Fumigation using 1,3-dichloropropene manages Meloidogyne enterolobii in sweetpotato more effectively than fluorinated nematicides

Meloidogyne enterolobii is an emerging global threat and damaging to sweetpotato (Ipomoea batatas) production in the Southeast United States. Nematicide application is one of the few management strategies currently available against this nematode and field testing is urgently needed. The objective of this study was to assess common nematicides for management of M. enterolobii and non-target effects on free-living nematodes in sweetpotato field production. Treatments were (i) untreated control, (ii) fumigation using 1,3-dichloropropene, or at-transplant drench of fluorinated nematicides (iii) fluazaindolizine, (iv) fluopyram, or (v, vi) fluensulfone at 2 or 4 kg a.i./ha. In 2022 a field trial was conducted under severe M. enterolobii pressure and repeated in 2023 in the same location without treatment re-randomization. Fumigation using 1,3-dichloropropene (1,3-D) was the only consistently effective nematicide at improving marketable yield relative to control and also consistently reduced most storage root galling measurements and midseason Meloidogyne soil abundances. Fluensulfone at 4 kg a.i./ha consistently improved total yield, but not marketable yield whereas fluensulfone at 2 kg a.i./ha, fluazaindolizine, and fluopyram did not improve yield. Each fluorinated nematicide treatment reduced at least one nematode symptom or nematode soil abundances relative to control, but none provided consistent benefits across years. Even with 1,3-D fumigation, yield was poor, and none of the nematicide treatments provided a significant return on investment relative to forgoing nematicide application. There were minimal effects on free-living nematodes. In summary, 1,3-D is an effective nematicide for M. enterolobii management, but additional management will be needed under severe M. enterolobii pressure.

Different Size Formulations of Fluopyram: Preparation, Antifungal Activity, and Accumulation in the Fungal Pathogen Botrytis cinerea

Nanotechnology is revolutionizing the efficient production and sustainable development of modern agriculture. Understanding the pesticide activity of both nano- and conventional methods is useful for developing new pesticide formulations. In this study, three solid fluopyram formulations with varying particle sizes were developed, and the mechanisms underlying the difference in the antifungal activity among these formulations were investigated. Wet media milling combined with freeze drying was used to prepare fluopyram nanoparticles (FLU-NS) and a micron-sized solid formulation (FLU-MS), and a jet grinding mill was employed to fabricate fluopyram wettable powder (FLU-WP). The mean particle sizes of FLU-NS, FLU-MS, and FLU-WP were 366.8 nm, 2.99 μm, and 10.16 μm, respectively. Notably, FLU-NS displayed a toxicity index against Botrytis cinerea (gray mold) that was approximately double those of FLU-MS and FLU-WP. Similar trends were noticed in the antifungal tests on Alternaria solani. The uptake of FLU-NS by B. cinerea was approximately twice that of FLU-MS and FLU-WP, indicating that fluopyram nanoparticles are more easily taken up by the pathogen (B. cinerea), and display better bioactivity than the larger fluopyram particles. Therefore, the nanosizing of pesticides appears to be a viable strategy to enhance efficiency without increasing the amount of pesticide used.

Influence of Integrated Management Strategies on Soybean Sudden Death Syndrome (SDS) Root Infection, Foliar Symptoms, Yield and Net Returns

Three soybean field trials were conducted in Indiana to evaluate the integration of seed treatment, cultivar selection, and seeding rate on sudden death syndrome (SDS) root rot, pathogen load in the root, foliar symptoms, yield, and net return. Two soybean cultivars, one moderately resistant and one susceptible to SDS, were planted at three seeding rates (272,277 seeds/ha, 346,535 seeds/ha, and 420,792 seeds/ha). Fluopyram and pydiflumetofen seed treatments were applied to both cultivars, and the cultivars were then compared with a control. Low foliar SDS disease pressure was observed in our study. Seed treatment with either fluopyram or pydiflumetofen and the use of a moderately resistant cultivar decreased Fusarium virguliforme DNA concentration in the root relative to the control and the use of a susceptible cultivar. Fluopyram significantly reduced visual root rot severity by 8.8% and increased yield by 105 kg/ha relative to the control but was not different from pydiflumetofen. However, pydiflumetofen performed the same as the control with respect to root rot severity and yield. Findings from this study support the use of a seed treatment to protect roots from infection and the use of a moderately resistant cultivar planted at a seeding rate of 346,535 seeds/ha to protect yield and maximize net returns when a field has low foliar SDS pressure.

Spatiotemporal dynamics of fluopyram trunk-injection in Pinus massoniana and its efficacy against pine wilt disease

BACKGROUND

Pine wilt disease (PWD) is a destructive disease of pine trees caused by the pinewood nematode, Bursaphelenchus xylophilus. Fluopyram, a novel nematicide compound with systemic activity, is a prospective trunk-injection agent against pinewood nematodes. The disadvantage of current trunk-injection agents is that they were not evenly distributed in tree tissues and were poor in the persistence of effect and efficiency. Therefore, we investigated the spatiotemporal transport pattern and residue behavior of fluopyram following its injection into the trunk of Pinus massoniana.

RESULTS

Fluopyram transport in the trunk occurred through radial diffusion and vertical uptake within 1 week of the injection, reaching all tissues of P. massoniana, including apical branches and needles. Three years after the field test, the infection of PWD declined substantially with treatment using the fluopyram trunk-injection agent, which demonstrated 100% efficacy in both the mild and moderate occurrence areas, and 71.1% efficacy in the severe occurrence area. Fluopyram as trunk-injection agent exerted substantial control over PWD, with its efficacy being influenced by the infection time of PWD. The half-life of 10% fluopyram in treated pine trees was 346.6 days with 3-year persistence.

CONCLUSION

The advantages of overall distribution and long persistence of fluopyram in the tree after injection help explain its evident efficacy against PWN. Overall, fluopyram trunk-injection has potential to prevent PWD. © 2023 Society of Chemical Industry.

Modification of the existing maximum residue levels and setting of import tolerances for fluopyram in various crops

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant Bayer AG Crop Science Division submitted a request to the competent national authority in Italy to modify the existing maximum residue level (MRL) for the active substance fluopyram in kiwi. Additionally, the applicants Bayer Crop Science SA and Bayer SAS Crop Science Division submitted two applications to the competent national authority in Germany to modify the MRLs for fluopyram in certain stem vegetables, seed spices, apples and soyabeans based on intended EU uses as well as to lower the existing EU MRL in pome fruits and to raise the existing EU MRL in peanuts on the basis of authorised use of fluopyram in the USA. The data submitted in support of the request were found to be sufficient to derive MRL proposals for all the crops under assessment except for palm hearts and bamboo shoots. Adequate analytical methods for enforcement are available to control the residues of fluopyram in commodities under consideration at the validated limit of quantification (LOQ) of 0.01 mg/kg. Based on the risk assessment results, EFSA concluded that the short-term intake of residues resulting from the use of fluopyram according to the reported agricultural practices is unlikely to present a risk to consumer health. A long-term consumer intake concern is identified if the current MRL of 0.8 mg/kg in pome fruits is maintained and new MRLs for other commodities under consideration are supported, with apples being the highest contributing commodity to the diet for which exposure exceedances were noted. The chronic risk for consumers is unlikely if a lower MRL of 0.6 mg/kg in pome fruits proposed by the applicant is considered. Further risk manager considerations are required.

