Allelism of theFcu-1 andFoc genes conferring resistance to fusarium wilt in cucumber

The inheritance of resistance toFusarium oxysporum f.sp.cucumerinum race 1 was determined in the cucumber cv. WIS-248 by analyzing segregation of F₁, F₂, and BC populations of crosses with the susceptible cv. Straight-8. Resistance was conferred by a single dominant gene. In an allelism test, it was proven that theFcu-1 gene, which confers resistance toF. oxysporum f.sp.cucumerinum races 1 and 2 in cucumber cv. SMR-18 and theFoc gene, which confers resistance toF. oxysporum f.sp.cucumerinum race 2 in cucumber cv. WIS-248, are indistinguishable.     

OS-诱抗剂诱导植物抗病性的作用探讨

用PDA培养基平板法测定了0.4%OS-诱抗剂水剂对水稻纹枯病菌、小麦纹枯病菌、油菜菌核病菌、辣椒立枯病菌、瓜类绵腐病菌、黄瓜枯萎病菌的生物活性,其EC₅₀值分别为34.56、59.33、33.17、85.92、91.91、122.87μg/mL,OS-诱抗剂对水稻纹枯病、油菜菌核病较好。高效液相色谱分析表明,经OS-诱抗剂处理后的植物提取液中酚类物质的种类和含量相对于对照有明显的变化,说明OS-诱抗剂对植物的防病作用可能是促使植物体内产生了酚类抗病物质。     

Acquired resistance to pimaricin in Cladosporium cucumerinum and Fusarium oxysporum f.sp. narcissi associated with decreased virulence

In laboratory experiments strains ofCladosporium cucumerinum andFusarium oxysporum f.sp.narcissi were selected, which showed resistance to the fungicidal antibiotic pimaricin. Increased resistance appeared associated with decreased fitness in vitro (radial growth and sporulation on agar media) and in vivo (pathogenicity). The physiological background of a link between sensitivity to the fungicide and pathogenicity is discussed. Samenvatting In laboratoriumproeven werden stammen vanCladosporium cucumerinum enFusarium oxysporum f.sp.narcissi verkregen, die resistent waren tegen het fungicide antibioticum pimaricine. Toegenomen resistentie bleek gepaard te gaan met een verminderde vitaliteit in vitro (radiale groei en sporulatie op een agar voedingsbodem) en in vivo (pathogeniteit) (Tabel 1 en 2). Het niveau van de resistentie tegen pimaricine bleek erg beperkt (Fig. 1). De fysiologische achtergrond van een koppeling tussen gevoeligheid voor het fungicide en pathogeniteit wordt besproken.     

Biofumigation with Brassica plants and its effect on the inoculum potential of Fusarium yellows of Brassica crops

The use of Brassica crops as green manure in the so-called biofumigation treatment has been successfully exploited for the management of soilborne pathogens and is gaining interest particularly in the case of less intensive agricultural systems. A study was undertaken to investigate possible negative side-effects of biofumigation in order to prevent possible damage caused by wilt pathogens able to attack both plants used for biofumigation as well as agricultural crops. To do so, firstly the response of different Brassicas, including some used in biofumigation, to the formae speciales of Fusarium oxysporum known for being pathogenic on Brassica crops was evaluated. Secondly, the effect of green manure treatments on yield, quality of crops, and inoculum densities, infection and survival of Fusarium oxysporum f. sp. conglutinans and F. oxysporum f. sp. raphani was evaluated. In the second part of the work, four Brassica crops, selected for their response (susceptibility or resistance) to F. oxysporum f. sp. conglutinans and to F. oxysporum f. sp. raphani were evaluated in order to determine their response to the two pathogens during subsequent crops grown in soil where plants were incorporated as green manure into the soil at the end of each cycle. Moreover, the dynamics of the populations of F. oxysporum f. sp. conglutinans and F. oxysporum f. sp. raphani in the soil after several biofumigation cycles was studied. Many of the Brassica crops used for biofumigation tested were susceptible to F. oxysporum f. sp. conglutinans and or to F. oxysporum f. sp. raphani. Green manure treatment, carried out by growing nine cycles of biocidal plants, with a short crop cycle of 30–35 days, did not reduce Fusarium wilts on susceptible Brassica hosts. The population of the pathogen was partially increased as a result of the incorporation of tissues of the susceptible plants. When Brassica crops grown were resistant to the two F. oxysporum pathogens used for soil infestation, green manure simulation did inhibit both pathogens, thus confirming its biocidal activity. The results obtained under our experimental conditions show that biofumigation treatment is not applicable for soil disinfestation on crops susceptible to the same formae speciales of F. oxysporum affecting Brassica species used for biofumigation. Brassica crops resistant to Fusarium yellows should be grown where biofumigation is applied. Moreover, alternation of crops used for biofumigation should be encouraged.     

