Germ Tube Elongation Research Articles

Sensitivity of difenoconazole to Colletotrichum fructicola at major pear cultivation areas in South China

In this work, the toxicity of difenoconazole to Colletotrichum fructicola at different development stages and its indoor control efficacy were determined. The sensitive baseline of C.fructicola to difenoconazole at major pear cultivation areas in South China（Hubei, Anhui, Jiangxi,Jiangsu, Zhejiang and Fujian Province） was established. The conidia germination and germ tube elongation of six representative strains treated by difenoconazole were determined by spore germination rate method. And its indoor efficacy was tested using detached pear leaves. The sensitivity of 120 strains of C. fructicola to difenoconazole was determined by mycelial growth rate method. The results indicated that difenoconazole had high inhibitory activities against mycelial growth and germ tube elongation. However, the inhibition against conidia germination of C. fructicola was weak, with the average EC50 values of（0.33 ± 0.03） μg/mL,（2.61 ± 0.26） μg/mL and（29.87 ± 1.31） μg/mL,respectively. The protective and curative effects of 160 μg/mL difenoconazole to pear anthracnose were92% and 79%, respectively. And those of 1 000 μg/mL carbendazim were 51% and 23%, respectively.120 strains from major pear cultivation areas in South China were sensitive to difenoconazole, and the EC50 values were in the range of 0.27-1.12 μg/mL. The frequency curves of EC50 value was continuous and unimodal, and following the positive skewness distribution. Hence, the mean EC50 value（0.59 ±0.02） μg/mL could be recognized as baseline sensitivities of C. fructicola to difenoconazole. The study laid the foundation for the evaluation and monitoring of the field resistance of C. fructicola to the difenoconazole, and provided a theoretical basis for the application of this fungicide to control pear anthracnose in the pear cultivation area.

The Search for Quorum Sensing in Botrytis cinerea: Regulatory Activity of Its Extracts on Its Development.

Botrytis cinerea is a phytopathogenic fungus that causes large crop and post-harvest losses. Therefore, new and effective strategies are needed to control the disease and to reduce resistance to fungicides. Modulating pathogenicity and virulence by manipulating microbial communication is a promising strategy. This communication mechanism, called Quorum Sensing (QS), has already been reported in bacteria and yeasts; however, it has not yet been studied in B. cinerea. To establish the existence of this biochemical process in B. cinerea, we prepared extracts at different growth times (D1-D12), which were applied to fresh cultures of the same fungi. The chemical analysis of the extracts obtained from several fermentations showed different compositions and biological activities. We confirmed the presence of several phytotoxins, as well as compounds 1-phenylethanol and 3-phenylpropanol. Day five extract (0.1%) inhibited conidia germination and elongation of germ tubes, day seven extract (1%) produced the greatest phytotoxic effect in tomato leaves, and day nine extract (0.1%) was a sporulation inhibitor. In contrast, the extracts from days 7, 9, and 12 of fermentation (0.1% and 0.01%) promoted pellet and biofilm formation. Sporulation was slightly induced at 0.01%, while at 0.1% there was a great inhibition. At the highest extract concentrations, a biocidal effect was detected, but at the lowest, we observed a QS-like effect, regulating processes such as filamentation, morphogenesis, and pathogenesis. These results of the biological activity and composition of extracts suggest the existence of a QS-like mechanism in B. cinerea, which could lead to new non-biocidal alternatives for its control through interference in the pathogenicity and virulence mechanisms of the fungi.

Exogenous β-aminobutyric acid application attenuates Aspergillus decay, minimizes aflatoxin B1 accumulation, and maintains nutritional quality in fresh-in-hull pistachio kernels.

