Fusarium Proliferatum Strain Research Articles

Exploring the efficacy of endophytic Diaporthe caatingaensis as a biocontrol agent targeting Fusarium strains afflicting coffee plants in Saudi Arabia

BackgroundThe coffee plant is a strategic crop in Saudi Arabia that makes a substantial contribution to the country’s economy. Therefore, it is crucial to continuously monitor and control the fungal phytopathogens that affect coffee plants in order to minimize crop losses and ensure sustainable cultivation. This is the first surveillance report of Fusarium phytopathogens associated with coffee plants in Saudi Arabia. Moreover, the antagonistic efficiency of the endophytic fungus, Diaporthe caatingaensis, was evaluated against the isolated Fusarium phytopathogens. MethodsThe isolated strains were preliminary identified using cultural and microscopic methods and the identification was confirmed using internal transcribed spacer (ITS) sequencing technique. The detached leaf assay was conducted to assess the disease severity of Fusarium phytopathogens against detached coffee leaves. Moreover, dual culture assay was utilized to assess the antagonistic activity of D. caatingaensis. Results and conclusionFusarium oxysporum was found to be the most frequent isolated strain followed by F. solani, F. proliferatum and F. verticillioides strains. Fusarium proliferatum strain was found to be the most severe strain whereas F. solani strain showed the lowest disease severity. On the other hand, propiconazole fungicide was tested for its efficiency against Fusarium pathogens using food poisoning technique, showing that F. oxysporum strain 1 of accession number OP955665 was the most sensitive strain. However, F. proliferatum, F. oxysporum st. 2 (OP959851) and F. solani strains showed no significant response when the propiconazole concentration increase from 150 to 200 ppm. Scanning electron microscope proved the potent antagonistic activity of D. caatingaensis against F. proliferatum and F. oxysporum OP959874 strains through mycoparasitic modes of action as coiling, appressorium formation resulting in complete lysis of fungal mycelium. Accordingly, the current investigation provides the first surveillance data about Fusarium strains associated with coffee plants and also the utilization of D. caatingaensis as a potential biocontrol agent for effective management of Fusarium phytopathogens, avoiding the incidence of fungal resistance to fungicides and the harmful effects of commercial fungicides for sustainable cultivation of coffee in Saudi Arabia.

In vitro production of gibberellic acid and fusaric acid by Fusarium spp. and their role in bakanae disease development

Gibberellic acid (GA3) and fusaric acid (FA) are directly correlated with the symptom development of bakanae disease in rice plants. The role of GA3 and FA, produced in vitro by several Fusarium species associated with bakanae disease, was studied to understand the disease’s etiology and its impact on symptom development. In total, 121 Fusarium strains were obtained from bakanae-infected rice plants collected from various rice cultivation regions in Bangladesh. Finally, 18 highly virulent Fusarium strains were selected based on virulence assay and further evaluated for GA3 and FA production through ultra-performance liquid chromatography analysis. Among the Fusarium strains, Fusarium fujikuroi strains produced a high amount of GA3 and a low amount of FA. In contrast, Fusarium proliferatum and Fusarium verticillioides strains produced a high amount of FA and a low amount of GA3. In exception, the Fusarium strain BD117R of F. fujikuroi produced no GA3 but a high amount of FA. Interestingly, Fusarium commune produced only FA in high concentration. In bakanae disease development, GA3 production was positively related to elongation symptoms whereas FA contributes to stunting symptoms. This is the first record of the production of GA3 and FA by Fusarium species causing bakanae disease of rice in Bangladesh.

Two novel aliphatic unsaturated alcohols isolated from a pathogenic fungus Fusarium proliferatum

Phytopathogenic fungi have attracted great attention as a promising source for new drug discovery. In the progress of our ongoing study for bioactive natural products from an in-house phytopathogenic fungi library, a pathogenic fungus, Fusarium proliferatum strain 13294 (FP13294), was selected for chemical investigation. Two novel aliphatic unsaturated alcohols named fusariumnols A and B (1 and 2), together with one previously characterized sesquiterpenoid lignoren (3) were identified. Structures of 1–3 were assigned by mass spectrometry and NMR spectroscopy. Their bioactivities were assessed against Staphylococcus epidermidis, S. aureus, and Methicillin-resistant S. aureus (MRSA). Compounds 1 and 2 exhibited weak antibacterial activity against S. epidermidis (MIC = 100 μM).

