Potential Mycoherbicide Research Articles

Genome sequences of Colletotrichum eleusines and C. echinochloae: two pathogens from Poaceae weeds.

We present two whole-genome sequences of Colletotrichum strains which were isolated from Eleusine indica and Echinochloa crus-galli using Nanopore and Illumina technologies, as part of screening for potential mycoherbicide. The genome sequences will provide important genetic information and will be useful for further research into secondary metabolites of Colletotrichum.

Physiological and Biochemical Responses of Sagittaria trifolia L. to Phytotoxic Ethyl Acetate Fungal Extract from Curvularia lunata Strain CLST-01.

Curvularia lunata (No. CLST-01), a fungal pathogen isolated from the threeleaf arrowhead (Sagittaria trifolia L.), has been proposed as a potential mycoherbicide for grass weeds. This paper investigated the physiological and biochemical effects of CLST-01 phytotoxic ethyl acetate fungi extract on the leaves of the threeleaf arrowhead. The results showed that the ethyl acetate fungi extract from CLST-01 can accelerate damage to the cell membrane, increase the production of malondialdehyde, and damage the cellular structure, which could decrease the number of chloroplasts after 96 h treatments. In addition, the content of chlorophyll was reduced by 49.5%, and the net photosynthetic rate, stomatal conductance, and transpiration rate were inhibited. The rates of inhibition were 90.13%, 83.74%, and 79.31%, respectively, and the intercellular CO2 concentration increased by 51.87% on Day 9 after treatment with a concentration of 200 μg/mL. In summary, the phytotoxic ethyl acetate fungal extract from C. lunata CLST-01 can inhibit the photosynthesis of the threeleaf arrowhead leaves, destroy the ultrastructure of leaves, and affect the growth of this invasive weed. Therefore, it has the potential to be developed into a mycoherbicide for weed control in crops as a natural photosynthetic inhibitor.

Production of (10S,11S)-(-)-epi-Pyriculol and Its HPLC Quantification in Liquid Cultures of Pyricularia grisea, a Potential Mycoherbicide for the Control of Buffelgrass (Cenchrus ciliaris).

(10S,11S)-(-)-epi-pyriculol is a phytotoxic metabolite produced by Pyricularia grisea, a fungus identified as a foliar pathogen on the invasive weed species buffelgrass (Cenchrus ciliaris) in North America. The effective control of buffelgrass has not yet been achieved, and there is a need to develop effective and green solutions. Herbicides based on natural products and the use of phytopathogenic organisms could provide the most suitable tools for the control of weeds such as buffelgrass. Thus, one of the most relevant points to study about potential suitable phytotoxins such as (10S,11S)-(-)-epi-pyriculol is its production on a large scale, either by isolation from fungal fermentations or by synthesis. For these purposes, rapid and sensitive methods for the quantification of (10S,11S)-(-)-epi-pyriculol in complex mixtures are required. In this study, a high-pressure liquid chromatography (HPLC) method for its quantification was developed and applied to organic extracts from twelve P. grisea isolates obtained from diseased buffelgrass leaves and grown in potato dextrose broth (PDB) liquid cultures. The analysis proved that the production of (10S,11S)-(-)-epi-pyriculol is fungal-isolate dependent and strongly correlated with phytotoxic activity, shown by the P. grisea organic extracts in a buffelgrass radicle elongation test. The HPLC method reported herein allowed us to select the best strain for the production of (10S,11S)-(-)-epi-pyriculol and could be useful for selecting the best cultural conditions for its mass production, providing a tool for the use of this promising metabolite as a new bioherbicide for the control of buffelgrass.

Diversity, Lifestyle, Genomics, and Their Functional Role of Cochliobolus, Bipolaris, and Curvularia Species in Environmental Remediation and Plant Growth Promotion under Biotic and Abiotic Stressors.

