Ferulic acid may prevent infection of Cicer arietinum by Sclerotium rolfsii

High performance liquid chromatography analysis of different parts of Sclerotium rolfsii-infected and healthy seedlings of chickpea (Cicer arietinum) was carried out to examine the status of phenolic compounds. Three major peaks that appeared consistently were identified as gallic, vanillic and ferulic acids. Gallic acid concentrations were increased in the leaves and stems of infected plants compared to healthy ones. Vanillic acid detected in stems and leaves of healthy seedlings was not detected in infected seedlings. There was a significant increase of ferulic acid in those stem portions located above the infected collar region compared to minimal amounts in the roots of healthy seedlings. In vitro studies of ferulic acid showed significant antifungal activity against S. rolfsii. Complete inhibition of mycelial growth was observed with 1000 g of ferulic acid/ml. Lower concentrations (250, 500 and 750 g/ml) were also inhibitory and colony growth was compact in comparison with the fluffy growth of normal mycelium. Higher amounts of phenolics were found in the stems and leaves of S. rolfsii-infected seedlings in comparison to the healthy ones. A role for ferulic acid in preventing infections by S. rolfsii in the stems and leaves of chickpea plants above the infection zone is therefore feasible.     

Phenolic compounds of Sorghum vulgare in response to Sclerotium rolfsii infection

Abstract

Identification of individual phenolic acids of Sorghum vulgare Pers. cv. M.P. after interaction with Sclerotium rolfsii Sacc. using high performance liquid chromatograph (HPLC) showed the presence of phenolics namely tannic, gallic, ferulic, chlorogenic and cinnamic acids in varying amounts. After 72 h inoculation with S. rolfsii, a maximum amount of ferulic acid (166.6 µg g^?1 fresh wt) was present in the collar of inoculated plants, followed by leaves and roots and its level decreased gradually with time. Similarly, the presence of chlorogenic acid was traced after 48 h, while that of cinnamic acid was traced after 72 h of inoculation. Reddish-brown pigmentation at the collar region of inoculated plants was also observed along with the high content of tannic acid. Among other phenolics, the presence of gallic acid was recorded consistently and maximum accumulation (139.3 µg g^?1 fresh wt) was noticed at the zone of interaction (collar region) after 72 h of inoculation. In contrast, maximum lignin deposition was observed at collar region after 96 h of inoculation. Induction of phenolic acids in S. vulgare along with the lignin deposition and red pigmentation at collar region is considered a key biomarker in the non-host-pathogen interaction in the S. valgare–S. rolfsii pathosystem.     

Antimicrobial efficacy,disease inhibition and phenolic acid-inducing potential of chloroform fraction of cow urine

High-performance liquid chromatographic (HPLC) analysis of chloroform fraction (CF) of cow urine showed rich pool of phenolic acids. Antifungal and antibacterial bioassays of CF have shown its tremendous efficacy against some fungal plant pathogens as well as human pathogenic bacteria at very low concentrations. The CF also inhibited powdery mildew (Erysiphe cichoracearum) of balsam (Impatiens balsamania) under field conditions during pre- and post-inoculation treatments. HPLC analysis of pre- and post-inoculation-treated plant leaves indicated that CF induced phenolic acid synthesis as compared to control. The results revealed that CF of cow urine has the potential for controlling some important human diseases. The result on balsam powdery mildew is a good signal that CF may also be effective against other plant diseases in the field.     

Foliar spray of aqueous extract of neem (Azadirachta indica) cake to control balsam (Impatiens balsaminia) powdery mildew

Neem cake is used as a soil amendment. It releases nutrient into the soil very slowly. It is also an insect repellent. It improves the physical as well as biological conditions of the soil such as soil aeration, water holding capacity and also the microflora in the rhizosphere. Aqueous extract of neem cake was used against powdery mildew (Erysiphe cichoracearum) of balsam (Impatiens balsaminia) in the field at 25, 50, 75 and 100%. The efficacy was observed even at low concentrations (25%). Foliar application of aqueous extract of neem cake induced synthesis of phenolic acids in balsam. Maximum phenolic acid was detected in balsam plant leaves treated with 50% neem cake followed by 75% in both pre-and post-inoculation treatments. The induction of phenolic acid in plants was correlated with the induction of resistance in treated plants against powdery mildew.     

