Dissecting negative effects of two root-associated bacteria on the growth of an invasive weed.

Plant-associated microorganisms can negatively influence plant growth, which makes them potential biocontrol agents for weeds. Two Gammaproteobacteria, Serratia plymuthica and Pseudomonas brassicacearum, isolated from roots of Jacobaea vulgaris, an invasive weed, negatively affect its root growth. We examined whether the effects of S. plymuthica and P. brassicacearum on J. vulgaris through root inoculation are concentration-dependent and investigated if these effects were mediated by metabolites in bacterial suspensions. We also tested whether the two bacteria negatively affected seed germination and seedling growth through volatile emissions. Lastly, we investigated the host specificity of these two bacteria on nine other plant species. Both bacteria significantly reduced J. vulgaris root growth after root inoculation, with S. plymuthica showing a concentration-dependent pattern in vitro. The cell-free supernatants of both bacteria did not affect J. vulgaris root growth. Both bacteria inhibited J. vulgaris seed germination and seedling growth via volatiles, displaying distinct volatile profiles. However, these negative effects were not specific to J. vulgaris. Both bacteria negatively affect J. vulgaris through root inoculation via the activity of bacterial cells, while also producing volatiles that hinder J. vulgaris germination and seedling growth. However, their negative effects extend to other plant species, limiting their potential for weed control.

Assessment of Puccinia polliniicola as a potential biological control agent for Microstegium vimineum.

BACKGROUND: Microstegium vimineum (Trin.) A. Camus, commonly called stiltgrass, is a dominant weed in the United States and China. Although a lot of control approaches have been attempted, an economic, effective and practical measure has not been available to control the weed so far. RESULTS: A serious rust disease of Microstegium vimineum was observed in three regions of Wenzhou city in China, from 2019 to 2021, with a disease incidence ranging from 82% to 97%. Typical rust disease symptoms on Microstegium vimineum were prominently visible during the early monsoon season (June-July), with chlorotic spots on the leaf surfaces. The morphological characterization of the strain WZ-1 which was isolated from the diseased leaves was consistent with Puccinia polliniicola. The virulence tests showed that the average disease index of Microstegium vimineum plants could reach 35% at 10 days post-inoculation. The host specificity of Puccinia polliniicola was tested on 64 plant species from 12 families and it did not cause any diseased symptoms on 24 major crops and 36 weeds, but slightly infected four gramineous weeds, Arthraxon hispidus, Polypogon fugax, Cynodon dactylon, and Microstegium ciliatum. However, newly-produced urediniospores were not observed on the slightly infected plants. The urediniospores of strain WZ-1 infected the Microstegium vimineum leaves by two main approaches: mycelium or appressorium invaded the stoma; and mycelium or appressorium directly invaded intercellular spaces. Field experiments showed that the rust disease naturally prevailed among Microstegium vimineum populations, causing severe rust disease symptoms on the leaf surface. The rust epidemic effectively controlled all of the target plants in the closed plot where the rust was released. CONCLUSION: Puccinia polliniicola strain WZ-1 has great potential to be used as a classical biological control agent against Microstegium vimineum. © 2024 Society of Chemical Industry.

Enhancing rice growth and yield with weed endophytic bacteria Alcaligenes faecalis and Metabacillus indicus under reduced chemical fertilization.

