest resistance to the disease in terms of TKW and yield reductions after inoculation.     

Development and Evaluation of an in vitro Detached Leaf Assay forc Pre-Screening Resistance to Fusarium Head Blight in Wheat

An in vitro detached leaf assay, involving the inoculation of detached leaves with Microdochium nivale, was further developed and used to compare with whole plant resistance ratings to Fusarium head blight (FHB) of 22 commercial cultivars and published information on 21 wheat genotypes, identified as potential sources for FHB resistance. An incubation temperature of 10 °C and isolates of M. nivale var. majus of intermediate pathogenicity were found to be the most suitable for the differential expression of several components of partial disease resistance (PDR), namely incubation period, latent period and lesion length, in wheat genotypes used in the detached leaf assay. There were highly significant differences (P < 0.001) for each component of PDR within commercial cultivars and CIMMYT genotypes. Positive correlations were found between incubation period and latent period (r = 0.606; P < 0.001 and r = 0.498; P < 0.001, respectively, for commercial cultivars and CIMMYT genotypes), inverse correlations between incubation period and lesion length (r = -0.466; P < 0.01 and r = –0.685; P < 0.001, respectively) and latent period and lesion length (r = –0.825; P < 0.001 and r = –0.848; P < 0.001, respectively). Spearman rank correlations between individual PDR components and UK 2003 recommended list ratings were significant for incubation period (r_s = 0.53; P < 0.05) and latent period (r_s = 0.70; P < 0.01) but not for lesion length (r _s = –0.26). Commercial cultivars identified with high resistances across all three PDR components in the detached leaf assay also had high whole plant FHB resistance ratings, with the exception of cv. Tanker which is more susceptible than the results of the detached leaf assay suggested, indicating an additional susceptibility factor could be present. Agreement between resistances found in the detached leaf assay and resistance to FHB suggests resistances detected in detached leaves are under the same genetic control as much of the resistances expressed in the wheat head of the commercial cultivars evaluated. In contrast, high resistances in each of the PDR components were associated with higher susceptibility across 19 CIMMYT genotypes previously evaluated as potential breeding sources of FHB resistance (incubation period: r = 0.52; P < 0.01, latent period: r = 0.53; P < 0.01, lesion length: r = –0.49; P < 0.01). In particular, the CIMMYT genotypes E2 and E12 together with Summai #3, known to have high levels of whole plant FHB resistance, showed low levels of resistance in each PDR component in the detached leaf assay. Such whole plant resistances, which are highly effective and not detected by the detached leaf assay, do not appear to be present in Irish and UK commercial cultivars. The most resistant Irish and UK commercial cultivars were comparable to the genotype Frontana and the most resistant CIMMYT germplasm evaluated in the leaf assay.     

Pathogenicity and RAPD analysis of Phytophthora nicotianae pathogenic to pepper in Tunisia

Nine isolates of Phtophthora nicotianae were isolated from infected pepper plants. Their pathogenicity was studied in Capsicum annuum in comparison with P. nicotianae isolates from tomato and tobacco. The pathogenicity test showed that pepper isolates of P. nicotianae are adapted to their host. Banding patterns obtained by RAPD analysis with six oligonucleotide primers revealed polymorphism that grouped the isolates independently of the plant host. The polygenic dendrogram showed that pepper isolates were more similar to tomato isolates than to tobacco isolates. The RAPD bands of 1300 and 1500 bp, detected with primers OPD-01 and OPD-10, respectively, appeared specific to the most pathogenic pepper isolates. The OPK-08-1950 seems specific to the isolates of P. nicotianae from tomato. These results suggest that host specified might occur in P. nicotianae and that may be due to interspecific hybridization events resulting in novel pathogenic behavior.     

Biosynthesis of Depsipeptide Mycotoxins in Fusarium

The cyclic hexadepsipeptide enniatin is known as a phytopathogenic compound from Fusaria causing necrosis and wilt. The molecule consists of three alternating residues each of a branched chain amino acid and D-hydroxyisovaleric acid (D-Hiv). Enniatins are synthesized by a 347kDa multienzyme (enniatin synthetase) via a thiol template mechanism. The corresponding gene esyn1 has an open reading frame of 9393 nucleotides and harbours two modules, one responsible for D-hydroxy acid activation and one for L-amino acid activation with an integrated N-methyltransferase domain. Such methyltransferases build an homologous group among N-methyl peptide synthetases. Enniatins are synthesized by step-wise condensation of dipeptidol building blocks in an iterative manner resembling fatty acid synthesis. A key enzyme in enniatin biosynthesis is the NADPH-dependent D-2-hydroxyisovalerate dehydrogenase, that supplies enniatin synthetase with D-Hiv. Enniatins contribute to the wilt toxic character of Fusaria. Virulence was significantly reduced in F. avenaceum after disruption of the esyn1 gene.     

