Evaluation of drench treatments with phosphonate derivatives against Pseudomonas syringae pv. syringae on pear under controlled environment conditions

Several phosphonate derivatives including theoomycetic antifungal agents phosphonate andtris-o-ethylphosphonate (fosetyl), theethylene-releasing compound 2-chloroethylphosphonate(ethephon), and the antibiotic2-epoxypropylphosphonate (phosphomycin) were evaluatedfor in vitro and in planta activityagainst Pseudomonas syringae pv. syringae.Inhibition of colony growth in CYE agar byphosphonate, fosetyl and etephon was very slight(minimal inhibitory concentrations MIC= 0.31–;0.62 gHP /l). Also, survival of P. syringae pv. syringae in aqueous solutions ofphosphonate or fosetyl was high. Only phosphomycinshowed significant antibacterial activity invitro (MIC=10-20 µg HP /ml) comparedto streptomycin (1-2 µg a.i./ml). Potted pearplants irrigated with these chemicals and inoculatedwith Pseudomonas syringae pv. syringae had significantly less disease than non-treatedcontrols ( P<0.001). Phosphomycin was the mostactive compound with a median effective dose(ED₅₀) of less than 0.62 g HP /l.Activities of the other phosphonates were weak butconsistent between experiments. The ED₅₀s on wholeplants were 2.1, 3.3, and 6.9 g HP /l for ethephon, phosphonate and fosetyl, respectively. TheED₅₀of P. syringae pv. syringaeincreased from 6.5 in non-treated controls to 7.7-8.8log₁₀ cfu/ml on plants treated with phosphonatesat 1.86 g HP /l. It was concluded thatdrench treatment with fosetyl is not a practicaloption for control of P. syringae pv. syringae on pear.     

Genetic variability of Iranian strains of Pseudomonas syringae pv. syringae causing bacterial canker disease of stone fruits

Strains of Pseudomonas syringae pv. syringae (Pss) were isolated from healthy and diseased stone fruits tissues sampled from 38 stone fruits orchard sites in Iran in 2010 and 2011. These strains were tested for pathogenicity and the presence of the syrB gene and were genetically characterized by using ERIC (enterobacterial repetitive intergenic consensus), REP (repetitive extragenic palindromes), and BOXAIR and IS50 (insertion sequences) primers and PCR. All 78 strains of Pss tested were moderately to highly pathogenic on Loring peach seedlings. A total of 78 isolates of the Pss amplified a 752-bp fragment with the syrB primers. To assess genetic diversity among the strains, genomic DNA was extracted from strains and used in rep-PCR and IS50-PCR analysis. Cluster analysis was performed using UPGMA. The strains of Pss were separated into nine distinguishable genotypic groups by the combination data set of both rep-PCR and IS50-PCR at 73 % similarity level. There was no significant correlation between genetic diversity and geographical origin of the isolates. These results indicate that a combination of rep-PCR and IS50-PCR fingerprinting can be used as a high resolution genomic fingerprinting method for elucidating intrapathovar diversity among strains of Pss. The results of this study demonstrated the existence of a considerable genetic diversity among Pss strains causing canker of stone fruit trees in Iran. In this study, genetic variability in Iranian strains of Pss were established, which will be of immense use in the development of resistant genotypes against this bacterial pathogen.     

Bacterial inflorescence rot of grapevine caused by Pseudomonas syringae pv. syringae

