Fusarium oxysporum f. sp. radicis‐vanillae is the causal agent of root and stem rot of vanilla

Root and stem rot (RSR) is a very detrimental disease of vanilla worldwide. Fusarium oxysporum is frequently associated with the disease but other Fusarium species are also reported. In this international study, 52 vanilla plots were surveyed in three of the most important vanilla producing countries (Madagascar, Reunion Island and French Polynesia) in order to determine the aetiology of RSR disease. Subsets from the 377 single‐spored Fusarium isolates recovered from rotten roots and stems in the surveys were characterized by molecular genotyping (EF1α and IGS gene sequences) and pathogenicity assays on Vanilla planifolia and V. ×tahitensis, the two commercially grown vanilla species. Fusarium oxysporum was shown to be the principal species responsible for the disease, representing 79% of the isolates recovered from the RSR tissues, 40% of which induced severe symptoms on inoculated plantlets. Fusarium oxysporum isolates were highly polyphyletic regardless of geographic origin or pathogenicity. Fusarium solani, found in 15% of the samples and inducing only mild symptoms on plantlets, was considered a secondary pathogen of vanilla. Three additional Fusarium species were occasionally isolated in the study (F. proliferatum, F. concentricum and F. mangiferae) but were nonpathogenic. Histopathological preparations observed in wide field and multiphoton microscopy showed that F. oxysporum penetrated the root hair region of roots, then invaded the cortical cells where it induced necrosis in both V. planifolia and V. ×tahitensis. The hyphae never invaded the root vascular system up to 9 days post‐inoculation. As a whole, the data demonstrated that RSR of vanilla is present worldwide and that its causal agent should be named F. oxysporum f. sp. radicis‐vanillae.     

Characterization of Fusarium oxysporum f. sp. radicis-cucumerinum attacking melon under natural conditions in Greece

A severe root and stem rot disease of melon was observed during the 2001 growing season on four glasshouse crops in Heraklio, Greece. A total of 43 isolates of F. oxysporum , obtained in Crete from glasshouse-grown melon and showing fusarium wilt or root and stem rot symptoms, were characterized by pathogenicity and vegetative compatibility. The majority of these isolates was also fingerprinted via amplified fragment length polymorphic (AFLP) analysis. Of the total number of isolates, 22 were identified by pathogenicity tests as F. oxysporum f. sp. melonis , 20 as F. oxysporum f. sp. radicis-cucumerinum , while one isolate was nonpathogenic on cucumber, melon, sponge gourd and pumpkin. All 22 isolates of F. oxysporum f. sp. melonis were assigned to vegetative compatibility group (VCG) 0134, and all 20 isolates of F. oxysporum f. sp. radicis-cucumerinum to VCG 0260. Isolates of F. oxysporum f. sp. radicis-cucumerinum were incompatible with isolates of F. oxysporum f. sp. melonis. AFLP fingerprinting allowed for the clustering of the isolates of the two formae speciales of F. oxysporum along two separate phenetic groups: f. sp. melonis to AFLP major haplotype I, and f. sp. radicis-cucumerinum to AFLP major haplotype II. Overall, pathogenicity, vegetative compatibility grouping and AFLP analysis were correlated and effectively distinguished isolates of F. oxysporum from melon. This appears to be the first report of natural infection of melon by F. oxysporum f. sp. radicis-cucumerinum worldwide.     

Trichothecene production is detrimental to early root colonization by Fusarium culmorum and F. graminearum in fusarium crown and root rot of wheat

