Pathotypes of Colletotrichum sublineolum in Response to Sorghum Populations with Different Levels of Genetic Diversity in Sete Lagoas‐MG

Sorghum anthracnose is one of the most important and destructive diseases of sorghum. Genetic resistance has been the most efficient strategy to control the disease, but the high variability of the pathogen population in Brazil has resulted in only modest efficacy. Accordingly, we investigated the variability of Colletotrichum sublineolum in response to sorghum populations with three levels of genetic diversity: pure stand, three‐way hybrids and physical mixtures of three‐way hybrids. Six plots of each treatment were planted in different areas and at different dates. A total of 480 isolates, that is 40 single‐conidium isolates per plot, were collected from the field experiment to characterize the variability of the pathogen in each host population. Isolates were inoculated in a greenhouse on a differential line set composed of eight sorghum inbred lines. Our results reveal that the pathogen populations derived from three‐way combinations had higher pathotype diversity than did those derived from pure stand host populations. More complexly, virulent phenotypes were also developed in genetically diverse stands compared to pure stand host populations. The diversification of the host population limits pathogen adaptation, thus resulting in a significantly higher number of pathotypes. The results of this study will improve the management of sorghum anthracnose in the field by helping sorghum breeders maintain disease resistance.     

RESISTANCE AND VIRULENCE STRUCTURE IN TWO LINUM MARGINALE-MELAMPSORA LINI HOST-PATHOGEN METAPOPULATIONS WITH DIFFERENT MATING SYSTEMS

Different patterns of resistance to six pathotypes of Melampsora lini were detected in 11 populations of Linum marginale distributed across two metapopulations. The two metapopulations (mountains and plains of New South Wales, Australia) differed in the annual cycle of disease development, which barely overlapped, and in the growth cycle and mating system of the host. Host populations in the mountains metapopulation were highly inbred, whereas those on the plains showed appreciable levels of outcrossing. Within each metapopulation there was significant variation among component populations in (1) levels of host resistance to individual pathogen isolates; (2) mean levels of resistance to all six isolates; (3) the number of resistance phenotypes present and the evenness of their distribution within the population; and (4) the average number of pathogen lines to which individual hosts were resistant. A more limited comparison of pathogen populations from the two metapopulations (two from each) found greater similarities in the structure of populations and particular virulence frequencies within, rather than among, the two metapopulations. Differences in host outcrossing rates between the two metapopulations are reflected in marked differences in the overall level of resistance, its partitioning within and among populations, the number and distribution of resistance phenotypes in the two areas, and the level of polymorphism for specific virulence factors in the pathogen, with the plains metapopulation showing consistently higher values. However, these differences were not significant. In general, variation for all parameters was just as great among populations within a metapopulation as between the two metapopulations.     

Aggressiveness and diversity of Phytophthora capsici on vegetable crops in Georgia

Phytophthora blight induced by Phytophthora capsici causes significant yield loss in a number of vegetable crops. It is imperative to understand the diversity and aggressiveness of the pathogen to design more efficient disease management programs. A collection of P. capsici strains isolated from different vegetable crops in Georgia, USA, were characterised in this study. Of the 49 isolates tested, 24 were A1 and 25 were A2 mating type, respectively, with both mating types found in the same fields. Variability of the isolates was assessed in terms of their aggressiveness on six pepper genotypes. The isolates differed in their aggressiveness on different pepper cultivars with 10 pathotypes identified. No correlation between aggressiveness of the isolates and their host origin or geographical location of isolation was observed. Randomly amplified polymorphic DNA (RAPD) analysis was used to evaluate genetic variability among P. capsici populations. RAPD analysis using 15 random primers resulted in 133 reproducible bands and cluster analysis separated the isolates into 5 groups. Analysis of molecular variance showed that there was moderate genetic differentiation associated with host origin and geographical location of the isolates. No correlation was found between RAPD groups and pathotypes or mating types. These results indicate that P. capsici populations infecting vegetable crops in Georgia were genetically diverse, which should be taken into account in developing resistant cultivars or other disease management programmes.     