Molecular sequencing (rpoB) and standard pathological and microbiological methods identified Pseudomonas syringae pv. syringae (Pss) as the causal agent of bacterial inflorescence rot of grapevines (Vitis vinifera) in three vineyards in Tumbarumba, NSW, Australia in 2006 and 2007. Pss strains from shrivelled berries and necrotic inflorescences of diseased grapevines were used to inoculate leaves and inflorescences of potted cv. Semillon grapevines. Pss caused disease symptoms similar to those experienced in the field, including angular leaf lesions, longitudinal lesions in shoot tissues and rotting of inflorescences from before flowering until shortly after fruit set. High humidity promoted symptom severity. The necrotic bunch stem and leaf lesions were susceptible to the development of Botrytis cinerea infections. Cryo‐scanning electron microscopy (cryoSEM) indicated that Pss entered leaves and inflorescence tissues via distorted, open, raised stomata surrounded by folds of tissue that appeared as ‘star‐shaped’ callose‐rich complexes when viewed by UV light microscopy. In necrotic tissues, cryoSEM revealed Pss within petiole parenchyma cells and air‐filled rachis xylem vessels. This is the first report of inflorescence and hence fruit loss caused by Pss in grapevines. The disease is described as ‘bacterial inflorescence rot’ and regarded as one that expands the previously reported pathology of grapevines caused by P. syringae. This study also indicated that infection by Pss might promote destructive B. cinerea infections when the fungus is already present but latent, although further experimentation is needed to prove such an interaction.     

Pathogenicity and genetic variation of Phytophthora cactorum from silver birch and strawberry

Phytophthora cactorum strains isolated from necrotic stem lesions on Betula pendula seedlings or from Fragaria ananassa plants suffering from crown rot were pathogenic to their host plants. Only isolates from birch caused clear lesions on non-wounded bark of birch. P. cactorum isolates from birch were not detrimental to strawberry. Random Amplified Polymorphic DNA (RAPD) analysis revealed variation within P. cactorum, isolates from silver birch having different banding patterns than those from strawberry. UPGMA analysis clustered isolates from silver birch and strawberry plants into separate groups. The data show that the recent outbreak in Finland of P. cactorum in birch could not be caused by the import of strawberry plants affected by crown rot.     

Phylogenetic,genetic, and phenotypic diversity of Pseudomonas syringae pv. syringae strains isolated from citrus blast and black pit in Tunisia

Citrus blast and black pit caused by Pseudomonas syringae pv. syringae (Pss) is the only bacterial disease reported in Tunisian Citrus orchards. The phylogenetic relationship between Pss strains was studied based on multilocus sequence analysis (MLSA), using partial sequences of housekeeping genes rpoD, rpoB, gyrB, cts, and pfk for 14 representative Pss Citrus strains, including the reference strain LMG5496. The MLSA revealed that the studied Tunisian Citrus strains are closely related to LMG5496 and cluster in phylogroup 02. Based on the cts gene, the majority of Citrus strains clustered in clades “a” and “b”. However, five strains were placed in a newly defined clade “g”. We describe the presence of six different type III secreted effectors (T3SEs). These were found with frequencies of 100% for the effector hopAN1 and the helper hrpK1, 65% for hopT1-2, and 14% for hopN1, hopR1, and hopQ1-2. Investigation of copper resistance showed that 67% of our Pss Citrus strains from Tunisia are resistant to copper sulphate in vitro, and the copper resistance genes copABCDR were detected in 23% of the strains. Our results present new data concerning the genetic diversity and phylogeny, presence of T3SEs, and copper resistance within the Pss populations that affect Citrus in Tunisia.     

Identification and Discrimination of Pseudomonas syringae Isolates from Wild Cherry in England

A survey of wild cherry (Prunus avium) woodland plantations and nurseries was carried out in 2000/01. Trees with symptoms of bacterial canker were found in 20 of the 24 plantations visited and in three of seven nurseries. Fifty-four Pseudomonas syringae isolates from wild cherry together with 22 representative isolates from sweet cherry and 13 isolates from other Prunus spp., pear and lilac were characterised by physiological, biochemical, serological and pathogenicity tests. Isolates from wild cherry were predominantly P. syringae pv. syringae (Pss), but P. syringae pv. morsprunorum (Psm) races 1 and 2 were also found. Physiological and biochemical tests discriminated Psm races 1 and 2 from other P. syringae isolates. Agglutination and indirect-enzyme-linked immunosorbent assay tests with three different antisera showed that Psm race 1 and race 2 were very uniform and indicated high variability amongst other P. syringae isolates. However, pathogenic Pss isolates could not be distinguished from non-pathogenic isolates of P. syringae on the basis of physiological, biochemical or serological tests. Pathogenicity tests on rooted lilac plants and on micropropagated plantlets of lilac and two wild cherry clones differentiated Pss and Psm isolates and demonstrated a range of aggressiveness amongst Pss isolates. Serological tests could be used as an alternative to the classical physiological and biochemical tests to increase the speed of detection and discrimination of isolates, but pathogenicity tests are still necessary to discriminate the pathogenic Pss isolates.     