Pistachio fruits suffer from postharvest decay, caused by Aspergillus flavus. This results in aflatoxin B1 (AFB1 ) accumulation in kernels, which is hazardous for human health due to its carcinogenic activity. In this study, the mechanism used by exogenous β-aminobutyric acid (BABA) treatment for attenuating Aspergillus decay, minimizing aflatoxin B1 (AFB1 ) accumulation, and maintaining nutritional quality in fresh-in-hull pistachio kernels, infected by A. flavus during storage at 25 °C for 18 days, was investigated. Results of an in vivo assay showed that the spore germination and germ tube elongation of A. flavus was repressed by BABA treatment at 7.5 mM. Aspergillus decay accompanied by AFB1 accumulation was also minimized in fresh-in-hull pistachio kernels treated with BABA at 7.5 mM and infected by A. flavus. Fresh-in-hull pistachio kernels, infected by A. flavus, treated with BABA at 7.5 mM, also exhibited higher phenol and flavonoid accumulation and 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging capacity accompanied by higher phenylalanine ammonia lyase (PAL) enzyme activity. Promoting phenylpropanoid pathway activity with higher PAL enzyme activity in fresh-in-hull pistachio kernels treated with BABA may not only reduce Aspergillus decay in kernels by cell wall fortification but also may be favorable for maintaining the kernels' nutritional quality through its effects on ROS scavenging capacity. As oxidative stress, represented by ROS accumulation, is responsible for A. flavus growth and AFB1 accumulation, higher phenol and flavonoid accumulation in fresh-in-hull pistachio kernels treated with BABA may be beneficial for attenuating Aspergillus decay and minimizing AFB1 accumulation. © 2019 Society of Chemical Industry.

Compost tea-mediated induction of resistance in biocontrol of strawberry Verticillium wilt

In vitro and in vivo trials were conducted to assess the biocontrol efficacy of the tea prepared from maize straw compost against Verticillium wilt of strawberry caused by Verticillium dahliae and the mechanisms involved in suppression of the phytopathogen. The compost tea used in the present study inhibited the mycelial growth and conidial germination of V. dahliae by 90.60% and 78.24%, respectively. However, sterilization of compost tea by autoclaving diminished the inhibitory effect, suggesting that microflora in the compost tea play a pivotal role in the prevention of Verticillium wilt. The elongation of germ tubes was suppressed by filter-sterilized compost tea and revealed the presence of thermolabile and low molecular weight antifungal substances in the compost tea. Greenhouse trials indicated that preventive application of compost tea on strawberry plants exhibited control efficacy of 41.85% against Verticillium wilt. Moreover, the compost tea treatment could induce resistance in the primed state, which led to enhanced production of defense-related enzymes in strawberry plants upon pathogen attack. Our results demonstrated that direct inhibition of V. dahliae by microorganisms and induction of plant defense response are main mechanisms involved in compost tea-based disease suppression.

In Vitro Effects of Five Different Classes of Fungicides on Growth and Development of Botrytis cinerea Isolated from Tree Peony in China

Gray mold caused by Botrytis cinerea has become an important limiting factor for tree peony production. Currently, chemical control is still the main means of managing the disease in China. The objective of this study was to test fungicides with different mechanisms of action in controlling B. cinerea on tree peony. The inhibitory efficacy of five fungicides on four asexual stages was measured in the petri dish containing culture medium amended with a tested fungicide at various concentrations. The results showed that carbendazim had the strongest inhibition effect against all four stages of B. cinerea, with the EC50 values of 0.1037, 0.0563, 0.5578, and 0.0797 mg·L–1, respectively. The inhibitory effect of diethofencarb was only slightly less than that of carbendazim on conidia production, germination, and germ tube elongation. The inhibitory effect of procymidone was second only to that of carbendazim on colony expansion. The results indicated that carbendazim and diethofencarb could be used as protective fungicides to spray in the early stage of disease occurrence to inhibit conidia germination and germ tube elongation, so as to reduce the infection rate of B. cinerea and prevent disease occurrence. Carbendazim, procymidone, and diethofencarb mainly inhibit the reinfection of B. cinerea by inhibiting the growth of mycelium and the production of conidia, so they could be used as control fungicides during the occurrence phase of the disease.