Endophytic bacteria, recognized as eco-friendly biofertilizers, have demonstrated the potential to enhance crop growth and yield. While the plant growth-promoting effects of endophytic bacteria have been extensively studied, the impact of weed endophytes remains less explored. In this study, we aimed to isolate endophytic bacteria from native weeds and assess their plant growth-promoting abilities in rice under varying chemical fertilization. The evaluation encompassed measurements of mineral phosphate and potash solubilization, as well as indole-3-acetic acid (IAA) production activity by the selected isolates. Two promising strains, tentatively identified as Alcaligenes faecalis (BTCP01) from Eleusine indica (Goose grass) and Metabacillus indicus (BTDR03) from Cynodon dactylon (Bermuda grass) based on 16S rRNA gene phylogeny, exhibited noteworthy phosphate and potassium solubilization activity, respectively. BTCP01 demonstrated superior phosphate solubilizing activity, while BTDR03 exhibited the highest potassium (K) solubilizing activity. Both isolates synthesized IAA in the presence of L-tryptophan, with the detection of nifH and ipdC genes in their genomes. Application of isolates BTCP01 and BTDR03 through root dipping and spraying at the flowering stage significantly enhanced the agronomic performance of rice variety CV. BRRI dhan29. Notably, combining both strains with 50% of recommended N, P, and K fertilizer doses led to a substantial increase in rice grain yields compared to control plants receiving 100% of recommended doses. Taken together, our results indicate that weed endophytic bacterial strains BTCP01 and BTDR03 hold promise as biofertilizers, potentially reducing the dependency on chemical fertilizers by up to 50%, thereby fostering sustainable rice production.

Comparative analysis of root associated microbes in tropical cultivated and weedy rice (Oryza spp.) and temperate cultivated rice.

Weedy rice is a major problem in paddy fields around the world. It is well known that weedy rice appears to grow faster and mature earlier than cultivated rice. It is possible that differences in the root microbial genetics are correlated with this characteristic. This study incorporated 16S rRNA amplicon sequencing to study the microbial composition in the rhizosphere and endosphere of rice root. No significant difference was found between the microbiota associated with weedy and cultivated rice lines grown in the same field. It was found that the endosphere had less microbial diversity compared to the rhizosphere. The major groups of bacteria found in the endosphere are from the phylum Proteobacteria, Myxococcota, Chloroflexota, and Actinobacteria. In addition, by analyzing the microbiome of japonica rice grown in the field in a temperate climate, we found that despite differences in genotype and location, some bacterial taxa were found to be common and these members of the putative rice core microbiome can also be detected by in situ hybridization. The delineation of a core microbiome in the endosphere of rice suggests that these bacterial taxa might be important in the life cycle of a wide range of rice types.

Variation in Pathogenicity and Subsequent Production of Sclerotia of Sclerotinia sclerotiorum Isolates in Different Cover Crops, Flower Strips, and Weeds.

Cover crops and flower strips are used in agricultural fields as part of integrated pest management strategies. However, their potential as secondary hosts of soilborne pathogens such as Sclerotinia sclerotiorum in oilseed rape cultivation is not fully comprehended. In the current study, we evaluated the effect of pathogen virulence on the development of Sclerotinia stem/leaf rot and sclerotia production in 33 plant species from 11 botanical families using two S. sclerotiorum isolates. Furthermore, the effect of sclerotial size on carpogenic germination was studied. Results showed that the pathogen's virulence significantly affected the occurrence and development of Sclerotinia stem/leaf rot and the subsequent production of sclerotia. Among all plant species tested, 26 were more susceptible to the highly aggressive S. sclerotiorum isolate, which produced more and bigger sclerotia in 17 species than the less aggressive isolate. Moreover, a stronger positive correlation was found between the relative lesion length of plants inoculated with the highly aggressive isolate and the number of sclerotia produced by this isolate (Spearman's rank correlation coefficient [rs] = 0.572; P = 0.004). Additionally, we found that larger and heavier sclerotia produced stipes and apothecia earlier and at a greater rate than smaller ones. The heavyweight class had the highest carpogenic germination rate (82.4%), followed by the average (67.2%) and lightweight classes (59.5%). Our findings highlight the need for further investigation into the potential risks associated with cover crops, weeds, and flower strips as secondary hosts of soilborne pathogens in agricultural fields.

Weeds Harbor Fusarium Species that Cause Malformation Disease of Economically Important Trees in Western Mexico.

