A new race of Fusarium oxysporum f. sp. lactucae of lettuce

Fusarium oxysporum f. sp. lactucae, the causal agent of fusarium wilt of lettuce (Lactuca sativa), occurs in most countries in which lettuce is grown and causes serious economic losses. Three races (1, 2 and 3) of the pathogen have previously been identified on the basis of their ability to cause disease on differential lettuce cultivars, as well as by means of molecular tools developed to characterize different races of this pathogen. Only race 1 has been detected in Europe so far. In this study, two isolates of F. oxysporum, obtained from lettuce plants grown in the Netherlands showing symptoms of wilt, have been characterized by combining the study of pathogenicity with differential cultivars of lettuce and molecular assays to determine whether the isolates are different from the known races of F. oxysporum f. sp. lactucae. This study reports the presence of F. oxysporum f. sp. lactucae for the first time in the Netherlands. The causal pathogen has been identified, using the IRAP‐SCAR technique, as a new race of F. oxysporum f. sp. lactucae. Specific primers have been designed to identify this new race.     

Genetic diversity in Fusarium oxysporum f.sp. dianthi and Fusarium redolens f.sp. dianthi

Pathogenic isolates were selected representing all known vegetative compatibility groups (VCGs) and races of Fusarium oxysporum sensu lato from Dianthus spp. On basis of differences in the internal transcribed spacer region of the ribosomal DNA, six VCGs were classified as F. oxysporum f.sp. dianthi and four as F. redolens f.sp. dianthi. All VCGs of F. oxysporum f.sp. dianthi were characterized by unique restriction fragment length polymorphisms (RFLPs), unique overall esterase profiles, and unique virulence spectra, supporting a clonal lineage concept. Two VCGs of F. oxysporum f.sp. dianthi nevertheless comprised more than one race, but races within the same VCG shared the same distinct overall virulence spectrum. VCGs belonging to F. redolens f.sp. dianthi also had unique RFLPs and unique virulence spectra, but had grossly identical esterase profiles. Three new races (9, 10 and 11) are described for F. oxysporum f.sp. dianthi, and four for F. redolens f.sp. dianthi. Two races previously considered lost were recovered; race 7 was identified as a member of VCG 0021 of F. oxysporum f.sp. dianthi while race 3 was identified as a distinct VCG and race of F. redolens f.sp. dianthi. A summary of races and VCGs in F. oxysporum f.sp. dianthi and F. redolens f.sp. dianthi is presented.     

香蕉枯萎病菌群体多样性研究进展

香蕉枯萎病严重威胁世界香蕉产业,而目前尚无有效防治药剂。开发快速诊断技术以加强检疫,控制其传播速度,同时加快选育抗病品种是有效控制该病的根本策略。然而,无论是研发快速诊断的分子技术还是进行抗病品种的选育,都需要深入了解病原菌的群体结构及其基因多样性背景。香蕉枯萎病菌经过一个多世纪的变异与进化,已分化出4个生理小种,23个营养亲合群和多个基因多样性类群。本文从香蕉枯萎病的起源及其病原菌培养性状、生理小种、致病性、营养亲合群及基因多样性等方面研究进展进行梳理和分析,以期为下一步的研究提供思路和启发。     

Biological control of Fusarium oxysporum f. sp. lycopersici

Fungi known to produce lytic enzymes were used in an attempt to control wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici (FOL). Some of the fungal species (Penicillium oxalicum, Penicillium purpurogenum and Aspergillus nidulans) damaged hyphae of FOL in vitro and reduced the numbers of microconidia in the soil. Treatments with fungi did not result in a reduction in either chlamydospores of FOL in soil or populations of FOL in the rhizosphere of tomato. P. oxalicum was the most effective agent of biocontrol, and it reduced disease severity in both non-autoclaved (20% decrease) and sterile soil. In sterile soil, P. oxalicum reduced disease with different levels of severity (27% decrease at high levels and 50% decrease at low levels). Disease control by A. nidulans and P purpurogenum was only achieved when disease severity was low in sterile soil (55% and 45%, respectively).     