Vegetative Compatibility and Virulence Diversity of <i>Verticillium dahliae</i> from Okra (<i>Abelmoschus esculentus</i>) Plantations in Turkey and Evaluation of Okra Landraces for Resistance to <i>V. dahliae</i>

Forty-four V. dahliae isolates were collected from symptomatic vascular tissues of okra plants each from a different field in eight provinces located in the eastern Mediterranean and western Anatolia regions of Turkey during 2006- 2009. Nitrate-nonutilizing (nit) mutants of V. dahliae from okra were used to determine heterokaryosis and genetic relatedness among isolates. All isolates from okra plants were grouped into two vegetative compatibility groups (VCGs) (1 and 2) and three subgroups as 1A (13.6%, 6/44), 2A (20.5%, 9/44) and 2B (65.9%, 29/44) according to international criteria. Pathogenicity tests were performed on a susceptible local okra (A. esculentus) landrace in greenhouse conditions. All isolates from VCG1A and VCG2B induced defoliation (D) and partial defoliation (PD) symptoms, respectively. Other isolates from VCG2A gave rise to typical leaf chlorosis symptoms without defoliation. The obtained data showed that the virulence level of V. dahliae isolates from okra was related to their VCG belongings. Eighteen okra landraces from diverse geographical origins were screened for resistance to VCG2B and VCG1A of V. dahliae. The results indicated that all landraces were more susceptible to highly virulent VCG1A-D pathotype displaying D or PD symptoms depending on their susceptibility levels with a mean disease severity index of 3.52 than to less virulent VCG2B-PD pathotype of V. dahliae displaying PD and ND symptoms with a mean disease severity index of 2.52. Significant differences were observed among the landraces; however, none of them exhibited a level of resistance. Okra landraces; Çorum, Hatay Has and Şanlıurfa displayed the lowest level of susceptibility or little tolerance to both D and PD pathotypes. VCG2B of PD was prevailing in the surveyed areas and VCG1A of D was the most virulent of the VCGs identified. Introduction of resistant genotypes to Turkish okra germplasm from different sources and breeding new resistant okra cultivars are critical for the sustainability of okra production.     

Enhanced pathogenicity of Leptosphaeria maculans Pycnidiospores from paired co-inoculation of Brassica napus cotyledons with ascospores

BACKGROUND AND AIMS: Blackleg, caused by Leptosphaeria maculans, is a major disease of oilseed rape (Brassica napus) worldwide, including Australia. In most cases, the severity of the disease in the field is related to infections caused by airborne ascospores. In contrast, pycnidiospores originating from leaf and stem lesions and stubble are widely assumed to play only a relatively minor role in the epidemiology of blackleg. It is not clear whether, under certain conditions, pycnidiospores can cause severe disease in the field. The aim of the work reported was to determine if the pathogenicity of pycnidiospores is enhanced by paired co-inoculation of B. napus cotyledons with ascospores. METHODS: Three investigations were carried out under controlled-environment conditions using various L. maculans isolates and B. napus cultivars with different levels of host resistance to blackleg. KEY RESULTS: In all three experiments, co-inoculation with ascospores increased the ability of pycnidiospores to cause more disease on B. napus than when inoculations consisted of pycnidiospores alone. This effect was significantly influenced by the host resistance of the cultivar, but overall was independent of the L. maculans isolate used in the different experiments. This effect was also independent of timing of inoculation with the ascospores, with increased disease from pycnidiospores occurring on the cotyledon of the seedling in situations where inoculations with ascospores were carried out 0, 1 or 2 d after pycnidiospore inoculation. This enhanced pathogenicity of pycnidiospores was evident even when low concentrations of pycnidiospores were applied to the other cotyledon of the same seedling. CONCLUSIONS: These results may explain continuing severe blackleg disease cycles throughout the cropping season even when ascospore fallout was low or constrained only to a brief period or phase of the cropping season, and suggest that disease epidemics may be polycyclic rather than monocyclic.     

Opposing effects of allogrooming on disease transmission in ant societies

To prevent epidemics, insect societies have evolved collective disease defences that are highly effective at curing exposed individuals and limiting disease transmission to healthy group members. Grooming is an important sanitary behaviour—either performed towards oneself (self-grooming) or towards others (allogrooming)—to remove infectious agents from the body surface of exposed individuals, but at the risk of disease contraction by the groomer. We use garden ants (Lasius neglectus) and the fungal pathogen Metarhizium as a model system to study how pathogen presence affects self-grooming and allogrooming between exposed and healthy individuals. We develop an epidemiological SIS model to explore how experimentally observed grooming patterns affect disease spread within the colony, thereby providing a direct link between the expression and direction of sanitary behaviours, and their effects on colony-level epidemiology. We find that fungus-exposed ants increase self-grooming, while simultaneously decreasing allogrooming. This behavioural modulation seems universally adaptive and is predicted to contain disease spread in a great variety of host–pathogen systems. In contrast, allogrooming directed towards pathogen-exposed individuals might both increase and decrease disease risk. Our model reveals that the effect of allogrooming depends on the balance between pathogen infectiousness and efficiency of social host defences, which are likely to vary across host–pathogen systems.     