Plant growth-promoting rhizobacteria-mediated induction of phenolics in pea ( Pisum sativum) after infection with Erysiphe pisi

Qualitative and quantitative estimation of phenolic compounds was done through high performance liquid chromatography (HPLC) in different parts of pea (Pisum sativum) after treatment with two plant growth-promoting rhizobacteria (PGPR), viz., Pseudomonas fluorescens (strain Pf4) and Pseudomonas aeruginosa (referred to here as Pag) and infection by Erysiphe pisi. The phenolic compounds detected were tannic, gallic, ferulic, and cinnamic acids on the basis of their retention time in HPLC. In all the treated plants, synthesis of phenolic compounds was enhanced. The induction of gallic, ferulic, and cinnamic acids was manyfold more than those in the control. Maximum accumulation of phenolic compounds was observed in plants raised from PGPR-treated seeds and infection with E. pisi. Under pathogenic stress, Pag performed better because a relatively higher amount of phenolics was induced compared with plants treated with Pf4. Received: 20 August 2001 / Accepted: 20 September 2001     

Effect of Plant Growth-Promoting Rhizobacteria and Culture Filtrate of <Emphasis Type="Italic">Sclerotium rolfsii</Emphasis> on Phenolic and Salicylic Acid Contents in Chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis>)

Two plant growth-promoting rhizobacteria (PGPR), viz., Pseudomonas fluorescens strain Pf4 and P. aeruginosa strain Pag, protected chickpea (Cicer arietinum) plants from Sclerotium rolfsii infection when applied singly or in combination as seed treatment. Pag gave the best protection to the seedlings, applied either singly (mortality 16%) or in combination with Pf4 (mortality 17%) compared with 44% and 24% mortality in control and Pf4 treatment, respectively. The two PGPR strains induced the synthesis of specific phenolic acids, salicylic acid (SA), as well as total phenolics at different growth stages of chickpea seedlings with varied amount. The maximum amount of total phenolics was recorded in all the aerial parts of 4-week-old plants. Gallic, ferulic, chlorogenic, and cinnamic acids were the major phenolic acids detected in high-performance liquid chromatography (HPLC) analysis. Induction of such phenolic acids in the seedlings was observed up to 6 weeks in comparison with control. Salicylic acid (SA) was induced frequently during the first 3 weeks of growth only. Between the two strains, Pag was more effective in inducing phenolic acid synthesis applied either singly or in combination with strain Pf4 during the entire 6 weeks of growth of chickpea. In the presence of a culture filtrate of S. rolfsii, the two Pseudomonas strains induced more phenolic acids in treated than in non-treated and control plants. The occurrence of salicylic acid was frequent in the first 24 h, but infrequent at 48 and 96 h. Foliar spray of Pseudomonas strains also enhanced the phenolic acid content as well as total phenolics within 24 h of application. Gallic, chlorogenic, and cinnamic acids were consistently discerned in the treated leaves, whereas SA was absent even up to 96 h of application. Resistance in chickpea plants by Pseudomonas strains through induction of phenolic compounds as well as induced systemic resistance via SA-dependent pathway was evident. Received: 1 April 2002 / Accepted: 4 May 2002     

Antifungal activity of ethanolic extract of Archu (Rheum emodi) on powdery mildew (Erysiphe cichoracearum) and its role in the induction of resistance in balsam (Impatiens balsamania)