Association of Fusarium Species in the Wheat Stem Rot Complex

Data from a national survey were analysed to investigate whether there was interdependence among the Fusarium species, which cause the stem rot complex of wheat. About 25 wheat stems were sampled from each of 260 sites over the main wheat growing areas in the UK. Occurrence of each Fusarium species on individual stems was determined. Fusarium culmorum, F. avenaceum and Microdochium nivale were the three dominant species, detected in 248, 185 and 239 out of the 260 sites. There were no interactions among species in the distribution of the three species over the 260 sites. Several statistical tests were used to determine whether there was interdependence among the three species on the same stem within each site. Of the three species, there was only limited evidence of competition between F. culmorum and F. avenaceum.     

Effect of Dose Rate of Azoxystrobin and Metconazole on the Development of Fusarium Head Blight and the Accumulation of Deoxynivalenol (DON) in Wheat Grain

Glasshouse studies were undertaken to determine if fungicides used for the control of Fusarium head blight (FHB) result in elevated concentrations of the trichothecene mycotoxin, deoxynivalenol (DON) in harvested wheat grain. Metconazole and azoxystrobin, at double, full, half or quarter the manufacturer's recommended dose rate, were applied to ears of wheat (cv. Cadenza), artificially inoculated with conidia of either Fusarium culmorum or F. graminearum. Metconazole demonstrated high activity against both pathogens, reducing significantly the severity of FHB and the DON concentrations at each of the four dose rates tested when compared to untreated controls. Applications of azoxystrobin significantly reduced FHB and DON compared to unsprayed controls. However, their effectiveness was significantly less than that of metconazole and no dose rate response was observed. Quantification of the amount of trichothecene-producing Fusarium present in harvested grain was determined using a competitive PCR assay based on primers derived from the trichodiene synthase gene (Tri5). Simple linear regression analyses revealed strong relationships between the amount of trichothecene-producing Fusarium present in grain and the DON concentrations (r ²=0.72–0.97). It is concluded that fungicides, applied for the control of FHB, affect DON concentrations indirectly by influencing the amount of trichothecene-producing Fusarium species present in wheat grain. There was no evidence that fungicide applications directly increase the concentration of DON in grain.     

Epidemiology of Fusarium Infection and Deoxynivalenol Content in Winter Wheat in the Rhineland, Germany

Details of our long-term research programme concerning the epidemiology of Fusarium spp. and mycotoxin production are summarized. Evaluation of the occurrence of Fusarium spp., mainly on winter wheat (Triticum aestivum), was carried out by investigating Fusarium infection and mycotoxin contamination. Two to 15% of grains were infested during 1995–1998 at three climatologically differing localities of the Rhineland, Germany. Disease progress was accelerated by rainfall during the flowering season. The species most frequently isolated were Fusarium avenaceum, F. poae, F. culmorum and F. graminearum. The mean deoxynivalenol (DON) content varied from 19gkg^–1 (1995) to 310gkg^–1 (1998) and was not always correlated with disease severity. Organic farming systems showed lower rates of infection with ear blight and lower mycotoxin contamination than conventional farming systems.     

Strategies for the Control of Fusarium Head Blight in Cereals

Fusarium head blight (FHB) is a widespread and destructive disease of small grained cereals caused by a number of Fusarium species and Microdochium nivale. In addition to causing significant reductions in grain yield, FHB can result in the reduction of grain quality, either by affecting grain processing qualities or by producing a range of toxic metabolites that have adverse effects on humans and livestock. Control of FHB can be achieved by a number of cultural, biological and chemical strategies along with the exploitation of host plant resistance. In recent years, much of the research undertaken for the control of FHB has been concentrated on understanding and exploiting the genetic resistance of cereal plants to FHB-causing pathogens. Although, a brief overview of genetic resistance is presented, this review seeks to summarise the significance of FHB and review the effectiveness of cultural, biological and chemical control strategies that have been investigated for the control the disease.     