Host-pathogen diversity in a wild system: Chondrilla juncea–Puccinia chondrillina

The resistance structure of a Turkish population of the clonal, apomictic composite Chondrilla juncea and the pathotypic structure of a co-occurring population of its obligate rust pathogen, Puccinia chondrillina, was determined by sequential inoculation of 19 host lines with 15 pathogen isolates each derived from single pustules collected from separate plants among the host population. The resultant matrix of resistant and susceptible reactions provides strong circumstantial evidence for a gene-for-gene interaction. Seven distinct pathotypes were detected in the pathogen population. One of these comprised 53% of the population, a second comprised 13%, while the remaining five pathotypes were each detected only once. The host population was similarly diverse, being composed of eight resistance phenotypes, only two of which were represented by more than one host line. Although C. juncea is apomictic, there was only 58% congruence between host resistance and multi-locus isozyme phenotype categories within this population. Pathotypic phenotypes of 13 other isolates of P. chondrillina collected from ten other Turkish and three more distant populations of C. juncea were markedly different from those found in the population studied in detail. There was no obvious relationship between the degree of geographic separation of pathotypes and their ability to attack particular C. juncea lines in this or three other populations represented by single host lines. Received: 10 March 1997 / Accepted: 4 August 1997     

Climate change accelerates local disease extinction rates in a long‐term wild host–pathogen association

Pathogens are a significant component of all plant communities. In recent years, the potential for existing and emerging pathogens of agricultural crops to cause increased yield losses as a consequence of changing climatic patterns has raised considerable concern. In contrast, the response of naturally occurring, endemic pathogens to a warming climate has received little attention. Here, we report on the impact of a signature variable of global climate change – increasing temperature – on the long‐term epidemiology of a natural host–pathogen association involving the rust pathogen Triphragmium ulmariae and its host plant Filipendula ulmaria. In a host–pathogen metapopulation involving approximately 230 host populations growing on an archipelago of islands in the Gulf of Bothnia we assessed changes in host population size and pathogen epidemiological measures over a 25‐year period. We show how the incidence of disease and its severity declines over that period and most importantly demonstrate a positive association between a long‐term trend of increasing extinction rates in individual pathogen populations of the metapopulation and increasing temperature. Our results are highly suggestive that changing climatic patterns, particularly mean monthly growing season (April‐November) temperature, are markedly influencing the epidemiology of plant disease in this host–pathogen association. Given the important role plant pathogens have in shaping the structure of communities, changes in the epidemiology of pathogens have potentially far‐reaching impacts on ecological and evolutionary processes. For these reasons, it is essential to increase understanding of pathogen epidemiology, its response to warming, and to invoke these responses in forecasts for the future.     

A Single,Plastic Population of Mycosphaerella pinodes Causes Ascochyta Blight on Winter and Spring Peas (Pisum sativum) in France

Plant diseases are caused by pathogen populations continuously subjected to evolutionary forces (genetic flow, selection, and recombination). Ascochyta blight, caused by Mycosphaerella pinodes, is one of the most damaging necrotrophic pathogens of field peas worldwide. In France, both winter and spring peas are cultivated. Although these crops overlap by about 4 months (March to June), primary Ascochyta blight infections are not synchronous on the two crops. This suggests that the disease could be due to two different M. pinodes populations, specialized on either winter or spring pea. To test this hypothesis, 144 pathogen isolates were collected in the field during the winter and spring growing seasons in Rennes (western France), and all the isolates were genotyped using amplified fragment length polymorphism (AFLP) markers. Furthermore, the pathogenicities of 33 isolates randomly chosen within the collection were tested on four pea genotypes (2 winter and 2 spring types) grown under three climatic regimes, simulating winter, late winter, and spring conditions. M. pinodes isolates from winter and spring peas were genetically polymorphic but not differentiated according to the type of cultivars. Isolates from winter pea were more pathogenic than isolates from spring pea on hosts raised under winter conditions, while isolates from spring pea were more pathogenic than those from winter pea on plants raised under spring conditions. These results show that disease developed on winter and spring peas was initiated by a single population of M. pinodes whose pathogenicity is a plastic trait modulated by the physiological status of the host plant.     

