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1.
Rice blast is a devastating fungal disease resulting in major losses to rice crops. Owing to continuous acquisition of resistance by the causal fungus, several fungicide chemicals are no longer effective. Therefore, there is a need to identify natural components and develop new agents to control fungal pathogens. We previously demonstrated that the culture filtrate of Biscogniauxia sp. O821 inhibited infection behavior of Magnaporthe oryzae and subsequent blast lesion formation. In the present study, we isolated a new compound, (3aS,4aR,8aS,9aR)-3a-hydroxy-8a-methyl-3,5-dimethylenedecahydronaphto[2,3-b]furan-2(3H)-one (HDFO), from the culture filtrate of Biscogniauxia sp. O821 and determined its molecular weight as 248. The HDFO structure was determined by electrospray ionization-mass spectrometry and nuclear magnetic resonance spectroscopy after purification with column chromatography and high-performance liquid chromatography. The structure of this antifungal compound was similar to that of alantolactone and isoalantolactone. The growth inhibition zone against M. oryzae in presence of HDFO was observed at Rf 0.5–0.6 on a thin layer chromatography plate. HDFO inhibited conidial germination of M. oryzae in a dose-dependent manner (1–200 ppm). Furthermore, blast lesion formation was significantly suppressed by HDFO at over 5 ppm. These results suggest that HDFO from the culture filtrate of Biscogniauxia sp. O821 can protect rice from rice blast disease caused by M. oryzae. This is the first report that HDFO produced by Biscogniauxia sp. can serve as an antifungal compound against M. oryzae.  相似文献   

2.
Pyricularia oryzae (rice blast) conidial development at pre-penetration stage determines success or otherwise of infection inside the rice host plants. Studies on conidial germination and growth on the leaf surface in commercial rice (Oryza sativa) report differently, dependent upon host type and level of blast resistance. Although wild rice (O. australiensis) is known to be an alternative host of blast, the interaction between P. oryzae conidia and wild O. australiensis on its leaf surface has not been previously studied. We found significant (P?<?0.001) differences in conidial development between two blast isolates with different virulence in terms of conidial germination, germ tube growth and appressoria formation on both wild and cultivated rice. Conidial germination at 6 h post-inoculation (hpi) for the virulent isolate was significantly (P?<?0.001) delayed. Germ tubes of the avirulent isolate conidia grew significantly (P?<?0.001) faster and with significantly (P?<?0.001) longer germ tubes than from virulent conidia. Appressoria development for the virulent isolate was significantly (P?<?0.001) faster at its later growth stages of 12 and 18 hpi when approximately 100% of germ tubes formed appressoria. In contrast, formation rate of appressoria for the avirulent isolate was significantly (P?<?0.001) slower and only reached 76% of germ tubes forming appressoria. Appressoria formation on O. australiensis was significantly (P?<?0.001) greater than the formation on O. sativa for both virulent and avirulent P. oryzae at 12 hpi, a clear indication that host type influences the extent of appressoria formation.  相似文献   

3.
Plant volatile compounds, including terpenes, are known to be involved in the rice defense system. In the present analysis of a terpene synthase, OsTPS18, in rice, we found that OsTPS18 was localized in the cytoplasm and synthesized the sesquiterpenes (E)-nerolidol and (E)-β-farnesene. The amounts of (E)-nerolidol and (E)-β-farnesene increased after jasmonic acid (JA) treatment. (E)-Nerolidol had significant antibacterial activity against Xanthomonas oryzae pv. oryzae (Xoo). These results suggest that (E)-nerolidol plays an important role in JA-induced resistance against Xoo and that it functions as an antibacterial compound in rice.  相似文献   

4.
Competitive effects between Fusarium graminearum, causing Fusarium head blight, and the endophyte Epicoccum nigrum, were performed in in vitro competition assays between the two species. Two E. nigrum isolates were isolated from wheat grains and tested as competitors against two F. graminearum isolates. A dual petri dish assay showed that E. nigrum reduced the mycelial growth of F. graminearum and vice versa. A glass slide assay revealed that E. nigrum crude cultural filtrate also had reducing effect on the growth of F. graminearum comparable to that of E. nigrum spore suspensions. Microscopy showed hyphae of F. graminearum and E. nigrum with many side branches when in close proximity, in contrast to pronounced apical hyphal growth when growing alone. Combinations of F. graminearum and E. nigrum on sterilised wheat grains were studied over time by qPCR. F. graminearum biomass was significantly reduced in inoculations applying E. nigrum three days prior to F. graminearum. In conclusion, these results showed competition and mycelial behaviour effects between F. graminearum and E. nigrum and support that E. nigrum may have potential to reduce F. graminearum infections in wheat. Competition experiments should be carried out in planta to study the interaction further.  相似文献   