Cochliobolus, Bipolaris, and Curvularia genera contain various devastating plant pathogens that cause severe crop losses worldwide. The species belonging to these genera also perform a variety of diverse functions, including the remediation of environmental contaminations, beneficial phytohormone production, and maintaining their lifestyle as epiphytes, endophytes, and saprophytes. Recent research has revealed that despite their pathogenic nature, these fungi also play an intriguing role in agriculture. They act as phosphate solubilizers and produce phytohormones, such as indole acetic acid (IAA) and gibberellic acid (GAs), to accelerate the growth of various plants. Some species have also been reported to play a significant role in plant growth promotion during abiotic stresses, such as salinity stress, drought stress, heat stress, and heavy metal stress, as well as act as a biocontrol agent and a potential mycoherbicide. Similarly, these species have been reported in numerous industrial applications to produce different types of secondary metabolites and biotechnological products and possess a variety of biological properties, such as antibacterial, antileishmanial, cytotoxic, phytotoxic, and antioxidant activities. Additionally, some of the species have been utilized in the production of numerous valuable industrial enzymes and biotransformation, which has an impact on the growth of crops all over the world. However, the current literature is dispersed, and some of the key areas, such as taxonomy, phylogeny, genome sequencing, phytohormonal analysis, and diversity, are still being neglected in terms of the elucidation of its mechanisms, plant growth promotion, stress tolerance, and bioremediation. In this review, we highlighted the potential role, function, and diversity of Cochliobolus, Curvularia, and Bipolaris for improved utilization during environmental biotechnology.

Colletotrichum echinochloae: A Potential Bioherbicide Agent for Control of Barnyardgrass (Echinochloa crus-galli (L.) Beauv.).

Barnyardgrass (Echinochloa crus-galli (L.) Beauv.) is one of the most troublesome weeds in transplanted and direct-seeded rice worldwide. To develop a strategy for the biocontrol of barnyardgrass, fungal isolates were recovered from barnyardgrass plants that exhibited signs of necrosis and wilt. An isolate B-48 with a high level of pathogenicity to barnyardgrass was identified after pathogenicity tests. From cultural and DNA sequence data, this strain was identified as Colletotrichum echinochloae. The inoculation of the barnyardgrass plant with C. echinochloae caused a significant reduction in fresh weight. The isolate B-48 was highly pathogenic to barnyardgrass at the three- to four-leaf stages. When inoculated at a concentration of 1 × 107 spores/mL, barnyardgrass could achieve a reduction in fresh weight of more than 50%. This strain was safe for rice and most plant species. The results of this study indicated that this strain could be a potential mycoherbicide for barnyardgrass control in paddy fields in the future.

A Review of Research and Developments with Insect Agents Used for Biological Control of Australian Acacia Species (Caesalpinioideae) in South Africa

There are 14 species of Australian Acacia now known to be invasive in South Africa, ten of which are under some form of biological control (biocontrol). The biocontrol agents introduced against this group include a fungal pathogen, Uromycladium morrisii Doungsa-ard, McTaggart, Geering & R.G. Shivas (Pucciniales: Raveneliaceae) for Acacia saligna (Labill.) H.L.Wendl., and ten insect species, including two bud-galling wasps, five seed-feeding weevils and three flower-galling fly species, all of which supress reproductive output of their hosts. There are also two native fungal pathogens that have become associated with the introduced acacias, and which have been developed for potential mycoherbicide use. Screening and importation of new agents has seen limited activity in the ten-year period reviewed here (i.e., 2011–2020). Most attention has been focussed on efforts to evaluate the effectiveness of the established agents and, importantly, to gain an understanding of the role of seeds in the population dynamics of the host plants.

Evaluation of the Response of Four Species of Weeds and Some Rice Cultivars to Pathogenicity of Curvularia lunata and Alternaria pellucida