Fusarium culmorum (Fc) and F. graminearum (Fg) belong to the predominant causal agents of fusarium crown and root rot (FCR) in wheat. While many studies have been done to investigate crown rot, including stem base infection, root colonization and mycotoxin production associated with root rot is not well understood. In this study the impact of mycotoxins on the colonization of wheat roots and stem bases was analysed by using Fc and Fg isolates that varied in both quantity and types of trichothecenes they produce. Seedling inoculations in growth chambers with a high deoxynivalenol (DON)- and 3-acetyldeoxynivalenol (3ADON)-producing isolate led to more severe symptoms and 20-times greater colonization of the stem base, as measured by Fc DNA accumulation, than isolates that produced less DON/3ADON. In contrast to stem base colonization, in vitro inoculations of roots with a Tri5 deletion mutant deficient in Fg trichothecene production led to three-times higher colonization than the wildtype. Furthermore, an Fc isolate that produced low levels of zearalenone resulted in twice the level of colonization of a high DON/3ADON-producing isolate included in the study. When root inoculation with a low DON/3ADON-producing Fc isolate was supplemented with exogenous DON, DON production decreased by more than half per unit weight of Fc DNA, and root colonization doubled compared to the untreated control. Therefore, in contrast to its potential role as an aggressiveness factor in stem base infection, trichothecene production by Fc and Fg is detrimental to the early stages of wheat root colonization in FCR.     

Histology of root rot of flax seedlings (Linum usitatissimum) infected by Fusarium oxysporum f.sp. lini

The histology of root rot of flax seedlings infected by Fusarium oxysporum f.sp. lini was studied using semi-thin sections of plastic-embedded roots. Within two days, the fungus colonised the root cap cell layers by intercellular and intracellular growth. Attempted intercellular penetration of root cap cells via the middle lamella induced the formation of appositions next to penetrating hyphae. Other cells next to invading hyphae collapsed, which was accompanied by swelling of the cells neighbouring the collapsing cells. Invasion of the root cap and growth towards the protodermis seemed retarded to some extent by the natural sloughing off of root cap cell layers. The protodermis and cortex were reached and penetrated in four days, which was followed by rapid and massive colonisation of the entire root tip. The protoxylem was reached in eight days. From eight to sixteen days after inoculation, the lower parts of the roots were colonised throughout and the cortical region was degraded. Colonised tissues were severely plasmolyzed. Heavily colonised roots were hollowed out, the only remaining tissues being the epidermis and exodermis outside, and remainders of the colonised xylem inside. Upward spread of root rot was restricted in the period studied to the first 10 mm from the root tip, the upper parts of the root and the hypocotyl being unaffected except for invasion through lateral roots infected at their respective tips. Mature roots with a well-developed epidermis and exodermis were not invaded from outside. Disease development was similar in partially resistant Hermes and susceptible Regina, except for rot development that was consistently slightly more extensive in the susceptible cultivar. Distinct extravascular resistance factors were not detected in Hermes, suggesting that extravascular resistance in flax to F. oxysporum f.sp. lini is of a quantitative nature.     

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.     

抗、感大豆品种对尖镰孢根腐病菌侵染及毒素的反应

为了进一步明确大豆抗感品种对根腐尖镰孢的抗病机制,通过透射电镜和形态观察分析了尖镰孢(M38)侵染及产生的毒素对抗感大豆品种的影响。研究表明大豆幼苗胚根经粗毒素处理后,抗病品种‘东农56’幼苗胚根生长没有显著差别,但显著抑制了感病品种‘黑农53’胚根的伸长和侧根的生长;尖镰孢毒素高浓度和低浓度(V粗毒素∶V无菌水=1∶0和1∶15)对抗感品种的致萎能力无显著差异,高浓度处理平均萎蔫指数为100,低浓度处理为17.9~18.1左右;但中等浓度(V粗毒素∶V无菌水=1∶1,1∶5,1∶10)对于感病品种的致萎作用更大;同时,发现尖镰孢侵染感病大豆品种根内侵染量要明显多于抗病品种,且感病品种组织中菌丝的直径明显大于抗病品种,都出现很明显的质壁分离和细胞壁加厚的现象。     

Vegetative compatibility and heterokaryon stability in Fusarium oxysporum f.sp. radicis-lycopersici from Italy