5.
Arabidopsis thaliana exhibits a durable resistance called nonhost resistance against nonadapted fungal pathogens. A. thaliana activates preinvasive resistance and terminates entry attempts by nonadapted fungi belonging to the genus Colletotrichum, which cause anthracnose disease in many plants. In the interaction between A. thaliana and nonadapted C. tropicale, the preinvasive resistance involves the PENETRATION 2-related antifungal secondary metabolite pathway and the ENHANCED DISEASE RESISTANCE 1-dependent antifungal peptide pathway. The development of invasive hyphae by C. tropicale owing to the reduction of preinvasive resistance then triggers the blockage of further hyphal expansion via the activation of the second layer of resistance, i.e., postinvasive resistance, which guarantees the robustness of the nonhost resistance of A. thaliana against Colletotrichum pathogens. Both the tryptophan-derived metabolic pathway and glutathione synthesis play critical roles in the postinvasive resistance against C. tropicale, although the molecular mechanism of postinvasive resistance remains to be elucidated. In this review, we describe the current understanding of the molecular background of the Arabidopsis nonhost resistance against Colletotrichum fungi and discuss perspectives for future research on this durable resistance.  相似文献   

6.
The vector competence of Frankliniella occidentalis for Chrysanthemum stem necrosis virus (CSNV) was evaluated. Three vector strains with distinct competences for Tomato spotted wilt virus (TSWV) transmission were investigated, including an artificially selected strain (TsH) that has a particularly high competence (>90 %). Newly hatched larvae of F. occidentalis were given an acquisition access period of 5 days on CSNV-infected D. stramonium leaves, and reared to maturity. Their transmission efficiencies were examined using a leaf disk assay using Petunia x hybrida leaves. Following the leaf disk assay, the virus accumulation in the vectors was examined via a double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) of their bodies. The results showed that the CSNV acquisition and transmission efficiency of the TsH strain did not differ from those of the others, indicating that the competence of F. occidentalis as a vector for CSNV is not related to that for TSWV. The CSNV transmission and acquisition efficiencies of two F. intonsa strains (Hiroshima and Fukuoka) were also evaluated. In Hiroshima strain, 35 % of adults were viruliferous, but only two transmitters (3 %) were observed. In Fukuoka strain, 6 % were viruliferous, and no transmitters were observed. These results indicate that F. intonsa cannot be a major vector for CSNV. The accumulation of CSNV in the adults of F. occidentalis and F. intonsa evaluated using DAS-ELISA showed a significant difference in ELISA values among transmitter, viruliferous non-transmitter, and non-viruliferous individuals. These results clearly demonstrated that only transmitters that accumulated a threshold quantity of virus can transmit CSNV to plants.  相似文献   

7.
Entomopathogenic nematodes in the genus Steinernema are associated with Xenorhabdus spp. bacteria. When steinernematid colonise an insect host the nematode-bacterium association overcomes the insect immune system and kills the host within 48 h. Xenorhabdus spp. produce secondary metabolites that are antifungal to protect nematode-infected cadavers from fungal colonization. The concentrated, or cell-free metabolites of X. szentirmaii exhibit high toxicity against various fungal plant pathogens and show potential as natural bio-fungicides. In the current study, we determined 1) thermo-stability, 2) dose-response, and 3) shelf-life of antifungal metabolites of X. szentirmaii against Monilinia fructicola (cause of brown rot of peach and other stone fruit) and Glomerella cingulata (cause of antharacnose). Thermo-stability was determined by autoclaving bacterial culture broths (121 °C and 15 psi for 15 min) and measuring fungal growth on in potato dextrose agar (PDA) containing 10% of the supernatants. Autoclaving had no impact on the antifungal activity of the secondary metabolites. Over a test period of 9 months, the activity of both extract types did not decline when stored at 4 or 20 °C. A dose-response study (10, 20, 40, 60, 80 and 100% supernatant-containing metabolite) using both phytopathogens demonstrated that a greater dose of supernatant increased antifungal activity. The antifungal-metabolite containing supernatant of X. szentirmaii has potential as a bio-fungicide. These results demonstrate the metabolite(s) are thermo-stable, they have a long shelf-life and require no stabilizing formulation, even at room temperature.  相似文献   

