Petri Dish Assay Research Articles

Maize resistance to Spodoptera frugiperda and its relationship to landrace variety, plant stage, and larval origin

AbstractPrevious studies have raised the hypothesis that laboratory‐reared insects may lose their ability to induce plant defenses because induction‐associated gut bacteria may be eliminated by antibiotics used in artificial diets. The present study was conducted to determine whether maize (Zea mays L., Poaceae) responses to Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae) differ when field‐collected vs. laboratory‐reared insects are feeding. One fifth instar from the laboratory or field was released onto a resistant or a susceptible landrace variety at vegetative stages 4 and 6 (V4 and V6), or plants remained uninfested. Five days later, damage was estimated and sections of maize leaves were fed to forth instars in a Petri dish assay to assess the effects of previous feeding on weight gain, leaf consumption, and nutritional indices of conspecifics. Initially, field‐collected larvae caused more damage on V4, but not on V6 maize plants, than laboratory‐reared larvae. In V6 plants, the resistant variety showed less leaf damage than the susceptible variety. In a Petri dish assay, there were no differences between effects of laboratory‐reared and field‐collected larvae on the measured parameters, but larvae from both sources promoted increased susceptibility in maize plants at the V4, but not the V6 stage. This was characterized by higher weight gain and higher efficiency of conversion of ingested food (ECI) (on both maize varieties), and lower metabolic cost (MC) (on one variety) when S. frugiperda larvae fed on leaves pre‐infested with laboratory‐reared larvae compared to leaves of uninfested plants. Conversely, S. frugiperda larvae fed on leaves pre‐infested with field‐collected larvae consumed a greater amount of leaf tissue (on both varieties) compared to leaves of uninfested plants. A similar experiment with neonates showed no effects of landrace variety or previous infestation on insect weight and survival, but insects obtained a higher body weight when fed on V4 compared to V6 plants. In conclusion, S. frugiperda laboratory‐reared larvae were equally able as field‐collected larvae to induce susceptibility in V4 maize plants, and maize plants were more resistant to the pest at the V6 than at the V4 stage.

Volatile Organic Compounds from Rice Rhizosphere Bacteria Inhibit Growth of the Pathogen Rhizoctonia solani

Rice sheath blight, a fungal disease caused by Rhizoctonia solani, seriously threatens rice production. Some of the volatile organic compounds (VOCs) produced by microbes are inhibitory to the growth of the plant pathogen, and hence may have the potential as environmentally friendly antifungal substances. However, information on the inhibitory effect of VOCs released by rice rhizosphere bacteria on R. solani is scarce. In this study, bacteria from the rice rhizosphere capable of inhibiting the growth of R. solani via releasing VOCs were screened using a double Petri dish assay. Headspace solid phase microextraction and gas chromatography mass spectrometry (GC/MS) were used to identify and quantify the VOCs. The contributions of VOCs to the inhibition of the growth of R. solani were estimated by constructing a random forest model, and were verified using pure compounds. Nine strains (i.e., Pseudomonas sp. No. 3, Enterobacter sp. No. 26, Enterobacter sp. No. 34, Pseudomonas sp. No. 35, Ralstonia sp. No. 50, Bacillus sp. No. 62, Arthrobacter sp. No. 146, Brevibacillus sp. No. 2–18, and Paenisporosarcina sp. No. 2–60) showed various inhibition on R. solani growth via VOCs. The inhibitory effect ranged from 7.84% to 100%, with Ralstonia sp. No. 50 completely inhibiting the growth of R. solani. Five VOCs (i.e., benzoic acid ethyl ester, 3-methyl-butanoic acid, 2-ethyl-1-hexanol, 3-methyl-1-butanol, and 6-methyl-5-hepten-2-one) identified by random forest model were confirmed to be toxic to R. solani when applied as a pure chemical compound. In particular, benzoic acid ethyl ester, 3-methyl-butanoic acid, and 2-ethyl-1-hexanol were lethal to R. solani. In summary, the rice rhizosphere bacteria (Ralstonia sp. No. 50) and VOCs (benzoic acid ethyl ester, 3-methyl-butanoic acid, and 2-ethyl-1-hexanol) showed potential to be used as new resources for biological control of rice sheath blight.