Uptake of Fungicide Fluopyram from Soil by Scallions during Greenhouse Cultivation

Unintentional pesticide contamination in rotational crops, often caused by soil contamination from pesticide use in the preceding crops, is a major concern in a positive list system. The residue and dissipation pattern of fluopyram in soil and scallions were investigated to evaluate the uptake of fluopyram from the soil by scallions. In addition, the management concentration in soil (MC_soil) was calculated based on bioconcentration factors (BCFs) and the maximum residue limit (0.2 mg/kg) in leaf-and-stem vegetables. In a field experiment, plots in two different trials, A and B, were treated with 0.06 g fluopyram/m² and maintained for 30 days according to OECD guidelines. Scallion seedlings were cultivated for 48 days. Soil samples were taken at three different time points: DAP (Days after planting) 0, 34, and 48. Scallion samples were collected at five different time points: DAP 20, 27, 34, 41, and 48. The initial amounts of fluopyram in soil at DAP 0 were 0.94 ± 0.03 and 0.96 ± 0.04 mg/kg in trials A and B, respectively. The half-life of fluopyram in the soil was 87-231 days. Fluopyram uptake by the roots increased over time, but fluopyram residue in the scallions decreased due to the dilution effect caused by an increase in plant weight. The residues in the scallions at DAP 48 were 0.22 ± 0.01 and 0.15 ± 0.01 mg/kg in trials A and B, respectively. The BCFs of scallions for fluopyram were 0.21-0.24 (trial A) and 0.14-0.18 (trial B). The MC_soil was proposed as 0.8 mg/kg, and may be utilized as a safe management guideline for precautionary practices to cultivate safe rotational crops.

Field and Greenhouse Assessment of Seed Treatment Fungicides for Management of Sudden Death Syndrome and Yield Response of Soybean

Seed treatments for the management of sudden death syndrome (SDS) caused by Fusarium virguliforme are available in the United States and Canada; however, side-by-side comparisons of these seed treatments are lacking. Sixteen field experiments were established in Illinois, Indiana, Iowa, Michigan, and Wisconsin, United States, and Ontario, Canada, in 2019 and 2020 to evaluate seed treatment combinations. Treatments included a nontreated check (NTC), fungicide and insecticide base seed treatments (base), fluopyram, base + fluopyram, base + saponin extracts from Chenopodium quinoa, base + fluopyram + heat-killed Burkholderia rinojenses, base + pydiflumetofen, base + thiabendazole + heat-killed B. rinojenses, and base + thiabendazole + C. quinoa extracts + heat-killed B. rinojenses. Treatments were tested on SDS moderately resistant and susceptible soybean cultivars at each location. Overall, NTC and base had the most root rot, most foliar disease index (FDX), and lowest yield. Base + fluopyram and base + pydiflumetofen were most effective for managing SDS. Moderately resistant cultivars reduced FDX in both years but visual root rot was greater on the moderately resistant than the susceptible cultivars in 2020. Yield response to cultivar was also inconsistent between the 2 years. In 2020, the susceptible cultivar provided significantly more yield than the moderately resistant cultivar. Treatment effect for root rot and FDX was similar in field and greenhouse evaluations. These results reinforce the need to include root rot evaluations in addition to foliar disease evaluations in the breeding process for resistance to F. virguliforme and highlights the importance of an integrated SDS management plan because not a single management tactic alone provides adequate control of the disease.

Changes to Soil Microbiome Resulting from Synergetic Effects of Fungistatic Compounds Pyrimethanil and Fluopyram in Lowbush Blueberry Agriculture, with Nine Fungicide Products Tested

Lowbush blueberries (Vaccinium spp.) are a crop of economic significance to Atlantic Canada, Quebec, and Maine. The fruit is produced by the management of naturally occurring plant populations. The plants have an intimate relationship with the soil microbiome and depend on it for their health and productivity. Fungicides are an important tool in combatting disease pressure but pose a potential risk to soil health. In this study, amplicon sequencing was used to determine the effects of six fungistatic compounds both alone and in combination via nine commercially available fungicide products on the bacterial and fungal microbiomes associated with lowbush blueberries and to study whether these effects are reflected in crop outcomes and plant phenotypes. One fungicide, Luna Tranquility, a combination of fluopyram and pyrimethanil, was found to impart significant effects to fungal and bacterial community structure, fungal taxonomic abundances, and bacterial functions relative to control. The two fungicides which contained fluopyram and pyrimethanil as single ingredients (Velum Prime and Scala, respectively) did not induce significant changes in any of these regards. These results suggest the possibility that these microbiome changes are the result of the synergistic effect of fluopyram and pyrimethanil on soil microbiomes. While these results suggest a significant disruption to the soil microbiome, no corresponding changes to crop development and outcomes were noted. Ultimately, the majority of the fungicides analysed in this trial did not produce significant changes to the soil microbiome relative to the untreated group (UTG). However, one of the fungicide treatments, Luna Tranquility, did produce significant changes to the soil ecosystem that could have longer-term effects on soil health and its future use may merit additional investigation onto its ecotoxicological properties.

Impact of non-fumigant nematicides on reproduction and pathogenicity of Meloidogyne enterolobii and disease severity in tobacco

Meloidogyne enterolobii is a highly aggressive quarantine pathogen which threatens the multibillion-dollar tobacco industry and is not manageable with the currently available management methods in tobacco. There is currently no known host plant resistance in tobacco and previous studies have shown that the lower level of the currently recommended rate of non-fumigant nematicides does not provide satisfactory management of M. enterolobii. The current study was conducted with the hypothesis that M. enterolobii can be better managed using a single soil application of the maximum allowed rate of non-fumigant nematicides. Treatments involved three non-fumigant chemical nematicides (oxamyl, fluopyram, and fluensulfone), a biological nematicide derived from Burkholderia, and a non-treated control. Fluensulfone significantly suppressed the nematode reproduction relative to the control, the suppression being 71% for eggs and 86% for the second stage juveniles (J2). Fluopyram also suppressed nematode reproduction, although this was statistically insignificant, with the suppression being 26% and 37% for eggs and J2, respectively. Oxamyl significantly suppressed J2 (80%), but not eggs (50%) in relation to the control. The most significant reduction of disease severity was achieved by the application of fluensulfone (64%), followed by oxamyl (54%) and fluopyram (48%). Except for fluensulfone, which significantly reduced the root biomass, none of the nematicides significantly impacted root and shoot biomass. The biological nematicide did not significantly affect nematode reproduction, pathogenicity, or disease severity. The results from the current study suggest that while the non-fumigant nematicides provided a good level of the nematode suppression, more research is needed to improve the efficacy of non-fumigant nematicides through employing better application methods or finding better chemistries.