8.
Type IV pili of X. fastidiosa are regulated by pilG, a response regulator protein putatively involved in chemotaxis-like operon sensing stimuli through signal transduction pathways. To elucidate the roles of pilG in pathogenicity of X. fastidiosa, the pilG-deletion mutant XfΔpilG and complemented strain XfΔpilG-C were generated. While all strains had similar growth curves in vitro, XfΔpliG showed significant reduction in cell-matrix adherence and biofilm production compared with wild-type X. fastidiosa and XfΔpilG-C. The genes pilE, pilU, pilT, and pilS were down-regulated in XfΔpliG when compared with its complemented strain and wild-type X. fastidiosa. Finally, no Pierce’s disease symptoms were observed in grapevines inoculated with XfΔpilG, whereas grapevines inoculated with the wild-type X. fastidiosa and complemented strain of XfΔpilG-C developed typical Pierce’s Disease (PD) symptoms. The results indicate that pilG has a role in X. fastidiosa virulence in grapevines.  相似文献   

9.
Infection by Pyrenophora teres f. teres (Ptt) or P. teres f. maculata (Ptm), the causal agents of the net and spot forms of net blotch of barley, respectively, can result in significant yield losses. The genetic structure of a collection of 128 Ptt and 92 Ptm isolates from the western Canadian provinces of Alberta (55 Ptt, 27 Ptm), Saskatchewan (58 Ptt, 46 Ptm) and Manitoba (15 Ptt, 19 Ptm) were analyzed by simple sequence repeat (SSR) marker analysis. Thirteen SSR loci were examined and found to be polymorphic within both Ptt and Ptm populations. In total, 110 distinct alleles were identified, with 19 of these shared between Ptt and Ptm, 75 specific to Ptt, and 16 specific to Ptm. Genotypic diversity was relatively high, with a clonal fraction of approximately 10 % within Ptt and Ptm populations. Significant genetic differentiation (PhiPT = 0.230, P = 0.001) was found among all populations; 77 % of genetic variation occurred within populations and 23 % between populations. Lower, but still significant genetic differentiation (PhiPT = 0.038, P = 0.001) was detected in Ptt, with 96 % of genetic variation occurring within populations. No significant genetic differentiation (PhiPT = 0.010, P = 0.177) was observed among Ptm populations. Isolates clustered in two distinct groups conforming to Ptt or Ptm, with no intermediate cluster. The high number of haplotypes observed, combined with an equal mating type ratio for both forms of the fungus, suggests that P. teres goes through regular cycles of sexual recombination in western Canada.  相似文献   

10.
The virulence spectrum of 300 isolates of Xanthomonas oryzae pv. oryzae (Xoo), representing 17 districts of Punjab, Pakistan was elucidated through inoculation on a set of six rice IRRI-differentials. The virulence level was assessed by using principal component and cluster analysis. Among six principal components (PCs), PC-1 exhibited 59.3 % of the total variance. The highly virulent isolates clusters on the positive side of the ordination away from the point of intersection of PC1 and PC2 and classifies the Xoo isolates from slow disease to the highest disease causing entities. The 300 isolates were categorized into 29 pathotypes (Pt1-29) wherein the highly virulent pathotype (Pt-1), comprises of 39 Xoo isolates were widespread in 12 districts. The majority of Xoo isolates were moderately to least virulent (21.7–43 %) and average disease progress curves confirmed the field reactions of these pathotype clusters for an efficient recognition of Xoo isolates. Interaction of the pathogen with differentials harboring different resistant genes was well investigated in the current study for future management approaches for which the surveillance of the new Xoo pathotypes may expedite the disease resistant rice breeding programme in the country.  相似文献   

11.
Nicandra physaloides, a common weed in South America, was found to be infected by an isolate of Tomato severe rugose virus (ToSRV), a bipartite begomovirus. The plants developed severe yellow rugose mosaic and were collected in São Paulo State, Brazil. This isolate of ToSRV was transmitted by Bemisia tabaci B biotype from infected plants of N. physaloides to healthy plants of N. physaloides and tomato in a glasshouse. This is the first report of natural infection of N. physaloides by ToSRV in Brazil.  相似文献   