Purification, N-terminal amino acid sequencing and antifungal activity of chitinases from pepper stems treated with mercuric chloride

Different isoforms of chitinases were purified from pepper (Capsicum annuumL. cv. Hanbyul) stems treated with mercuric chloride. The acidic isoform a1 (69kDa, pI5.0), basic isoforms b1 (32kDa, pI9.0) and b2 (22kDa, pI9.1) were purified by chitin-affinity chromatography, with subsequent electroelution from nondenaturing polyacrylamide gel electrophoresis (PAGE) gels. The acidic isoform a1 has chitin-binding properties, but no antifungal activity. The basic isoforms b1 and b2 contain high ratios of cysteine and glycine at the N-terminal chitin-binding domain, exhibit chitinase activity, and show antifungal activities againstColletotrichum gloeosporioides, Fusarium oxysporumf.sp.cucumerinum, Magnaporthe grisea, andTrichoderma viride in vitro.Moreover, their antifungal activity shows a high degree of specificity to filamentous fungi. The chitinases b1 and b2 show a high sequence identity in their N-terminal residues with those from wheat, tobacco, potato, rice andArabidopsis thaliana.None of the purified isoforms of chitinases inhibited hyphal growth of the Oomycete fungus which lacks chitinPhytophthora capsici. In contrast, zoospore germination and germ tube elongation ofP. capsiciwere effectively inhibited by treatment with b1 and b2.     

晋南地区黄瓜、黑籽南瓜死秧的病原菌鉴定及品种抗性研究

经分离、培养对不同菌种培养性状的观察,确定了侵染黄瓜、黑籽南瓜造成死秧的镰刀菌主要为尖镰孢菌黄瓜专化型、尖镰孢菌西瓜专化型、串珠镰刀菌和腐皮镰孢菌4种。经致病性测定,4种镰刀菌均能侵染黄瓜,引起发病造成死秧,可分为强致病类型和中强致病类型。经抗病性鉴定,黑籽南瓜种子只有南瓜4号为耐病品种;黄瓜种子也只有津优31号为耐病品种。     

Identification of potential native chitinase-producing Trichoderma spp. and its efficacy against damping-off in onion

Chitinase-producing Trichoderma species have been recognized long ago against the phytopathogenic fungi. In this study, we evaluated the production of chitinase enzyme for seventeen isolates of Trichoderma isolated from onion growing districts of Punjab and assessed their bio-efficacy against damping-off in onion. In vitro, these Trichoderma isolates were screened for their antagonistic activity against the damping-off pathogen Fusarium oxysporum f.sp. cepae by dual culture assay. These isolates were also screened for their chitinase enzyme activity; it was found that isolates T5 and T8 are showing higher antagonistic activity on Fusarium oxysporum f.sp. cepae and also produced large amounts of chitinase enzymes in the presence of commercial colloidal chitin. The selected chitinolytic isolates were used in field studies to confirm the feasibility of their biological control efficacy against onion damping-off. In the field experiment, the seed+soil treatment of chitinolytic isolate (T8) showed a critical decrease of damping-off in onion by 88.75% over control.

     

Involvement of antifungal compounds from rockmelon fruit rind (<Emphasis Type="Italic">Cucumis melo</Emphasis> L.) in resistance against the fruit rot pathogen <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">melonis</Emphasis>.

Fusarium rot caused by Fusarium oxysporum f. sp. melonis, causes significant postharvest losses in rockmelon crops. Although latent infection is often present in the field, symptoms of the disease may not appear until fruit maturity. The susceptibility of different-aged rockmelon fruit cv. “Colorado” was determined by inoculating fruit at different stages of development with a spore suspension of F. oxysporum f. sp. melonis. Disease symptoms appeared first and were more severe in older fruit compared to younger fruit. Disease symptoms on fruit 35 DAA (Days After Anthesis) and 42 DAA appeared within 3 days of inoculation and rapidly covered the fruit within 5 days. In contrast, disease symptoms on fruit 7 DAA appeared 6 days after inoculation and grew slowly. Extraction of antifungal compounds without involving acid hydrolysis from 7 DAA fruit rind did not show antifungal activity on TLC plates. However, hydrolysis of the ethyl acetate fraction resulted in a strong fungal inhibitory zone on agar plates against colonies of F. oxysporum f. sp. melonis. Separation of the hydrolysed crude extracts on TLC plates indicated the presence of two distinct antifungal zones with R_f 0.36 and 0.13 in young fruit 7, 14 and 21 DAA. The area of fungal inhibition of compound R_f 0.36 was greater than that of R_f 0.13 on the TLC plate. Extracts from mature fruit of 35 and 42 DAA did not have detectable levels of antifungal compounds. The decrease in the susceptibility of rockmelon fruit during maturity may be correlated to a decrease in the antifungal compounds in the fruit with maturity.     

