Population Dynamics of Fusarium Oxysporum f. Sp. Radicis-lycopersici in Relation to the Onset of Fusarium Crown and Root Rot of Tomato

Fusarium oxysporum f. sp. radicis-lycopersici the causal agent of crown and root rot in tomato comprises two overlapping separate phases: monocyclic and polycyclic. Oversummering inoculum is the source of primary infection (the monocyclic phase) and the spread from plant to plant via root-to-root contact is the source of the secondary infection (the polycyclic phase). In the present work, relationships between initial inoculum density, population dynamics of the pathogen in the root zone of diseased plants, and disease onset were studied. For the monocyclic phase, 55.1% of the variance of disease onset was attributed to the rate of pathogen proliferation in the root zone of plants, and only 12.8% of the variance was attributed to the amount of initial inoculum density. For the polycyclic phase, disease onset was not related to either initial inoculum density or the rate of pathogen proliferation in the root zone. At disease onset, the inoculum density of the pathogen in the root zone of plants infected from oversummering inoculum reached an average of 4.08 log cfu g soil^–1. The inoculum density of the pathogen in the root zone of plants infected by their diseased neighbors was 3.23 log cfu g soil^–1. A large variation in pathogen proliferation rate in the root zone was found among individual plants, suggesting that differences in the level of soil suppressiveness may occur not only between fields, but even in the same field over short distances.     

Pathogenicity of Phytophthora austrocedrae on Austrocedrus chilensis and its relation with mal del ciprés in Patagonia

Field observations, isolations and pathogenicity tests were performed on Austrocedrus chilensis (Cupressaceae) trees to determine the pathogenicity of Phytophthora austrocedrae and its role in the aetiology of the cypress disease mal del ciprés (MDC) in Argentina. It was found that P. austrocedrae is a primary pathogen of A. chilensis. It was isolated from large necrotic lesions in the inner bark, and superficially in the sapwood, at the root collar and stem, in most of the MDC‐affected stands surveyed along the range of A. chilensis in Argentina. The main symptom in naturally infected trees was a necrotic lesion extending from killed roots up to 1 m up the tree bole. Seedlings, saplings and adult trees were all susceptible to inoculation with P. austrocedrae. Under favourable experimental conditions (flooding), inoculated seedlings suffered massive mortality in less than a month. The importance of diseases caused by Phytophthora spp. in South American forests is discussed.     

木霉对土传病原真菌的拮抗作用

 分别在体外及温室测定了筛选菌株哈茨木霉Trichoderma harzianum(T₈₂)和Tricho-derma sp.(NF9)对土传病原真菌的拮抗作用。体外测定表明,木霉菌株T₈₂和NF₉对白绢病菌Sclerotium rolfsii,立枯丝核菌Rhizoctonia solani,瓜果腐霉Pythium aphanidermatum刺腐霉P.spinosum和尖镰孢Fusarium oxysporum在对崎培养中的拮抗系数分别为2或2~3和2。温室测定表明,用0、6%(W/W)T₈₂麸皮培养物(10⁷cfu/g)处理土壤。在人工接种白绢病菌,立枯丝核菌及瓜果腐霉20天后,黄瓜发病率分别比未用木霉处理的对照减少46、5%,28.4%和81。2%;用T₈₂和NF₉木霉孢子悬浮液(10⁸cfu/ml)处理黄瓜种子,人工接种白绢病菌11天后,黄瓜成苗率分别比未用木霉处理的对照增加14%的20%。分别在光学显微镜和扫描电镜下观察到木霉T₈₂对白绢病菌菌丝和菌核的重寄生以及木霉T₈₂和NF₉对立枯丝核菌菌丝的缠绕。穿入及寄生。作者认为重寄生可能是试验木霉菌株T₈₂和NF₉对白绢病菌和立枯丝核菌的主要拮抗机制。     

Isolation and pathogenicity of Phytophthora species from declining Rubus anglocandicans