Background and Objectives: Herbicides are essential inputs in agriculture that despite their many benefits in controlling weeds, can cause damages such as creation resistance to weeds, environmental effects and threats to human health. Therefore, to reduce consumption or reduce their concentration, alternative methods such as weed control using biological microorganisms have been proposed, which to achieve this goal, it is necessary to have a complete understanding of pathogen-host relationships. Achieving such understanding can be difficult and challenging, particularly for large data sets with complex host genotype-by-pathogen strain interactions. To evaluate the pathogenicity of fungi in plant species, in addition to conventional quantitative and descriptive evaluations, the host genotype-pathogen isolates biplot can be used in a single scatter plot. This study was conducted to evaluate the virulence of two funguses on five rice cultivars and four weeds. Materials and Methods: In this research, pathogenicity of Curvularia lunata and Alternaria pellucida were studied in two separate experiments on five rice cultivars (Hashemi, Alikazemi, Sepidroud, Khazar, Binam), Eichinochloa oryzicola, E. crus-galli, Sagitaria trifolia and Alisma plantago – aquatica in a completely randomized design with three replications in pot condition, in the greenhouse of Islamic Azad University, Rasht Branch, at 2018. Principal component analysis was performed on two-way data of host genotype -pathogen. The biplot was plotted with the first two principal axes (PC1 and PC2) using GGEBiplotGUI packages (Bernal & Villardon, 2016) in R software. Results: Analysis of variance was performed separately for weed species and rice cultivars. There were significant differences between rice cultivars in terms of reduction of plant height and fresh and dry weight of the plant in inoculation with C. lunata and in terms of reduction in plant height and dry weight of the plant in inoculation with A. pellucida. In addition, there was a significant difference between weed species in terms of disease rating, decrease in plant height and fresh weight of the plant in inoculation with C. lunata and in all four traits in terms of inoculation with A. pellucida. Comparison of means showed that Hashemi and Ali Kazemi cultivars had the highest disease rating, reduction of plant height and fresh and dry weight of the plant in treatment with C. lunata. Biplot analysis showed the relationships between fungi (as pathogens) and weed species and rice cultivars (as host genotypes) in a pathogen-host view in terms of traits. Average-Tester-Coordination (ATC) view (average of PC1 and PC2 scores for all genotypes) of biplot were indicated that A. plantago – aquatica and E. crus-galli were as the most sensitive and Sepidroud as tolerant genotypes to two fungi according to their disease rating. Based on disease rating, C. lunata can be used for biocontrol of A. plantago–aquatica and E. crus-galli in Ali Kazemi and Binam genotypes. Based on this trait, A. pellucida can be used for biocontrol of S. trifolia in Hashemi. According to dry weight, C. lunata can be used for biocontrol of Sagitaria trifolia in all of the genotypes. Conclusion: In conclusion, based on disease rating and reduction of plant height and dry and fresh weight of plants, C. lunata was a better antagonistic fungus in dealing with weeds compared to the other fungus especially for A. plantago–aquatica and this fungus could be a potential mycoherbicide for weeds control in paddy fields in the future.

Pathogenicity and Lipid Composition of Mycelium of the Fungus Stagonospora cirsii VIZR 1.41 during Submerged Cultivation

In order to identify qualitative markers of a potential mycoherbicide against Canada thistle based on the mycelium of the fungus Stagonospora cirsii VIZR 1.41, changes in its pathogenicity and lipid profiles during submerged cultivation on liquid sucrose-soybean medium were analyzed. The fatty-acid composition of major lipids and the identification of molecular species of structural lipids were determined. The lipid composition during fungal growth changed together with its pathogenicity. The highly pathogenic mycelium of the fungus (at the log phase of growth) was characterized with the relatively highest content of structural lipids: phosphatidylcholine (PC), phosphatidylethanolamine (PE), and ergosterol (ES). Their relative concentration decreased with culture age and a decrease in pathogenicity. The highest lipid yield was found at the beginning of stationary growth phase (at the maximal biomass yield) of S. cirsii; triacylglycerides (TAGs) were the most abundant. The double-bond index of fatty acids in glycerolipids decreased with culture age, and the substitution of molecular PC species (34:2 versus 36:4) and PE (36:4 versus 34:2) was observed as well. High levels of ES, TAG, PC (in particular, 34:2 forms) and PE (36:4 forms) were presumed to be qualitative markers of S. cirsii mycelium.

First report of stem blight and leaf spot in horse purslane caused by Gibbago trianthemae in Sinaloa, Mexico

Horse purslane (Trianthema portulacastrum L.) is a common weed in Mexico, where it competes with different agricultural crops and grows along watercourses, railways and roadsides, abandoned fields, and urban communities. In Sinaloa, this weed grows abundantly during the rainy season (July–September) and competes with summer crops such as corn and sorghum during the fall-winter season, and with common bean and corn mainly in alluvial soils. In recent years, horse purslane has suffered a 100% incidence of stem blight and leaf spot, with a diseased foliar area ranging from 35% to 80%. Ten isolates of an unknown fungus were obtained from symptomatic tissue and identified as Gibbago trianthemae Simmons, based on morphological features of the anamorph, with this identification confirmed in nine isolates by ITS rDNA sequence analysis. The identity of the fungus coincides with previous reports from other parts of the world, where it causes symptoms on horse purslane similar to those described here. In particular, due to its host specificity and aggressiveness towards horse purslane, G. trianthemae has been considered as a potential mycoherbicide. The pathogenicity of six fungal isolates was demonstrated according to Koch’s postulates. Our study provides new research directions for determining host specificity, obtaining aggressive strains, establishing the most appropriate inoculum levels, and demonstrating the influence of climatic conditions on the severity of the disease, which will help to assess the utility of the pathogen as a potential mycoherbicide.