Phylogeny and mycotoxin profile of Fusarium species isolated from sugarcane in Southern Iran

Sugarcane is an important crop in Southern Iran for agri-food, energy, and pharmaceutical industries. Among the pathogens that colonize sugarcane, mycotoxigenic Fusarium species are reason of serious concern for both their pathogenicity on plants and ability to produce harmful mycotoxins to humans and animals. We studied 104 Fusarium strains, selected within a wider Fusarium set isolated from sugarcane in Southern Iran, for molecular identification, phylogeny and mycotoxin analyses. Most of Fusarium strains belonged to Fusarium fujikuroi Species Complex (FFSC) and identified mainly as F. proliferatum, at minor extent as F. sacchari, and rarely as F. thapsinum, and F. verticillioides. Moreover, 14 strains identified as FFSC could not be assigned to any known species, although they were phylogenetically closely related to F. andiyazi, likely representing a new phylogenetic species. A subset of FFSC strains were analyzed for in vitro production of fumonisins (FBs), beauvericin (BEA), and enniatins (ENNs). Fusarium proliferatum strains produced FBs at high amount, and, at a lesser extent, BEA, and ENNs; F.sacchari produced only BEA and B ENNs at very low level; Fusarium sp. strains produced only B ENNs. The paper provides new insights on the genetic diversity of Fusarium species and their mycotoxin profile occurring on sugarcane in Iran.

In Vitro Evaluation of the Inhibitory Activity of Different Selenium Chemical Forms on the Growth of a Fusarium proliferatum Strain Isolated from Rice Seedlings.

In this study, the in vitro effects of different Se concentrations (5, 10, 15, 20, and 100 mg kg−1) from different Se forms (sodium selenite, sodium selenate, selenomethionine, and selenocystine) on the development of a Fusarium proliferatum strain isolated from rice were investigated. A concentration-dependent effect was detected. Se reduced fungal growth starting from 10 mg kg−1 and increasing the concentration (15, 20, and 100 mg kg−1) enhanced the inhibitory effect. Se bioactivity was also chemical form dependent. Selenocystine was found to be the most effective at the lowest concentration (5 mg kg−1). Complete growth inhibition was observed at 20 mg kg−1 of Se from selenite, selenomethionine, and selenocystine. Se speciation analysis revealed that fungus was able to change the Se speciation when the lowest Se concentration was applied. Scanning Electron Microscopy showed an alteration of the fungal morphology induced by Se. Considering that the inorganic forms have a higher solubility in water and are cheaper than organic forms, 20 mg kg−1 of Se from selenite can be suggested as the best combination suitable to inhibit F. proliferatum strain. The addition of low concentrations of Se from selenite to conventional fungicides may be a promising alternative approach for the control of Fusarium species.

Phylogeny and Mycotoxin Profile of Pathogenic Fusarium Species Isolated from Sudden Decline Syndrome and Leaf Wilt Symptoms on Date Palms (Phoenix dactylifera) in Tunisia.

In 2017–2018, extensive symptoms of sudden decline and fruit rot were observed on date palms in southern Tunisia. Samples of diseased plants were randomly collected in six localities. Based on morphological identification, Fusarium was the most frequent fungal genus detected. A sequencing of translation elongation factor, calmodulin, and second largest subunit of RNA polymerase II genes was used to identify 63 representative Fusarium strains at species level and investigate their phylogenetic relationships. The main species detected was Fusarium proliferatum, and at a much lesser extent, Fusarium brachygibbosum, Fusarium caatingaense, Fusarium clavum, Fusarium incarnatum, and Fusarium solani. Pathogenicity on the Deglet Nour variety plantlets and the capability to produce mycotoxins were also assessed. All Fusarium species were pathogenic complying Koch’s postulates. Fusarium proliferatum strains produced mainly fumonisins (FBs), beauvericin (BEA), and, to a lesser extent, enniatins (ENNs) and moniliformin (MON). All F. brachygibbosum strains produced low levels of BEA, diacetoxyscirpenol, and neosolaniol; two strains produced also T-2 toxin, and a single strain produced HT-2 toxin. Fusarium caatingaense, F. clavum, F. incarnatum produced only BEA. Fusarium solani strains produced MON, BEA, and ENNs. This work reports for the first time a comprehensive multidisciplinary study of Fusarium species on date palms, concerning both phytopathological and food safety issues.