Fusarium crown and root rot, caused by Fusarium oxysporum f.sp. radicis-lycopersici ( Forl ), is one of the most destructive soilborne diseases of tomato in Italy. Chlorate-resistant, nitrate-nonutilizing ( nit ) mutants were used to determine vegetative compatibility among 191 isolates of Forl collected in five geographic regions (Calabria, Emilia-Romagna, Liguria, Sardinia, Sicily) in Italy. The isolates were assigned to five vegetative compatibility groups (VCGs): 65 isolates to VCG 0090; 99 to VCG 0091; 23 to VCG 0092; two to VCG 0093; and two to VCG 0096. The population structure of Forl in Italy is similar to that reported for Israel, and differs from that found in North Atlantic European countries, where VCG 0094 is predominant. The stability of prototrophic heterokaryons originating from hyphal anastomosis between compatible complementary nit mutants was assessed through conidial analysis and mycelial mass transfer. Most monoconidial cultures (84%) recovered from 117 prototrophic heterokaryons were nit mutants, indicating that heterokaryons generally do not proliferate well through conidiation; most of the 177 prototrophic heterokaryons examined were unstable, and only 9% sustained prototrophic growth through the tenth mycelial transfer upon subculturing. The prototrophic growth is proposed to be maintained through restoration of the heterokaryotic state by continual anastomosis between adjacent homokaryotic hyphae. Since heterokaryosis is a prerequisite for parasexual recombination, we speculate that this mechanism is unlikely to play a major role in generating the VCG diversity found among Forl or other strains of F. oxysporum.     

Combining nonpathogenic strains of Fusarium oxysporum with sodium chloride to suppress fusarium crown rot of asparagus in replanted fields

Nonpathogenic strains of Fusarium oxysporum (NPFO) were tested alone, and in combination with rock salt (NaCl), for their ability to suppress fusarium crown and root rot of asparagus in replanted fields. Five NPFO strains were first screened with and without NaCl in the glasshouse using autoclaved asparagus soil mixed with potting mix. Asparagus roots were treated with NPFO suspensions or water, then inoculated 1 week later with pathogenic F. oxysporum ; then after 1 week pots received 100 mL 1% NaCl or water. After 12 weeks the NPFO strain CS-20 increased root weight when compared with controls. Rock salt did not affect root growth. Root lesions were reduced relative to the control by all NPFO strains and by NaCl applications, but there were no interactions between NPFO and NaCl. The NPFO strains CS-20, CWB 314 and CWB 318 were compared with no treatment in two 4-year replanted field studies in Hamden, and Windsor, CT, USA. Crowns were treated with NPFO at planting, and NaCl was broadcast at 280 kg ha⁻¹, and at 560 kg ha⁻¹ in later years. CWB 318 reduced disease at both sites and increased marketable yield in Hamden. Treatment with NaCl increased yield by 29% over controls in Windsor, but did not increase yield in Hamden. Recovered root isolates of F. oxysporum categorized by heterokaryon tests revealed that, in the glasshouse, CS-20 colonized roots better than other strains, while CWB 318 was the only strain found on roots from field plots after 4 years. Applications of NaCl did not hinder the suppressive ability of the nonpathogenic strains. The perennial nature of asparagus may require that nonpathogenic strains possess superior survival traits along with biocontrol traits.     

一种马铃薯根茎腐烂病病原鉴定

正马铃薯(Solanum tuberosum)为茄科茄属植物,是全世界广泛种植的重要粮食作物~([1])。马铃薯为人们提供了丰富的营养物质,如碳水化合物、多种微量营养素和有利于健康的膳食纤维~([2,3])。马铃薯根茎腐烂病由多种病原菌引起,是马铃薯采后的主要病害~([4])。甘薯长喙壳菌也引起多种植物果实腐烂,如巴西首次报道甘薯长喙壳菌侵染鸡蛋     

Vascular colonization patterns in susceptible and resistant tomato cultivars inoculated with Fusarium oxysporum f.sp. lycopersici races 0 and 1