Rubus anglocandicans is the most widespread and abundant blackberry species within the European blackberry (Rubus fruticosus) aggregate in Western Australia (WA). European blackberry is also one of the 32 Weeds of National Significance in Australia. A disease recorded as ‘blackberry decline’ was first observed in some blackberry sites in WA in 2006. A disease survey was conducted in the Manjimup‐Pemberton region along the Warren and Donnelly River catchments in WA between 2010 and 2012. Phytophthora amnicola, P. bilorbang, P. cryptogea, P. inundata, P. litoralis, P. multivora, P. taxon personii, P. thermophila and a P. thermophila × amnicola hybrid were recovered from declining and adjacent decline‐free sites, as well as from streams and rivers. Phytophthora cinnamomi was isolated from dying Banksia and Eucalyptus species from two non‐decline sites. Of these species, P. bilorbang and P. cryptogea were more pathogenic than the others in under‐bark inoculations using excised stems (primocanes), in planta primocane inoculations in blackberry growing wild in native forest stands, and in glasshouse pot trials. It was concluded that blackberry decline is a complex syndrome and Phytophthora species, in particular P. bilorbang and P. cryptogea, together with temporary inundation, are major biotic and abiotic factors contributing to blackberry decline.     

核桃叶水浸液对四种作物的化感作用

研究了核桃叶水浸液对玉米、花生、豌豆和辣椒种子萌发及幼苗生长的化感作用.结果表明,不同浓度核桃叶水浸液对4种作物各项测定指标抑制作用各异,随着处理浓度增大,抑制作用不断增强,其中对4种受体发芽势和根长的抑制效应与对照相比差异显著;随处理浓度降低,抑制作用减弱,在0.025g/mL处理时甚至表现为促进作用,体现出双重浓度...     

Specific detection of Phytophthora cactorum in diseased strawberry plants using nested polymerase chain reaction

Validated protocols for DNA purification and PCR amplification are reported for detection of Phytophthora cactorum in diseased strawberry plants. To remove PCR inhibitors, necrotic strawberry tissues were soaked in 5% alconox solution for >12 h before DNA extraction, and the extracted genomic DNA was embedded in an agarose gel chamber and subjected to electrophoresis. The purified DNA was amplified reliably by PCR. Nested PCR was used to detect a portion of the rRNA gene of P. cactorum in samples. In the first round of PCR, primers ITS1 and ITS4 amplified fragments of varying sizes from total genomic DNA from diseased strawberry plants. In the second round of PCR, a 1:25 dilution of the first-round PCR products was used as template with two P. cactorum- specific primer pairs (BPhycacL87FRG and BPhycacR87RRG, which amplified a 340-bp fragment and a 480-bp fragment from the rRNA gene; and BPhycacL89FRG and BPhycacR176RRG, which amplified a 431-bp fragment). Validation tests using culture-based isolations as a standard for comparison indicated that the DNA purification and PCR primers and amplification protocols were reliable and specifically amplified a portion of the rRNA gene of P. cactorum from necrotic root, crown and petiole tissues of strawberry naturally infected by the pathogen.     

Detection and quantification of Ilyonectria spp. associated with black‐foot disease of grapevine in nursery soils using multiplex nested PCR and quantitative PCR

Three nursery fields and three rootstock mother fields from commercial nurseries located in Comunidad Valenciana region (central‐eastern Spain) were surveyed in July 2011 to detect the presence and to quantify Ilyonectria spp. in the soil. In each field, ten soil samples were taken randomly with a soil probe at a depth of 10–30 cm, and 10–20 cm from the base of the plant. Three replicate subsamples (10 g each) were taken from each soil sample. DNA was extracted and a multiplex nested PCR with species‐specific primer pairs (Mac1/MaPa2, Lir1/Lir2 and Pau1/MaPa2) was used to identify the species present. Among the 180 soil DNA samples analysed, Ilyonectria spp. were detected in 172 of them. Ilyonectria macrodidyma complex was the most frequently detected, being identified in 141 samples from all the fields evaluated. However, I. liriodendri was detected in only 16 samples, but was present in all open‐root field nurseries and in two rootstock mother fields. In addition, quantitative PCR (qPCR) assays were done to assess the levels of I. liriodendri and I. macrodidyma‐complex DNA in the soil samples. Detection of Ilyonectria spp. DNA using qPCR correlated with the fields found positive with the nested multiplex PCR. DNA concentrations of Ilyonectria spp. ranged from 0·004 to 1904·8 pg μL^?1. In general, samples from rootstock mother fields showed the highest DNA concentrations. The ability to detect and quantify Ilyonectria spp. genomic DNA in soil samples from nursery fields and rootstock mother fields confirms soils from both field types as important inoculum sources for black‐foot pathogens.     