Rheum emodi, vernacularly known as Archu, is one of the important high altitude medicinal plants widely distributed in Himalayan regions. Though widely used in Ayurveda for curing various human diseases, its use in plant diseases is limited. Ethanolic extract of Rheum rhizome was assayed against spore germination of Alternaria solani, Heliminthosporium penniseti and Curvularia palliscens. The inhibition of spore germination was concentration dependent. Maximum inhibition was obtained at 4000 and 5000 ppm followed by 3000, 2000 and 1000 ppm. However, the extract was highly effective in the pre-inoculation treatment against powdery mildew (Erysiphe cichoracearum) of balsam (Impatiens balsamania) under field conditions. High performance liquid chromatographic (HPLC) analysis of balsam leaves showed increased synthesis of phenolic acids, which has been correlated with induced resistance in inhibiting the disease intensity of balsam powdery mildew.     

Germination of Erysiphe gratninis f.sp. hordei conidia on barley leaves

Germination of Erysiphe graminis f.sp. hordei conidia on leaves of several barley cultivars was studied in the laboratory. On both detached leaves and intact plants, within 48 h of inoculation a higher proportion of conidia had germinated on the basal and middle portions of the adaxial leaf surface than on the corresponding portions of the abaxial surface. Such differences between surfaces were not observed near the leaf tip. Similar results were obtained with all the cultivars and growth stages tested, and with five isolates of E. graminis, and are consistent with the observation that there is usually less powdery mildew on the abaxial than the adaxial surface of barley leaves. With most of the barley genotype/mildew isolate combinations tested, within 48 h of inoculation higher proportions of conidia germinated on seedlings and juvenile plants than on older plants. Inherited characteristics which affect spore germination on the leaf surface may be important factors in the development of adult-plant resistance of barley to powdery mildew, particularly in certain genotypes.     

Antifungal activity of two alkaloids of Zephyranthes citrina and their field efficacy against powdery mildew (Erysiphe cichoracearum) of balsam

The anti-fungal activity of two alkaloids isolated from bulbs of Zephyranthes citrina was observed against 10 fungi, viz, Aternaria solani, A. triticina, Curvularia lunata, C. maculuns, Cercospora malvacearum, Erysiphe sp., Fusarium udum, Helminthosporium pisi, H. speciferum and Ustilago cynodontis. Different concentrations (200, 400, 600, 800, 1000 µg/ml of alkaloids (A and B) were used. Spore germination was inhibited at 600, 800, 1000 µg/ml. B alkaloid was used against Erysiphe cichoracearum causing powdery mildew in balsam (Impatiens balsamina) in the field as pre- and post-inoculation treatments at 1000, 1500, 2000 µg/ml doses. The extract was effective in both pre- and post-inoculation treatments. Foliar application of this alkaloid resulted in inducing synthesis of phenolic acid in the leaves of balsam. Maximum phenolics were detected in the leaves treated with 1500 µg/ml in both pre- and post-inoculation treatments. The increase in the production of phenolics in treated leaves of balsam can be correlated with the induction of resistance in treated plants against powdery mildew. The significant efficacy of the alkaloid under field conditions opens the possibility of its use by farmers for also controlling other diseases.     

Transient silencing of VvCSN5 enhances powdery mildew resistance in grapevine (Vitis vinifera)

As one of the most economically important fruit crops in the world, the grapevine (Vitis vinifera) suffers significant yield losses from various pathogens including powdery mildew caused by Erysiphe necator. In contrast, several wild Chinese grapevines, including Vitis pseudoreticulata accession Baihe-35-1, are highly resistant to powdery mildew pathogens. Here, we identified a grapevine gene CSN5 (COP9 signalosome complex subunit 5), designated VvCSN5, that was differentially expressed between the resistant ‘Baihe-35-1’ and susceptible ‘Thompson Seedless’ during powdery mildew isolate Erysiphe necator NAFU1 infection. Moreover, transient silencing of VvCSN5 in ‘Thompson Seedless’ leaves enhanced resistance to En NAFU1. This resistance manifested in cell wall callose deposition at attempted infection sites and hypersensitive response-like cell death of penetrated epidermal cells. Several defense-related marker genes (VvPR1, VvPR3, VvPAD4, and VvRBOHD) had higher basal expression levels in VvCSN5-silenced leaves. In addition, we found the structure and activity of CSN5 promoters in ‘Thompson Seedless’ and ‘Baihe-35-1’ were different, which may have been behind their different resistances to powdery mildew infection. Taken together, these results implied that grapevine CSN5 plays an important role in the response to powdery mildew infection.