Mango malformation disease (MMD) caused by Fusarium spp. is an important limiting factor in most production areas worldwide. Fusarium mexicanum and F. pseudocircinatum have been reported as causing MMD in Mexico. These two pathogens also cause a similar disease in Swietenia macrophylla (big-leaf mahogany malformation disease) in central western Mexico, and F. pseudocircinatum was recently reported as causing malformation disease in Tabebuia rosea (rosy trumpet) in the same region. These studies suggest that additional plant species, including weeds, might be hosts of these pathogens. The role that weed hosts might have in the disease cycle is unknown. The objectives of this work were to recover Fusarium isolates from understory vegetation in mango orchards with MMD, identify the Fusarium isolates through DNA sequence data, and determine whether F. mexicanum is capable of inducing disease in the weedy legume Senna uniflora (oneleaf senna). Additional objectives in this work were to compare Fusarium isolates recovered from weeds and mango trees in the same orchards by characterizing their phylogenetic relationships, assessing in vitro production of mycotoxins, and identifying their mating type idiomorph. A total of 59 Fusarium isolates from five species complexes were recovered from apical and lateral buds from four weed species. Two of the species within the F. fujikuroi species complex are known to cause MMD in Mexico. Trichothecene production was detected in five isolates, including F. sulawense and F. irregulare in the F. incarnatum-equiseti species complex and F. boothii in the F. sambucinum species complex. Both mating types were present among mango and weed isolates. This is the first report of herbaceous hosts harboring Fusarium species that cause mango malformation in Mexico. The information provided should prove valuable for further study of the epidemiological role of weeds in MMD and help manage the disease.

Cruciferous Weeds Do Not Act as Major Reservoirs of Inoculum for Black Rot Outbreaks in New York State.

Cruciferous weeds have been shown to harbor diverse Xanthomonas campestris pathovars, including the agronomically damaging black rot of cabbage pathogen, X. campestris pv. campestris. However, the importance of weeds as inoculum sources for X. campestris pv. campestris outbreaks in New York remains unknown. To determine if cruciferous weeds act as primary reservoirs for X. campestris pv. campestris, fields that were rotating between cabbage or had severe black rot outbreaks were chosen for evaluation. Over a consecutive 3-year period, 148 cruciferous and noncruciferous weed samples were collected at 34 unique sites located across five New York counties. Of the 148 weed samples analyzed, 48 X. campestris isolates were identified, with a subset characterized using multilocus sequence analysis. All X. campestris isolates originated from weeds belonging to the Brassicaceae family, with predominant weed hosts being shepherd's purse (Capsella bursa-pastoris), wild mustard (Sinapis arvensis), yellow rocket (Barbarea vulgaris), and pennycress (Thlaspi arvense). Identifying pathogenic X. campestris weed isolates was rare, with only eight isolates causing brown necrotic leaf spots or typical V-shaped lesions on cabbage. There was no evidence of cabbage-infecting weed isolates persisting in an infected field by overwintering in weed hosts; however, similar cabbage and weed X. campestris haplotypes were identified in the same field during an active black rot outbreak. X. campestris weed isolates are genetically diverse both within and between fields, but our findings indicate that X. campestris weed isolates do not appear to act as primary sources of inoculum for B. oleracea fields in New York.

Selection of rhizobacteria isolates with bioherbicide potential against Palmer amaranth (Amarathus palmeri S. Wats.).

Crop yield and quality are affected by the presence of weeds such as Palmer amaranth. Chemical control is the most commonly used method to eradicate weeds, due to its quickness and efficacy. However, the inappropriate use of chemical herbicides can lead to resistant weed biotypes, as well as problems related to environmental pollution and human health hazards. One ecological alternative to combat weeds is the use of deleterious rhizobacteria (DRB). We evaluated the potential bioherbicidal effect in 15 DRB isolates from the rhizosphere of Palmer amaranth, both in vitro and in greenhouse tests. Isolates TR10 and TR18 inhibited seed germination in vitro, whereas the TR25 and TR36 isolates showed the potential to inhibit Palmer amaranth plant development in growth room assays without affecting maize and common bean germination and growth. These four isolates were molecularly identified as either Pseudomonas sp. (TR10 and TR36), Enterobacter sp. (TR18), or Bacillus sp. (TR25). In addition, the production of volatiles and diffusible metabolites were identified as possible mechanisms of germination arrestment and plant development inhibition. This study suggests the bioherbicide potential of some indigenous rhizobacteria against Palmer amaranth.