Identification of novel nematode succinate dehydrogenase inhibitors: Virtual screening based on ligand-pocket interactions

To discover new nematicidal succinate dehydrogenase (SDH) inhibitors with novel structures, we conducted a virtual screening of the ChemBridge library with 1.7 million compounds based on ligand-pocket interactions. The homology model of Caenorhabditis elegans SDH was established, along with a pharmacophore model based on ligand-pocket interactions. After the pharmacophore-based and docking-based screening, 19 compounds were selected for the subsequent enzymatic assays. The results showed that compound 1 (ID: 7607321) exhibited inhibitory activity against SDH with a determined IC₅₀ value of 19.6 μM. Structural modifications and nematicidal activity studies were then carried out, which provided further evidence that compound 1 exhibited excellent nematicidal activity. Molecular dynamics simulations were then conducted to investigate the underlying molecular basis for the potency of these inhibitors against SDH. This work provides a reliable strategy and useful information for the future design of nematode SDH inhibitors.

Assessment of Selected Commercially Available Seed Treatments on Suppressing the Effects of Red Crown Rot on Soybeans Under a Controlled Environment

Calonectria ilicicola is a soilborne fungus responsible for red crown rot (RCR) in soybeans. Recently, this disease has been detected in new areas within the United States and Asia, where it has been reported to cause significant yield losses. To date, no data on the efficacy of fungicide seed treatments for suppressing RCR in soybeans are available. We screened three commercially available soybean seed treatments (Acceleron STANDARD; Acceleron STANDARD + IleVO; Cruiser MAXX + Saltro) for impacts on germination, seedling growth, and disease caused by C. ilicicola under controlled laboratory conditions. The Cruiser MAXX + Saltro treatment improved final plant dry mass to levels similar to noninoculated controls. Both Acceleron STANDARD + IleVO and Cruiser MAXX + Saltro reduced percent root rot. Acceleron STANDARD alone did not impact root rot, indicating that the IleVO component was efficacious on C. ilicicola. These data indicate that IleVO and Cruiser MAXX + Saltro have potential for reducing early season impacts of RCR in soybeans. Future work assessing these seed treatments in field-grown soybeans is needed to better understand the role of seed treatments as components of an integrated management program for RCR.

Meta-Analysis of the Field Efficacy of Seed- and Soil-Applied Nematicides on Meloidogyne incognita and Rotylenchulus reniformis Across the U.S. Cotton Belt

Meta-analysis was used to compare yield protection and nematode suppression provided by two seed-applied and two soil-applied nematicides against Meloidogyne incognita and Rotylenchulus reniformis on cotton across 3 years and several trial locations in the U.S. Cotton Belt. Nematicides consisted of thiodicarb- and fluopyram-treated seed, aldicarb and fluopyram applied in furrow, and combinations of the seed treatments and soil-applied fluopyram. The nematicides had no effect on nematode reproduction or root infection but had a significant impact on seed cotton yield response ([Formula: see text]), with an average increase of 176 and 197 kg/ha relative to the nontreated control in M. incognita and R. reniformis infested fields, respectively. However, because of significant variation in yield protection and nematode suppression by nematicides, five or six moderator variables (cultivar resistance [M. incognita only], nematode infestation level, nematicide treatment, application method, trial location, and growing season) were used depending on nematode species. In M. incognita-infested fields, greater yield protection was observed with nematicides applied in furrow and with seed-applied + in-furrow than with solo seed-applied nematicide applications. Most notable of these in-furrow nematicides were aldicarb and fluopyram (>131 g/ha) with or without a seed-applied nematicide compared with thiodicarb. In R. reniformis-infested fields, moderator variables provided no further explanation of the variation in yield response produced by nematicides. Furthermore, moderator variables provided little explanation of the variation in nematode suppression by nematicides in M. incognita- and R. reniformis-infested fields. The limited explanation by the moderator variables on the field efficacy of nematicides in M. incognita- and R. reniformis-infested fields demonstrates the difficulty of managing these pathogens with nonfumigant nematicides across the U.S. Cotton Belt.

Sensitivity of Meloidogyne enterolobii and M. incognita to fluorinated nematicides

BACKGROUND

Meloidogyne enterolobii (Yang and Eisenback) was recently introduced into Louisiana on contaminated sweetpotato planting material. Given the known variation in sensitivity to nematicides within the genus Meloidogyne, there is question as to whether fluorinated nematicides will be as efficacious toward M. enterolobii as they are with M. incognita (Chitwood). Using a series of in vitro and growth cabinet experiments, this study compared the sensitivity of M. enterolobii and M. incognita to four synthetic non-fumigant nematicides (fluopyram, fluensulfone, fluazaindolizine, and oxamyl).

RESULTS

Meloidogyne enterolobii had lower sensitivity to nematicides than M. incognita in the majority of the in vitro exposure assays. Similar levels of reduction in root infectivity were observed after nematicide exposure among both nematode species. Fluopyram showed high hatching inhibition for both Meloidogyne species at low concentrations [median effective concentration (EC₅₀ ) values of 0.273 to 0.018 mg L^-1 ], whereas fluensulfone showed high root penetration inhibition at low concentrations (EC₅₀ values of 0.151 to 0.065 mg L^-1 ) relative to that of other evaluated nematicides. For both Meloidogyne species, each of the four non-fumigant nematicides reduced root galling (58-96% reduction for M. enterolobii, 71-100% reduction for M. incognita) and egg production (63-99% reduction for M. enterolobii, 58-96% reduction for M. incognita) on sweetpotato when applied at the label recommended rate.

CONCLUSION

Fluorinated nematicides and oxamyl show capacity to suppress M. enterolobii on sweetpotato. © 2021 Society of Chemical Industry.