Assessment of in vitro Antifungal Prospective of Fungicides against Alternaria alternata, A Causal Organism of Potato Brown Spot and Early Blight Disease

Efficacy evaluation of three fungicides was undertaken against phytopathogenic fungi Alternaria alternata. Fungicide copper oxychloride was found to restrict the growth of fungi at 500ppm concentration, whereas at 5000ppm concentration of benomyl and mancozeb growth of fungi was not occurred. At 1000ppm concentration growth of fungi was fifty percent compare to control on PDA medium. At 5000ppm concentration of copper oxychloride and mancozeb spore germination did not occur. In case of both the fungicides at 1000ppm concentration percent germination was found between 56 and 75 percent. Germination percent of spores was always lesser than control in all the treatments. Similarly germ tube growth was not occurred in copper oxychloride and mancozeb treated spores at 5000ppm concentration. Germ tube growth was found always influenced by the treatment of fungicides. Inhibitory effect of fungicides was dose dependent and proportional to the concentration of fungicides. Reduction in growth, spore germination and germ tube elongation increased on increasing the concentration of fungicides.

Streptomyces pactum may control Phelipanche aegyptiaca in tomato

Phelipanche aegyptiaca (syn. Orobanche aegyptiaca), achlorophyllous obligate root parasitic weed attacks economically important crops in several plants families including Solanaceae. Of the Solanaceous crops tomato (Solanum lycopersicum) is the most susceptible. Available records showed that an array of microorganisms could give adequate control of the parasite and alleviate its damage in tomato. In the present study 88 actinobacterial strains, associated with antagonistic activity against plant pathogens, were assayed for their effects on germination of P. aegyptiaca seeds. Of the strains Streptomyces pactum Act12 was selected for detailed laboratory, greenhouse and field studies. The results showed that S. pactum Act12 cell-free culture filtrate inhibited seed germination and germ tube elongation of P. aegyptiaca by 93.9% and 97.4%, respectively. In potted plants S. pactum Act12 culture reduced P. aegyptiaca emergence and dry weight by 85.7% and 55.4%, respectively, increased tomato biomass, total number of bacteria and the ratio of bacteria to fungi in tomato rhizosphere by 25.8%, 84.9% and 123.6% over the control, respectively. In the field experiment S. pactum Act12 decreased P. aegyptiaca emergence by 32.3% and increased tomato fruit yield by 57.1%. The results indicate the potential of S. pactum Act12 as a bioagent for P. aegyptiaca control in tomato and suggest that the suppressive effects of S. pactum Act12 on P. aegyptiaca parasitism is an outcome of decreased germination, alteration of composition of rhizospheric microbiota and promotion of host defense mechanisms.

Elmada mavi küfe neden olan Penicillium expansum’a karşı bazı bor tuzlarının antifungal etkisi

Penicillium expansum causing blue mold disease is one of the most important pathogens of pome fruit and is a necrotrophic fungus that requires wounds to infect the fruit. In the present study, the efficacy of etidot-67 and borax decahydrate against P. expansum were evaluated in both in vitro and in in vivo . In in vitro experiments, both etidot-67 and borax decahydrate strongly inhibited mycelial growth, spore germination and germ tube elongation of P. expansum . The inhibitory effects of both salts were closely correlated with their increasing concentrations. While boron salts completely inhibited the mycelial growth of P. expansum at %0.25 concentration, these salts completely inhibited spore germination and germ tube elongation of the fungus at %0.125 concentration. Additionally, it was determined that the toxicity of the salts tested were close to each other, namely EC 50 values of Etidot-67 and borax decahydrate were 0.067 and 0.071, respectively. While the minimum inhibition concentration (MIC) values of the etidot-67 and borax decahydrate were %0.25, the minimum fungicidal concentration (MFC) values of the same salts were found to be greater than 1%. In in vivo experiments, blue mold development in apple fruits treated with 3.0% concentration of etidot-67 and borax decahydrate after fungal inoculation (curative activity) was significantly reduced by %92.8 and %78.9, respectively, compared with the control treatment (P<0.05). However, at same concentration, lesion area on apple fruits treated with the salts before inoculation with the fungus (1x10 4 conidia mL -1 ) (preventive activity) reduced by %94.3 and %98.3, respectively. These results show that both boron salts can be used as a potential alternative to synthetic fungicides for the control of the postharvest disease of apple fruit caused by P. expansum .

Ultra-Structural Alterations in Botrytis cinerea-The Causal Agent of Gray Mold-Treated with Salt Solutions.