Effective methane production from the Japanese weed Gyougi-shiba (Cynodon dactylon) is accomplished by colocalization of microbial communities that assimilate water-soluble and -insoluble fractions.

Weed, an abundant biomass, is considered unsuitable as a raw material for methane production. There are few reports on the anaerobic digestion of weeds without the addition of other organic wastes. To solve this problem, a methane-producing microbial community with weed as a sole feedstock was established. This study mainly focused on the degree of contribution between water-soluble and -insoluble fractions of the weed to methane production; thus, methane production from both fractions was tested separately. Methane production after 80-day batch cultures with whole weed, water-soluble and water-insoluble fractions was 184.5, 96.8 and 26.5 NmL g-1 dry matter (DM), respectively. The results of 16S rRNA gene amplicon sequence analysis revealed that Proteiniphilum saccharofermentans and several Methanobacterium species commonly dominated all cultures, whereas the population dynamics of minor species differed in every culture. Moreover, the remixed culture of microbial communities adapted to water-soluble and -insoluble fractions recovered methane production (252.4 NmL g-1 DM). Based on these results, it can be strongly inferred that colocalizing the minor species in water-soluble and -insoluble fractions is important for effective methane production.

Remotididymella ageratinae sp. nov. and Remotididymella anemophila sp. nov., two novel species isolated from the invasive weed Ageratina adenophora in PR China.

To determine if Ageratina adenophora can accumulate diverse pathogens from surrounding native plants, we intensively sampled fungal communities, including endophytes, leaf spot pathogens and canopy air fungi, associated with Ag. adenophora as well as native plants in its invasive range. In total, we collected 4542 foliar fungal strains from 10 geographic sites, including 1340 from healthy leaves of Ag. adenophora, 2051 from leaf spots of Ag. adenophora and 1151 from leaf spots of 56 species of native plants and crops. Taxonomically, the common fungal genera included Colletotrichum, Diaporthe, Alternaria, Nemania, Xylaria, Neofusicoccum, Nigrospora, Epicoccum, Gibberella, Pestalotiopsis, Irpex, Schizophyllum and Clonostachys. We also isolated the cultivable fungi from 12 air samples collected from six areas in Yunnan Province, PR China. Among the total of 1255 air fungal isolates, the most common genera were Cladosporium, Trichoderma and Epicoccum. Among them, two new Remotididymella species, Remotididymella ageratinae from leaf spot of Ag. adenophora and Remotididymella anemophila from canopy air of Ag. adenophora were found. The two species showed both asexual and sexual reproductive structures. The conidia of R. ageratinae and R. anemophila are larger than those of R. anthropophila and R. destructiva. The size of ascospores of R. ageratinae and R. anemophila also differ from R. bauhiniae. Phylogenetic analysis of the combined ITS, LSU rRNA, rpb2 and tub2 sequences showed that R. ageratinae and R. anemophila each formed a distinct clade, separated from all species previously described in Remotididymella and confirmed them as new species belonging to Remotididymella. Full descriptions of R. ageratinae and R. anemophila are provided in this study.

Population genetic structure and marker-trait associations in East and West African Striga hermonthica with varying phenotypic response to Fusarium oxysporum f. sp. strigae isolates Foxy-2 and FK3.