Characterization of potato potyvirus Y (PVY) isolates from seed potato batches. Situation of the NTN, Wilga and Z isolates

A collection of 38 PVY isolates from seed potato batches, originating from several Western European countries, was characterized by using current biological, serological and molecular tools differentiating PVY strains and groups. The correlation between the three kinds of tests was good but not absolute. No single serological or PCR method was able to discriminate among the five isolate groups found. Twenty-nine isolates belonged to the PVY^N strain and six to the PVY^O strain. No PVY^C was found. Two other isolates reacted serologically like PVY^O, but were unable to elicit a hypersensitive response from the Ny_tbr gene and probably represent the PVY^Z group. At the molecular level, these two isolates showed a combination of both PVY^O and PVY^N and could be recombinants of these strains. Another isolate reacted serologically like PVY^O, but induced vein necrosis in tobacco, like PVY^N-Wilga. Some PVY^N isolates caused tuber ring necrosis in glasshouse conditions. These might belong to the PVY^NTN group. The PVY^NTN, PVY^N-Wilga and PVY^Z groups probably represent pathotypes within strains PVY^N and PVY^O, respectively. The present study also confirms previous reports showing a high genetic variation at the 5 end within the PVYN strain.     

Measures of disease intensity in powdery mildew (Erysiphe graminis) of winter wheat. 1. Errors in estimating pustule number

Assessments of pustule number and severity of powdery mildew on winter wheat in the Netherlands were made in commercial fields and in experimental plots. The sample variance (s²) of the number of pustules per leaf (m) was fairly constant over years, varieties, growth stages and leaf postitions, but depended strongly on the average pustule number: . The effect of sample size on the precision of the estimate is discussed and it is concluded that it is difficult to estimate low disease intensities accurately. Estimates are given for the detection level of pustule counts in relation to sample size.Mildew intensity on the lower surface of leaves can be estimated from the intensity on the upper surface. This method reduces the duration of the observation, but introduces an additional error. At low disease intensities and small sample sizes this method is more efficient than sampling mildew on both surfaces of leaves. The common practice of assessments of the upper surface of leaves only may not be the most efficient method.Samenvatting Aantallen puistjes meeldauw per blad werden geteld in praktijkpercelen en veldproeven met wintertarwe. De steekproefvariantie van het aantal puistjes was tamelijk constant in de jaren, rassen, gewasstadia en bladposities, maar was sterk afhankelijk van het gemiddeld aantal puistjes . Het effect van de steekproefgrootte op de nauwkeurigheid van de schatting wordt besproken en het blijkt dat het moeilijk is om lichte aantastingen nauwkeurig te schatten. Er worden schattingen gegeven van de detectiegrens in afhankelijkheid van de steekproefgrootte.Meeldauwaantastingen aan de onderkant van het blad, kunnen worden geschat uit de aantasting op de bovenkant van het blad. Deze methode levert een tijdsbesparing op, maar ook een extra onnauwkeurigheid. Alleen bij lichte aantastingen en kleine steekproeven is deze methode efficiënter dan een directe tweezijdige bemonstering. Het schatten van meeldauw op de bovenkant van bladeren is, hoewel algemeen gebruikelijk, waarschijnlijk niet de meest efficiënte methode.     