     

Time course study on accumulation of cell wall-bound phenolics and activities of defense enzymes in tomato roots in relation to <Emphasis Type="Italic">Fusarium</Emphasis> wilt

Major cell wall-bound phenolic compounds were detected and identified in roots of tomato at different stages of growth. Alkaline hydrolysis of the cell wall material of the root tissues yielded ferulic acid as the major bulk of the phenolic compounds. Other phenolic compounds identified were 4-hydroxybenzoic acid, vanillic acid, 4-hydroxybenzaldehyde, vanillin and 4-coumaric acid. All the six phenolic acids were higher in very early stage of plant growth. Ferulic acid, 4-hydroxybenzoic acid and 4-coumaric acid exhibited a decreasing trend up to 60 days and then the content of these phenolic acids increased somewhat steadily towards the later stage of growth. Total phenolics, phenylalanine ammonia-lyase (PAL) activity and peroxidase (POD) activity were in tandem match with the occurrence pattern of the phenolic acids. Ferulic acid showed highest antifungal activity against tomato wilt pathogen Fusarium oxysporum f. sp. lycopersici. The results of this study may be interpreted to seek an explanation for high susceptibility of tomato plants at flowering stage to Fusarium wilt. It may also be concluded that greater amounts of ferulic acid in combination with other phenolics and higher level of PAL and POD activities after 60 days of growth may have a role in imparting resistance against Fusarium wilt at a late stage of plant growth.     

Genetic variability and mycohost association of Ampelomyces quisqualis isolates inferred from phylogenetic analyses of ITS rDNA and actin gene sequences

Ampelomyces quisqualis complex is well known as the most common and widespread hyperparasite of the family Erysiphaceae, the cause of powdery mildew diseases. As commercial biopesticide products it is widely used to control the disease in field and plastic houses. Although genetic diversity within Ampelomyces isolates has been previously recognized, a single name A. quisqualis is still applied to all pycnidial intracellular hyperparasites of powdery mildew fungi. In this study, the phylogenetic relationships among Ampelomyces isolates originating from various powdery mildew fungi in Korea were inferred from Bayesian and maximum parsimony analyses of the sequences of ITS rDNA region and actin gene. In the phylogenetic trees, the Ampelomyces isolates could be divided into four distinct groups with high sequence divergences in both regions. The largest group, Clade 1, mostly accommodated Ampelomyces isolates originating from the mycohost Podosphaera spp. (sect. Sphaerotheca). Clade 2 comprised isolates from several genera of powdery mildews, Golovinomyces, Erysiphe (sect. Erysiphe), Arthrocladiella, and Phyllactinia, and was further divided into two subclades. An isolate obtained from Podosphaera (sect. Sphaerotheca) pannosa was clustered into Clade 3, with those from powdery mildews infecting rosaceous hosts. The mycohosts of Ampelomyces isolates in Clade 4 mostly consisted of species of Erysiphe (sect. Erysiphe, sect. Microsphaera, and sect. Uncinula). The present phylogenetic study demonstrates that Ampelomyces hyperparasite is indeed an assemblage of several distinct lineages rather than a sole species. Although the correlation between Ampelomyces isolates and their mycohosts is not obviously clear, the isolates show not only some degree of host specialization but also adaptation to their mycohosts during the evolution of the hyperparasite.     