First Report of Mycoleptodiscus terrestris Causing Crown and Root Rot of Alfalfa (Medicago sativa) in Minnesota.

Mycoleptodiscus terrestris (Gerd.) Ostaz. has been studied extensively as a potential mycoherbicide against aquatic weeds since the early 1970s (Mathur and Gehlot 2018; Shearer 1998). However, it is also a pathogen on many legumes including alfalfa (Gerdemann 1953; Smith et al. 1998). In August 2019, alfalfa plants with stunted yellow foliage and rotted stems at the base of the crown were observed in a variety trial planted in spring 2018 at the University of Minnesota, St. Paul, Minnesota. Affected plants were in patches across the field with approximately 20% of plants showing symptoms. Plants from patches had few lateral and fibrous roots and dark lesions appeared in the crown and root tissue. Tissue samples (5 mm2) from 10 plants with symptomatic crown and root tissues were surface disinfested with 70% ethanol for 5 min, followed by 30 s in 10% NaOCl, and then rinsed three times in sterile distilled water. Samples were air-dried and placed on water agar (WA) amended with 25 µg/ml rifampicin. Plates were incubated at room temperature for 3 days and fungal hyphal tips from tissue samples were transferred to potato dextrose agar (PDA). After 7 days, isolates were tentatively identified by morphological characteristics as M. terrestris (Ostazeski 1967). The hyaline mycelia turned from olive-gray to dark gray with age. Abundant dark microsclerotia formed 5 days after incubation that varied in size and shape, measuring 300-860 x 270-600 µm. Molecular identification of two representative isolates (DAZ5 and DAZ9) was done by sequencing the internal transcribed spacer (ITS) regions of the rDNA, the translation elongation factor 1α (TEF1), and the second largest subunit of RNA polymerase II (RPB2) genes. For both isolates the ITS, TEF1, and RPB2 genes were amplified and sequenced with primers ITS1/4 (White et al. 1990), 983F/1567R (Rehner and Buckley 2005), and fRPB2-7cR/RPB-5F2 (Liu et al. 1999; Sung et al. 2007), respectively. ITS amplification conditions followed White et al. (1990), the TEF and the partial RPB2 gene was obtained by using a touchdown PCR protocol as described in Rehner and Buckley (2005) and Woudenberg et al. (2017), respectively. Based on a BLAST search of the NCBI nucleotide database, the ITS sequences (GenBank MN851265.1 and MN851266.1) had 100% identity with M. terrestris strain CBS 231.53 (MK487754.1). The TEF1 (MN873019, MN873020) and RPB2 sequences (MN873021, MN873022) had 100% identity with M. terrestris strain IMI 159038 (MK495977.1, MK492735.1). A pathogenicity test was performed by inoculating five 3-week-old alfalfa plants per cultivar (cv. DKA44-16RR, Vernal, 53V52, and Agate) with isolates DAZ5 and DAZ9. Plants were inoculated around the exposed stem base with three 5 mm diameter PDA plugs from a culture of M. terrestris covered with microsclerotia. Control plants were inoculated with sterile PDA plugs. After inoculation plants were incubated at 25 0C with a 16-h photoperiod in a growth chamber. The first symptoms appeared two months after inoculation on all cultivars as a dark lesion at the stem base followed by yellowing and rotting of stems. Inoculated plants had more fibrous roots than the controls. The control plants were symptomless with healthy root development. The pathogen was re-isolated from all infected alfalfa cultivars and had the same morphology as isolates DAZ5 and DAZ9, fulfilling Koch's postulates. To our knowledge, this is the first report of M. terrestris causing crown and root rot disease of alfalfa in Minnesota.