Antagonistic activity of Trichoderma harzianum and Trichoderma viride strains against some fusarial pathogens causing stalk rot disease of maize, in vitro

ObjectivesA high incidence of stalk rot disease of maize causes huge economic losses as well as deleterious effects on the environment and human health resulting from fungicide use. Against this background, the current study was established to evaluate the antagonistic efficacy of Trichoderma viride and Trichoderma harzianum strains against Fusarium proliferatum and Fusarium verticillioides strains, the most common causative agents of stalk rot disease of maize. MethodsDual culture assay was performed to determine the antagonistic efficacy of Trichoderma strains against some fusarial pathogens of maize. Mycoparasitic relationships of the antagonistic fungal strains against fungal pathogens were investigated using a slide culture technique. Furthermore, a food poisoning technique was performed to detect the antimycotic efficacy of Trichoderma culture filtrates against fusarial pathogens of maize. Antifungal activity of organic solvent extracts of T. harzianum and T. viride was evaluated using the disc diffusion method. GC–MS analysis was used to detect the active components of these extracts. Results and conclusionTrichoderma viride showed antagonistic activity against F. proliferatum and F. verticillioides with mycelial inhibition rates of 80.17% and 70.46%, while T. harzianum exhibited rates of 68.38% and 60.64%, respectively. The culture filtrates of T. viride and T. harzianum strains exhibited antifungal activity against F. verticillioides strain with suppressive rates of 56.7% and 32.2%, while the mycelial inhibition rates against F. proliferatum strain were 44.09% and 23.50%, respectively. Mycoparasitic action of T. harzianum strain against fusarial strains was detected, while no mycoparasitism was observed between T. viride and fungal pathogens. The fungicidal concentration of carbendazim fungicide against F. proliferatum was 2.00 ppm, while F. verticillioides strain exhibited resistance to carbendazim fungicide. Moreover, the acetonic extracts of T. viride and T. harzianum strains exerted the highest antifungal potency against F. proliferatum strain, recording minimum inhibitory concentrations of 0.25 and 0.50 mg/ml, respectively. The main bioactive constituents of the acetonic extracts of T. viride and T. harzianum strains were palmitic acid (22.87%) and acetic acid (21.36%), respectively. In conclusion, the antagonistic strains could be a potential source of novel biological fungicides, especially against carbendazim-resistant F. verticillioides strain, avoiding side effects of chemical fungicides.

Stolon rot and vascular wilt diseases of Mentha arvensis L. caused by Fusarium proliferatum strain MaKf1 in Uttar Pradesh, India

Mentha arvensis L. is a perennial herb and one of the main essential (menthol) oil producing crops cultivated worldwide. Mint oil is used as a stomachic, carminative, anaesthetic, disinfectant agent and has an indispensable role in pharmaceutical and aromatic industries. The most promising varieties of M. arvensis L. such as Himalaya, Kranti, and Kosi have been developed by CSIR-CIMAP and are under cultivation in various parts of India. In this study, different varieties of M. arvensis, cultivated for the production of planting material/sucker, were screened for soil-borne fungal infections. Various districts of Uttar Pradesh were surveyed, and vascular wilt disease incidences were found between 3-15 % in the year 2018. The districts Barabanki and Lucknow recorded a high percent (13- 15 %) of disease incidence on M. arvensis var. Kosi. Moderate incidence, 7% and 11%, of vascular wilt disease were observed on M. arvensis var. Himalaya in Barabanki and Lucknow, respectively. In comparison with other varieties, very few incidences (3-5%) were observed on Kranti variety at Sitapur, Raebareli and Lucknow districts. The vascular wilt causing pathogen (MaKf1) was isolated and characterized on the basis of colony morphology, microscopic examination of spores and molecular identification targeting the ITS region of the rDNA gene cluster and was identified as Fusarium proliferatum.