Identification and pathogenicity of<Emphasis Type="Italic">Fusarium</Emphasis> spp. from stem bases of winter wheat in Erzurum,Turkey

Four-hundred-sixty-eightFusarium andFusarium-like isolates were obtained from crowns and subcrown internodes of winter wheat grown in Erzurum, Turkey. Of these isolates, 34.8% wereFusarium acuminatum, 32.3% wereF. equiseti, 16.9% wereF. oxysporum, 15.0% wereMicrodochium nivale (formerlyFusarium nivale), 0.6% wereF. tabacinum and 0.4% wereF. solani. In pathogenicity tests on wheat, the highest disease severity was caused by isolates ofM. nivale, whereas isolates ofF. acuminatum, F. equiseti, F. oxysporum andF. solani were slightly virulent; isolates ofF. tabacinum were nonpathogenic. This is the first report ofM. nivale andF. tabacinum from wheat in Turkey. http://www.phytoparasitica.org posting Jan. 29, 2003.     

Pathogenicity of Fusarium solani f.sp. cucurbitae race 1 to courgette

Fusarium solani f. sp.cucurbitae race 1 causes foot rot in courgette (Cucurbita pepo). The pathogen could be distinguished fromFusarium solani from sweet pepper (Capsicum annuum) both morphologically and in its host range.In inoculation experiments all nine cultivars of the six species of Cucurbitaceae tested were susceptible. Courgette Green became diseased after inoculation with a spore suspension by root dipping or adding the suspension to the soil around the stem base or spraying the whole plant with it.Both wounded and young plants died more quickly than unwounded and older plants. With low inoculum densities the plants were affected more slowly than with high densities and the differences in susceptibility of the Cucurbitaceae tested were more pronounced.From infected courgette seeds the fungus could be reisolated until 6 months after harvest.This is the first record of this pathogen in courgettes in the Netherlands.Samenvatting Fusarium solani f. sp. cucurbitae fysio 1 is de oorzaak van een voetrot in courgette. Het pathogeen is morfologisch en door middel van een waardplantenreeks goed vanF. solani uit paprika te onderscheiden.In inoculatieproeven waren de getoetste Cucurbitaceae in meer of mindere mate gevoelig voorF. solani f. sp.cucurbitae. Bij courgette Green werden zowel gedompelde, als aangegoten, als bespoten planten door het pathogeen aangetast. Zowel verwonde als niet-verwonde planten werden aangetast als ook planten van verschillende leeftijden. Niet-verwonde en ook oudere planten stierven minder snel af dan verwonde en jongere planten. Bij lagere inoculumdichtheden werden de planten minder snel aangetast dan bij hogere dichtheden en waren de verschillen in vatbaarheid voor het pathogeen tussen de getoetste Cucurbitaceae duidelijker.Uit courgette zaad, dat met het pathogeen was besmet, kon de schimmel tot 6 maanden na zaadwinning opnieuw worden geïsoleerd.Dit is de eerste melding van dit pathogeen in courgette in Nederland.     

In vitro Variability of a number of characteristics ofSclerotinia sclerotiorum

Studies were made of the variability ofSclerotinia sclerotiorum (Lib.) de Bary: (i) growth rate when cultivated on potato-dextrose agar (PDA); (ii) thein vitro resistance of this organism to the fungicides benomyl, vinclozolin and procymidone; and (iii) the size and number of sclerotia formed on PDA. The isolates used were collected from eggplants, French beans and tomatoes cultivated in the same locality, but although marked differences were observed among them, especially in growth rate and formation of sclerotia, it was not possible to establish groups or categories among the isolates studied, or to relate the observed variability to their origins. Temperature was a decisive factor for formation of sclerotia on PDA. No correlation was found between size and number of sclerotia, and growth rate. The ED₅₀ level for both vinclozolin and procymidonein vitro was 2 mg l⁻¹, whereas that for benomyl was below the minimum level used, and therefore could not be established.     