12.
Fusarium wilt, one of the destructive diseases of cucumber can be effectively controlled by using biocontrol agents such as Trichoderma harzianum. However, the mechanisms controlling T. harzianum-induced enhanced resistance remain largely unknown in cucumber plants. Here we screened the potent T. harzianum isolate TH58 that could effectively control F. oxysporum (FO). Glasshouse efficacy trials also showed that TH58 decreased disease incidence by 69.7 %. FO induced ROS over accumulation, while TH58 inoculation suppressed ROS over accumulation and improved root cell viability under F. oxysporum infection. TH58 inoculation could reverse the FO-induced cell division block and regulate the proportional distribution of nuclear DNA content through inducing 2C fraction. Moreover, the expression levels of cell cycle-related genes such as CDKA, CDKB, CycA, CycB, CycD3;1 and CycD3;2 in TH58 - pre-inoculated seedlings were up-regulated compared with those infected with FO alone. Taken together, these results suggest that T. harzianum improved plant resistance against Fusarium wilt disease via alterations in nuclear DNA content and cell cycle-related genes expression that might maintain a lower ROS accumulation and higher root cell viability in cucumber seedlings.  相似文献   

13.
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14.
Miscanthus x giganteus is a fast growing, perennial energy crop for temperate climates. Because of its high annual biomass production rates and its characteristics as a low-input crop, an expansion of field cultivation can be anticipated to cover increasing demands for sustainable biomass production. However, knowledge about pathogens that could have an impact on biomass production is still limited for M. giganteus. Here, we report about the isolation of the filamentous fungus Apinisia graminicola from necrotic leaf lesions of M. giganteus grown on a field trial plot in Northern Germany. Inoculation assays with the isolated A. graminicola strain confirmed its capacity to cause a leaf spot disease on M. giganteus. Additional inoculation assays revealed that A. graminicola also caused necrotic lesions on leaves of the model grass Brachypodium distachyon. Generally, symptoms of A. graminicola-caused leaf spot disease were stronger on B. distachyon compared to M. giganteus. Incubation temperatures above 22 °C during A. graminicola infection resulted in stronger disease symptoms on both, M. giganteus and B. distachyon leaves. Microscopic analysis of cross sectioned, infected leaf tissue revealed an epiphytic mycelium formation on the surface and an endophytic colonization of the mesophyll leave tissue, especially in M. giganteus. Our results revealed that the isolated A. graminicola strain is a causal agent of a leaf spot disease on grass leaves. Its potential on endophytic growth in M. giganteus might open new possibilities in studying this type of plant-fungal interaction on a cellular and molecular level in an energy crop.  相似文献   

15.
Two hymenopteran parasitoids of the cactus scale Diaspis echinocacti (Bouché) (Hemiptera: Diaspididae) on Opuntia ficus-indica (L.) Mill. (Cactaceae) are recorded in Greece. Aphytis debachi Azim, 1963 (Aphelinidae) is first recorded for Europe and Plagiomerus diaspidis Crawford, 1910 (Encyrtidae) is first recorded for Greece. Preliminary data on phenology and natural enemies of the scale D. echinocacti on O. ficus-indica are presented. Parasitism of D. echinocacti by P. diaspidis reached 86% in southern Greece (Kalamata) and parasitism by A. debachi reached 9.3% and 12% in Kalamata and Athens, respectively. Two predators, Cybocephalus fodori Endrödy-Youga (Coleoptera: Nitidulidae) and a mite species (Prostigmata: Bdellidae), were found to be associated with D. echinocacti.  相似文献   

16.
Tomato (Solanum lycopersicum L.) ARGINASE2 (ARG2) and THREONINE DEAMINASE2 (TD2) are involved in plant defense. These enzymes act in the midgut of herbivores fed on tomato plants to degrade the essential amino acids Arg and Thr, respectively. Although it has been demonstrated that overexpression of the SlARG2 gene in tomato enhanced its resistance against M. sexta larvae, knock-down the expression of SlTD2 reduced the resistance of tomato to lepidopteran herbivores; it remains unclear whether overexpression of SlTD2 could enhance the resistance of the host plants to herbivores, or whether combined overexpression of SlARG2 and SlTD2 could lead to synergistically enhanced resistance to insects. Here, we generated transgenic Arabidopsis plants overexpressing SlARG2 (SlARG2 OE) and SlTD2 (SlTD2 OE) individually as well as in combination (SlARG2-SlTD2 OE). Overexpression of these genes did not affect Arabidopsis development, seed yield, or Arg and Thr content. Insect-feeding bioassay was performed by feeding diamondback moth (Plutella xylostella L.) larvae on detached leaves of wild-type, SlARG2 OE, SlTD2 OE, and SlARG2-SlTD2 OE plants. Larvae fed on SlARG2 OE leaves showed approximately 31% to 35% reduction in weight and 6% to 10% reduction in survival rate compared to those fed on wild-type leaves. Although larvae fed on SlTD2 OE leaves showed no reduction in survival rate, they gained less weight. Whereas larvae fed on SlARG2-SlTD2 OE leaves showed neither reduction in weight nor reduction in survival rate. We further investigated the arginase enzymatic activity of the SlARG2 OE and SlARG2-SlTD2 OE transgenic plants. The SlARG2 OE line most resistant to diamondback moth larvae displayed the highest arginase activity. Our data indicate that overexpression of SlARG2 or SlTD2 in Arabidopsis can enhance its resistance against diamondback moth, whereas combined overexpression of SlARG2 and SlTD2 did not generate synergistically increased resistance to diamondback moth.  相似文献   