Genome-wide transcriptional response of the causal soybean sudden death syndrome pathogen Fusarium virguliforme to a succinate dehydrogenase inhibitor fluopyram

BACKGROUND

Succinate dehydrogenase inhibitors (SDHIs) have been widely used to manage plant diseases caused by phytopathogenic fungi. Although attention to and use of SDHI fungicides has recently increased, molecular responses of fungal pathogens to SDHIs have often not been investigated. A SDHI fungicide, fluopyram, has been used as a soybean seed treatment and has displayed effective control of Fusarium virguliforme, one of the causal agents of soybean sudden death syndrome. To examine genome-wide gene expression of F. virguliforme to fluopyram, RNA-seq analysis was conducted on two field strains of F. virguliforme with differing SDHI fungicide sensitivity in the absence and presence of fluopyram.

RESULTS

The analysis indicated that several xenobiotic detoxification-related genes, such as those of deoxygenase, transferases and transporters, were highly induced by fluopyram. Among the genes, four ATP-binding cassette (ABC) transporters were characterized by the yeast expression system. The results revealed that expression of three ABCG transporters was associated with reduced sensitivity to multiple fungicides including fluopyram. In addition, heterologous expression of a major facilitator superfamily (MFS) transporter that was highly expressed in the fluopyram-insensitive F. virguliforme strain in the yeast system conferred decreased sensitivity to fluopyram.

CONCLUSION

This study demonstrated that xenobiotic detoxification-related genes were highly upregulated in response to fluopyram, and expression of ABC or MFS transporter genes was associated with reduced sensitivity to the SDHI fungicide. This is the first transcriptomic analysis of the fungal species response to fluopyram and the finding will help elucidate the molecular mechanisms of SDHI resistance. © 2021 Society of Chemical Industry.

Fungicide Sensitivity of Colletotrichum Species Causing Bitter Rot of Apple in the Mid-Atlantic U.S.A

Apple growers in the Mid-Atlantic region of the U.S.A. have reported increased losses to bitter rot of apple. We tested the hypothesis that this increase is because the Colletotrichum population has developed resistance to commonly used single-mode-of-action (single-MoA) fungicides. We screened 220 Colletotrichum isolates obtained from 38 apple orchards in the Mid-Atlantic region for resistance to 11 fungicides in Fungicide Resistance Action Committee (FRAC) groups 1, 7, 9, 11, 12, and 29. Eleven (5%) of these isolates were resistant to FRAC group 1 with confirmed β-tubulin E198A mutations, and two (<1%) were also resistant to FRAC group 11 with confirmed cytochrome-b G143A mutations. Such low frequencies of resistant isolates indicate that fungicide resistance is unlikely to be the cause of any regional increase in bitter rot. A subsample of isolates was subsequently tested in vitro for sensitivity to every single-MoA fungicide registered for apple in the Mid-Atlantic U.S.A. (22 fungicides; FRAC groups 1, 3, 7, 9, 11, 12, and 29), and 13 fungicides were tested in field trials. These fungicides varied widely in efficacy both within and between FRAC groups. Comparisons of results from our in vitro tests with results from our field trials and other field trials conducted across the eastern U.S.A. suggested that EC₂₅ values (concentrations that reduce growth by 25%) are better predictors of fungicide efficacy in normal field conditions than EC₅₀ values. We present these results as a guideline for choosing single-MoA fungicides for bitter rot control in the Mid-Atlantic U.S.A.

Effects of Pesticides on Longevity and Bioenergetics in Invertebrates-The Impact of Polyphenolic Metabolites

Environmentally hazardous substances such as pesticides are gaining increasing interest in agricultural and nutritional research. This study aims to investigate the impact of these compounds on the healthspan and mitochondrial functions in an invertebrate in vivo model and in vitro in SH-SY5Y neuroblastoma cells, and to investigate the potential of polyphenolic metabolites to compensate for potential impacts. Wild-type nematodes (Caenorhabditis elegans, N2) were treated with pesticides such as pyraclostrobin (Pyr), glyphosate (Gly), or fluopyram (Fluo). The lifespans of the nematodes under heat stress conditions (37 °C) were determined, and the chemotaxis was assayed. Energetic metabolites, including adenosine triphosphate (ATP), lactate, and pyruvate, were analyzed in lysates of nematodes and cells. Genetic expression patterns of several genes associated with lifespan determination and mitochondrial parameters were assessed via qRT-PCR. After incubation with environmentally hazardous substances, nematodes were incubated with a pre-fermented polyphenol mixture (Rechtsregulat^®Bio, RR) or protocatechuic acid (PCA) to determine heat stress resistance. Treatment with Pyr, Glyph and Fluo leads to dose-dependently decreased heat stress resistance, which was significantly improved by RR and PCA. The chemotaxes of the nematodes were not affected by pesticides. ATP levels were not significantly altered by the pesticides, except for Pyr, which increased ATP levels after 48 h leads. The gene expression of healthspan and mitochondria-associated genes were diversely affected by the pesticides, while Pyr led to an overall decrease of mRNA levels. Over time, the treatment of nematodes leads to a recovery of the nematodes on the mitochondrial level but not on stress resistance on gene expression. Fermented extracts of fruits and vegetables and phenolic metabolites such as PCA seem to have the potential to recover the vitality of C. elegans after damage caused by pesticides.

Apple Fruit Core Rot Agents in Greece and Control with Succinate Dehydrogenase Inhibitor Fungicides

Core rot is a major postharvest disease of apple fruit that occurs worldwide and is caused by a complex of fungi. Despite the importance of the disease, little is known about its etiology in Greece. In this study, 325 fungal isolates obtained from fruit with core rot symptoms were identified to the species level using morphological characteristics and phylogenetic analysis. Fungal identification revealed that Alternaria alternata was the major disease agent (57.8% of the isolates), followed by Kalmusia variispora (27.8%), Botrytis cinerea (12%), and Fusarium spp. (3.3%). K. variispora is reported for the first time as an agent of core rot of apple and its pathogenicity was confirmed by artificial inoculation tests. In addition to disease etiology, field experiments were performed at two different orchards for 3 consecutive years (2017 to 2019). Experiments were conducted to determine the effectiveness of several classes of fungicides and the timing of application for control of the disease. Greater efficacy was achieved when fungicides were applied at the petal fall stage (flowers fading BBCH 67), while the most effective fungicides were the succinate dehydrogenase inhibitors fluxapyroxad, fluopyram, adepidyn, and penthiopyrad. The results of this study are expected to contribute to the optimization of disease management and reduce the yield losses caused by core rot pathogens in Greece.