Evidences of biological control capacities of Streptomyces spp. against Sclerotium rolfsii responsible for damping-off disease in sugar beet (Beta vulgaris L.)

Ten antibiotic-producing Streptomyces spp. isolated from Moroccan soils were evaluated for their ability to inhibit in vitro Sclerotium rolfsii development. Four isolates having the greatest pathogen inhibitory capabilities were subsequently tested for their ability to inhibit sclerotial germination in sterile soil. This test was carried out by using biomass inoculum, culture filtrate, and spore suspension of the isolates as treatment. Treatment with biomass inoculum and culture filtrate gave the highest inhibition of sclerotia. Biological control tests against Sclerotium rolfsii damping-off of sugar beet seeds showed that the selected Streptomyces isolates reduced significantly the disease severity, the J-2 isolate being the more potent. In addition, treatment with the isolate J-2 resulted in a significant increase (P ≤ 0.05) in seedling development compared to the control. All antagonistic Streptomyces selected here were able to grow in the rhizosphere soil from infected sugar beet culture.     

Evidence for Resistance-inducing Compounds in Conidia of Erysiphe graminis f.sp. hordei

Preparations of Erysiphe graminis f.sp. hordei conidia were spray-applied to the first leaf of barley plants which were subsequently challenge inoculated with virulent powdery mildew. The powdery mildew reducing effect of the preparations was assessed by scoring the outcome of the challenge inoculation. Homogenates of ungerminated conidia, germinated conidia, and methanol-water extracts of germinated conidia reduced the number of powdery mildew colonies. Cell wall fragments from ungerminated conidia, germinated conidia, and conidial germination fluid obtained from conidia germinated in aqueous suspension did not reduce the number of powdery mildew colonies. Microsconical analysis of the infection course following challenge inoculation indicated that the powdery mildew reducing effect is due partly to induced resistance.     

Interspecific and intraspecific diversity in oak powdery mildews in Europe: coevolution history and adaptation to their hosts

Quercus has been reported as the genus with the largest number of attacking powdery mildews. In Europe, oak powdery mildew was rarely reported before 1907, when severe outbreaks were observed. These epidemics were attributed to the newly described species Erysiphe alphitoides, presumed to be of exotic origin. After the burst of interest following the emergence of the disease, research on this topic remained very limited. Interest in research was recently reactivated in response to the availability of molecular tools. This review summarizes current knowledge on the diversity of oak powdery mildews in Europe and their possible evolutionary relationships with European oaks. The most striking results are the evidence of cryptic diversity (detection in France of a lineage closely related to Erysiphe quercicola, previously thought to only have an Asian distribution), large host range (similarity of E. alphitoides and E. quercicola with powdery mildews of tropical plants) but also local adaptation to Quercus robur. These recent findings highlight the complexity of the history of oak powdery mildew in Europe and point to the question of host specialization and host jumps in the evolution of powdery mildew fungi.     

Synthesis and antifungal activity of six benzylic diamines

Six benzylic diamines were synthesised and examined for antifungal activity. Four of the compounds, KB 2, KB 4, KB 5 and KB 6, reduced radial growth of the oat leaf stripe pathogen Pyrenophora avenae, the largest reduction obtained with 25 μM KB 4, which reduced radial growth by 47%. Surprisingly, these four amines had no effect against infection of barley seedlings with the powdery mildew fungus Erysiphe graminis f.sp. hordei. Instead, two different amines, KB 1 and KB 3, reduced powdery mildew infection on barley. The greatest reduction was obtained with 25 μM KB 3, which reduced mildew infection by 69%. All of the amines which exhibited antifungal or fungicidal properties perturbed polyamine formation as measured by the incorporation of labelled ornithine into polyamines.     