Morphgenomics based identification of Fusarium proliferatum causing Syagrus romanzoffiana wilt and exploitation of antifungal potential of Trichoderma species against this pathogen

Chlorosis on rachis followed by plant wilting of Syagrus romanzoffiana (Queen Palm) was observed during the survey of commercial ornamental plant growing nurseries and landscapes of sixteen locations from five districts of Punjab province. About 25% plants were found affected by the disease. Symptomatic root and leaf tissues were sliced, surface sterilized, transferred on PDA medium and incubated at 26 °C. Frequently whitish to purple fungal colony pigmentation was observed with club shaped microconidia and slender shaped macroconidia. Based on morpho-cultural characters the fungal isolate was identified as Fusarium proliferatum. The internal transcribed spacer (ITS) region and translation elongation factor 1-α (TEF1-α) region were sequenced for molecular characterization. Phylogenetic trees were constructed based on the sequences of both investigated loci to explore the place of investigated fungal isolate FMB-F-P-QP in evolutionary hierarchy of Fusarium species. In phylograms, this isolate was clearly nested with the strains of Fusarium proliferatum. The morphogenomic studies proved this isolate as F. proliferatum. The characterized culture deposited in FMB-Culture Collection-UAF (FMB 0133) and generated sequences of both loci were submitted to GenBank (accession No. MH557215 for ITS; accession No. MH568689 for TEF1-α). Koch’s postulates were accomplished by applying F. proliferatum and yellowing of leaves started three weeks post inoculation while chlorosis on one side of rachis or complete wilting appeared after six months. This is the first reported study of Syagrus romanzoffiana wilt caused by F. proliferatum in Pakistan. Four strains of three Trichoderma species (one strain of T. harzianum, two strains of T. atroviridae and one strain of T. viridae) were evaluated for their antagonistic potential against F. proliferatum. T. harzianum showed higher antifungal potential 85%, as compared to the other tested strains.

Biodegradation of Allethrin by a Novel Fungus Fusarium proliferatum Strain CF2, Isolated from Contaminated Soils.

Continuous use of allethrin has resulted in heavy environmental contamination and has raised public concern about its impact on human health, yet little is known about the kinetics and microbial degradation of this pesticide. This study reported the degradation kinetics in a novel fungal strain, Fusarium proliferatum CF2, isolated from contaminated agricultural fields. Strain CF2 utilized 50 mg·L−1 of allethrin as the sole carbon source for growth in minimal salt medium and tolerated high concentrations of allethrin of up to 1000 mg·L−1. The optimum degradation conditions for strain CF2 were determined to be a temperature of 26 °C and pH 6.0 using response surface methodology. Under optimum conditions, strain CF2 completely degraded allethrin within 144 hours. The degradation kinetics of allethrin followed first order reaction kinetics. Kinetics analysis showed that its half-life was substantially reduced by 507.1 hours, as compared to the uninoculated control. This study provides new insights into the microbial degradation of allethrin with fungal F. proliferatum CF2.

In vitro Antifungal Activity of Olive (Olea europaea) Leaf Extracts Loaded in Chitosan Nanoparticles.

Olive leaf extract is characterized by a high content of phenols and flavonoids (oleuropein, luteolin, and their derivatives). These compounds are defined as secondary metabolites and exert such as anti-inflammatory, antioxidant, and antimicrobial activities. We investigated the in vitro antifungal activity of two olive leaf extracts (named EF1 and EF2) against a Fusarium proliferatum (AACC0215) strain that causes diseases to many economically important plants and synthesizing diverse mycotoxins. In this work, we aimed to identify the most appropriate concentration between the tested two olive leaf extracts to develop a safe, stable and efficient drug delivery system. Qualitative and quantitative analyses of the two olive leaf extracts by (HPLC) were performed. Furthermore, we also evaluated the antifungal effects of the two leaf extracts when encapsulated in chitosan-tripolyphosphate nanoparticles. The major compound in both EF1 and EF2 was oleuropein, with 336 and 603 mg/g, respectively, however, high concentrations of flavonoid were also present. EF1 and EF2 showed a concentration depended effect on F. proliferatum (AACC0215) viability. Our results showed a great efficacy of EF1/nanoparticles at the higher concentration tested (12X) against the target species. In this case, we observed an inhibition rate to both germination and growth of 87.96 and 58.13%, respectively. We suggest that EF1 olive leaf extracts, as free or encapsulated in chitosan-tripolyphosphate nanoparticles, could be used as fungicides to control plant diseases. Finally, future application of these findings may allow to reduce the dosage of fungicides potentially harmful to human health.