Resistance to the SDHI Fungicides Boscalid and Fluopyram in Podosphaera xanthii Populations from Commercial Cucurbit Fields in Spain

Powdery mildew is caused by Podosphaera xanthii, and is one of the most important diseases that attacks Spanish cucurbit crops. Fungicide application is the primary control tool; however, its effectiveness is hampered by the rapid development of resistance to these compounds. In this study, the EC₅₀ values of 26 isolates were determined in response to the succinate dehydrogenase inhibitor (SDHI) fungicides boscalid and fluopyram. From these data, the discriminatory doses were deduced and used for SDHI resistance monitoring during the 2018 and 2019 growing seasons. Of the 298 isolates analysed, 37.9% showed resistance to boscalid and 44% to fluopyram. Although different phenotypes were observed in leaf disc assays, the resistant isolates showed the same phenotype in plant assays. Compared to sensitive isolates, two amino acid changes were found in the SdhC subunit, A86V and G151R, which are associated mostly with resistance patterns to fluopyram and boscalid, respectively. Furthermore, no significant differences were observed in terms of fitness cost between the selected sensitive and resistant isolates analysed here. Lastly, a loop-mediated isothermal amplification (LAMP) assay was developed to detect A86V and G151R mutations using conidia obtained directly from infected material. Our results show that growers could continue to use boscalid and fluopyram, but resistance management practices must be implemented.

Wheat Root Protection From Cereal Cyst Nematode (Heterodera avenae) by Fluopyram Seed Treatment

Cereal cyst nematode (Heterodera avenae), an important plant-parasitic nematode causing yield losses of wheat, has been found in many provinces in China. It is urgent to develop an effective method of protecting wheat from H. avenae damage. Because of its novel mode of action, fluopyram has been registered for controlling root-knot nematodes on cucumber and tomato in China. However, the bioactivity of fluopyram against H. avenae and whether this seed treatment can effectively control H. avenae on wheat remains unknown. In this study, a bioactivity assay revealed that fluopyram increased the mortality of H. avenae second-stage juveniles (J2), with lethal concentrations (LC) required to kill 50% (LC50) and 90% (LC90) of 0.92 mg⋅liter^-1 and 2.92 mg⋅liter^-1_, respectively. Hatching tests showed that the H. avenae egg hatching percent was reduced by 35.2 to 69.2% with fluopyram at rates of 1.6 to 6.4 mg⋅liter^-1, and that the egg hatching period was delayed by 3 to 9 days compared with the control. During pot and field trials, fluopyram seed treatment significantly reduced the H. avenae population density and increased wheat yield by 3.0 to 13.7%. Therefore, fluopyram seed treatment is an effective approach for the management of H. avenae on wheat in China.

Two adjacent mutations in the conserved domain of SdhB confer various resistance phenotypes to fluopyram in Corynespora cassiicola

BACKGROUND

For Corynespora cassiicola (Berk. & M.A. Curtis) C.T. Wei, a necrotrophic pathogen with a broad host range and a worldwide distribution, resistance to fluopyram has been attributed to mutations in SdhB/C/D subunit of the succinate dehydrogenase (SDH) complex. In our previous study, two point mutations in SdhB from isoleucine to valine at position 280 (I280V) and histidine to tyrosine at position 278 (H278Y) showed different resistance phenotypes to fluopyram and boscalid. This research was conducted to explore the correlation between the mutation of SdhB-I280V or SdhB-H278Y and resistance to fluopyram or boscalid and its effect on the fitness characteristics of C. cassiicola.

RESULTS

The sdhB gene in a succinate dehydrogenase inhibitor (SDHI)-sensitive C. cassiicola strain (wild type) was successfully replaced with the mutant sdhB gene (GTT at position 280, SdhB-I280V) or with the mutant sdhB gene (TAC at position 278, SdhB-H278Y,). Compared with the wild-type strain, the replacement mutants exhibited significantly different resistance phenotypes, with SdhB-V280 demonstrating moderate resistance to fluopyram and low resistance to boscalid, while SdhB-Y278 was supersensitive to fluopyram and very highly resistant to boscalid. Both of the mutants exhibited decreased sensitivity to salt stress and increased SDH activity. These two mutations had no effect on the mycelial growth rate, sporulation ability, pathogenicity in vivo, sensitivity to osmotic stress and oxidative stress, cell wall damaging agents, or SHAM.

CONCLUSION

Two adjacent mutations in the SdhB gene conferred different resistance phenotypes to SDHIs in C. cassiicola, which is important for the development of alternative antifungal fungicides and fluopyram resistance management. © 2021 Society of Chemical Industry.

Efficacy of nonfumigant nematicides against Meloidogyne javanica as affected by soil temperature under pasteurized and natural soil conditions

BACKGROUND

Biotic and abiotic factors such as microbes and soil temperature can affect nematicide efficacy. Two experiments were conducted to test the effect of three soil temperatures on the efficacy of nonfumigant nematicides (fluopyram, fluensulfone, oxamyl and fluazaindolizine) against Meloidogyne javanica in pasteurized and natural soil in planta.

RESULTS

The results showed that all tested nematicides were more efficacious in pasteurized than in natural soil. Temperature affected the nematicides differently with no effect of soil temperature on oxamyl and fluazaindolizine, whereas fluopyram and fluensulfone had greater efficacy at higher soil temperatures.

CONCLUSION

Temperature effects were noted for some but not all nonfumigant nematicides. Fluopyram and fluensulfone were less effective when applied in cold soil, whereas oxamyl and fluazaindolizine were not affected by soil temperature. Although all nematicides resulted in almost complete control of M. javanica in pasteurized soil, this was not the case in natural soil, and much more root damage and nematode reproduction was noted in the latter. © 2021 Society of Chemical Industry.

Evaluation of fluopyram for management of Meloidogyne ethiopica and migratory nematodes in commercial tomato greenhouses in the Metropolitan Region of Chile

BACKGROUND

The nematicidal effects of fluopyram were evaluated for the suppression of Meloidogyne ethiopica and migratory nematodes, Xiphinema americanum s. l., Hemicycliophora spp. and Pratylenchus spp., in two commercial tomato greenhouses in Chile. The effects of fluopyram on plant-parasitic nematodes, plant vigor and fruit yield were determined.

RESULTS

Fluopyram demonstrated good potential for the management of M. ethiopica and migratory nematodes, especially during the early stages of evaluation (30-60 days after planting). There were also improvements in vigor of treated plants. A general trend in improved fruit quality was also observed, however, no significant differences in total yield were found between treatments.

CONCLUSIONS

Our study is one of the first evaluations of fluopyram under field conditions against M. ethiopica. The findings suggest that this new nematicide has good potential for the management of M. ethiopica and some migratory nematodes in tomatoes cropped in greenhouses in the Metropolitan Region of Chile. © 2021 Society of Chemical Industry.