Potassium bicarbonate (PB), calcium chelate (CCh), and sodium silicate (SSi) have been extensively used as antifungal generally recognized as safe (GRAS) compounds against plant pathogenic fungi. In this research, in in vitro tests, the radial growth, conidial germination, and germ tube elongation of Botrytis cinerea was completely inhibited at 0.3% of PB, SSi, and CCh. In in vivo tests, application of PB, SSi, and CCh completely inhibited the occurrence of gray mold incidence of inoculated ‘Italia’ grape berries at concentrations of 1.0, 0.8, and 0.8%, respectively. In order to investigate the detailed mechanisms by which salts exhibited antifungal activity, we analyzed their influence on morphological changes by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and also on reactive species of oxygen (ROS), mitochondrial membrane potential (MMP), and adenosine triphosphate (ATP) content. Defects such as malformation and excessive septation were detected on salt-treated hyphae morphology observed by SEM. The internal structure of conidia treated or not with salt solutions was examined by TEM. In treated conidia, most of the conidia were affected and cellular vacuolization and cytoplasmic disorganization was observed. For ROS accumulation, a higher increase was observed in fluorescent conidia in presence of PB, SSi, and CCh by 75, 68, and 70% as compared to control, respectively. MMP was significantly decreased after salt application indicating a loss of mitochondria function. Also, luminescence showed that B. cinerea-conidia treated with salts contained less ATP than the untreated conidia. The results obtained herein are a step towards a comprehensive understanding of the mode of action by which salts act as antifungal agents against B. cinerea.

Electrolysed water and salt solutions can reduce green and blue molds while maintain the quality properties of ‘Valencia’ late oranges

The effect of four salt solutions; sodium metabisulfite (SM), potassium sorbate (PS), potassium carbonate (PC) and sodium chloride (SC) as electrolyte to generate alkaline (alEW) and acidic (acEW) electrolysed water was assessed in vitro and ex vivo under artificial and natural infection against Penicillium digitatum and P. italicum, the causal agents of green and blue molds, respectively. Generally, both components of the electrolysed water have exhibited decontaminating activity against the two tested Penicillium species, with clear stronger effect for the acidic component. The effect of alEW and acEW on physical and chemical properties of ‘Valencia’ sweet orange quality, including mass loss, total soluble solids (TSS), citric acid, pH, ascorbic acid and fruit color index was investigated. The results suggest that neither alEW nor acEW may have any negative impact in term of orange quality as compared to control treatments. alEW produced by PS and PC have increased citric acid content of orange fruits. The inhibitory effect of alEW and acEW against naturally occurring microbial population of filamentous fungi in the fruit washing tank was recorded. The direct effect of alEW and acEW on radial growth, conidial germination, germ tube elongation and the morphological changes of both pathogens by scanning electron microscopy (SEM) was examined. Results have shown that treatments have caused abnormal mycelia growth, irregular branching of hyphae in the apical part and loss of linearity in the tested fungal structures. Some salts, as electrolytes, have shown potential to produce robust electrolysed water that may represent valuable ecofriendly tool in controlling citrus postharvest decay.

Curcumin inhibits Diaporthe phaseolorum and reduces postharvest decay in kiwifruit

Curcumin is a promising antifungal agent because of its wide range of antifungal activities. In the present study, the effect of curcumin on postharvest decay of kiwifruit, caused by Diaporthe phaseolorum, was evaluated. We found that spore germination, germ tube elongation, and mycelial growth of D. phaseolorum were all significantly inhibited by curcumin. Cell viability and ATP content were also reduced by the addition of curcumin. Curcumin induced the production of reactive oxygen species in D. phaseolorum hyphae, resulting in apoptosis and accelerated rate of cell death. The activities of antioxidant enzymes, including catalase, peroxidase, superoxide dismutase and glutathione peroxidase, increased upon curcumin treatment. Mycelia exposed to curcumin exhibited a greater sensitivity to osmotic and oxidative stresses than untreated mycelia, and they lost their ability to penetrate plant cell walls. Application of curcumin effectively inhibited disease development in kiwifruit in a dose dependent manner. Collectively, the results indicated that curcumin can effectively inhibit postharvest decay of kiwifruit caused by D. phaseolorum by inhibiting the vegetative growth and cell viability, promoting apoptosis and cell death, and decreasing pathogenicity of the pathogen.