Role of new bacterial surfactins in the antifungal interaction between Bacillus amyloliquefaciens and Fusarium oxysporum

The aim of this work was to investigate the major mechanisms involved in antagonism of BO7, a novel strain of Bacillus amyloliquefaciens isolated from orchard soil, against the vascular wilt fungus Fusarium oxysporum f. sp. lycopersici (Fol). BO7 markedly reduced the incidence of Fol vascular wilt on tomato plants and displayed strong in vitro inhibitory activity against Fol. Scanning electron microscopy demonstrated the ability of BO7 cells to adhere to fungal hyphae and to efficiently colonize tomato roots. The low molecular weight fraction of BO7 culture filtrate displayed high antifungal activity against Fol, resulting in growth inhibition and dramatic alterations of hyphal morphology. Three structurally related surfactin lipopeptides, identified as the major components of the bioactive fraction, were assayed for their inhibitory activity against Fol. One of these compounds exerted a strong and uncommon antifungal activity for lipopeptides of the surfactin family, accounting for most of the inhibitory activity of the BO7 culture filtrate. Among a collection of Fol knockout isolates tested, mutants altered in cell wall structure showed increased sensitivity to the bacterial compounds. These results suggest that the fungal cell wall might have a key role in the sensitivity of Fol towards bacterial surfactins from B. amyloliquefaciens.     

A new genus of Cryphonectriaceae isolated from Lagerstroemia speciosa in southern China

Numerous species in the Cryphonectriaceae have been recorded on the Myrtales and many of these are economically important pathogens of Eucalyptus. Some species have also recently been shown to be endophytes of native Myrtaceae and to have undergone host jumps to infect Eucalyptus species established as exotics in plantations. Recent surveys in the GuangDong and HaiNan Provinces of South China reveal the presence of a species of Cryphonectriaceae associated with cankers on trees of Lagerstroemia speciosa (Lythraceae, Myrtales). Fungal structures were observed on the surface of dead bark covering cankers and on branch stubs. Multigene phylogenetic analyses were conducted based on DNA sequence comparisons of the partial LSU gene, ITS region of the nuclear ribosomal RNA gene and two regions of the β‐tubulin (BT) gene. The results revealed the presence of a previously undescribed genus and species in the Cryphonectriaceae. The fungus is described here as Chrysomorbus lagerstroemiae gen. et sp. nov. Inoculation tests showed that it is an aggressive pathogen on L. speciosa and that it can also infect Eucalyptus.     

The potential for using cyanobacteria (blue-green algae) and algae in the biological control of plant pathogenic bacteria and fungi