A Method for the Examination of SDHI Fungicide Resistance Mechanisms in Phytopathogenic Fungi Using a Heterologous Expression System in Sclerotinia sclerotiorum

Succinate dehydrogenase inhibitors (SDHIs) are a class of broad-spectrum fungicides used for management of diseases caused by phytopathogenic fungi. In many cases, reduced sensitivity to SDHI fungicides has been correlated with point mutations in the SdhB and SdhC target genes that encode components of the succinate dehydrogenase complex. However, the genetic basis of SDHI fungicide resistance mechanisms has been functionally characterized in very few fungi. Sclerotinia sclerotiorum is a fast-growing and SDHI fungicide-sensitive phytopathogenic fungus that can be conveniently transformed. Given the high amino acid sequence similarity and putative structural similarity of SDHI protein target sites between S. sclerotiorum and other common phytopathogenic ascomycete fungi, we developed an in vitro heterologous expression system that used S. sclerotiorum as a reporter strain. With this system, we were able to demonstrate the function of mutant SdhB or SdhC alleles from several ascomycete fungi in conferring resistance to multiple SDHI fungicides. In total, we successfully validated the function of Sdh alleles that had been previously identified in field isolates of Botrytis cinerea, Blumeriella jaapii, and Clarireedia jacksonii (formerly S. homoeocarpa) in conferring resistance to boscalid, fluopyram, or fluxapyroxad and used site-directed mutagenesis to construct and phenotype a mutant allele that is not yet known to exist in Monilinia fructicola populations. We also examined the functions of these alleles in conferring cross-resistance to more recently introduced SDHIs including inpyrfluxam, pydiflumetofen, and pyraziflumid. The approach developed in this study can be widely applied to interrogate SDHI fungicide resistance mechanisms in other phytopathogenic ascomycetes.

Economic Impact of Fluopyram-Amended Seed Treatments to Reduce Soybean Yield Loss Associated with Sudden Death Syndrome

Soybean (Glycine max) sudden death syndrome (SDS), caused by Fusarium virguliforme, is a key limitation in reaching soybean yield potential, stemming from incomplete disease management through cultural practices and partial host resistance. A fungicidal seed treatment was released in 2014 with the active ingredient fluopyram and was the first chemical management strategy to reduce soybean yield loss stemming from SDS. Although farm level studies have found fluopyram profitable, we were curious to discover whether fluopyram would be beneficial nationally if targeted to soybean fields at risk for SDS yield loss. To estimate economic benefits of fluopyram adoption in SDS at-risk acres, in the light of U.S. public research and outreach from a privately developed product, we applied an economic surplus approach, calculating ex ante net benefits from 2018 to 2032. Through this framework of logistic adoption of fluopyram for alleviation of SDS-associated yield losses, we projected a net benefit of $5.8 billion over 15 years, considering the costs of public seed treatment research and future extension communication. Although the sensitivity analysis indicates that overall net benefits from fluopyram adoption on SDS at-risk acres are highly dependent upon the market price of soybean, the incidence of SDS, the adoption path, and ceiling of this seed treatment, the net benefits still exceeded $407 million in the worst-case scenario.

Dissipation and residue determination of fluopyram and its metabolites in greenhouse crops

BACKGROUND

Fluopyram is a pesticide widely used in tomato and cucumber crops cultivation to control fungal diseases that develop especially in environments with moderate temperatures and high humidity, such as in a greenhouse. The pathway of fluopyram dissipation has been monitored in cucumber and cherry tomato under greenhouse conditions.

RESULTS

In the greenhouse trials, cherry tomato and cucumber were treated by irrigation water with the commercial product at the manufacturer's recommended dose and double dose. High-resolution mass spectrometry (HRMS) coupled to ultra-high-performance liquid chromatography (UHPLC) has been selected as the technique to obtain the identification of fluopyram and metabolites. The fate of fluopyram in greenhouse tomato and cucumber was investigated over 44 days. The metabolic pathway of fluopyram was: in a first step there was a primary transformation to fluopyram-7-hydroxy and fluopyram-8-hydroxy, isomeric compounds, and in a second phase to fluopyram-benzamide and fluopyram-pyridyl-carboxylic acid. The behavior of fluopyram does not fit any type of kinetic classical model of degradation.

CONCLUSIONS

Greenhouse trials revealed that the fluopyram is a very persistent compound, and their terminal residues do not exceed maximum residue level (MRL) at the end of the study. © 2020 Society of Chemical Industry.

Modification of the existing maximum residue levels for fluopyram in herbal infusions from leaves, herbs and flowers

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant Landesanstalt fuer Landwirtschaft und Gartenbau Sachsen-Anhalt submitted a request to the competent national authority in Germany to modify the existing maximum residue levels (MRLs) for the active substance fluopyram in certain herbal infusions. The data submitted in support of the request were found to be sufficient to derive MRL proposals for the herbal infusions from leaves and herbs. A risk management decision needs to be taken whether the proposed MRL is considered appropriate for herbal infusions from flowers. Adequate analytical methods for enforcement are available to control the residues of fluopyram in the commodities under consideration at the validated limit of quantification (LOQ) of 0.01 mg/kg. Based on the risk assessment results, EFSA concluded that the dietary intake of residues resulting from the use of fluopyram according to the reported agricultural practice is unlikely to present a risk to consumer health.

Sensitivity to fluensulfone of inactivated Meloidogyne spp. second-stage juveniles

BACKGROUND

Nonfumigant nematicide efficacy is affected by several factors, such as nematode species and environmental conditions. However, the influence of nematodes' physiological status on nematicide efficacy is unknown. Inactive nematodes, such as those in quiescence or dormancy, seem to be more tolerant to nematicides than active ones. Second-stage juveniles of Meloidogyne species were inactivated by low temperatures and reversible nematicides before and during exposure to fluensulfone. The sensitivity of inactive juveniles to fluensulfone the nematicide was compared to that of active juveniles by EC₅₀ (median effective concentration) for juvenile immobilization and root gall reduction.

RESULTS

Inactivating Meloidogyne hapla and Meloidogyne javanica juveniles at 5 °C increased the EC₅₀ (median effective concentration) of fluensulfone for immobilization of and root galling by Meloidogyne spp. 3.6 to 9.5 times. When the exposure temperature was decreased from 25 to 15 °C, EC₅₀ for M. javanica root gall reduction after 24 and 48 h exposure increased 3.1 and 4.9 times, respectively, whereas for M. hapla, it increased 2.3 and 2.0 times, respectively. Juveniles of M. javanica and M. incognita immobilized by fenamiphos were as sensitive to fluensulfone as active juveniles based on the number of root galls. However, juveniles of these species immobilized by fluopyram were more tolerant to fluensulfone than untreated active juveniles. An interaction of fluopyram and fluensulfone activities is suggested.