Coconut malformation: An emerging disease caused by Fusarium proliferatum in southern Iran

AbstractSymptoms of vegetative malformation were observed on coconut palms (Cocos nucifera L.) in the Qeshm Island, Bandar Abbas and Minab, in Hormozgan province, southern Iran. The symptoms included misshapen and dwarfed leaves with shortened, thickened and tightened leaflets in wavy and zigzag form. The aim of this study was to identify the causal pathogen of coconut palm malformation and complete Koch's postulates for putative pathogen. Small pieces of surface‐disinfested malformed vegetative tissues of coconut palms were cultured on potato dextrose agar (PDA) medium. Fusarium isolates were permanently obtained from the symptomatic tissues. Sequence data from the internal transcribed spacer region (ITS1–5.8S‐ITS2) and translation elongation factor 1 alpha (TEF‐1α) gene were used for molecular identification of the isolates. BLAST search of the sequences showed 99%–100% identity to several Fusarium proliferatum strains in the GenBank, FUSARIUM‐ID and Fusarium MLST databases. A phylogeny inferred using individual sequence data from ITS region and TEF‐1α gene placed our isolates together with the other F. proliferatum sequences retrieved from the GenBank. Pathogenicity tests were carried out using one‐year‐old healthy coconut palm seedlings and conidial suspensions (106 conidia/ml) of the F. proliferatum isolates. The first visible symptoms appeared on newly produced leaves of the inoculated seedlings during the 16th week after inoculation, wherease no disease symptoms were observed on the control plants until the end of the experiment. Reisolation from symptomatic tissues of the inoculated seedlings yielded isolates of F. proliferatum with morphological and molecular characteristics identical to those of the isolates used for inoculations. This is the first report of coconut palm malformation caused by F. proliferatum worldwide.

The Relationship Analysis on Corn Stalk Rot and Ear Rot According to Fusarium Species and Fumonisin Contamination in Kernels.

Fusarium diseases, including corn root rot, sheath rot, stalk rot, and ear rot are frequently occurring in maize producing areas of China. Fusarium stalk rot and ear rot are the most serious diseases and often occur at the same time, but it is unclear whether there is a correlation between Fusarium composition and disease occurrence. This study was conducted to clarify the relationship between the two diseases. A total of 49 corn stalk rot samples were collected from 15 regions of eight provinces in China from 2016 to 2018. The pathogens were isolated and identified separately from stalks, ear stems, and kernels. The contents of the fumonisins (FB1 and FB2) were detected in kernels. The results showed that the main Fusarium species were found in corn kernels, ear stems and stalks at the same time. The results showed that 1201 strains of Fusarium verticillioides, 668 strains of Fusarium oxysporum, 574 strains of Fusarium graminearum species complex (FGSC), 318 strains of Fusarium equiseti, 95 strains of Fusarium proliferatum, and 40 strains of Fusarium subglutinans were isolated from 1470 corn kernels, 245 ear stems, and 1225 stalks randomly selected from 49 samples. The contamination rate of fumonisins in the 49 samples was 57.1% with an average content of 1.9 μg/g, of which four samples exhibited higher levels as set by the European Commission (4.0 μg/g). These results provide a certain association between stalk rot and ear rot and lay a foundation to study the relationships among Fusarium maize diseases.