The vascular colonization pattern of Fusarium oxysporum f.sp. lycopersici races 0 and 1 in tomato was studied in five susceptible and five resistant cultivar–fungus combinations during a 26-day period after inoculation by root immersion. Propagules spread discontinuously along the stems in all five cultivars 1 day after inoculation, irrespective of cultivar resistance. Five days later the fungus was limited to the stem bases in all cultivars. Between the fifth and 12th days, stem colonization by the fungus stopped in all cultivar–race combinations. Thereafter, the situation remained stable in resistant combinations, with inoculum distributed discontinuously, and no disease symptoms were apparent. By contrast, in the susceptible combinations a gradual upward colonization of the stems was seen such that fungal distribution was no longer discontinuous and disease symptoms appeared. These results suggest that a fungal 'incubation' period in the base of the vascular system is required before a secondary invasion of tissues occurs in susceptible genotypes. The slope of the regression line fitted between the height reached by the fungus up the stem ( y ) and the time after inoculation ( x ) provides a measure of the horizontal (polygenic) resistance in tomato cultivars     

香蕉枯萎病菌侵染香蕉根系的组织学过程

 为探明香蕉枯萎病菌侵染香蕉根系的过程,利用绿色荧光蛋白标记的香蕉枯萎病菌4号生理小种（Fusarium oxysporum f. sp. cubense race 4 tagged with green fluorescent protein,GFP-FOC4）,接种香蕉根系以观察病原菌侵染香蕉根系的组织学过程。结果表明,接种1 d后病原菌以菌丝体、大型分生孢子和小型分生孢子的形式附着于根系表皮细胞,优先沿细胞胞间层生长。接种7 d后,观察到病原菌以菌丝体、大型分生孢子和小型分生孢子的形式直接侵染维管束,在维管束内以两种方式扩展繁殖,一种在维管束内横向扩展,菌丝体随机分支,逐步形成网状分布;另一种是菌丝体在维管束内纵向生长,倾向于呈束状沿维管束单侧生长繁殖,形成大量菌丝体。本研究首次从组织病理学的角度观察并分析了GFP-FOC4侵染香蕉根系的过程,为研究香蕉枯萎病菌的致病过程机理提供参考。     

Vegetative compatibility grouping in Fusarium oxysporum f.sp. radicis-lycopersici from the UK, the Netherlands, Belgium and France

The population structure of Fusarium oxysporum f.sp. radicis-lycopersici ( F.o.r.l .), the causal agent of crown and root rot disease in tomato, was studied using the vegetative compatibility grouping approach. Four vegetative compatibility groups (VCGs) were identified among 37 isolates from the UK, the Netherlands, Belgium and France. Three of these VCGs (0090, 0091, 0094) had already been described, whereas VCG 0097 was new. VCG 0094 was dominant in the UK, the Netherlands and Belgium, but not in France. The opposite was true for the cosmopolitan VCG 0091, while the cosmopolitan VCG 0090 was only found in France. Based on hyphal interactions, VCG 0094 was divided into three subgroups, each comprising isolates from at least two countries. One isolate of VCG 0094 did not belong to any of these subgroups, suggesting further variability in this VCG. Isolate FORL-19R from France, previously assigned to VCG 0090 I, was reassigned to VCG 0090 III, a new subgroup of VCG 0090 found in Israel. FORL-19R and additional members of its subgroup manifest cross-VCG compatibility between VCG 0090 and VCG 0092. Along with previous studies, the multiple VCGs and subgroups found among F.o.r.l . in western Europe demonstrate a high level of genetic diversity in this pathogen.     

我国甘薯新病害-茎腐病的研究初报

 2006年以来广东省主要甘薯产区发现1种甘薯新病害,主要症状表现为叶片变黄,茎基部呈黑色水浸状腐烂,并逐渐沿茎枝向顶端腐烂,后整株倒伏、死亡。从甘薯病茎部分离得到了病菌,经柯赫法则验证为致病病原菌。根据病原菌的形态特征、培养性状、生理生化及16S rDNA序列分析,鉴定其为菊欧文氏菌(Erwinia chrysanthemi)。采用茎枝、菌液共培养法接种8个甘薯品种,结果表明8个品种均无抗病性,病原菌致病性较强。这是我国首次发现该病害。      

Induced suppressiveness to<Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f.sp.<Emphasis Type="Italic">radicis lycopersici</Emphasis> in rockwool substrate used in closed soilless systems