Microbial community responses associated with the development of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">cucumerinum</Emphasis> after 24-epibrassinolide applications to shoots and roots in cucumber

Fusarium wilt, caused by Fusarium oxysporum f. sp. cucumerinum (FO), is one of the major diseases in cucumber (Cucumis sativus) production. Root and foliar applications of 24-epibrassinolide (EBL), an immobile phytohormone with antistress activity, were evaluated for their effects on the incidence of Fusarium wilt and changes in the microbial population and community in roots of cucumber plants. EBL pre-treatment to either roots or shoots significantly reduced disease severity followed by an improved plant growth regardless of the treatment methods applied. EBL applications decreased the Fusarium population on root surfaces and in nutrient solution, but increased the population of fungi and actinobacteria on root surfaces. PCR-DGGE analysis showed that FO-inoculation had significant effects on the bacterial community on root surfaces as expressed by a decreased diversity index and evenness index, but EBL applications alleviated these changes. Moreover, several kinds of decomposing bacteria and growth-promoting bacteria were identified from root surfaces of FO-inoculated plants and EBL-pre-treated plants, respectively. Overall, these results show that the microbial community on root surfaces was affected by a complex interaction between phytohormone-induced resistance and plant pathogens.     

The effect of pollen in the phyllosphere of rye on colonization by saprophytic fungi and on infection by Helminthosporium sativum and other leaf pathogens

It is demonstrated that benomyl, applied as a soil drench, is highly efficient in reducing the quantity of mycelium in muskmelon plants infected byFusarium oxysporum f. sp.melonis. When treated before symptoms appear, plants are generally cured. The blending technique used for assessing fungal spread in the xylem vessels is particularly convenient for studying the action of a systemic fungicide in a plant with vascular wilt.Samenvatting Met behulp van een mixertechniek wordt aangetoond, dat na een begieting van de wortels van jonge meloenen met benomyl (75 mg actieve stof/pot van 450 ml) de infektie doorFusarium oxysporum f. sp.melonis in kunstmatig besmette aarde heel laag blijft. In geïnfekteerde planten veroorzaakt deze behandeling een sterke vermindering van de hoeveelheidFusarium in de stengel. Wanneer de planten behandeld worden juist voor zij de eerste symptomen aantonen, wordt gewoonlijk de ontwikkeling van de parasiet gestopt zodat de planten kunnen genezen. Het produkt blijft tenminste 10 weken actief in de grond.     

Pathogenicity, vegetative compatibility and RAPD analysis of Fusarium oxysporum isolates from tobacco fields in Extremadura

Fusarium wilt of tobacco could be caused by Fusarium oxysporum f. sp. batatas or f. sp. vasinfectum since f. sp. nicotianae was rejected because there was no evidence of isolates specific to tobacco. Forty isolates of F. oxysporum from soil and plants from tobacco fields in Extremadura (south-western Spain) were characterized by pathogenicity on burley and flue-cured tobacco, for vegetative compatibility group (VCG), and by random amplified polymorphic DNA (RAPD). Isolates from burley were identified as race 1 of F. oxysporum f. sp. batatas based on pathogenicity on tobacco, sweet potato and cotton, and those from flue-cured as race 2. Most isolates from soil were heterokaryon self-incompatible (HSI) and the remaining isolates from soil and tobacco were grouped into four VCGs: VCG 1 (5 isolates from burley), VCG 2 (17 isolates from flue-cured and 4 from soil), VCG 3 (2 isolates from flue-cured) and VCG 4 (2 isolates from soil). This is the first report of the two races and VCGs of F. oxysporum f. sp. batatas in Spain. Analysis of RAPD revealed two clusters (C-I and C-II) related to race and VCGs. C-I included race 1 (VCG 1) isolates from burley and nonpathogenic (VCG 4 or HSI) isolates from soils. C-II included nonpathogenic (VCG 2) and race 2 (VCG 2 or VCG 3) isolates from flue-cured. VCG and RAPD markers were effective in distinguishing race 2 from race 1, suggesting that there are two genetically differentiated groups of F. oxysporum f. sp. batatas on tobacco in Extremadura.     