Biological weed control using Trichoderma polysporum strain HZ-31

To develop a potential bio herbicide, herbicide activity and crop safety of fungal strain HZ-31 isolated from naturally infected weed Cirsium arvense (L.) Scop. were investigated. The study was conducted in vitro and in vivo during the summers of 2017 and 2018. Strain HZ-31 showed broad-spectrum herbicidal activity, both in vitro and in vivo, when targeting Elsholtzia densa Benth., Polygonum lapathifolium L., Lepyrodiclis holosteoides (C.A. Mey.) Fenzl ex Fisch. & C.A. Mey., Avena fatua L., Chenopodium album L. and Polygonum aviculare L. Exposure to HZ-31 in vitro induced heavy levels of damage in the leaves of E. densa, A. fatua, and P. aviculare. Exposure to HZ-31 in vivo resulted in high mortality in E. densa, A. fatua, and P. lapathifolium. Although the exposure of various weeds to HZ-31 caused severe damage, the strain did not cause any deleterious effects in Vicia faba L. and Pisum sativum L., two of the five crops tested. Our results suggest that fungal strain HZ-31 could be a potential mycoherbicide candidate for weed control in V. faba and P. sativum fields. Based on its morphological characteristics and ITS nucleotide sequence analysis, the fungus was classified as Trichoderma polysporum (Louk:Fr.) Rifai. New perspectives for weeds control by T. polysporum and its use in V. faba and P. sativum crops were prospected, considering the bioherbicide selectivity described in this study.

Potential of Colletotrichum typhae H.C Greene mycoherbicide for bio-control of Southern cattail (Typha domingensis Pers.) plants

The anthropic interference in aquatic ecosystems favors the disordered colonization of T. domingensis, damaging the production of hydroelectric power and river traffic. Because of this, studies report the efficacy of fungal mycoherbicides, with control rates reaching as high as 90%. Thus, the objective of this study was to evaluate the potential of C. typhae as a mycoherbicide in bio control of T. domingensis, at in vitro and greenhouse conditions. 107 samples of symptomatic T. domingensis leaves were collected in flooded areas of rivers in Brazil, with identification and isolation of the collected fungal species. The concentration of inoculum was determined to evaluate the incidence and severity of the disease, the influence of temperature on mycelial growth and conidia germination, the effect of temperature and leaf wetness period on T. domingensis infection by C. typhae and the host range test in vitro. The growth of the colonies of C. typhae was higher at 25 to 30 ºC. There was no interference of the photoperiod on germination of the spores, but the highest percentage of germination was occurred at 20 ºC. The influence of environmental conditions on infection of inoculated leaves of T. dominguensis revealed that at 15 ºC and the period of leaf wetness of 48 hours the highest incidence of the disease was observed, as well as the severity for the same period of leaf wetness. The specificity test showed that C. typhae is specifically pathogenic to T. domingensis. This the first report of the occurrence of this pathogen in aquatic macrophytes of this species and in T. domingensis, a potential mycoherbicide for the control of this aquatic weed.

The influence of the carbohydrate levels on viability of Stagonospora cirsii drying mycelium

The Stagonospora cirsii mycelium is considered as the infectious basis of a potential mycoherbicide for the control of Canadian thistle and perennial sow thistle. Successful commercialization of mycoherbicides is often constrained by poor drying survival. In this study was shown that the highest viability of mycelium S. cirsii during drying is achieved in the stationary phase of growth. The mycelium in the stationary phase is characterized by maximum level of carbohydrates. We suggest the level of arabitol as a criterion evaluation of the mycelium resistance to drying. Culturing conditions, and especially the fermentation time, allow prediction of polyols and trehalose levels, which are very critical in enhancing the storage life and efficacy of biological control agent.

Effects of Substrate and Cultivation Duration on the Productivity, Biological Activity, and Chromatography Profiles of Extracts Obtained from Stagonospora cirsii S-47