Identification of resistance to bacterial canker (<Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">syringae</Emphasis>) disease on apricot genotypes grown in Turkey

Bacterial canker caused by Pseudomonas syringae pv. syrinage (Pss) in apricot has widely spread in Turkey, especially in Malatya province, in recent years. The main objective of this study was to determine resistance of apricot cultivars to bacterial canker caused by Pss in apricot cultivars grown in Turkey. During the 2006–2007 growing period, bacterial isolations were taken from diseased apricot trees in Malatya and 53 Pseudomonas syringae isolates were obtained. Forty-two isolates were determined as Pseudomonas syringae pv. syringae and 11 isolates as pv. morsprunorum. In a pathogenicity test, leaves of cv. Hacihalilo?lu were used and five Pss isolates (K24, K25, K43, K47 and K51) were detected to be the most virulent and were used to test for cultivar resistance to Pss. Leaves of fifteen apricot cultivars (Alyanak, Çatalo?lu, Çölo?lu, Erken A?erik, Hacihalilo?lu, Hasanbey, ?smaila?a, Kabaa?i, Karacabey, Sakit 2, So?anci, ?am, ?ekerpare, Tokalo?lu (Erzincan) and Turfanda Eski Malatya) were tested for resistance to Pss. Green shoots were spray-inoculated with a concentration of 10⁸ cfu ml^?1 Pss mixed culture. Sprayed shoots were covered with moist plastic bags for 3 days and maintained in the growth chamber and monitored for symptom development. Hasanbey, Çölo?lu, So?anci and ?ekerpare apricot cultivars were resistant and ?am, Tokalo?lu (Erzincan) and Erken A?erik apricot cultivars were susceptible to Pss. This is the first report of a resistance source in apricot cultivars grown in Turkey against Pss.     

Characterization of the pathogenicity of strains of Pseudomonas syringae towards cherry and plum

Bacterial canker is a major disease of Prunus avium (cherry), Prunus domestica (plum) and other stone fruits. It is caused by pathovars within the Pseudomonas syringae species complex including P. syringae pv. morsprunorum (Psm) race 1 (R1), Psm race 2 (R2) and P. syringae pv. syringae (Pss). Psm R1 and Psm R2 were originally designated as the same pathovar; however, phylogenetic analysis revealed them to be distantly related, falling into phylogroups 3 and 1, respectively. This study characterized the pathogenicity of 18 newly genome‐sequenced P. syringae strains on cherry and plum, in the field and laboratory. The field experiment confirmed that the cherry cultivar Merton Glory exhibited a broad resistance to all clades. Psm R1 contained strains with differential specificity on cherry and plum. The ability of tractable laboratory‐based assays to reproduce assessments on whole trees was examined. Good correlations were achieved with assays using cut shoots or leaves, although only the cut shoot assay was able to reliably discriminate cultivar differences seen in the field. Measuring bacterial multiplication in detached leaves differentiated pathogens from nonpathogens and was therefore suitable for routine testing. In cherry leaves, symptom appearance discriminated Psm races from nonpathogens, which triggered a hypersensitive reaction. Pathogenic strains of Pss rapidly induced disease lesions in all tissues and exhibited a more necrotrophic lifestyle than hemibiotrophic Psm. This in‐depth study of pathogenic interactions, identification of host resistance and optimization of laboratory assays provides a framework for future genetic dissection of host–pathogen interactions in the canker disease.     