Response of an International Triticale Collection toPuccinia triticinaandPuccinia reconditasensu stricto and Assessment of Temperature Sensitivity in Leaf Rust Isolates

Triticale is derived from a cross between wheat and rye and the leaf rust pathogen of wheat, Puccinia triticina (Pt), and that of rye, P. recondita sensu stricto (Pr), can potentially cause disease in this crop. Recent studies showed that wheat rust fungi could adapt to warmer temperatures. In this paper, we report on the comparative virulence of three Pt races and one Pr isolate (all were collected in South Africa) on triticale as well as their in vitro response to temperature. Seedling infection types (SITs) of 169 triticale entries to Pt races 3SA144 (North American code SDDN), 3SA145 (CCPS) and 3SA248 (CFPS) and Pr isolate UVPr2 revealed that 3SA144 is the most virulent with 106 triticale entries found susceptible to this race. The three Pt races were avirulent to the four rye cultivars included as controls. UVPr2 was avirulent on all the triticale entries and 49 entries were considered resistant to the Pt races tested. Freshly harvested urediniospores of the above isolates were tested at constant temperature regimes of 10 °C, 22.5 °C and 35 °C to study germination characteristics. Mean urediniospore germination percentages as determined for 3SA144 (61.3%) and UVPr2 (62.6%) were significantly lower when compared to 3SA145 (83.7%) and 3SA248 (84.9%). Race 3SA144 was most sensitive to the higher temperature regime of 35 °C (5.2% germination). Among the investigated races, 3SA144 showed significantly lower mean germ tube elongation rates at all three incubation temperatures. This is the first report of differences in temperature adaptation between Pt races from SA.

Identification of phenylamide phytoalexins and characterization of inducible phenylamide metabolism in wheat

Changes in specialized metabolites were analyzed in wheat leaves inoculated with Bipolaris sorokiniana, the causal agent of spot blotch of Poaceae species. HPLC analysis detected the accumulation of six compounds in B. sorokiniana-infected leaves. Of these, we purified two compounds by silica gel and ODS column chromatography and preparative HPLC, and identified them as cinnamic acid amides, N-cinnamoyl-9-hydroxy-8-oxotryptamine and N-cinnamoyl-8-oxotryptamine, by spectroscopic analyses. The remaining four compounds were predicted to be p-coumaric acid amides of hydroxyputrescine, hydroxyagmatine, hydroxydehydroagmatine, and agmatine by mass spectrometry. The accumulation of two cinnamic acid amides was also induced by Fusarium graminearum infection, and by treatment with CuCl2, jasmonic acid, and isopentenyladenine. Antifungal activity of these amides was shown by inhibition of conidial germination and germ tube elongation of F. graminearum and Alternaria brassicicola, indicating that they act as phytoalexins. The accumulation of these amides also detected in barley leaves treated with CuCl2. We examined the accumulation of 25 phenylamides in B. sorokiniana-infected wheat leaves using LC-MS/MS. Hydroxycinnamic acid amides of tryptamine, serotonin, putrescine, and agmatine, were induced after infection with B. sorokiniana. Thus, the induced accumulation of two groups of phenylamides, cinnamic acid amides with indole amines, and p-coumaric acid amides with putrescine and agmatine related amines, represents a major metabolic response of wheat to pathogen infection.

Effect of apple cultivars and storage periods on the virulence of Neofabraea spp.

Bull’s eye rot is a typical quiescent postharvest apple disease in major fruit‐growing areas. The susceptibility of different apple cultivars to Neofabraea spp. (N. vagabunda and N. malicorticis) was assessed, with Granny Smith showing the most resistance and Cripps Pink the most susceptibility. To assess the factors involved in conidial germination, Neofabraea spp. were grown on crude protein extracts (CPEs) collected from apple fruits at different storage periods. Fungal germ tube growth rate and pathogenic enzyme (cellulase and xylanase) activity were assessed. Results showed that CPEs collected after 2 and 4 months of storage progressively stimulated conidial germination and germ tube elongation, while a lesser effect was observed from CPEs after 1 month of storage. Xylanase proved to be the main degrading enzyme secreted by all the isolates, while cellulase was produced only by N. vagabunda isolates. Overall, the isolate ID02 was the most virulent, based on more rapid germ tube elongation and greater activity of the lytic enzymes.