Dispersal of Formulations of Fusarium oxysporum f. sp. erythroxyli and F. oxysporum f. sp. melonis by Ants

ABSTRACT A natural epidemic of Fusarium wilt on coca (Erythroxylum coca) in Peru prompted the suggestion of possibly using the pathogen Fusarium oxysporum f. sp. erythroxyli as a mycoherbicide against this narcotic plant. During field trials conducted in Kauai, HI, to test the pathogenicity of the coca wilt pathogen, ants were observed removing formulations from test plots. While removal of formulations by ants was considered detrimental with respect to conducting field tests, ant removal was considered potentially beneficial in disseminating the mycoherbicide. Thus, research was initiated to assess the ability of formulation additives to alter the preference of ants for the formulated mycoherbicide. In Hawaii, preference of indigenous ants for removing formulations was tested using three different food bases (rice, rice plus canola oil, and wheat flour [gluten]). Similar tests were conducted at Beltsville, MD, using F. oxysporum f. sp. melonis, in which the formulation based on wheat flour was replaced by a formulation based on canola meal. Formulations based on wheat were preferred by ants in both locations; up to 90% of the wheat plus rice flour granules (C-6) and the wheat gluten plus kaolin granules (pesta) were removed within 24 h, while only 20% of those containing rice without oils were taken. However, when either canola, sunflower (Maryland only), or olive oil was added to the rice formulation, up to 90% of the granules were taken. The formulation based on canola meal was less attractive to ants, as only 65% of the granules were removed within a period of 24 h. Ants showed no preference with respect to presence or absence of fungal biomass. To alter the attractiveness of the C-6 formulation to ants, C-6 was amended with three natural products. Canna and tansy leaves were added to C-6 at a ratio of 1:5 (wt/wt), while chili powder was added at 1:25 or 1:2.5 (wt/wt). Canna, tansy, and the higher rate of chili powder significantly reduced the number of C-6 granules removed by ants. Canna and tansy leaves affected neither germination nor sporulation of the mycoherbicide, while the high concentration of chili powder reduced viability of propagules in the formulation. More F. oxysporum f. sp. erythroxyli-type colonies were recovered from inside ant nests (9 cm depth) than from nest surfaces, indicating that ants may distribute the mycoherbicide in the soil profile. Ants passively carried propagules of F. oxysporum f. sp. erythroxyli outside their bodies, as well as either very closely adhering to the outside or within their bodies.     

The infestation of tomato seed by Fusarium oxysporum f.sp. radicis-lycopersici

The infestation of seed by Fusarium oxysporum f.sp. radicis-lycopersici occurred at rates of 0-1 to 0-01 % in fruit on stem-infected plants. Direct infection of fruit in the flower or young developing fruit stage resulted in a grayish-brown lesion on the stylar end of the fruit or mummification. F. oxysporum f.sp. radicis-lycopersici was isolated from all seeds in such fruit. Picked fruit inoculated on the stem scar also became infected but 96 h after inoculation of the fruit, the seed was not infested or infected. The contact of clean seed with hands that had previously handled F. oxysporum f.sp. radicis-lycoperisid-infesied sawdust resulted in a high level of seed infestation. The fungus survived on seed sent across Canada and stored for up to 12 weeks. Treatment with NaOCl or 0·1 N HCl did not completely disinfest infested seed.     

农杆菌介导的西瓜枯萎病菌遗传转化

为获得带GFP标记的西瓜枯萎病菌转化株,用于后期观察病原菌侵染过程,采用农杆菌介导的方法,对西瓜枯萎病菌1号生理小种进行了遗传转化。结果表明:共培养时间为36h,枯萎病菌孢子和农杆菌AGL1比例为1∶1时该菌株的遗传转化效率最高,可以达到117.33个转化子/107个孢子。转化株的孢子、菌丝体及萌发的孢子均能发出稳定而强的绿色荧光。转化株的致病力检测显示其致病力与转化前的野生菌株致病力无明显差异。结果表明本研究获得的带GFP标记的西瓜枯萎病菌转化株可用于观察病菌在西瓜根系的侵染过程。     

Sensitivity of Fusarium oxysporum f. sp. cubense to phosphonate

Phosphonate (0.1 mM) significantly reduced growth of Fusarium oxysporum f. sp. cubense (Foc) race 4 grown at an optimal phosphate concentration of 0.3 mM in vitro. At higher phosphate concentrations, closer to physiological conditions within the plant, the sensitivity of Foc race 4 to phosphonate was greatly reduced, with 25 mM phosphonate required to reduce growth by 50% at 1 mM phosphate. Two isolates of Fusarium oxysporum f. sp. dianthi and another race of Foc, race 1, were shown to be similar to Foc race 4 in their sensitivity to phosphonate, while another species of Fusarium, F. avenaceum , was more sensitive to phosphonate in vitro.     