Cyanobacteria (blue-green algae) and eukaryote algae occur in freshwater, marine, and terrestrial (soil) habitats. In fact, these microorganisms comprise most of the world's biomass. Although the cyanobacteria are mostly photoautotrophic, some are facultative heterotrophs, capable of growing on certain substrates in darkness. Also, some are non-phototrophic and hence, are obligate heterotrophs. A number of cyanobacteria and eukaryote algae, particularly macroalgae, produce various, biologically active compounds. These include antibiotics which in laboratory tests inhibited bacteria and fungi that incite diseases of humans. In addition, the following fungi which are of interest to plant pathologists, were inhibitedin vitro by substances produced by various cyanobacteria: The saprophytesChaetomium globosum, Cunninghamella blakesleeana, andAspergillus oryzae and the plant pathogensRhizoctonia solani andSclerotinia sclerotiorum. Extracts from seaweeds (macroalgae) sprayed on plants have been reported to reduce the incidence ofBotrytis cinerea (gray mold) on strawberries,Erysiphe polygoni (powdery mildew) on turnips, and damping-off of tomato seedlings. Because many cyanobacteria and algae produce a large number of antibacterial and antifungal materials, are almost never a threat to the environment, and many can be grown in quantity in mass culture, they are suitable candidates for exploitation as biocontrol agents of plant pathogenic bacteria and fungi. Much additional work remains to be done however, to thoroughly evaluate cyanobacteria and algae and their products for this role.     

水稻种子携带恶苗病菌种类及其致病性研究

水稻恶苗病是水稻上的一种重要病害,每年给我国的水稻生产造成严重的经济损失.本文旨在探究我国主要稻作区水稻种子携带恶苗病菌的种类及其致病性情况.采用洗涤法和平板培养法对收集我国主要稻作区的66份水稻种子样本进行恶苗病病菌分离,共获得111株病菌分离物,并从中选取24株代表性分离物,采用翻译延伸因子TEF-1α序列、形态学...     

一种筛选稗草生防潜力菌的简易生测方法

将催芽至露白的稗草和水稻种子直接接种在于PDA培养基上培养形成的 4种稗草病原菌 (交链孢菌、弯孢菌、禾长蠕孢菌稗草专化型、尖角突脐孢菌 )菌落上 ,观察稻、稗苗感病情况 ,调查根、芽生长抑制率。结果表明 ,4种菌对稻、稗的致病性和生长抑制率与常规生测法结果基本吻合。说明在培养基中初步测定、筛选稗草生防潜力菌是可行的。该方法与常规生测法比较 ,可节省一半时间左右 ,同时可减少工作量。     

Identification of a genetic lineage within Xanthomonas arboricola pv. juglandis as the causal agent of vertical oozing canker of Persian (English) walnut in France

A new bacterial disease of Persian (English) walnut (Juglans regia) has been observed in France. This disease, called vertical oozing canker (VOC), is characterized by vertical cankers on trunks and branches of affected walnut trees with oozing exudates. To determine the aetiology of the disease, a study was carried out in 79 walnut orchards and nurseries located in southeastern and southwestern France. Bacterial analysis from diseased samples yielded 36 strains identified as Xanthomonas arboricola and 32 strains identified as Brenneria nigrifluens on the basis of biochemical tests. The causal agent of VOC was identified as X. arboricola by pathogenicity tests on walnut. Fluorescent amplified fragment length polymorphism (F‐AFLP) was carried out on 36 strains of X. arboricola collected in this study, 24 strains of X. arboricola pv. juglandis isolated from walnut blight symptoms and one strain of X. arboricola pv. corylina included as an outgroup. Based on cluster analysis of F‐AFLP data, most X. arboricola strains responsible for main VOC outbreaks showed a high degree of similarity, forming a cluster clearly separate from strains of X. arboricola pv. juglandis isolated from walnut blight symptoms. It is suggested that VOC is caused by a distinct genetic lineage within the pathovar juglandis of X. arboricola that is also able to cause classical bacterial blight symptoms on walnut leaves and fruits.     

珍珠李枝枯病病原鉴定及致病性测定

In order to confirm the pathogen of branch blight on pearl plum and its virulence, 14 samples were collected from Guangxi and Guizhou Province, and 21 isolates were obtained and were identified as Botryosphaeriaceae. The results of colony morphology, conidial observation and molecular identification of internal transcribed spacer region (ITS1-5.8S-ITS2) and the translation elongation factor 1-α (EFl-α) showed that the pathogens of branch blight on pearl plum were Botryosphaeria dothidea (66.67%), Neofusicoccum parvum (19.05%), N. algeriense (9.52%), and Lasiodiplodia pseudotheobromae (4.76%). The pathogenicity of different species of Botryosphaeriaceae was tested by mycelial dishes inoculation, and it was found that typical isolates of the four species were pathogenic, among which L. pseudotheobromae was the most virulent one and B. dothidea was the weakest one. This is the first report that L. pseudotheobromae causes branch blight on pearl plum.     