To examine the genetic basis for the variable susceptibility of Striga hermonthica from differing zones of sub-Saharan Africa to Fusarium oxysporum f. sp. strigae (Fos) isolates Foxy-2 and FK3, 10 S. hermonthica populations from Eastern and Western Africa were phenotyped for their susceptibility response to Foxy-2 and FK3, and then genotyped with 22 simple sequence repeat (SSR) markers. There is low genetic differentiation between East African and West African S. hermonthica populations (i.e. the proportion of the total genetic variance contained in the subpopulation relative to the total genetic variance, FST  = 0.012, P < 0.05), but intermediate genetic differentiation (FST  = 0.143, P < 0.01) underlies the S. hermonthica groups that are differentiated by their phenotypic responses to Fos isolates. An expressed sequence tag SSR (EST-SSR) marker Y53 (P < 0.01) and a genomic SSR marker E1009 (P < 0.05) were associated with the S. hermonthica class susceptible to Foxy-2 and FK3 (group A). A divergent S. hermonthica class, consisting of groups with intermediate susceptibility to Foxy-2 (group B) and susceptibility to either FK3 (group C) or Foxy-2 (group D), showed no marker-trait association, instead demonstrated linkage disequilibrium decay. Owing to point substitutions and insertion-deletion mutations, the unique, protein-coding nucleotide sequence at the E1009 locus in group A was partly dissimilar to group B, but was totally distinct from groups C and D. These findings implied that the inconsistent effectiveness of a Fos isolate is better explained by genomic variation in S. hermonthica, rather than by S. hermonthica sampling zones.

Chloroplast DNA analysis of the invasive weed, Himalayan balsam (Impatiens glandulifera), in the British Isles.

Impatiens glandulifera or Himalayan balsam (HB), is an invasive alien weed throughout the British Isles (BI). Classical biological control of HB in the BI using a rust fungus from the Himalayan native range was implemented in 2014. However, not all HB populations are susceptible to the two rust strains currently released. Additional strains are needed that infect resistant populations in order to achieve successful control. These are best sourced from the historical collecting sites. A molecular analysis was conducted using six chloroplast DNA sequences from leaf material from across the BI and the native range. Herbarium samples collected in the Himalayas between 1881 and 1956 were also included. Phylogenetic analyses resulted in the separation of two distinct groups, one containing samples from the BI and the native range, and the other from the BI only; suggesting that HB was introduced into the BI on at least two occasions. The former group is composed of two subgroups, indicating a third introduction. Ten and 15 haplotypes were found in the introduced and native range respectively, and with two of these found in both regions. Results show where to focus future surveys in the native range to find more compatible rust strains.

Characterization of an endophytic bacterium (Pseudomonas aeruginosa), originating from tomato (Solanum lycopersicum L.), and its ability to inhabit the parasitic weed Phelipanche aegyptiaca.

PHELIPANCHE AEGYPTIACA: is an obligate holo-parasitic weedlacking a functional photosynthetic system, which subsists on roots of a wide range of host crops, causing severe losses in yield quality and quantity. The parasite and its host are connected through their vascular system, forming a unique ecological system that enables the exchange of various substances. In a previous study, it was suggested that endophytic bacteria, which naturally inhabit the internal tissues of plants, can also be transmitted from the parasitic weed to its host and vice versa. In the current study, we investigate the characteristics of a previously isolated Pseudomonas sp. PhelS10 strain using both biochemical and molecular methods. This isolate was obtained from tomato plant tissue and was able to reduce P. aegyptiaca parasitism, and thus it may serve as a biocontrol agent. Our results revealed that production of Pseudomonas aeruginosa quinolone signal (PQS) was 2.1 times higher than that of the standard Pseudomonas aeruginosa strain (PAO1), which contributed to a 22% higher biofilm formation capability. PhelS10 strain was detected in the xylem of tomato plants using FISH analysis. In addition, PhelS10 strain was found in the parasitic weed's inner tissues, confirming the hypothesis that endophytic bacteria traffic between the host plant and its parasitic weed.