Silicon-Induced changes in antifungal phenolic acids, flavonoids, and key phenylpropanoid pathway genes during the interaction between miniature roses and the biotrophic pathogen Podosphaera pannosa

Application of 3.6 mm silicon (Si+) to the rose (Rosa hybrida) cultivar Smart increased the concentration of antimicrobial phenolic acids and flavonoids in response to infection by rose powdery mildew (Podosphaera pannosa). Simultaneously, the expression of genes coding for key enzymes in the phenylpropanoid pathway (phenylalanine ammonia lyase, cinnamyl alcohol dehydrogenase, and chalcone synthase) was up-regulated. The increase in phenolic compounds correlated with a 46% reduction in disease severity compared with inoculated leaves without Si application (Si-). Furthermore, Si application without pathogen inoculation induced gene expression and primed the accumulation of several phenolics compared with the uninoculated Si- control. Chlorogenic acid was the phenolic acid detected in the highest concentration, with an increase of more than 80% in Si+ inoculated compared with Si- uninoculated plants. Among the quantified flavonoids, rutin and quercitrin were detected in the highest concentrations, and the rutin concentration increased more than 20-fold in Si+ inoculated compared with Si- uninoculated plants. Both rutin and chlorogenic acid had antimicrobial effects on P. pannosa, evidenced by reduced conidial germination and appressorium formation of the pathogen, both after spray application and infiltration into leaves. The application of rutin and chlorogenic acid reduced powdery mildew severity by 40% to 50%, and observation of an effect after leaf infiltration indicated that these two phenolics can be transported to the epidermal surface. In conclusion, we provide evidence that Si plays an active role in disease reduction in rose by inducing the production of antifungal phenolic metabolites as a response to powdery mildew infection.     

Phenolic acid content – a criterion for selection of resistant apple cultivars against Podosphaera leucotricha (Ell. and Ev.) Salmon

Development of powdery mildew (Podosphaera leucotricha) on five popular cultivars of apple, viz., Scarlet Gala, Golden spur, Mollies Delicious, Red Fuzi and Red Chief was studied to determine incidence–severity relationship. The disease was confined primarily to the vegetative terminal shoots early in the season which also traversed later onto other leaves. Several biochemical changes occur in the trees due to fungal/microbial infection. We studied the qualitative/quantitative changes in phenolic acids in apple-powdery mildew pathosystems. Scarlet Gala and Red Chief are very rich in phenolic acids, and had shown resistances to the pathogen but those with low amount of phenolic acids, viz., Golden spur, Mollies Delicious, and Red Fuzi, were highly susceptible. Thus, the quantity of phenolic acids (secondary metabolites) has been taken as a biochemical parameter in screening apple cultivars for resistance/susceptibility against powdery mildew of apple.     

Structure-activity Relationships of Fungicidal N-Benzoylanthranilic Esters

The antifungal activity of 37 N-(methoxy-substituted benzoyl)anthranilic esters was tested on the powdery mildew of barley caused by Erysiphe graminis by the pot test. Among the methyl N-(methoxy-substituted benzoyl)anthranilates tested, 3,4-dimethoxybenzoyl derivative exhibited the highest activity. The variation in fungicidal activity of N-(3,4-dimethoxybenzoyl)anthranilic esters was shown to be related with variation in hydrophobicity and the electronic property of the alcohol moiety of the ester. The branching at the α-position of the alcohol moiety of the ester was detrimental to the activity.     

Cloning and sequencing of cDNAs encoding a pathogen-induced putative peroxidase of wheat (Triticum aestivum L.)

We report here the complete amino acid sequence of a pathogen-induced putative peroxidase from wheat (Triticum aestivum L.) as deduced from cDNA clones representing mRNA from leaves infected with the powdery mildew fungus Erysiphe graminis. The protein consists of 312 amino acids, of which the first 22 form a putative signal sequence, and has a calculated pI of 5.7. Sequence comparison revealed that the putative wheat peroxidase is most similar to the turnip (Brassica rapa) peroxidase, with which it shares 57% identical and 13% conserved amino acids.