17.
Streptomyces griseorubens E44G is a chitinolytic bacterium isolated from cultivated soil in Saudi Arabia (a hot, arid climatic region). In vitro, antifungal potential of S. griseorubens E44G was assessed against the phytopathogenic fungus, Fusarium oxysporum f. sp. lycopersici (the causative agent of the Fusarium wilt disease of tomato). An inhibition zone of 24 mm was recorded. The chitinolytic activity of S. griseorubens E44G was proved when the colloidal chitin agar plate method was used. A thermostable chitinase enzyme of 45 kDa molecular weight was purified using gel filtration chromatography. The optimum activity was obtained at 60 °C and pH 5.5. The purified enzyme has shown a very pronounced activity against the phytopathogenic fungus, F. oxysporum. The molecular characterization of the chitinase gene indicated that it consists of 1218 bp encoding 407 amino acids. The phylogentic analysis based on the nucleotide DNA sequence and the deduced amino acids sequence showed high similarity percentages with other chitinases isolated from different Streptomyces species. In the field evaluation, application of both S. griseorubens E44G treatments significantly increased all tested growth and yield parameters and decreased the disease severity compared with the infected-untreated tomato plants suggesting potential as a biocontrol agent.  相似文献   

18.
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19.
A Carica papaya plant with severe yellow leaf mosaic, leaf distortion, and systemic necrosis was found in the municipality of Piracicaba, state of São Paulo, Brazil. Transmission electron microscopy (TEM) analysis revealed the presence of potyvirus-like particles and bacilliform particles similar to those of the Alfamovirus genus. The potyvirus was identified as Papaya ringspot virus-type P (PRSV-P). Biological, serological, and molecular studies confirmed the bacilliform virus as an isolate of Alfalfa mosaic virus (AMV). Partial nucleotide and amino acid sequences of the coat protein gene of this AMV isolate shared 97–98% identity with the AMV isolates in the GenBank database. This report is the first of the natural infection of papaya plants by AMV.  相似文献   

20.
Bacillus subtilis CPA-8, a strain with demonstrated ability to control Monilinia spp. in peaches, was studied to elucidate its mechanisms of antifungal activity. Growth inhibition assays using cell-free supernatants and butanolic extracts showed strong antifungal activities against Monilinia laxa and Monilinia fructicola. By comparison with the reference B. subtilis strains UMAF6614 and UMAF6639, fengycin, iturin and surfactin lipopeptides were identified by thin layer chromatography in butanolic extracts from cell-free supernatants, indicating that antibiosis could be a major factor involved in the biological control ability of CPA-8. TLC-bioautography analysis confirmed the presence of fengycin, iturin and surfactin lipopeptides but strong antifungal activity could be associated only with fengycin lipopeptides. These results were definitively supported by mutagenesis analysis targeted to suppress fengycin biosynthesis by disruption of the B. subtilis fenB gene. By TLC-bioautography analysis it was possible to identify transformants from CPA-8 with reduced or suppressed antifungal activity, and this phenotype was associated with the lack of fengycin bands. Fruit trials confirmed that fengycin-defective mutants and their cell-free supernatants lost their ability to control peach brown rot disease in comparison with CPA-8 wild type strain or Serenade Max®, a commercial formulation based on B. subtilis. Furthermore, population dynamics studies determined that CPA-8 fengycin-deficient mutants survived in wounds in peach fruit equally well as the CPA-8 wild type. Taken together our data indicate that fengycin-like lipopeptides play a major role in the biological control potential of B. subtilis CPA-8 against peach brown rot.  相似文献   

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