Phytoplasmas diversity and identification of new aster yellows subgroup (16SrI) associated with weed species in Argentina.

Symptoms of phytoplasma infection were observed in different weed species, Bidens subalternans, Conyza bonariensis, Heterosperma ovatifolium and Conium maculatum, collected from diverse geographical regions in Argentina. To confirm the association of phytoplasma infection with symptomatic plants, PCR, RFLP and phylogenetic analyses based on 16S rRNA-encoding sequences were performed. In this work, we report the presence of phytoplasmas from group 16SrVII (subgroup 16VII-B) infecting C. bonariensis and B. subalternans and from group 16SrIII (subgroup 16SrIII-X) B. subalternans, H. ovatifolium, and C. maculatum. Phytoplasmas from the aster yellows group were detected infecting C. bonariensis and B. subalternans. Analysis of 16S rRNA-encoding genes revealed the presence of two distinct operons, rrnB (16SrI-B) and newly described rrnA, which is different from the reference RFLP patterns of all previously established 16SrI-subgroups. A single rp operon sequence analysis reveals the presence of simple infection and confirms a description of a novel subgroup. On the basis of these results we propose a designation of new subgroup 16SrI-(B/AJ) AJ (rp-AJ). To our knowledge, this is the first report of phytoplasmas infecting Bidens subalternans¸ Heterosperma ovatifolium and Conium maculatum.

Harnessing the microbiome to control plant parasitic weeds.

Microbiomes can significantly expand the genomic potential of plants, contributing to nutrient acquisition, plant growth promotion and tolerance to (a)biotic stresses. Among biotic stressors, root parasitic weeds (RPWs), mainly of the genera Orobanche, Phelipanche and Striga, are major yield-limiting factors of a wide range of staple crops, particularly in developing countries. Here, we provide a conceptual synthesis of putative mechanisms by which soil and plant microbiomes could be harnessed to control RPWs. These mechanisms are partitioned in direct and indirect modes of action and discussed in the context of past and present studies on microbe-mediated suppression of RPWs. Specific emphasis is given to the large but yet unexplored potential of root-associated microorganisms to interfere with the chemical signalling cascade between the host plant and the RPWs. We further provide concepts and ideas for future research directions and prospective designs of novel control strategies.

Weed Roots Facilitate the Spread of Rosellinia necatrix, the Causal Agent of White Root Rot.

Rosellinia necatrix causes white root rot in various plants, including the Japanese pear. PCR assays using specific primers for R. necatrix detected the fungus on the roots of nine weed species from infested pear orchards. The soil inoculation experiment revealed that the spread of R. necatrix was similar between weed-mowed and non-weed-mowed treatments under field conditions. The spread of R. necatrix was also observed when rescue grass (Bromus catharticus) was grown in planter boxes under greenhouse conditions, but was limited without the grass, suggesting that some weeds facilitate the spread of R. necatrix in soil.

Enhanced inulinase production by Fusarium solani JALPK from invasive weed using response surface methodology.

The present study is the first report of utilizing Tithonia rotundifolia weed as a substrate for inulinase production from Fusarium solani JALPK. It also deals with the statistical optimization of culture conditions to enhance the enzyme yield. Amongst the 11 variables screened by Plackett- Burman design, Inulin in combination with Agave sisalana extract, Tithonia rotundifolia extract and NaNO3 had a significant influence on inulinase production and their concentrations were further optimized employing Box Behnken design. An enhancement of inulinase production from 970 EU/mL to 3261.011 EU/mL was gained after media optimization. Amongst the screened carbon sources Tithonia rotundifolia was found to be very effective in stimulating elevated inulinase synthesis. The Tithonia rotundifolia weed extract was treated with inulinase from Fusarium solani JALPK to form fructose which was estimated spectrophotometrically. This liberated fructose was also confirmed by osazone formation test and FTIR. HPTLC analysis of product revealed the exoinulinase nature of the enzyme produced by Fusarium solani JALPK since fructose was the only end product after hydrolysis of inulin rich weed in fermented broth. Thus the elevated extracellular inulinase yielding novel property of Fusarium solani JALPK (KY914560) contributes in considering it as a potential candidate with food, pharmaceutical and bioremediation applications.