In order to determine the possible toxic properties of a potential mycoherbicide based on the fungus Stagonospora cirsii S-47, the effects of solid and liquid media composition on the yield of extractive matter (YEM), the spectrum of biological activity, and the chromatography profiles of extracts obtained from cultures of this fungus were studied. The maximal YEM (~250 mg/L) was obtained from filtrates taken from a 2-week culture of S. cirsii S-47 grown on a sucrose–soy meal medium. The same time was optimal for the production of maximal YEM (~1.5 g/kg) when the fungus was grown on pearl-barley substrate. The fungal extracts showed phytotoxic, antimicrobial, cytotoxic, and antiesterase activity. Extracts from culture filtrates generally demonstrated a higher level and wider spectrum of biological activity than extracts from solid S. cirsii S-47 culture. The maximal phytotoxic and antimicrobial activity was found in dichloromethane extracts from the filtrate of 3-week fungal culture on Czapek medium, while extracts from two-week-old culture strongly inhibited carboxyl esterase. The maximal cytotoxic activity against the U251 cell line was found in ethyl acetate extract from a 3-week culture of S. cirsii S-47 produced on YMG liquid medium. The extract compositions varied considerably depending on the culture substrate.

Pathogenicity and Lipid Composition of Mycelium of the Fungus Stagonospora cirsii VIZR 1.41 Produced on Liquid Media with Different Nitrogen Sources

The effect of the nitrogen source (sodium nitrate and soybean meal) on the growth, pathogenicity, and lipid composition of mycelium of Stagonospora cirsii Davis VIZR 1.41, a potential mycoherbicide against Canada thistle (Cirsium arvens (L.) Scop.), was studied. The fungus grew significantly (two times) faster on sucrose-soybean meal medium (SSM) than on modified Czapek medium (CM). The fungal mycelium during the exponential growth phase demonstrated the maximal pathogenicity level on the third day on SSM and on the sixth day on CM. Canada thistle leaf tissues were more susceptible (25% higher development of necrotic lesion) to mycelium obtained on SSM than to mycelium obtained on CM. The nitrogen source strongly affected the lipid composition of S. cirsii mycelium. In S. cirsii mycelium obtained on SSM, the total lipid content was 1.7 times lower; the ratio of nonpolar lipids to polar lipids was three times lower than that for fungal mycelium grown on CM. Considerable differences were found in the composition of nonpolar (sterols and fatty acid) and polar (sphingolipids) lipids with respect to the nitrogen source in the culture medium. The higher contents of sterols, free fatty acids, and some glycoceramides in the mycelium of S. cirsii obtained on SSM may be related to its higher pathogenicity level and can serve as a marker of mycoherbicide quality.

Potential control of Echinochloa crus-galli (Barnyard grass) by Curvularia lunata as a mycoherbicide

Echinochloa crus- galli (Barnyard grass) is a world’s most harmful weed species. Echinochloa crus-galli weed species compete with many economically important crops and causes serious problem in rice production. The virulent strain LD2 (leaf disease) of Curvularia lunata was screened out from 25 fungus strains isolated from the diseased leaves of barnyard grass (Echinochloa crus-galli). Greenhouse pot studies were conducted to the feasibility of the strain being as a mycoherbicide for barnyard grass control. The results of pathogenicity experiments showed that this strain was highly pathogenic to barnyard grass at the 2 to 3 leaf stages. Strain LD2 provided excellent barnyard grass control when it was applied at the concentration of 1×104, 1×106 conidia ml1. This strain was very safe to rice and the most plant species except wheat, barley and corn. Findings of this study indicated that this strain could be a potential mycoherbicide for barnyard grass control in paddy fields in the future. Keywords: Barnyard grass, Bioherbicides, Curvularia lunata, Echinochloa crus-galli, Mycoherbicide,

Effect of strain and cultural conditions on the production of cytochalasin B by the potential mycoherbicide Pyrenophora semeniperda (Pleosporaceae, Pleosporales)

The seed pathogen Pyrenophora semeniperda has demonstrated potential as a mycoherbicidal biocontrol for eliminating persistent seed banks of annual bromes on western North American rangelands. This pathogen exhibits variation in virulence that is related to mycelial growth rate, but direct laboratory tests of virulence on seeds often have low repeatability. We developed a rapid and sensitive high pressure liquid chromatography method for quantification of the phytotoxin cytochalasin B in complex mixtures in order to evaluate its use in virulence screening. All 10 strains tested produced large quantities of this metabolite in solid wheat seed culture, with production varying over a fourfold range (535–2256 mg kg−1). No cytochalasin B was produced in liquid potato dextrose broth culture, showing that its synthesis is strongly dependent on cultural conditions. In a Bromus tectorum coleoptile bioassay, solid culture extracts showed mild toxicity similar to the cytochalasin B standard at a concentration equivalent to 10−4 M cytochalasin B (72–95% of control), whereas at 10−3 M equivalent, the extracts exhibited significantly higher toxicity (8–18% of control) than the cytochalasin B standard (34% of control). This suggests the possible presence of other phytotoxic metabolites. Cytochalasin B production in solid wheat seed culture exhibited the predicted significant negative correlation with mycelial growth rate on potato dextrose agar, but the correlation was not very strong, possibly because cytochalasin B production and growth rate were measured under different cultural conditions.