The genetics of host-pathogen coevolution: implications for genetic resource conservation

The results of long-term studies of coevolution in the Hordeum vulgare-Rhynchosporium secalis pathosystem are summarized. The genetic systems of barley (host) and R. secalis (pathogen) are complementary: Gene-for-gene interactions among loci affect many traits, leading to self-regulating adjustments over generations between host and pathogen populations. Different pathotypes differ widely in their ability to damage the host, and different host-resistance alleles differ widely in their ability to protect the host from the pathogen. Among 29 resistance loci in the specific host population studied, several played major roles in providing stable resistance, but many had net detrimental effects on the yield and reproductive ability of the host. Resistance alleles that protected against the most damaging pathotypes increased sharply in frequency in the host populations. It is concluded that the evolutionary processes that take place in genetically variable populations propagated under conditions of cultivation can be highly effective in increasing the frequency of desirable alleles and useful multilocus genotypes. This enhances the value of the evolving populations as sources of genetic variability in breeding for disease resistance and other characters that affect adaptedness.     

Restriction Digest Patterns of Total DNA from Different Races of Fusarium oxysporum f. sp. pisi– an Improved Method for Race Classification

Seven isolates of Fusarium oxysporum f. sp. pisi were allocated to either race 2 or race 6 by their ability or inability to cause disease on the six host differentials New Season, New Era, Dark Skin Perfection, WSU 28, WSU 23 and Little Marvel. The isolates showed similar colony morphology on various solid media and their growth rates were inhibited to a similar extent by nystatin, cycloheximide and trichodermin when these compounds were included in potato dextrose agar. Total DNA waspurified from each isolate, digested separately with the restriction endonucleases EcoRI, EcoRV, Pstl, BamHl, SmaI and PvuII and the resulting DNA fragments separated by agarose gel electrophoresis. The patterns obtained were indicative of the presenceof repetitive DNA sequences. Moreover, the patterns obtained for the five race 2 isolates were identical for a given enzyme as were the patterns for the two race 6 isolates. Hence classification of isolates into races by their restrictive enzyme digestion, patterns coincided with that according to pathotypes and could be an improved, more reliable and reproducible method of race classification. An eighth isolate, originally classified as race 1, had lost its ability to cause disease on all six host differentials. The restriction digest patterns of its DNA were different from those of the DNA from both the race 2 and the race 6 isolates.     

Stability analyses for estimating relative durability of quantitative resistance

Summary Experiments in which a series of host cultivars are inoculated in all combinations with a series of pathogen isolates have been used to detect specificity in the host resistance. A theoretical model of polygenic resistance involving both general and specific interactions with pathogen virulence was developed to test the abilities of statistical analyses to discriminate between host genotypes with different levels of general and specific resistance. Estimates of levels of specific resistance could be obtained in regressions of disease severity scores for each host cultivar X pathogen isolate combination vs. the virulence index of each isolate. If the virulence index was based on the mean disease severity induced by the isolate over all host cultivars, the slopes of the regression lines were correlated with the levels of specific resistance in host cultivars. If the virulence index was based on the disease severity induced by the isolate on a host cultivar with a minimum of specific resistance, the mean squares for deviations from the regression were correlated with the levels of specific resistance in host cultivars. A method was developed to consistently choose host cultivars with minimum specific resistance. The two regression analyses gave estimates of specificity in randomly generated, model genotypes of approximately equal accuracy, although the second method appeared to be more accurate when the numbers of loci controlling resistance and virulence were small. The best estimates of numbers of genes for specific resistance were obtained by calculating a rating based on mean disease severity, the mean square for deviation from the regression on the virulence index based on disease severity on the cultivar with minimum specific resistance and the slope of the regression on the virulence index based on the mean disease severity. The best estimates of proportions of resistance genes that were specific were obtained by calculating a rating based on the above deviation mean square and slope alone.Cooperative investigation of the U.S. Department of Agriculture, Agricultural Research Service and the North Carolina Agricultural Research Service. Journal Series Paper No. 8326 of the North Carolina Agricultural Research Service     