Spatial and temporal changes in chlorophyll fluorescence images of Nicotiana benthamiana leaves following inoculation with Pseudomonas syringae pv. tabaci

Inoculation of Nicotiana benthamiana leaves with virulent and avirulent strains of Pseudomonas syringae pv. tabaci resulted in increasing changes in F_v/F_m, and NPQ over time. Images of these chlorophyll a fluorescence measurements revealed different changes in different zones of the leaf. For the virulent strain, the infiltrated zone and zone directly surrounding it showed decreased F_v/F_m, and NPQ before the appearance of visible symptoms, and these decreases corresponded with increasing bacterial populations and putative tabtoxin activity. Another distinct zone of reduced F_v/F_m and NPQ extended several centimetres from the lesion to the nearest leaf margin, but only very low bacterial populations and no putative tabtoxin activity were detected in this zone. For the avirulent strain, a hypersensitive response occurred, bacterial populations remained low, and there was little detectable putative tabtoxin activity. Decreased F_v/F_m and NPQ, but not , were observed in the infiltrated zone prior to the hypersensitive response, followed by decreased values in a zone directly surrounding it. Following that, no further changes were observed. These results demonstrate that in addition to detecting pre‐symptomatic impacts of bacteria, chlorophyll a fluorescence imaging can also show that there are highly distinct regions of affected tissue that can extend considerably beyond the area of bacterial colonization. This should be considered in selecting leaf tissues for examining the effects of pathogens on plants, such as altered host gene expression or protein levels.     

Role of Salicylic Acid in Systemic Resistance Induced by Pseudomonas spp. Against Pythium aphanidermatum in Cucumber Roots

Pseudomonas corrugata strain 13 and P. aureofaciens strain 63-28, applied to roots, induced systemic resistance against Pythium aphanidermatum in cucumber roots. Salicylic acid (SA) from bacterial culture or plant tissues was quantified by high performance liquid chromatography. Both strains produced SA in King's B broth and also induced cucumber root to accumulate endogenous SA one day after bacterial inoculation. Using a split root system, more SA accumulated in roots treated with bacteria than in distant roots on the opposite side of the root system in the first two days, but this difference disappeared after 3–4 days. SA levels were significantly higher in plants treated with bacteria compared to the split control, from one to five days after bacterization. SA did not inhibit mycelial growth of Pythium aphanidermatum at 100–200µgml^–1 in vitro, but higher levels inhibited mycelial growth. Zoospore germination increased at concentrations of 10–500µgml^–1, but decreased at 1000µgml^–1 compared to lower concentrations. Exogenously applied SA failed to induce local or systemic resistance against a challenge infection by the pathogen in planta. The results of this study show that exogenous applied SA does not induce systemic resistance to cucumber root rot caused by P. aphanidermatum, but endogenous SA accumulation in cucumber roots may be involved in induced systemic resistance.     

Distribution of the FoToml gene encoding tomatinase in formae speciales of Fusarium oxysporum and identification of a novel tomatinase from F. oxysporum f. sp. radicis-lycopersici, the causal agent of Fusarium crown and root rot of tomato

The antifungal glycoalkaloid -tomatine accumulates in tomato plants and may protect plants from fungal infection. Fusarium oxysporum f. sp. lycopersici, the causal agent of vascular wilt of tomato, produces a tomatinase (FoToml) that degrades -tomatine to the nontoxic compounds tetrasaccharide lycotetraose and tomatidine. Induction of tomatinases and the distribution of FoToml homologs were examined among 30 strains belonging to 16 formae speciales of F. oxysporum. Tomatinase activity was found in 27 strains belonging to 15 formae speciales, but FoToml homologs (>98% sequence identity) were detected in only six strains belonging to four formae speciales. To identify tomatinases other than FoToml, -tomatine-inducible proteins of another tomato pathogen F. oxysporum f. sp. radicis-lycopersici were analyzed by two-dimensional gel electrophoresis. A protein with a molecular mass of 64kDa accumulated in the -tomatine-induced culture filtrates, and the protein had tomatinase activity, degrading -tomatine to lycotetraose and tomatidine.     