Genetic diversity in Fusarium oxysporum f. sp. melonis*

Fusarium oxysporum f. sp. melonis is an important vascular wilt pathogen of melon. Races 1, 2 and 1–2 of this fungus have been identified in Portugal by pathogenicity tests with appropriate hosts. The aim of this research was to examine the relationships between different races of F. o. melonis of Portuguese and French origin through analysis of random amplified polymorphic DNAs (RAPDs). DNA fingerprint profiles were developed for all the accessions. Each isolate showed 5–10 DNA bands with each of the 16 primers employed. A total of 126 bands was obtained. The size of amplified DNA fragments generated with these primers ranged from 0.5 to 3.2 kb. A phenogram based on the Jaccard coefficient of similarity was computed by the unweighed pair group method using arithmetic averages (UPGMA). It was found that Portuguese race 2 is very similar to French race 1, while French race 2 is the most dissimilar being clearly separated from all other races. The genetic diversity of these isolates is also being studied for vegetative compatibility by using the nit mutant system.     

Physiological races of Fusarium oxysporum f.sp. melonis in Tunisia

Fusarium wilt of melon, caused by Fusarium oxysporum f.sp. melonis (Fom), is an important disease; races of the pathogen were identified by inoculating differential standard host cultivars. A total of ten isolates that were obtained from 23 fields located in four different geographical regions were identified as pathogenic. Results indicate that all four known Fom races, namely, 0, 1, 2 and 1.2, were found in north and middle Tunisia. Race 1.2 was the most prevalent.     

Phylogenetic relationships of Fusarium oxysporum f. sp. melonis in Iran

Fusarium wilt of melon caused by Fusarium oxysporum f. sp. melonis is a destructive fungal disease in melon growing regions. Isolates of F. oxysporum obtained from six major melon producing provinces in Iran, from melons and other hosts, were characterized based on pathogenicity to melon, vegetative compatibility groups (VCGs) and nuclear ribosomal DNA intergenic spacer (IGS) sequencing. Thirty-four of 41 isolates from Iran in this study were identified as race 1,2 which belonged to either VCG 0134 or an unassigned VCG, which based on IGS sequencing grouped with the VCG 0135 tester isolate. The seven remaining isolates were identified as nonpathogenic to melon belonging to two undescribed VCGs. Based on sequence analyses of the IGS region of Iranian and foreign isolates, nine lineages were identified, each including one VCG. The separation of VCGs into distinct lineages based on IGS sequences is mostly consistent with Repetitive extragenic palindromic PCR (Rep-PCR) results. Exceptions are VCGs 0130 and 0131, which could be differentiated with IGS sequences, but not with Rep-PCR. Different races from the USA, France and Iran associated with VCG 0134 grouped into one IGS lineage but could be differentiated with Rep-PCR, suggesting that this VCG is more diverse than previously thought. Given the long history of melon cultivation in Iran and the Rep-PCR diversity of isolates belonging to this VCG, it could be speculated that VCG 0134 perhaps evolved in Iran.     

香蕉枯萎病菌生理分化研究摘要本研究

本研究对香蕉枯萎病菌菌株FOCAAA9(来自香蕉)和FOCABB1(来自粉蕉)进行培养试验和接种试验;在含粉蕉和香蕉组织浸提液的培养基上2个菌株的培养性状、菌丝生长速度、孢子形态、大小型孢子比率和产孢量显示出差异;接种结果FOCAAA9能侵染香蕉(MusaAAA)品种巴西蕉、红香蕉和台蕉引起枯萎病,而FOCABB1对3个香蕉品种无致病性。研究结果表明侵染香蕉和粉蕉的古巴尖镰孢[Fusariumoxysporumf.sp.cubense(E.F.Smith)Snyder]存在生理分化现象。     

假单胞菌对香蕉枯萎病菌的抑制作用

从已感染香蕉枯萎病的果园中分离到1株对香蕉枯萎病菌（Fusarium oxysporum f.sp.cubense）抑制作用很好的菌种,命名为G1。采用固体和液体培养法从不同角度证实了G1对香蕉枯萎病菌生长的抑制作用。结果表明,G1的发酵液、无菌滤液、挥发性物质、非挥发性代谢产物的平均抑菌率分别为92.5%、27.4%、73.8%、57.7%,可见抑制作用与活菌体有直接关系,其中产生挥发性物质尤其重要。液体培养的病原菌浓度为1.0×107cfu/mL经G1作用10d后,取样镜检发现G1通过抑制病原菌菌丝正常生长以至不能产孢,从而导致菌丝消融;通过吸附在孢子的周围,融解细胞壁,造成原生质泄露致使孢子死亡。     