CONCLUSION

Changes in the sensitivity of inactive Meloidogyne spp. juveniles to fluensulfone depend on the inactivation method. Fluensulfone could be better applied when nematodes are active in the soil. © 2020 Society of Chemical Industry.

Review of the existing maximum residue levels for fluopyram according to Article 12 of Regulation (EC) No 396/2005

According to Article 12 of Regulation (EC) No 396/2005, EFSA has reviewed the maximum residue levels (MRLs) currently established at European level for the pesticide active substance fluopyram. To assess the occurrence of fluopyram residues in plants, processed commodities, rotational crops and livestock, EFSA considered the conclusions derived in the framework of Commission Regulation (EU) No 188/2011, the MRLs established by the Codex Alimentarius Commission as well as the import tolerances and European authorisations reported by Member States (including the supporting residues data). Based on the assessment of the available data, MRL proposals were derived and a consumer risk assessment was carried out. Some information required by the regulatory framework was missing and a possible chronic risk to consumers was identified. Hence, the consumer risk assessment is considered indicative only, some MRL proposals derived by EFSA still require further consideration by risk managers and measures for reduction of the consumer exposure should also be considered. Hence, the consumer risk assessment is considered indicative only and some MRL proposals derived by EFSA still require further consideration by risk managers.

Evaluation of new chemical and biological nematicides for managing Meloidogyne javanica in tomato production and associated double-crops in Florida

BACKGROUND

Two field experiments were conducted to determine the efficacy and field performance of three new non-fumigant chemical nematicides (fluensulfone, fluopyram, and fluazaindolizine) and two biological nematicides (Burkholderia rinojensis strain A396 and Purpureocillium lilacinus strain 251) for management of root-knot nematodes (Meloidogyne javanica) on tomato and associated double-crops in Florida.

RESULTS

In experiment 1, soil fumigation with metam potassium increased plant growth and reduced root galling on tomato by 77% relative to that of the untreated soil. All non-fumigant chemical nematicides reduced root galling on tomato (47-85% reduction); however, only fluensulfone showed a trend towards yield enhancement. In experiment 2, soil fumigation with chloropicrin increased plant growth and reduced root galling on tomato by 35% relative to that of the untreated soil; however, end-of-season populations of M. javanica in soil were larger than that of the non-fumigated soil. Fluensulfone showed a trend towards reduced root galling and enhanced fruit yield, whereas other non-fumigant nematicides did not. Double-cropped cucumber was 69% more galled when planted into soil previously fumigated with chloropicrin relative to that of untreated soil, and also showed reduced plant vigor and fruit yield.

CONCLUSION

Fluensulfone shows significant potential to be a component of an integrated pest management strategy for tomato in Florida. © 2019 Society of Chemical Industry.

Multi-Year Field Evaluation of Fluorinated Nematicides Against Meloidogyne incognita in Carrots

California grows approximately 80% of the U.S. carrot production. The primary production challenges derive from root-knot nematodes (Meloidogyne spp.). Between 2013 and 2016, we evaluated three novel fluorinated nonfumigant nematicides in five field trials. Fluensulfone, fluopyram, and fluazaindolizine were applied as product-ready formulations at various rates, dates, and formulations. They were rated for their efficacy against the Southern root-knot nematode (M. incognita), their ability to mitigate nematode-caused crop damage, and potential to produce marketable carrot yield under high disease pressure. All trials were conducted in randomized complete block designs in M. incognita-infested, sandy-loam fields. Soil population of M. incognita at seeding and harvest, midseason plant vigor and fibrous root galling, harvest taproot galling, and marketable carrot yield were analyzed by ANOVA. Midseason gall ratings were indicative of disease ratings at harvest. All fluazaindolizine and fluensulfone treatments reduced at-harvest galling compared with the untreated controls. Fluopyram resulted in less galling but did not sufficiently protect the lower part of the taproot. Overall, fluazaindolizine at 2.24 kg/ha resulted in the most consistent and highest marketable carrot yield, followed by fluensulfone at 2.95 kg/ha. Both fluazaindolizine and fluensulfone will likely provide effective and target-selective crop protection against root-knot nematodes in fresh carrot production.

javanica

BACKGROUND

Fluensulfone and fluopyram are new nematicides whose mode of action is not fully understood. Differences in the nematicidal activity of these compounds among two Meloidogyne incognita populations and a Meloidogyne javanica population, and the effect of sublethal exposure to the nematicide on their infection process were studied in vitro.

RESULTS

The M. incognita populations were more sensitive to fluensulfone than M. javanica, whereas M. javanica was more sensitive to fluopyram. A more than 10-fold difference in median lethal concentration (LC₅₀ ) was observed between the M. incognita populations after 17-h exposure to fluensulfone. Exposure of M. incognita and M. javanica to 4 mg L^-1 fluopyram for 48 h resulted in irreversible immobilization, whereas lower concentrations or 17-h exposure to fluopyram caused reversible immobilization. Pre-exposure of M. javanica to fluensulfone at sublethal concentrations reduced the number of juveniles attracted to root tips and caused smaller galls. Pre-exposure to fluopyram delayed the nematodes' attraction. Presence of fluopyram in a Pluronic gel at concentrations that immobilized the nematodes in water showed no or only slight inhibition of the nematodes' attraction to root tips and gall formation.

CONCLUSION

Different sensitivities to nematicides were observed among Meloidogyne species and populations. Sublethal exposure to fluensulfone reduced nematode attraction to root tips and infection. Pluronic gel negatively affected nematicidal activity, especially for fluopyram. © 2019 Society of Chemical Industry.

Modification of the existing maximum residue level for fluopyram in broccoli

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant Bayer Hellas AG submitted a request to the competent national authority in Greece to modify the existing maximum residue level (MRL) for the active substance fluopyram in broccoli. The data submitted in support of the request were found to be sufficient to derive MRL proposals for broccoli. Adequate analytical methods for enforcement are available to control the residues of fluopyram on the commodity under consideration at the validated limit of quantification (LOQ) of 0.01 mg/kg. Based on the risk assessment results, EFSA concluded that the short‐term and long‐term intake of residues resulting from the use of fluopyram according to the reported agricultural practice for broccoli will not result in consumer exposure exceeding the toxicological reference values and therefore are unlikely to present a risk to consumer health.