Characterization and differentiation of <Emphasis Type="Italic">Erwinia carotovora</Emphasis> strains from mulberry trees

We recently reported that two diverse types (types 1 and 2) were identified among strains of Erwinia carotovora from mulberry trees. Type 1 strains were similar to E. carotovora subsp. carotovora (Ecc), whereas type 2 strains were distinct from Ecc and other E. carotovora strains. In this study, seven more mulberry strains of type 2 and reference strains were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and randomly amplified of polymorphic DNA (RAPD). On the basis of SDS-PAGE profiles of whole-cell proteins, type 2 strains had high similarity with one another. In addition, they had an unique peptide band with a molecular mass of approximately 28kDa. RAPD analysis showed that they were also effectively differentiated by a strong, specific RAPD fragment for type 2 strains. Based on these two approaches, we have confirmed that the present type 2 strains from mulberry can be discriminated clearly from other soft rot Erwinia species.     

Spatial pattern of Cercospora leaf spot of sugar beet in fields in long- and recently-established areas

Spatial disease pattern of Cercospora beticola was characterised during natural epidemics of Cercospora leaf spot (CLS) in sugar beet. We applied linear regression and geostatistical analyses to characterise CLS spatial patterns in three field trials, in long-established and recently-established CLS-areas, during two consecutive years. Linear regression showed a positive influence of average disease severity of within-row neighbouring plants (0.38 < < 0.88). Semi-variograms modelled the spatial dependence of disease severity for two directions per week in both years. Disease severity displayed strong spatial dependence over time. The within-row spatial dependence was the largest, but across-row dependence was irregular and weaker. Both long- and recently established areas showed strong spatial dependence of disease severity within row, decrease in variability between years and within the second trial year and a relation between and the relative nugget. Observed differences were more field than area specific. These spatial and temporal analyses indicated that disease severities of adjacent plants were dependent; hence, we concluded that C. beticola is dispersed mainly over short distances from plant to plant.     

Salicylic Acid Induced Insensitivity to Culture Filtrate of Fusarium oxysporum f.sp. zingiberi in the Calli of Zingiber officinale Roscoe

Salicylic acid (SA) was used to induce insensitivity in the callus cultures of Zingiber officinale against culture filtrate (CF) of Fusarium oxysporum f.sp. zingiberi. The treatment of callus cultures with SA (10⁴M) prior to selection with CF of the pathogen-increased callus survival. Exogenous application of SA resulted in increased activity of peroxidase and -1,3-glucanase enzymes in the callus cultures. No increase in the activity of phenylalanine ammonia lyase was obtained. Two new protein bands of 97 and 38kDa molecular weights were obtained by SDS-PAGE analysis of soluble proteins extracted from SA-treated calli. The PR-1 monoclonal antibody used for immunodetection of induced proteins cross-reacted with the 38kDa protein band. In vitro antifungal activity of protein extract of calli treated with SA tested against the spores of F. oxysporum f.sp. zingiberi showed significant reduction in spore germination and germ tube elongation. It is concluded that in ginger, SA may result in the induction of resistance to F. oxysporum f.sp. zingiberi by inducing increased activity of peroxidase, -1,3-glucanase and antifungal PR-proteins.     

Roles of reactive oxygen species in interactions between plants and pathogens

The production of reactive oxygen species (ROS) by the consumption of molecular oxygen during host–pathogen interactions is termed the oxidative burst. The most important ROS are singlet oxygen (¹O₂), the hydroxyperoxyl radical (HO₂·), the superoxide anion , hydrogen peroxide (H₂O₂), the hydroxyl radical (OH^-) and the closely related reactive nitrogen species, nitric oxide (NO). These ROS are highly reactive, and therefore toxic, and participate in several important processes related to defence and infection. Furthermore, ROS also play important roles in plant biology both as toxic by-products of aerobic metabolism and as key regulators of growth, development and defence pathways. In this review, we will assess the different roles of ROS in host–pathogen interactions with special emphasis on fungal and Oomycete pathogens.     

