Publisher Correction: Science diplomacy for plant health.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Erwinia amylovora expresses fast and simultaneously hrp/dsp virulence genes during flower infection on apple trees.

BACKGROUND: Pathogen entry through host blossoms is the predominant infection pathway of the gram-negative bacterium Erwinia amylovora leading to manifestation of the disease fire blight. Like in other economically important plant pathogens, E. amylovora pathogenicity depends on a type III secretion system encoded by hrp genes. However, timing and transcriptional order of hrp gene expression during flower infections are unknown. METHODOLOGY/PRINCIPAL FINDINGS: Using quantitative real-time PCR analyses, we addressed the questions of how fast, strong and uniform key hrp virulence genes and the effector dspA/E are expressed when bacteria enter flowers provided with the full defense mechanism of the apple plant. In non-invasive bacterial inoculations of apple flowers still attached to the tree, E. amylovora activated expression of key type III secretion genes in a narrow time window, mounting in a single expression peak of all investigated hrp/dspA/E genes around 24-48 h post inoculation (hpi). This single expression peak coincided with a single depression in the plant PR-1 expression at 24 hpi indicating transient manipulation of the salicylic acid pathway as one target of E. amylovora type III effectors. Expression of hrp/dspA/E genes was highly correlated to expression of the regulator hrpL and relative transcript abundances followed the ratio: hrpA>hrpN>hrpL>dspA/E. Acidic conditions (pH 4) in flower infections led to reduced virulence/effector gene expression without the typical expression peak observed under natural conditions (pH 7). CONCLUSION/SIGNIFICANCE: The simultaneous expression of hrpL, hrpA, hrpN, and the effector dspA/E during early floral infection indicates that speed and immediate effector transmission is important for successful plant invasion. When this delicate balance is disturbed, e.g., by acidic pH during infection, virulence gene expression is reduced, thus partly explaining the efficacy of acidification in fire blight control on a molecular level.

Influence of the soil composition on the effects of benzoxazinoid allelochemicals on two soil nontarget organisms.

Seven selected benzoxazinoid allelochemicals and synthetic reference compounds were tested for their lethal and sublethal effects in different field soils and standard soil on Folsomia candida and Poecilus cupreus by applying standard laboratory test procedures. The higher microbial activity in the field soils was most probably responsible for the reduced effects of test compounds on F. candida in the majority of all tests, whereas the higher organic carbon content in field soils was likely the reason for the reduced effects of test substances on P. cupreus.

Transformation of benzoxazinones and derivatives and microbial activity in the test environment of soil ecotoxicological tests on Poecilus cupreus and Folsomia candida.

Benzoxazinones, such as 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA), and benzoxazolinones, such as 6-methoxy-2-benzoxazolinone (MBOA) and 2-benzoxazolinone (BOA), are biologically active secondary metabolites found in cereals. Because these compounds could be exploited as part of a strategy for reducing the use of synthetic pesticides, ecotoxicological tests were performed recently. In this paper, the transformation of the compounds in the test environment of the ecotoxicological tests was studied. DIMBOA was degraded and partly transformed to MBOA during the period of ecotoxicological testing of the compounds. During testing of MBOA on Poecilus cupreus test media the analysis showed that at the initial concentrations of 2 and 10 mg kg(-1) no MBOA was left after 45 days of testing, but the metabolite 2-amino-phenoxazin-3-one (AMPO) was formed. During testing of BOA on both Folsomia candida and Poecilus cupreus the more biologically active compound 2-amino-phenoxazin-3-one (APO) was formed. Thus, the ecotoxicological test results on MBOA and BOA were partly due to the microbial transformation of the compounds during the time of testing.

Preliminary analysis of toxicity of benzoxazinones and their metabolites for folsomia Candida.

The overall objective of this study was to explore the toxicity of benzoxazinone allelochemicals and their metabolites to Folsomia candida (Collembola: Isotomidae) (Willem, 1902). Experimental tests showed transformation products to have more pronounced toxicity than parent compounds. The underlying relationship between the chemical structure and toxicity was then studied using three-dimensional QSAR approaches, and results highlighted the role of the steric contribution.

Effects of the benzoxazoid DIMBOA, selected degradation products, and structure-related pesticides on soil organisms.

Both lethal and sublethal effects of the benzoxazoid 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA), the degradation products 6-methoxy-benzoxazolin-2(3H)-one (MBOA), 2-amino-7-methoxy-(3H)-phenoxazin-3-one (AMPO), and 2-acetylamino-7-methoxy-3(H)-phenoxazin-3-one (AAMPO) and the structure-related compounds 2-methoxy-N-(2-oxo-1,3-oxazolidin-3yl)acet-2'=6'-xylidide (oxadixyl), and O,O-diethyl S-[6-chloro-2-oxobenzoxazolin-3-yl)methyl]phosphorodithioate (phosalone) on the collembola Folsomia candida and on the carabid beetle Poecilus cupreus (except phosalone) were determined. Validated laboratory standard methods including reference and control treatments were applied in compliance with prescribed validity criteria. A risk assessment according to the EPPO risk assessment scheme for plant protection products (2003) was carried out. DIMBOA, MBOA, AMPO, AAMPO, and oxadixyl were classified as low-risk compounds for both test organisms. The reference compounds methyl-m-hydroxy-carbanilate-methyl-carbanilate (phenmedipham) and O,O-dimethyl S-[2-(methylamino)-2-oxoethyl]phosphoro-dithioate (dimethoate) were of low and medium risk respectively, to F. candida, but final assessment of the risk to P. cupreus requires further testing. Phosalone was of high risk to F. candida. The results obtained suggest that neither DIMBOA nor the tested degradation products pose a risk to either nontarget soil organism in the field.

Effects of the benzoxazolinone BOA, selected degradation products and structure related pesticides on soil organisms.

The benzoxazolinone BOA and the degradation products APO, AAPO and HPAA, as well as four structure related compounds to BOA, were tested for their lethal and sublethal effects on the collembola Folsomia candida and on the carabid beetle Poecilus cupreus applying validated standard laboratory methods. According to the results of the recommended risk assessment for plant protection products (EPPO, 2003), BOA and its structure related compounds carbendazim, benoxacor and benazolin (and additionally the formulated product Cresopur) were classified as low risk compounds for both test organisms. Phosalone was of high risk for F. candida. APO, AAPO and HPAA were of medium risk for F. candida, but were rated as low risk compounds for P. cupreus at the tested rates of about 2 mg/kg substrate. However, as the BOA degradation products have been found to occur at field rates below 0.2 mg/kg substrate or are often even not detectable, it is assumed that their potential risk for both non-target soil organisms in the field will be acceptable.