兰州百合枯萎病病原菌鉴定及罹病组织超微结构观察

为明确引起甘肃省兰州百合主产区百合枯萎病的致病镰孢菌种类,对从百合主产区枯萎病罹病植株上分离纯化的4株镰孢菌株进行形态学鉴定、分子生物学鉴定以及致病性测定,同时利用电子显微镜对尖孢镰孢菌Fusarium oxysporum侵入百合鳞片后的细胞超微结构进行观察。结果表明:4株镰孢菌菌株经鉴定分别为尖孢镰孢菌、茄病镰孢菌F. solani、三线镰孢菌F. tricinctum和燕麦镰孢菌F. avenaceum。4株镰孢菌菌株的致病力由强到弱的顺序依次是尖孢镰孢菌、燕麦镰孢菌、茄病镰孢菌、三线镰孢菌;尖孢镰孢菌侵入后,鳞片细胞壁、细胞质膜和细胞核结构被破坏,细胞核附近出现大量线粒体,细胞中淀粉粒数量减少。表明尖孢镰孢菌是兰州百合枯萎病防治的重点防控对象。     

Pathological evaluation of host-specific AAL-toxins and fumonisin mycotoxins produced by Alternaria and Fusarium species

Host-specific AAL-toxins and mycotoxin fumonisins are structurally related and were originally isolated from the tomato pathotype of Alternaria alternata and from Fusarium verticillioides, respectively. Previous reports on the production of fumonisin derivatives by the tomato pathotype suggested a possible involvement in the pathogenicity of the pathogen. Here, we have evaluated the role of fumonisin in A. alternata–tomato interactions. The results indicate that highly pathogenic isolates of A. alternata tomato pathotype produce AAL-toxin as the sole toxin, strongly implicating it as a pathogenicity factor. The related compound, fumonisin, is also toxigenic and has infection-inducing activity on susceptible tomato plants.     

Natural Occurrence and Distribution of Fusarium Toxins in Contaminated Barley Cultivars

Grain samples of 15 naturally contaminated barley cultivars, collected after harvest in southeastern Poland, were analysed for occurrence of Fusarium trichothecenes and zearalenone (ZEA). Barley kernels were contaminated with the following toxic metabolites: deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-AcDON), 15-acetyldeoxynivalenol (15-AcDON), nivalenol (NIV), HT-2 toxin (HT-2), T-2 toxin (T-2), diacetoxyscirpenol (DAS), T-2 tetraol and ZEA. Significant correlations between concentrations of individual toxins and the dominant Fusarium species were found. Moreover, significant differences in toxin concentrations between cultivars were detected. Distribution of these mycotoxins was studied in two fractions of kernels (diameter > 2.5 mm and < 2.5 mm). A two-factor analysis of variance revealed significant differences between the two fractions, and between the analysed cultivars. Most of the interactions between fractions and cultivars were also significant. The highest concentration of the analysed toxins was in the fraction of small kernels. Kernel fraction <2.5 mm, although accounting for only 12.8% of sample weight, contained high proportions of the total toxin content: 80% of DON, 94% of NIV, 85% of ZEA, 83% of T-2 tetraol, 80% of DAS, 68% of HT-2 toxin and 81% of T-2 toxin. The results indicate that the level of contamination with Fusarium trichothecenes and ZEA, can be reduced by rejection of small kernels.     

云南省稻瘟病菌群体的致病性分析及交配型分布

为明确云南省不同稻区稻瘟病菌Magnaporthe oryzae的毒性频率及交配型分布,利用2007—2013年分离自云南省不同稻区的112株稻瘟病菌单孢菌株,对23个持有不同抗性基因的单基因系和持有Pi57(t)的水稻渗入系IL-E1454进行致病性测定。结果表明,稻瘟病菌对不同抗病基因的毒性频率存在很大差异,分离自粳稻区的稻瘟病菌菌株对持有Piz-t、Pi5、Pi9、Pi20和Pi57(t)这5个水稻品系的毒性频率分别为14.29%、5.36%、5.51%、5.36%和0;分离自籼稻区的稻瘟病菌菌株对持有Pik-h、Piz、Pita、Piz-5、Pita-2、Pi5、Pi7和Pi9这8个水稻品系的毒性频率分别为18.25%、9.13%、9.64%、7.50%、15.72%、0、13.05%和0;分离自陆稻区的稻瘟病菌菌株菌株对持有Pik-h、Pib、Pish、Pi1、Pi5、Pi9、Pi11和Pi57(t)这8个水稻品系的毒性频率分别为6.67%、3.33%、13.79%、13.33%、7.69%、6.67%、0和3.23%;交配型测定结果显示,陆稻区菌株可交配率为100.00%,...     