Role of Adjuvants in the Management of Anthracnose-Change in the Crystal Morphology and Wetting Properties of Fungicides.

The hydrophobic wax layer of pepper fruit (Capsicum frutescens L.) increases the importance of selecting adjuvants that improve the wetting property of droplets on the target organism and increase the effective utilization of fungicides. In this study, the effect of adjuvants including nonionic, cationic, organosilicone, and oils on the wettability of fungicides was determined. The critical micelle concentrations for S903 (organosilicone), 1227 (cationic), AEO-5 (nonionic), GY-Tmax (oil), and XP-2 (oil) were 25, 1000, 100, 200, and 500 mg/L, respectively. Interface behaviors and in vivo tests suggested that adjuvants at appropriate concentrations (S903, 2.5 mg/L; 1227, 100 mg/L; AEO-5, 1 mg/L; GY-Tmax, 50 mg/L; and XP-2, 5 mg/L) resulted in optimum efficiency. Adjuvants significantly increased the inhibitory activity of pyraclostrobin against the mycelial growth, spore germination, and germ tube elongation of Colletotrichum scovillei by 41.3-58.8%, 28.2-44.6%, and 27.8-39.8%, respectively. Pyraclostrobin amended with S903 and XP-2 showed higher efficacy against anthracnose than the fungicide alone on pepper fruit. The increased efficacy may have resulted from the changed crystal morphology (ellipses of similar sizes), improved wettability, and rainfastness. A structural equation model indicated that surface tension and retention play the most important roles in the application properties of fungicide. In field experiments, the efficacy of pyraclostrobin with adjuvants showed no significant difference with pyraclostrobin alone, which indicated that, except for adjuvants, other spraying technologies are important for improving the field performance of fungicides. These results provide a foundation for the synthesis of highly efficient fungicides based on crystal structure and for the sustainable management of pepper anthracnose.

Inhibition of Tomato Early Blight Disease by Culture Extracts of a Streptomyces puniceus Isolate from Mangrove Soil.

This study investigates the potential of natural products derived from a mangrove rhizosphere bacterium in tomato early blight management. A Streptomyces puniceus strain L75 was isolated from the rhizosphere of Acanthus ilicifolius Linn in the Mai Po Reserve, Hong Kong. The crude ethyl acetate (EA) extract of L75 fermentation cultures has broad-spectrum antifungal bioactivities. L75 EA extract was significantly more effective in Alternaria solani growth inhibition at 25 μg/ml or lower compared with Mancozeb, with no observable negative impacts on tomato leaves or root development. Furthermore, L75 EA extract had significantly lower aquatic toxicity than Mancozeb at the same concentrations. L75 EA extract targets germ tube elongation of A. solani conidia, with a fungistatic mode of action. Liquid chromatography-quadrupole time-of-flight mass spectrometry analysis identified two possible antifungal compounds, Alteramide A and the Heat-Stable Antifungal Factor, which together contribute partially to the bioactivity of L75 EA extract. On detached tomato leaves, coinoculation of A. solani with L75 EA extract of 50, 25, or 5 μg/ml reduced diseased areas by ∼98, ∼90, and ∼48%, respectively, relative to the control after 5 days. This study demonstrates the potential of natural products from mangrove rhizosphere bacteria in agricultural applications.