Influence of water activity and temperature on growth and fumonisin production by Fusarium proliferatum strains on irradiated wheat grains

Wheat is the most important cereal consumed by the Argentine population. In previous studies performed in durum and common wheat grains in this country it has been observed fumonisin contamination as well as high incidence of Fusarium proliferatum. Fumonisins are toxic fungal metabolites, and consumption of fumonisin-contaminated maize has been epidemiologically associated with oesophageal cancer and neural tube defects in some human populations. Using irradiated wheat-grains, the effects of abiotic factors, temperature (15, 25, and 30°C) and water activity (aW; 0.995, 0.98, 0.96, 0.94, 0.92, and 0.88), on mycelial growth and fumonisin biosynthesis were compared for three F. proliferatum strains isolated from wheat grains in Argentina. Although all isolates showed similar profiles of growth, the fumonisin production profiles were slightly different. Maximum growth rates were obtained at the highest aW (0.995) and 25°C, with growth decreasing as the aW of the medium was reduced. Maximum amounts of total fumonisins (FB1, FB2 and FB3) were produced at 0.995 aW and 15°C for 2 strains, and at 25°C and 0.995 aW for the third one. Fumonisins concentrations varied considerably depending on the aW and temperature interactions assayed. Studied strains showed different fumonisin production profiles. Two-dimensional profiles of aW by temperature interactions were developed from these data to identify areas where conditions indicate a significant risk of fumonisins accumulation on wheat. As a result, temperature and aW conditions that resulted in fumonisins production are those found during wheat grain development (especially milk and dough stages) in the field. This is the first study made using irradiated wheat grains and provides useful baseline data on conditions representing a low or a high risk for fumonisins contamination of wheat grains which is of concern because this cereal is destined mainly for human consumption.

Abiotic conditions leading to FUM gene expression and fumonisin accumulation by Fusarium proliferatum strains grown on a wheat-based substrate

Fusarium proliferatum produces fumonisins B not only on maize but also on diverse crops including wheat. Using a wheat-based medium, the effects of abiotic factors, temperature and water activity (aW), on growth, fumonisin biosynthesis, and expression of FUM genes were compared for three F. proliferatum strains isolated from durum wheat in Argentina. Although all isolates showed similar profiles of growth, the fumonisin production profiles were slightly different. Regarding FUM gene transcriptional control, both FUM8 and FUM19 expression showed similar behavior in all tested conditions. For both genes, expression at 25°C correlated with fumonisin production, regardless of the aw conditions. However, at 15°C, these two genes were as highly expressed as at 25°C although the amounts of toxin were very weak, suggesting that the kinetics of fumonisin production was slowed at 15°C. This study provides useful baseline data on conditions representing a low or a high risk for contamination of wheat kernels with fumonisins.

Fusarium proliferatum strains change fumonisin biosynthesis and accumulation when exposed to host plant extracts

Fumonisin concentrations in mycelia and media were studied in liquid Fusarium proliferatum cultures supplemented with host plant extracts. Furthermore, the kinetics of fumonisin accumulation in media and mycelia collected before and after extract addition was analysed as well as the changes in the expression of the FUM1 gene. Fumonisin content in culture media increased in almost all F. proliferatum strains shortly after plant extracts were added. The asparagus extract induced the highest FB level increase and the garlic extract was the second most effective inducer. Fumonisin level decreased constantly until 14th day of culturing, though for some strains also at day 8th an elevated FB level was observed. Pineapple extract induced the highest increase of fum1 transcript levels as well as fumonisin synthesis in many strains, and the peas extract inhibited fungal growth and fumonisin biosynthesis. Moreover, fumonisins were accumulated in mycelia of studied strains and in the respective media.

Fusarium proliferatum causing head blight on oat in Hungary

A Fusarium proliferatum strain isolated from diseased oat seeds was shown to be pathogenic on two oat cultivars. During the pathogenicity tests the fungus was re-isolated from the seeds, glumes and stem pieces of the inoculated oat plants. This is the first reported occurrence of F. proliferatum, a fumonisin producing species, as a causal agent of Fusarium head blight of oat in Hungary, and indeed Europe.