Different Patterns of Host Genes are Induced in Rice by Pseudomonas syringae, a Biological Inducer of Resistance, and the Chemical Inducer Benzothiadiazole (BTH)

Rice seedlings treated with the synthetic compound benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH) acquired resistance to subsequent attack by the rice blast fungus Magnaporthe grisea (Hebert) Barr. BTH (trade name Bion) has been released to the market as a plant protecting agent for rice. Here, we analysed the pattern of expressed genes in rice plants treated with BTH, and compared this pattern with those induced by the formerly discovered resistance inducer 2,6-dichloroisonicotinic acid (INA) and by Pseudomonas syringae pv. syringae, a non-host pathogen inducing a hypersensitive response. Both INA and BTH induced similar patterns of genes, suggesting that these compounds are functional analogues. In contrast, the patterns induced by the chemical inducers and by P. syringae were clearly dissimilar.     

Production of Beauvericin by Different Races of Fusarium Oxysporum F. sp. Melonis, The Fusarium Wilt Agent of Muskmelon

Fourty-four strains of Fusarium oxysporum were isolated from plants of melon with Fusarium wilt symptoms. Among these strains, thirty-nine were characterized for their pathogenicity on melon. Thirty-seven strains belonged to known races of F. oxysporum f. sp. melonis, while two strains were non-pathogenic. Four strains belonged to race 0, seven to race 1, four to race 2, and twenty-two to race 1,2. Beauvericin was produced by thirty-six strains in a range from 1 to 310gg^–1. Eight isolates of race 1,2 did not produce the toxin. In addition, of the two non-pathogenic strains, only one strain produced the toxin (290gg^–1). The production of enniatin A₁, enniatin B₁, and enniatin B was also investigated. Enniatin B was the only enniatin detected, being produced by eleven strains belonging to all the races, with a range of production from traces to 60gg^–1. Finally, melon fruits belonging to two different cultivars (Cantalupo and Amarillo) were artificially inoculated with one strain of F. oxysporum f. sp. melonis (ITEM 3464). Beauvericin was detected in the fruit tissues of both cultivars at a level of 11.2 and 73.8gg^–1, respectively. These data suggest that the production of both the toxins is not related to the pathogenicity of F. oxysporum f. sp. melonis, nor to the differential specificity of the races. The results confirm that beauvericin is a common metabolite of phytopathogenic Fusarium species.     

Durantol - a phytosterol antifungal contributor from <Emphasis Type="Italic">Duranta repens</Emphasis> Linn. For organic Management of Sorghum Downy Mildew

Downy mildew of sorghum (DMS) has serious implications agronomically worldwide and to-date the search for a potent fungicide is a high priority and necessity. Phytochemicals have proven to be effective against various plant pathogens with minimal or no side effects. Duranta repens aqueous extract exhibited a promising potential as an organic fungicide for management of sorghum downy mildew (Peronosclerospora sorghi) in greenhouse conditions, at low concentration of 5 %. Activity guided bio-prospecting lead to the isolation of active principle which could control the DMS at as low as 0.1 % concentration. Spectral studies identified the bioactive contributor as a phytosterol namely 16-Hydroxy-8,10,13-trimethyl-1,2,8,10,12,13,14,15-octahydro cyclopenta [a] phenanthren-3-one, designated as Durantol. The results of microscopy exhibited the inhibition of conidial germ-tube growth by formation of bulb-like swellings at the tip, suggesting the mechanism of action of Durantol was via hampering the membrane integrity of the pathogen. Further, the same was virtually predicted using molecular docking for structure-activity relationship (SAR) against four best known membrane receptors namely 1-UDP-glycosyltransferases (UGT), cytochromes P450 (P450), oxidosqualene cyclase (OSC) and serine carboxypeptidase-like acyltransferase (SCPL), proposing that glycosylation onto the membrane would be a reason for inhibition and which is evident from atomic contact energy (ACE) values. The results of the study indicate that, organic management of airborne inoculum of downy mildew of sorghum is feasible and preferable, as compared to the use of chemical fungicides, considering human and environmental health concerns.

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