Fluopyram Sensitivity and Functional Characterization of SdhB in the Fusarium solani Species Complex Causing Soybean Sudden Death Syndrome

The succinate dehydrogenase inhibitor (SDHI) fungicide, fluopyram, is used as a soybean seed treatment to manage Fusarium virguliforme, the casual agent of sudden death syndrome (SDS). More recently, other species within clade 2 of the Fusarium solani species, F. tucumaniae in South America and F. brasiliense in America and Africa, have been recognized as additional agents capable of causing SDS. To determine if fluopyram could be used for management of SDS caused by these species, in vitro sensitivity tests of the three Fusarium species to fluopyram were conducted. The mean EC50 values of F. brasiliense and F. virguliforme strains to fluopyram were 1.96 and 2.21 μg ml-1, respectively, but interestingly F. tucumaniae strains were highly sensitive (mean EC50 = 0.25 μg ml-1) to fluopyram compared to strains of the other two species. A sequence analysis of Sdh genes of Fusarium strains revealed that the F. tucumaniae strains contain an arginine at codon 277 in the SdhB gene instead of a glycine as in other Fusarium species. Replacement of glycine to arginine in SdhB-277 in a F. virguliforme wild-type strain Mont-1 through genetic transformation resulted in increased sensitivity to two SDHI fungicides, fluopyram and boscalid. Similar to a F. tucumaniae strain, the Mont-1 (SdhBG277R) mutant caused less SDS and root rot disease than Mont-1 on soybean seedlings with the fluopyram seed treatment. Our study suggests the amino acid difference in the SdhB in F. tucumaniae results in fluopyram being efficacious if used as a seed treatment for management of F. tucumaniae, which is the most abundant SDS causing species in South America. The establishment of baseline sensitivity of Fusarium species to fluopyram will contribute to effective strategies for managing Fusarium diseases in soybean and other pathosystems such as dry bean.

Non-target site SDHI resistance is present as standing genetic variation in field populations of Zymoseptoria tritici

BACKGROUND

A new generation of more active succinate dehydrogenase (Sdh) inhibitors (SDHIs) is currently widely used to control Septoria leaf blotch in northwest Europe. Detailed studies were conducted on Zymoseptoria tritici field isolates with reduced sensitivity to fluopyram and isofetamid; SDHIs which have only just or not been introduced for cereal disease control, respectively.

RESULTS

Strong cross-resistance between fluopyram and isofetamid, but not with other SDHIs, was confirmed through sensitivity tests using laboratory mutants and field isolates with and without Sdh mutations. The sensitivity profiles of most field isolates resistant to fluopyram and isofetamid were very similar to a lab mutant carrying SdhC-A84V, but no alterations were found in SdhB, C and D. Inhibition of mitochondrial Sdh enzyme activity and control efficacy in planta for those isolates was severely impaired by fluopyram and isofetamid, but not by bixafen. Isolates with similar phenotypes were not only detected in northwest Europe but also in New Zealand before the widely use of SDHIs.

CONCLUSION

This is the first report of SDHI-specific non-target site resistance in Z. tritici. Monitoring studies show that this resistance mechanism is present and can be selected from standing genetic variation in field populations. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Modification of the existing maximum residue level for fluopyram in purslanes

In accordance with Article 6 of Regulation (EC) No 396/2005, the applicant Bayer CropScience submitted a request to the competent national authority in the Netherlands to modify the existing maximum residue level (MRL) for the active substance fluopyram in purslanes. The data submitted in support of the request were found to be sufficient to derive a MRL proposal for purslanes. Adequate analytical methods for enforcement are available to control the residues of fluopyram in plant matrices/on the commodity under consideration. Based on the risk assessment results, EFSA concluded that the short-term and long-term intake of residues resulting from the use of fluopyram according to the reported agricultural practice is unlikely to present a risk to consumer health.

Sensitivity of Meloidogyne incognita and Rotylenchulus reniformis to Fluopyram

Fluopyram is a succinate dehydrogenase inhibitor (SDHI) fungicide that is being evaluated as a seed treatment and in-furrow spray at planting on row crops for management of fungal diseases and its effect on plant-parasitic nematodes. Currently, there are no data on nematode toxicity, nematode recovery, or effects on nematode infection for Meloidogyne incognita or Rotylenchulus reniformis after exposure to low concentrations of fluopyram. Nematode toxicity and recovery experiments were conducted in aqueous solutions of fluopyram, while root infection assays were conducted on tomato. Nematode paralysis was observed after 2 hr of exposure at 1.0 µg/ml fluopyram for both nematode species. Using an assay of nematode motility, 2-hr EC50 values of 5.18 and 12.99 µg/ml fluopyram were calculated for M. incognita and R. reniformis, respectively. Nematode recovery in motility was greater than 50% for M. incognita and R. reniformis 24 hr after nematodes were rinsed and removed from a 1-hr treatment of 5.18 and 12.99 µg/ml fluopyram, respectively. Nematode infection of tomato roots was reduced and inversely proportional to 1-hr treatments with water solutions of fluopyram at low concentrations, which ranged from 1.3 to 5.2 µg/ml for M. incognita and 3.3 to 13.0 µg/ml for R. reniformis. Though fluopyram is nematistatic, low concentrations of the fungicide were effective at reducing the ability of both nematode species to infect tomato roots.

Molecular characterisation and detection of resistance to succinate dehydrogenase inhibitor fungicides in Botryotinia fuckeliana (Botrytis cinerea)

BACKGROUND

Succinate dehydrogenase inhibitors (SDHIs), interfering with fungal respiration, are considered to be fungicides at medium to high risk of resistance. Boscalid was the first molecule belonging to the SDHIs that was introduced for the control of Botryotinia fuckeliana. A range of different target-site mutations leading to boscalid resistance have been found in field populations of the fungus. The different types of mutation confer different cross-resistance profiles towards novel SDHIs, such as the recently introduced fungicide fluopyram. This study combines the determination of cross-resistance profiles and the setting-up of methods for fast molecular detection of the mutations.

RESULTS

By means of in vitro tests, a range of SdhB mutations were characterised for resistance levels towards boscalid and fluopyram. SdhB mutations conferring P225L and P225F substitutions conferred high resistance to boscalid and high or moderate resistance to fluopyram respectively. Mutants carrying the N230I replacement were moderately resistant to both SDHIs. Substitutions at position H272 responsible for a high level of resistance to boscalid conferred sensitivity (H272R), hypersensitivity (H272Y) or moderate resistance (H272V) to fluopyram. Allele-specific (AS) PCR was developed and used for genotyping 135 B. fuckeliana isolates. The assay confirmed the strict association between resistance profiles and allelic variants of the SdhB gene. Real-time AS-PCR proved to be sensitive and specific for quantitative detection of different SDHI-resistant genotypes.

CONCLUSION

Fluopyram-resistant mutants are currently rarely detected in the field sprayed with boscalid, but this may change with intensive exposure of the fungal population to fluopyram. PCR assays/methods developed in the study provide tools for fast monitoring of field populations and observing possible changes in population composition following fluopyram introduction, useful for the setting-up of appropriate preventive measures.