Gene genealogies support Fusarium oxysporum f. sp. ciceris as a monophyletic group

Fusarium oxysporum f. sp. ciceris (Foc), the causal agent of fusarium wilt of chickpea, consists of two pathotypes (yellowing and wilting) and eight races (races 0, 1B/C, 1A and 2–6) of diverse geographical distribution. Six Foc isolates, one each of races 0, 1B/C, 1A, 4, 5 and 6, representing the two pathotypes and the geographical range of the pathogen, showed identical sequences in introns of the genes for translation elongation factor 1α ( EF1 α), β-tubulin, histone 3, actin and calmodulin. Eleven additional Foc isolates representative of all races, pathotypes and geographical range, and three isolates of F. oxysporum (Fo) nonpathogenic to chickpea were further analysed for sequence variation in the EF1 α gene. All isolates pathogenic to chickpeas shared an identical EF1 α gene sequence, which differed from that shared by the three Fo isolates nonpathogenic to chickpea. EF1 α gene sequences from the 17 Foc isolates and the three Fo isolates were compared with 24 EF1 α gene sequences in GenBank from isolates of 11 formae speciales of F. oxysporum by parsimony analysis. Foc isolates formed a grouping distinct from other formae speciales and nonpathogenic isolates. These results indicate that F. oxysporum f. sp. ciceris is monophyletic.     

香蕉枯萎病菌生理分化研究

本研究对香蕉枯萎病菌菌株FOCAAA9（来自香蕉）和FOCABB1（来自粉蕉）进行培养试验和接种试验；在含粉蕉和香蕉组织漫提液的培养基上2个菌株的培养性状、菌丝生长速度、孢子形态、大小型孢子比率和产孢量显示出差异；接种结果FOCAAA9能侵染香蕉（Musa AAA）品种巴西蕉、红香蕉和台蕉引起枯萎病，而FOCABB1对3个香蕉品种无致病性。研究结果表明侵染香蕉和粉蕉的古巴尖镰孢[Fusarium oxysporum f．sp．cubeilse（E．F．Smith）Snyder]存在生理分化现象。     

棉花枯萎病菌新生理型菌株的分子鉴定

 Fusarium oxysporum f.sp. vasinfectum(Fov)已报道有8个生理小种和一个澳大利亚生理型,在我国只报道有3、7、8号小种。前期研究发现,我国还有一个与3、7、8号小种具有较大遗传差异的Fov新生理型。本研究通过对3、7、8号小种和新生理型菌株的翻译延伸因子(EF-1α)基因序列比对分析,发现该新生理型菌株具有特异性碱基序列。根据这些特异性碱基序列,设计了一对针对新生理型菌株的特异性引物,并证明该引物可以特异性检测Fov新生理型菌株。利用该引物对采自河北省主要植棉区的77株Fov菌株进行筛选,鉴定出2株潜在的新生理型菌株。从这2个Fov菌株中克隆出EF-1α和β-tubulin基因序列,通过构建系统发育树,证明这2个Fov菌株为新生理型菌株,而且与澳大利亚生理型菌株具有较近的亲缘关系。本研究建立的分子检测方法可用于棉花枯萎病菌新生理型菌株的鉴定。     

Phylogeny and origin of Fusarium oxysporum f. sp. vanillae in Indonesia

Vanilla stem rot, caused by Fusarium oxysporum f. sp. vanillae (Fov), is the main constraint to increasing vanilla production in the major vanilla‐producing countries, including Indonesia. The current study investigated the origin of Fov in Indonesia using a multigene phylogenetic approach. Nineteen Fov isolates were selected to represent Indonesia, the Comoros, Mexico and Réunion Island. The translation elongation factor 1 alpha gene and the mitochondrial small subunit ribosomal RNA gene phylogenies resolved the Fov isolates into three distinct clades in both phylogenetic species of the F. oxysporum species complex, indicating a polyphyletic pattern of evolution. In addition, Fov isolates from Indonesia were also polyphyletic. These results suggest that the vanilla stem rot pathogen in Indonesia has a complex origin. The implications for disease management are discussed.