Selection and Screening of Endorhizosphere Bacteria from Solarized Soils as Biocontrol Agents Against Verticillium dahliae of Solanaceous Hosts

Verticillium dahliae antagonistic endorhizosphere bacteria were selected from root tips of tomato plants grown in solarized soils. Fifty-three out of the 435 selected bacterial isolates were found to be antagonistic against V. dahliae and several other soilborne pathogens in dual cultures. Significant biocontrol activity against V. dahliae in glasshouse trials was demonstrated in three of 18 evaluated antagonistic isolates, provisionally identified as Bacillus sp. Although fluorescent pseudomonads were also isolated from root tips of tomato plants, none of the tested isolates exercised any significant antagonistic activity against V. dahliae in dual cultures. So these isolates were not tested in glasshouse trials in this study. Finally, two of the most effective bacterial isolates, designated as K-165 and 5-127, were shown to be rhizosphere colonizers, very efficient in inhibiting mycelial growth of V. dahliae in dual cultures and successfully controlling Verticillium wilt of solanaceous hosts. In glasshouse experiments, root dipping or soil drenching of eggplants with bacterial suspension of 10⁷cfu ml^–1 resulted in reduced disease severity expressed as percentage of diseased leaves (40–70%) compared to the untreated controls under high V. dahliae inoculum level (40 microsclerotia g^–1 soil). In heavily Verticillium infested potato fields, experiments with potato seeds dusted with a bacterial talc formulation (10⁸cfu g^–1 formulation), showed a significant reduction in symptom development expressed as percentage of diseased potato plants and a 25% increase in yield over the untreated controls. As for their effectiveness in increasing plant height, both bacterial isolates K-165 and 5-127 produced indolebutyric, indolepyruvic and indole propionic acids. Both antagonists are considered as plant growth promoting rhizobacteria bacteria since significantly increased the height of treated plants compared with the untreated controls. Chitinolytic activity test showed that both isolates were able to produce chitinase. Testing rhizospheric and endophytic activity of the antagonists it was shown that although the bacteria are rhizosphere inhabitants they also preferentially colonize the endorhizosphere of tomatoes and eggplants. Fatty acid analysis showed that isolate K-165 could belong to Paenibacillus alvei while 5-127 to Bacillus amiloliquefaciens.     

Variation in susceptibility of lettuce cultivars to fusarium wilt caused by Fusarium oxysporum f.sp. lactucae

Lettuce cultivars adapted to Californian growing conditions were screened for resistance to fusarium wilt caused by Fusarium oxysporum f.sp. lactucae in order to determine if differences in susceptibility among currently grown cultivars might contribute to management of this disease. Based on a preliminary evaluation of 46 cultivars, eight that were among the most resistant of their horticultural type (iceberg, romaine or leaf) were selected for further testing. The relative susceptibility of these cultivars was assessed by: (i) root-dip inoculation, (ii) sowing seeds into infested potting mix and (iii) transplanting seedlings into an infested field. Evaluations of disease severity showed that both methods (i) and (ii) produced cultivar rankings that were significantly correlated with rankings from field trials [method (iii)]. Two romaine and two leaf cultivars were highly resistant to fusarium wilt (mean disease severity rating of ≤1·3 on a 1–4 scale) under all test conditions. Other romaine and leaf cultivars, however, were highly susceptible in root–dip tests, so there was no consistent association between cultivar type and susceptibility to fusarium wilt. Likewise, there was considerable variation in susceptibility to wilt among iceberg cultivars, but all were significantly more susceptible than the most resistant romaine and leaf cultivars.