Effect of Legume Extracts on Germination, Seedling Health of Beans (Phaseolus vulgaris L.) and Soil Microorganisms

Application of undecomposed green manure has been reported to cause poor emergence and establishment of common beans in the field. Therefore, to understand the mechanisms’ contributing to the poor crop establishment, the effect of extracts from fresh and decomposed legume green manures on bean seed germination, fungal mycelial growth, spore germination and germ tube elongation were evaluated. The extracts were prepared in either ethanol or distilled water. Data was collected on percentage seed germination, seedling length, mycelial radial growth, spore germination and germ tube elongation. Ethanol extracts from fresh lablab inhibited bean germination by 56%, increased mean germination time to 8 days, and decreased germination index while ethanol extracts of groundnut and beans caused highest inhibition in bean shoot length and reduced biomass. Ethanol extracts from fresh green manures significantly inhibited fungal mycelial growth while the aqueous extracts from beans, groundnuts and soybean had significant level of antifungal activity while aqueous lablab extracts stimulated mycelial. Aqueous extract of lablab and soybean enhanced spore germination by over 70% with more pronounced effect on germ tube length and number of germ tubes by 8.0% and 13% respectively. The study comparatively reveals that the extract of lablab was inhibitory to common bean germination compared to other legume extracts and also stimulated the growth of root rot pathogens that may have resulted in poor establishment of beans.

Engineering a peptide aptamer to target calmodulin for the inhibition of Magnaporthe oryzae

To develop an antimicrobial agent for preventing the devasting damage caused by rice blast, a novel peptide aptamer was identified to interact with calmodulin (CaM) for the inhibition of the spore development in the pathogen Magnaporthe oryzae. A peptide aptamer designated as SNP-D4, consisted of the scaffold protein Staphylococcus aureus nuclease (SN) and an exposed surface loop of 16 random amino acids, was screened from the constructed peptide aptamer libraries by bacterial two-hybrid system using CaM of M. oryzae as the bait. The preliminary inhibition in the sporulation development was observed after treating with the crude extracts expressing SNP-D4. The inhibition efficacies of the purified SNP-D4 were quantified at the stages of conidial germination, germ tube elongation, and appressorium formation in M. oryzae. The binding affinity analysis revealed that SNP-D4 interacted with CaM at a dissociation constant (Kd) of about 20 μM. Moreover, the N-terminus of CaM was identified as the key binding region.

Natural Compounds That Modulate the Development of the Fungus Botrytis cinerea and Protect Solanum lycopersicum.

Botrytis cinerea is the causal agent of gray mold disease and is responsible for the loss of millions of dollars in crops in worldwide. Currently, this pathogen exhibits increasing resistance to conventional fungicides; therefore, better control methods and novel compounds with a more specific mechanism of action but without biocidal effects, are required. In this work, several natural compounds to control B. cinerea were analyzed in vitro. Detected effects were dependent on the stage of fungus development, and 3-phenyl-1-propanol displayed the most potent inhibition of in vitro germination, germ tube development, and sporulation. However, it had lower protection of leaves and postharvest fruit in plant infection. Isoeugenol and 1-phenylethanol exhibited lower inhibition of in vitro germination and sporulation, but at the highest concentrations, they inhibited germ tube elongation. Although the lowest rates of foliage infection were recorded using isoeugenol and 3-phenyl-1-propanol, 1-phenylethanol significantly decreased the disease in postharvest tomato fruit, with an efficacy like Mancozeb, but at 18 times lower micromolar concentration. All compounds resulted in high cell viability after spores were removed from the treatment solution exhibited high cell viability, suggesting a non-biocidal effect. The diversity of in vitro and in-plant effects seems to indicate a different mechanism of action.

Curcumin inhibits gray mold development in kiwifruit by targeting mitogen-activated protein kinase (MAPK) cascades in Botrytis cinerea

Curcumin is a promising antifungal agent because of its wide range of antifungal activity. In the present study, the effect of curcumin on gray mold (Botrytis cinerea) in kiwifruit was evaluated. Results showed that spore germination, germ tube elongation, and mycelial growth of B. cinerea were significantly suppressed by curcumin in a dose dependent manner. Mycelium treated with curcumin exhibited a higher sensitivity to osmotic stress, and the ability of hyphae to penetrate plant cell walls was also inhibited. Three mitogen-activated protein kinase (MAPK) genes, Bmp1, Bmp3, and Sak1, involved in vegetative growth, osmotic stress response, and pathogenicity, were down-regulated by curcumin. The application of curcumin up to 400 mg L−1 significantly delayed disease development in kiwifruit. These results indicate that curcumin can effectively inhibit gray mold in kiwifruit; and this effect involves alterations in the sensitivity of B. cinerea to pathogenicity-associated MAPK cascades.