Tomatoes grown in soilless systems can be seriously damaged byFusarium oxysporum Schlect f.sp.radicis lycopersici (Forl) causing Fusarium crown and root rot (FCRR). FCRR suppression can be achieved through the use of chemicals, selected substrates, composts and artificially introduced antagonistic microorganisms. This study evaluated the natural capacity of a used rockwool to suppress FCRR infections. New and used rockwool, sampled from closed soilless systems, was either autoclaved or not, either artificially inoculated withForl or not and, finally, sown with tomato seeds cv. ‘Cuore di Bue’. The effects of autoclaved/non-autoclaved and used/new rockwool on FCRR incidence were assessed by evaluating the symptoms of crown rot on the root — shoot transition zone of tomato seedlings. Non-autoclaved and inoculated used rockwool significantly reduced FCRR incidence when compared with non-autoclaved and inoculated new rockwool. Autoclaved and inoculated used rockwool did not suppress FCRR, similarly to new and inoculated rockwool. These findings are in accordance with other research that, on a cucumber/Pythium host/pathogen complex in a closed rockwool soilless system, demonstrated the key role of resident microflora in suppressing the root rot disease. http://www.phytoparasitica.org posting Dec. 8, 2006.     

甘薯茎腐病的研究进展

甘薯茎腐病是由达旦提狄克氏菌Dickeya dadantii Samson et al.引起的细菌性甘薯病害,属于我国新发生病害,其蔓延迅速、防治困难,严重影响甘薯的品质和产量,已成为我国南方甘薯产区主要病害之一。文章对该病症状、病原菌分类、致病机制、全基因组测序概况和防治措施等方面的研究进展进行了综述,并指出了今后的研究方向。     

2013-2016年河南省小麦茎基腐病的发生危害情况及特点

2013-2016年连续4年对河南省不同类型麦田小麦茎基腐病发生和危害情况等进行了调查。结果表明,小麦茎基腐病在河南省已经广泛分布,每年均都有不同程度发生,其中2013年病田率为45.8%,病田白穗率为0.4%~11%;2014年病田率为12.6%,病田白穗率为0.1%~3.7%;2015年病田率为32.5%,病田白穗率为0.1%~16.1%;2016年发生最重,病田率为65.1%,病田白穗率为0.1%~31.5%。调查还发现,河南省小麦茎基腐病发生的特点是北部和西部发生较重;小麦-玉米连作田发生较重,而小麦-水稻连作田块发生较轻;干旱的田块发生危害重。病害产量损失的初步测定结果表明,感病最严重的分蘖病茎高度减少55.8%,且不能结实;能结实病茎较健茎高度减少14.0%~18.0%,穗粒数减少22.7%~54.5%,穗粒重减少33.3%~90.5%,千粒重减少3.2%~73.2%;当病田白穗率为22%时,有效穗数减少33.3%,产量损失达51.6%。本文还针对目前国内对小麦茎基腐病研究薄弱的问题,提出了今后需要加强的研究工作。     

Induction of systemic disease resistance and pathogen defence responses in Asparagus officinalis inoculated with nonpathogenic strains of Fusarium oxysporum

The ability of nonpathogenic isolates of Fusarium oxysporum (np Fo ) to induce systemic resistance and defence responses against subsequent challenge with a pathogenic strain of F. oxysporum f. sp. asparagi ( Foa ) was examined in Asparagus officinalis . In a split-root experiment, roots inoculated with np Fo exhibited a hypersensitive response and those subsequently inoculated with Foa displayed resistance. Induction of systemic resistance in np Fo -treated plants led to significantly fewer necrotic lesions ( P  = 0·05) and reduced Foa disease severity compared with plants not treated with np Fo . In hyphal-sandwich root inoculation experiments, activities of peroxidase and phenylalanine ammonia-lyase and lignin content were higher in np Fo -treated plants and increased more rapidly than in np Fo -untreated plants after Foa inoculation. Antifungal activity (inhibition of fungal spore germination and germ-tube growth) from exudates of roots inoculated with Foa were observed for np Fo -treated plants but not for np Fo -untreated plants. Thus, isolates of np Fo may function as inducers of systemic acquired resistance (SAR) and defence responses against Foa invasion in A. officinalis .