Acquired resistance triggered by elicitins in tobacco and other plants

Elicitins are a family of proteins excreted byPhytophthora spp. They exhibit high sequence homology but large net charge differences. They induce necrosis in tobacco plants which then become resistant to the tobacco pathogenPhytophthora parasitica var.nicotianae. In stem-treated plants, resistance was not restricted to the site of elicitin application, but could be demonstrated by petiole inoculation at all levels on the stem. Resistance was already maximum after two days and lasted for at least two weeks. It was effective not only towardsP. p. var.nicotianae infection, but also against the unrelated pathogenSclerotinia sclerotiorum. In contrast to dichloroisonicotinic acid, an artificial inducer of systemic acquired resistance, which was increasingly effective with doses ranging from 0.25 to 5mole per plant, the basic elicitin cryptogein exhibited a threshold effect, inducing near total resistance and extensive leaf necrosis above 0.1 nmole per plant. Between 1 and 5 nmole, acidic elicitins (capsicein and parasiticein) protected tobacco plants with hardly any necrotic symptom. Elicitins exhibited similar effects in various tobacco cultivars andNicotiana species, although with quantitative differences, but induced neither necrosis nor protection in other SolanaceÆ (tomato, petunia and pepper). Among 24 additional species tested belonging to 18 botanical families, only some BrassicaceÆ, noticeably rape, exhibited symptoms in response to elicitins, in a cultivar-specific manner. Elicitins appear to be natural specific triggers for systemic acquired resistance and provide a tool for unraveling the mechanisms leading to its establishment.Abbreviations AR acquired resistance - HR hypersensitive response - INA 2,6-dichloroisonicotinic acid - Ppn Phytophthora parasitica var.nicotianae - SAR systemic acquired resistance     

Phylogenetic position and nucleotide diversity of Fusarium oxysporum f. sp. vanillae worldwide based on translation elongation factor 1α sequences

Fusarium oxysporum f. sp. vanillae is considered the most important fungus affecting vanilla crops around the world, causing rot on vanilla roots and stems. Previous studies showed that the ability to infect vanilla plants is a polyphyletic trait among strains of the Fusarium oxysporum species complex (FOSC). The same studies proposed a single origin for F. oxysporum f. sp. vanillae isolates sampled from Mexico, the centre of origin and distribution of vanilla. The aim of this work was to test the hypothesis of the monophyletic origin of a wider sample of isolates of F. oxysporum f. sp. vanillae infecting Mexican vanilla and estimate nucleotide diversity of pathogen isolates from the main vanilla‐producing countries. Sequence data for the TEF1α gene from 106 isolates was assembled. The phylogenetic analyses suggest that some Mexican isolates of F. oxysporum f. sp. vanillae belong in two well‐supported clades, mixed with isolates from Madagascar, Indonesia, Réunion and Comoros. The phylogenetic position of other Indonesian and Mexican isolates is unresolved. Estimations of nucleotide diversity showed that the population from Mexico is genetically more diverse than the other three populations from Madagascar, Indonesia and Réunion. The results support a polyphyletic origin of vanilla‐infecting isolates of F. oxysporum worldwide, and also reject the proposition that Mexican isolates have a single origin. The phylogenetic optimizations over the strict consensus tree of the ability to infect vanilla plants suggest that pathogenic strains around the world are the product of multiple shifts of pathogenesis and dispersion events.     

<Emphasis Type="Italic">In vivo</Emphasis> evaluation of essential oils and biocontrol agents combined with heat treatments on basil cv Genovese Gigante seeds against <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">basilici</Emphasis>

Seed treatments with essential oils (from savory and thyme) and biocontrol agents (Pseudomonas spp. and Fusarium oxysporum) have been evaluated in vivo after dry hot air treatments against Fusarium oxysporum f. sp. basilici on basil seeds. The savory and thyme essential oils showed a significant pathogen control activity because of their innate antifungal activity and because of the seed application method, but the dry hot pre-treatment did not show any obvious effect on the performance of the essential oil treatments. The dry heat treatment improved the Pseudomonas seed dressing effect against F.oxysporum f. sp. basilici, and showed important reductions in plant infection and the disease index on the treated seed plants, without any negative effect on seed germination. However, the pathogen control provided by the heat treatments combined with the application of the biocontrol agents never reached the same performance as the chemical treatments considered as the reference. Thus, short dry heat treatments on basil seeds have been shown to be a valid but complementary seed disinfection method against Fusarium wilt.     