Spectral Identification of Disease in Weeds Using Multilayer Perceptron with Automatic Relevance Determination.

Microbotryum silybum, a smut fungus, is studied as an agent for the biological control of Silybum marianum (milk thistle) weed. Confirmation of the systemic infection is essential in order to assess the effectiveness of the biological control application and assist decision-making. Nonetheless, in situ diagnosis is challenging. The presently demonstrated research illustrates the identification process of systemically infected S. marianum plants by means of field spectroscopy and the multilayer perceptron/automatic relevance determination (MLP-ARD) network. Leaf spectral signatures were obtained from both healthy and infected S. marianum plants using a portable visible and near-infrared spectrometer (310⁻1100 nm). The MLP-ARD algorithm was applied for the recognition of the infected S. marianum plants. Pre-processed spectral signatures served as input features. The spectra pre-processing consisted of normalization, and second derivative and principal component extraction. MLP-ARD reached a high overall accuracy (90.32%) in the identification process. The research results establish the capacity of MLP-ARD to precisely identify systemically infected S. marianum weeds during their vegetative growth stage.

Selection, isolation, and identification of fungi for bioherbicide production

Abstract Production of a bioherbicide for biological control of weeds requires a series of steps, from selection of a suitable microbial strain to final formulation. Thus, this study aimed to select fungi for production of secondary metabolites with herbicidal activity using biological resources of the Brazilian Pampa biome. Phytopathogenic fungi were isolated from infected tissues of weeds in the Pampa biome. A liquid synthetic culture medium was used for production of metabolites. The phytotoxicity of fungal metabolites was assessed via biological tests using the plant Cucumis sativus L., and the most promising strain was identified by molecular analysis. Thirty-nine fungi were isolated, and 28 presented some phytotoxic symptoms against the target plant. Fungus VP51 belonging to the genus Diaporthe showed the most pronounced herbicidal activity. The Brazilian Pampa biome is a potential resource for the development of new and sustainable chemical compounds for modern agriculture.

Phoma crystallifera with phytotoxic effects and pathogenic potential against field bindweed (Convolvulus arvensis L.) in Iran.

AIMS: To identify a potential pathogenic isolate of fungus on Convolvulus arvensis and to determine its phytotoxic activity, which revealed the presence of toxic metabolites responsible for the toxicity against the target weed. METHODS AND RESULTS: A high virulent isolate of the fungus, Phoma crystallifera was isolated from symptomatic field bindweed in the west of Iran and was screened for the production of phytotoxins, which promoted necrosis on the detached leaves and seedlings of field bindweed in the bioassays. The isolate was distinct from other isolates of the fungi on the basis of morphological characteristics and the combined sequence database of the ITS region, partial LSU rDNA and ß-tubulin gene. Isolate P. crystalifera P6 produced the highest amount of phytotoxins after 21 days in a shacked culture of Richard's broth. The active metabolites were isolated from a cell-free culture filtrate by ethyl-acetate and purified by thin layer chromatography. The result indicated that six out of nine spots had phytotoxic activity in the bioassays, with Rf values of 0·16, 0·30, 0·36, 0·43, 0·57 and 0·81. CONCLUSIONS: Phoma crystallifera P6 and its active metabolites showed significant phytotoxic effects on the detached leaves of C. arvensis. SIGNIFICANCE AND IMPACT OF THE STUDY: To date, there are no reports of possible biocontrol agent(s) on C. arvensis in Iran. Thus, P. crystallifera P6 is introduced here as a severe pathogenic fungus and which can be used as a biocontrol agent against C. arvensis.