江苏省水稻赤霉病病原菌分离鉴定与致病力分析

为明确江苏省水稻赤霉病的病原菌组成及致病特征,于2018—2019年从江苏省13个市41个县区采集341份水稻样品,采用组织分离法对病原菌进行分离纯化,基于翻译延伸因子（translationelongation factor-1α,TEF-1α）序列分析对分离菌株进行鉴定,通过TRI11基因序列鉴定及产毒力测定对其产毒化学型进行分析,并按照柯赫氏法则对其致病力进行验证。结果显示,从水稻样品中共分离获得病原菌392株,其中亚洲镰刀菌Fusarium asiaticum为385株,禾谷镰刀菌F. graminearum为7株。亚洲镰刀菌分为3-乙酰化脱氧雪腐镰刀菌烯醇（3-acetyldeoxynivalenol,3ADON）化学型和雪腐镰刀菌烯醇（nivalenol,NIV）化学型菌株,分别占亚洲镰刀菌总菌株数的 66.8% 和 33.2%;禾谷镰刀菌均为（15-acetyldeoxynivalenol,15ADON）化学型。产3ADON的亚洲镰刀菌在全省范围内为优势群体,而产15ADON的禾谷镰刀菌仅在淮北地区被发现;产NIV的亚洲镰刀菌对水稻的致病性要显著高于产3ADON的亚洲镰刀菌。不同产毒化学型亚洲镰刀菌对水稻均有一定致病性,但NIV化学型亚洲镰刀菌对水稻的致病力最强。     

Toxigenic Fusarium Species and Mycotoxins Associated with Maize Ear Rot in Europe

Several Fusarium species occurring worldwide on maize as causal agents of ear rot, are capable of producing mycotoxins in infected kernels, some of which have a notable impact on human and animal health. The main groups of Fusarium toxins commonly found are: trichothecenes, zearalenones, fumonisins, and moniliformin. In addition, beauvericin and fusaproliferin have been found in Fusarium-infected maize ears. Zearalenone and deoxynivalenol are commonly found in maize red ear rot, which is essentially caused by species of the Discolour section, particularly F. graminearum. Moreover, nivalenol and fusarenone-X were often found associated with the occasional occurrence of F. cerealis, and diacetoxyscirpenol and T-2 toxin with the occurrence of F. poae and F. sporotrichioides, respectively. In addition, the occurrence of F. avenaceum and F. subglutinans usually led to the accumulation of moniliformin. In maize pink ear rot, which is mainly caused by F. verticillioides, there is increasing evidence of the wide occurrence of fumonisin B₁. This carcinogenic toxin is usually found in association with moniliformin, beauvericin, and fusaproliferin, both in central Europe due to the co-occurrence of F. subglutinans, and in southern Europe where the spread of F. verticillioides is reinforced by the widespread presence of F. proliferatum capable of producing fumonisin B₁, moniliformin, beauvericin, and fusaproliferin.     

黑龙江省部分地区稻瘟病菌致病性分析及鉴别体系优化

为明确哈尔滨市及鸡西市稻瘟病菌致病性变化情况并优化鉴别体系,以24个水稻单基因系为鉴别体系,对2006—2008年采自2市的稻瘟病菌菌株进行致病型划分,并应用聚类分析方法完成鉴别体系优化。结果表明,应用水稻单基因系鉴别体系可将哈尔滨市2006—2008年采集的稻瘟病菌菌株划分为34、12和27个致病型,致病性相似系数分别为0.32~1.00、0~1.00和0.20~1.00;水稻单基因系对其抗性频率分别为2.86%~97.14%、8.33%~100.00%和10.00%~96.67%;鸡西市2006—2008年采集的菌株可划分为26、19和20个致病型,致病性相似系数分别为0.47~0.92、0.15~0.86和0.39~1.00;水稻单基因系对其抗性频率分别为3.85%~96.15%、5.26%~73.68%和4.76%~95.24%。适用于哈尔滨市的优化鉴别体系包括Pi-9、Pi-11、Pi-a、Pi-ks、Pi-5、Pi-i、Pi-sh、Pi-3、Pi-km和Pi-ta共10个基因,2006—2008年累计方差贡献率分别为86.15%、98.77%和87.39%;适用于鸡西市的优化鉴别体系包括Pi-9、Pi-11、Pi-a、Pi-ks、Pi-5、Pi-i、Pi-sh、Pi-1、Pi-7和Pi-t共10个基因,2006—2008年累计方差贡献率分别为82.58%、94.55%和90.37%。应用优化后的鉴别体系可将哈尔滨市2006—2008年采集的菌株划分为22、12和23个致病型,将鸡西市2006—2008年采集的菌株划分为22、14和18个致病型。