Detection of the defoliating and nondefoliating pathotypes of <Emphasis Type="Italic">Verticillium dahliae</Emphasis> in artificial and natural soils by nested PCR

In Spain, Verticillium wilt, caused by Verticillium dahliae, is the most important disease of cotton and olive. Isolates of V. dahliae infecting these crops can be classified into highly virulent, defoliating (D), and mildly virulent, nondefoliating (ND), pathotypes. Infested soil is the primary source of inoculum for Verticillium wilt epidemics in cotton and olive, and severity of disease relates to the prevailing V.dahliae pathotype. In this work we have adapted the use of previously developed primer pairs specific for D and ND V. dahliae for the detection of these pathotypes by nested PCR in artificial and natural soils. Success in the detection procedure depends upon efficiency in extracting PCR-quality DNA from soil samples. We developed an efficient DNA extraction method from microsclerotia infesting the soil that includes the use of acid washed sand during the grinding process and skimmed milk to avoid co-purification of Taq-polymerase inhibitors with DNA. The specific nested-PCR procedure effectively detected 10 or more microsclerotia per gram of soil. The detection procedure has proven efficient when used with a naturally infested soil, thus demonstrating usefullness of the diagnostic method for rapid and accurate assessment of soil contamination by V. dahliae pathotypes.     

Virulence Structure of the Powdery Mildew (Blumeria graminis) Population Occurring on Triticale (x Triticosecale) in Poland

Powdery mildew, caused by Blumeria graminis is an important disease of cereals in many production regions. Until end of the last century triticale had been regarded as a species characterized by high level of resistance for this disease. However, after several years of intensive production on a big area in Poland, Germany and other European countries it start to be susceptible for many pathogens including B. graminis. Because of this, virulence structure of this pathogen population on triticale in Poland was evaluated across 2008–2010. Leaf samples with symptoms of the powdery mildew disease were collected randomly from nineteen localities. As a total, 1402 B. graminis isolates were collected: 23–25 isolates per locality in each year. Standard differential set of 28 genotypes was used: twenty‐one wheat with known resistance genes and seven triticale. Based on the obtained results it was possible to observe significant differences in virulence structure between years and localities. No virulence's against Pm21 (Yangmai5), and Pm3d + 4b (Kadett) were found in any year. All tested isolates were virulent on Moreno and Lamberto cultivars. In a total, 36% of tested isolates possessed 9, 11 or 12 virulence's per genotypes. Twenty five percent of tested isolates were virulent to 5 triticale cultivars. Correlation between pathotypes frequency and sampling region were not found what suggest that local epidemics play the most important role in triticale growing regions in Poland.     

Genotype‐by‐genotype interactions between an insect and its pathogen

Genotype‐by‐genotype (G×G) interactions are an essential requirement for the coevolution of hosts and parasites, but have only been documented in a small number of animal model systems. G×G effects arise from interactions between host and pathogen genotypes, such that some pathogen strains are more infectious in certain hosts and some hosts are more susceptible to certain pathogen strains. We tested for G×G interactions in the gypsy moth (Lymantria dispar) and its baculovirus. We infected 21 full‐sib families of gypsy moths with each of 16 isolates of baculovirus and measured the between‐isolate correlations of infection rate across host families for all pairwise combinations of isolates. Mean infectiousness varied among isolates and disease susceptibility varied among host families. Between‐isolate correlations of infection rate were generally less than one, indicating nonadditive effects of host and pathogen type consistent with G×G interactions. Our results support the presence of G×G effects in the gypsy moth–baculovirus interaction and provide empirical evidence that correlations in infection rates between field‐collected isolates are consistent with values that mathematical models have previously shown to increase the likelihood of pathogen polymorphism.     

Ecological genetics of the Bromus tectorum (Poaceae)-Ustilago bullata (Ustilaginaceae) pathosystem: A role for frequency-dependent selection?