Differential Gene Expression for Curvularia eragrostidis Pathogenic Incidence in Crabgrass (Digitaria sanguinalis) Revealed by cDNA-AFLP Analysis

Gene expression profiles of Digitaria sanguinalis infected by Curvularia eragrostidis strain QZ-2000 at two concentrations of conidia and two dew durations were analyzed by cDNA amplified fragment length polymorphisms (cDNA-AFLP). Inoculum strength was more determinant of gene expression than dew duration. A total of 256 primer combinations were used for selective amplification and 1214 transcript-derived fragments (TDFs) were selected for their differential expression. Of these, 518 up-regulated differentially expressed TDFs were identified. Forty-six differential cDNA fragments were chosen to be cloned and 35 of them were successfully cloned and sequenced, of which 25 were homologous to genes of known function according to the GenBank database. Only 6 genes were up-regulated in Curvularia eragrostidis-inoculated D. sanguinalis, with functions involved in signal transduction, energy metabolism, cell growth and development, stress responses, abscisic acid biosynthesis and response. It appears that a few pathways may be important parts of the pathogenic strategy of C. eragrostidis strain QZ-2000 on D. sanguinalis. Our study provides the fundamentals to further study the pathogenic mechanism, screen for optimal C. eragrostidis strains as potential mycoherbicide and apply this product to control D. sanguinalis.

Occurrence and effectiveness of an indigenous strain of Myrothecium roridum Tode: Fries as a bioherbicide for water hyacinth (Eichhornia crassipes) in Nigeria

In a study to isolate fungal pathogens with potential for the biocontrol of water hyacinth (Eichhornia crassipes), some lakes in the Lagos State and its environs, Nigeria, were surveyed for diseased water hyacinth (E. crassipes). The fungi present in the diseased tissue were isolated and identified as: Aspergillus niger, Aspergillus flavus, Penicillium sp., Curvularia pallescens, Fusarium solani and Myrothecium roridum. The pathogenicity of isolates of these fungi on fresh, non-diseased water hyacinth plants was investigated. Myrothecium was the only species capable of inducing disease symptoms. Necrosis was observed on water hyacinth leaves three days post inoculation (DPI) with M. roridum (1 × 106 spores/ml). The leaves and the petioles were withered at the end of day 24, and the disease incidence and disease severity were 100% and 8.67%, respectively. Molecular analysis of the internal transcribed spacer rDNA of the M. roridum isolate from water hyacinth showed >98% homology to authenticated sequences of M. roridum. The isolate, deposited at the International Mycological Institute, UK, as M. roridum Tode: Fries (IMI 394934), possesses the level of virulence needed in a potential mycoherbicide for use in the management of water hyacinth.

Phomentrioloxin, a Fungal Phytotoxin with Potential Herbicidal Activity, and its Derivatives: A Structure–Activity Relationship Study

Phomentrioloxin is a phytotoxic geranylcyclohexenetriol produced in liquid culture by Phomopsis sp. (teleomorph: Diaporthe gulyae), a potential mycoherbicide proposed for the control of the annual weed Carthamus lanatus. In this study, seven derivatives obtained by chemical modifications of the toxin were assayed for phytotoxic, antimicrobial, and zootoxic activities, and the structure-activity relationships were examined. Each compound was tested on nonhost weedy and agrarian plants, fungi, Gram+ and Gram- bacteria, and on brine shrimp larvae. The results provide insights into an investigation of the structural requirements for activity. The hydroxy groups at C-2 and C-4 appeared to be important features for the phytotoxicity, as well as an unchanged cyclohexentriol ring. A role seemed also to be played by the unsaturations of the geranyl side chain. These findings could be useful for understanding the mechanisms of action of new natural products, for identifying the active sites, and possibly in devising new herbicides of natural origin.