Evaluation of antibacterial and antifungal properties of 9-oxo-10,11-dehydroageraphorone extracted from Eupatorium adenophorum

9-Oxo-10,11-dehydroageraphorone (ODA) is a cadinene sesquiterpene isolated from Eupatorium adenophorum. The antimicrobial activity of ODA was tested in vitro against four fungal strains and four bacterial strains. The fungitoxicity of ODA was evaluated by percentage radial growth inhibition using the poisoned food technique. ODA inhibited Fusarium oxysporum more than the other tested strains, giving EC50 values of 0.325 mg ml−1 at 48 h and 0.365 mg ml−1 at 96 h. Tests also revealed that ODA inhibits the germination of Fusarium oxysporum spores, reducing germination by 97 % at 0.5 mg ml−1 concentration. The minimum inhibitory concentrations (MIC) of ODA against four tested strains of Ralstonia solanacearum ranged from 0.25 to 1 mg ml−1 using a micro-well dilution method. In addition, our scanning electron microscopy study revealed previously unreported, pronounced effects of ODA on Fusarium oxysporum, Bipolaris sorokiniana, Fusarium proliferatum and Alternaria tenuissima, including marked shrinkage in the mycelia of all tested strains, swelling at the ends of Bipolaris sorokiniana mycelia and inhibition of spore production in the strains of Bipolaris sorokiniana and Fusarium proliferatum, providing firm evidence of the toxicity of ODA to these pathogenic fungi.

Natural occurrence of Fusarium proliferatum on chestnut in Italy and its potential entomopathogenicity against the Asian chestnut gall wasp Dryocosmus kuriphilus

The Asian chestnut gall wasp Dryocosmus kuriphilus (DK) is one of the most important pests of chestnut trees worldwide, and sustainable control measures are urgently required for its control. In this study, the recurring mycoflora associated with DK galls in some Italian chestnut orchards was identified, and two Fusarium proliferatum strains (I3 and I4) were tested for their entomopathogenicity toward DK and their pathogenicity to chestnut in order to evaluate their potential as biocontrol agents. The two F. proliferatum strains, both isolated from the inside of DK galls and often covering dead bodies of larvae, pupae, and adults, caused a natural insect infection of about 4 % and resulted to be non-pathogenic to chestnut plants, while they induced 33 and 97 % of larvae mortality when applied in laboratory experiments to intact DK fresh or sectioned galls, respectively. Both strains infected maize seedlings, used as non-target hosts, and produced fumonisins in vitro. The efficacy in controlling DK in the galls, the absence of pathogenicity to chestnut, and the lower mycotoxin production indicated strain I3 as a promising biocontrol agent of the considered pest.

Two-dimensional environmental profiles of growth and fumonisin production by Fusarium proliferatum on a wheat-based substrate

The effect of water activity (aW; 0.995, 0.99, 0.98, 0.96, 0.94, 0.92, and 0.90), temperature (15, 25, and 30°C), incubation time (7, 14, 21 and 28days), and their interactions on mycelial growth and fumonisin production on wheat-based medium by three Fusarium proliferatum strains isolated from wheat in Argentina was evaluated. Maximum growth rates were obtained at the highest aW (0.995) and 30°C, with growth decreasing as the aW of the medium was reduced. Maximum amounts of total fumonisins (FB1, FB2 and FB3) were produced at 0.99 aW and 25°C after 21 and 28days of incubation for 2 strains, and at 15°C and 0.98 aW after 28days of incubation for the third strain. The fumonisin concentrations varied considerably depending on the aW and temperature interactions assayed. The studied strains had different fumonisin production profiles. F. proliferatum ITEM 15661 and ITEM 15664 produced FB1 and FB2 whereas F. proliferatum ITEM 15654 was able to produce FB1, FB2 and FB3. Interestingly, fumonisin production profiles for each particular strain were related to incubation temperatures. Fumonisins were produced from 15 to 30°C and at aW values of 0.92 to 0.995 after 21 to 28days of incubation. However at 7 and 14days of incubation small amounts of fumonisin were produced at aW lower than 0.94. Two-dimensional profiles of aW by temperature interactions were developed from these data to identify areas where conditions indicate a significant risk from fumonisin accumulation on wheat. Temperature and aW conditions that resulted in fumonisin production are those found during wheat grain development (especially milk and dough stages) in the field. This study provides useful base line data on conditions representing a high and a low risk for contamination of wheat by fumonisins which is becoming of greater concern because this cereal is destined mainly for human consumption.