? Premise of the study: Evolutionary processes that maintain genetic diversity in plants are likely to include selection imposed by pathogens. Negative frequency-dependent selection is a mechanism for maintenance of resistance polymorphism in plant-pathogen interactions. We explored whether such selection operates in the Bromus tectorum-Ustilago bullata pathosystem. Gene-for-gene relationships between resistance and avirulence loci have been demonstrated for this pathosystem. ? Methods: We used molecular markers and cross-inoculation trials to learn whether the SSR genotypes of the host exhibited resistance to co-occurring pathogen races, whether host genotypes within a population had equal disease probability, and whether a common resistance locus and its corresponding avirulence locus exhibited predicted allele frequency changes during an epidemic. ? Key results: Five of six putative resistance loci that conferred resistance to co-occurring pathogen races occurred in common host SSR genotypes. Some common genotypes within populations were more likely to be diseased than others, and genotype frequencies sometimes changed across years in patterns consistent with frequency-dependent selection. Observed changes in frequency of resistance and virulence alleles during an epidemic provided further support, but evidence was inconclusive. ? Conclusions: Frequency-dependent selection may operate at endemic disease levels in this pathosystem, but is difficult to detect because many susceptible plants escape infection. Most pathogen isolates were virulent on most host genotypes, minimizing the apparent importance of frequency-dependent selection even during epidemics.     

Pathogenic Variability and Genetic Diversity of Phaeoisariopsis griseola Isolates from Two Counties in the State of Goias, Brazil

Angular leaf spot disease of common bean (Phaseolus vulgaris), caused by Phaeoisariopsis griseola, is one of the most important disease of this crop in Brazil. Control strategies for the disease include cultural practices, chemical control and genetic resistance. This pathogen is known to vary greatly in pathogenicity. For durable use of genetic resistance to control this disease, it is necessary to manage resistant cultivars by taking into account the population structure of P. griseola. Isolates of the pathogen from Goias, Brazil exhibited an important virulence polymorphism when inoculated on 12 differential cultivars. A total of 13 pathotypes was identified within a series of 96 isolates collected in Inhumas and Damolandia counties. Only pathotypes 63‐15, 63‐23, 63‐31 and 63‐63 were identified in both counties. Since all the isolates were capable of inducing disease in both Andean and Mesoamerican differential cultivars, they were considered to be of Mesoamerican origin. Random amplified polymorphic DNA (RAPD) analysis performed on the same 96 isolates revealed a great genetic diversity clustering the series into five groups at an Euclidean distance of 62.5%. Although the results did not show any clustering according to the isolate origin, it was possible to observe a tendency of the isolates to cluster in different groups according to their origin. No pathotype‐specific band was observed in the present study.     

Fitness consequences of infection of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> with its natural bacterial pathogen <Emphasis Type="Italic">Pseudomonas viridiflava</Emphasis>

Variation in plant resistance to pathogen infection is commonly observed in interactions between wild plants and their foliar pathogens. Models of host–pathogen interactions indicate that a large cost of infection is generally necessary to maintain this variation, yet there is limited evidence that foliar pathogens cause detectable fitness reductions in wild host plants. Most published work has focused on fungal pathogens. Pseudomonas viridiflava, a common bacterial pathogen of the annual weed Arabidopsis thaliana across its range, comprises two distinct genetic clades that cause disease symptoms of different severity. Here we measured the extent of infection of wild A. thaliana populations in the Midwest, USA, and examined the effect on seed production, in field and growth-chamber experiments, of experimental inoculation with isolates from the two clades. We found infection with P. viridiflava varied from 0 to 56% in Midwest A. thaliana populations, with the possibility of several leaves per plant infected later in the growing season. In the growth chambers, experimental inoculation reduced seed set by averages of 15 and 11% for clades A and B, respectively. In the field experiment, only clade A affected plant fitness significantly, reducing seed set by an average of 38%. Underlying these average effects we observed both negative and positive effects of infection, and variation in both fitness among plant genotypes and sensitivity to environmental conditions.     

3-hydroxypropionic acid as a nematicidal principle in endophytic fungi

3- Hydroxypropionic acid was isolated by bioactivity-guided fractionation of extracts obtained from submerged cultures of several endophytic fungi isolated from above-ground plant organs. This compound showed selective nematicidal activity against the plant-parasitic nematode Meloidogyne incognita with LD50 values of 12.5-15 microg/ml. Activity against the saprophytic Caenorhabditis elegans was fivefold lower. No antimicrobial, cytotoxic or phytotoxic effects were observed. Propionic acid and D- and L-lactic acids were not active against either nematode species. Based on morphological features and ITS, 18S and 28S rDNA analyses, the producing strains were identified as Phomopsis phaseoli isolated from the leaf of a tropical tree, and four strains of Melanconium betulinum isolated from twigs of Betula pendula and B. pubescens in Germany. This is the first report of 3-hydroxypropionic acid in fungi, and of the nematicidal activity of this metabolite.