Effect of mixed inoculations with Fusarium oxysporum f. sp. lycopersici and F. oxysporum f. sp. dianthi on the phenols content of tomato plants

Forms ofFusarium oxysporum specific on hosts other than tomato induce in this plant greater initial increases of the phenols content than the pathogenic f. sp.lycopersici. Mixed inoculations of f. sp.lycopersici and f. sp.dianthi are on the contrary no more effective in inducing the phenol accumulation 24 h after the infection than f. sp.lycopersici alone. This observation suggests that the pathogen can suppress the phenolic response that is typical of the incompatible combinations.Samenvatting Vormen vanFusarium oxysporum welke pathogeen zijn voor andere planten dan de tomaat induceren in deze plant aanvankelijk een grotere toename van het fenolgehalte dan de pathogene f. sp.lycopersici. Inoculaties met een gemengd inoculum van de f. sp.lycopersici en f. sp.dianthi hebben daarentegen geen groter effect op de toename van het fenolgehalte 24 uur na infectie dan de inoculaties met f. sp.lycopersici alleen. Verondersteld wordt dat het pathogeen de toename van het fenolgehalte, dat typerend is voor de incompatibele combinatie, kan onderdrukken.     

RNA silencing of PEX6 gene causes decrease in pigmentation,sporulation and pathogenicity of Fusarium oxysporum

Peroxisomes are single membrane‐bound organelles that play a pivotal role in various developmental processes in all eukaryotic cells. This study targeted the PEX6 gene, which encodes for peroxisomal biogenesis factor 6, by RNA interference (RNAi) in Fusarium oxysporum f. sp. lycopersici. Fusarium oxysporum is a soilborne filamentous, hemibiotrophic fungus that invades tomato roots and colonizes the xylem vessels, thereby causing complete wilting of infected tomato plants. The expression of FoPEX6 in F. oxysporum was found to be higher during early stages of growth and development. The FoPEX6 gene was isolated and a hairpin RNAi construct was prepared and introduced into F. oxysporum 4471 through glass‐bead transformation. The fungal transformation status, i.e. integration, expression and presence of the intended small interfering RNAs (siRNAs), was confirmed by PCR, qPCR and stem‐loop PCR, respectively. The silenced fungal transformants exhibited reduced pigmentation and a significant reduction in sporulation as compared to the wild type. They also showed dramatic reduction in pathogenicity (virulence) on tomato, based on root infection and fruit invasion assays. These results suggest that PEX6 has a central role in pigmentation, sporulation and pathogenicity in F. oxysporum.     

四季豆枯萎病病原鉴定及防治

从南宁市郊11个病区采集的四季豆枯萎病株标样,经分离培养鉴定和致病性测定,证明其病原菌为尖孢镰刀菌菜豆专化型(Fusarium oxysporum f. sp. phaseoli Kend & Syd)。此病在南宁于4月上中旬四季豆初花期开始发生,5月中下旬盛花至结荚期为发病高峰期。用滤纸碟法进行药效试验的结果,40%灭病威300-500倍液的抑菌圈最大,田间灌根防治也有一定效果。可用种子重量的0.5%多菌灵可湿性粉拌种。品种间抗病性有显著差异,秋抗19号和秋抗6号较抗病。     

Control of Fusarium oxysporum f. sp. cucumerinum of cucumbers by soil solarization with impermeable plastics and/or reduced doses of methyl bromide*

Soil solarization is not broadly adopted as a soil deinfestation method mainly because of its long duration (4–6 weeks). We present evidence showing that the duration of solarization can be reduced to nearly half using impermeable plastics and/or low doses of methyl bromide, while still ensuring effective control of Fusarium oxysporum f. sp. cucumerinum. Chlamydospores of a pathogenic isolate of F. o. cucumerinum, formed in sterile soil, were inserted into nylon mesh envelopes and incorporated into the soil prior to treatment at 20‐ and 30‐cm soil depths. Soil treatments included untreated control, soil solarization with polyethylene or impermeable plastics (LMG), and soil solarization with polyethylene or impermeable plastics plus 20 g m^?2 methyl bromide. According to the effects on artificial inocula of F. o. cucumerinum checked at weekly intervals for 4 weeks, soil solarization with impermeable plastics was most effective in destroying pathogen populations even two weeks after soil covering.