Evaluating the efficacy of osthole and matrine for control of Sorghum purple spot

Osthole is a coumarin compound extracted from the canopy flower of the umbelliferae. Matrine, whose main components are alkaloids and flavonoids, was extracted from the roots, stems, leaves and fruits of Sophora flavescens by ethanol or other organic solvents. In this study, the efficacy of the combined biological agents matrine and osthole against Sorghum purple spot caused by Cercospora sorghi was conducted by laboratory, greenhouse and field experiments. The results from petridish assay showed that the inhibitory effect of the mixture of osthole and matrine against C. sorghi was better than osthole or matrine alone or Zineb, and the best mixing ratio of osthole to matrine was 1:2. In greenhouse experiment, the efficacy of 25 μg/mL of matrine · osthole against Sorghum purple spot was similar to Zineb. Field experiment showed that the efficacy of 25 μg/mL of matrine · osthole on Sorghum purple spot reached 68.4% on the 30th day. These results suggested that the combined matrine and osthole had a good effect and could be used as an alternative fungicide against Sorghum purple spot.

Design, Synthesis, and Herbicidal Activity of N-Benzyl-5-cyclopropyl-isoxazole-4-carboxamides

Based on the structures of isoxaflutole (IFT) and N-isobutyl-N-(4-chloro-benzyl)-4-chloro-2-pentenamide, a series of N-benzyl-5-cyclopropyl-isoxazole-4-carboxamides was designed by connecting their pharmacophores (i.e., a multitarget drug design strategy). A total of 27 N-benzyl-5-cyclopropyl-isoxazole-4-carboxamides were prepared from 5-cyclopropylisoxazole-4-carboxylic acid and substituted benzylamines, and their structures were confirmed by NMR and MS. Laboratory bioassays indicated that I-26 showed 100% inhibition against Portulaca oleracea and Abutilon theophrasti at a concentration of 10 mg/L, better than the positive control butachlor (50% inhibition for both weeds). A strong growth inhibition was observed, but a typical bleaching phenomenon of IFT could not be observed in the Petri dish assay. I-05 displayed excellent postemergence herbicidal activity against Echinochloa crusgalli and A. theophrasti at a rate of 150 g/ha, and bleaching symptoms were observed in the leaves of treated weeds. The bleaching effect of Chlamydomonas reinhardtii treated by I-05 could be reversed by adding homogentisate. Enzymatic bioassays indicated that I-05 could not inhibit 4-hydroxyphenylpyruvate dioxygenase (HPPD) activity, but II-05, an isoxazole ring-opening product of I-05, could inhibit HPPD activity with an EC50 value of 1.05 μM, similar to that of mesotrione (with an EC50 value of 1.35 μM). Detailed discussion about observed herbicidal symptoms is provided in the Results and Discussion section. This investigation provided a proof-of-concept foundation that a multitarget drug design strategy could be applied in agrochemical research.

Susceptibility of Various Developmental Stages of the Fall Armyworm, Spodoptera frugiperda, to Entomopathogenic Nematodes.

Simple SummaryThe fall armyworm, Spodoptera frugiperda, native to Central and South America, has recently invaded Africa and Asia, causing serious economic damage to various crops. The chemical control of fall armyworm is not effective due to the development of pesticide resistance as well as environmental contamination. Alternatively, biological control using natural enemies can be used successfully in a sustainable way. Entomopathogenic nematodes are soil-dwelling natural enemies for many underground pest insects including lepidopteran caterpillars. This study evaluates the virulence of several entomopathogenic nematodes on different developmental stages of fall armyworm. We found that all the larval and pupal stages of fall armyworm were highly susceptible to the entomopathogenic nematodes. Our study provides important information of entomopathogenic nematodes for the practical application of biological control of fall armyworm.The fall armyworm, Spodoptera frugiperda, which is native to Central and South America, has recently invaded Africa and Asia, causing serious damage to various crops. Although management to date has been largely unsuccessful, entomopathogenic nematodes (EPNs) are a potential biological control agent that could be used to control the late larval and pupal stages of S. frugiperda that dwell under the ground. Here, we compared the virulence of seven EPNs against larval and pupal stages of S. frugiperda. In a Petri dish assay, both Heterorhabditis indica and Steinernema carpocapsae were highly virulent against younger larvae, whereas S. arenarium and S. longicaudum were highly virulent against older larvae. In contrast, H. bacteriophora, Heterorhabditis sp., and S. kushidai showed low virulence against all larval stages. In soil column and pot assays, H. indica, S. carpocapsae, and S. longicaudum were highly virulent against late larval and pupal stages compared with the other EPN species. Thus, H. indica, S. carpocapsae, and S. longicaudum are recommended for the biological control of S. frugiperda. Our study provides important information of EPNs for the practical application of biological control of fall armyworm.

Three molecules found in rosemary or nutmeg essential oils repel ticks (Dermacentor variabilis) more effectively than DEET in a no-human assay.

Development of new personal repellents to prevent tick bites is progressing to keep up with the increasing threat of tick-borne diseases in humans. However, the market share of natural, plant-based repellents is still quite small. We tested all of the major (>1%) components found in the essential oils of rosemary (Spanish variety) and nutmeg. These were tested with Dermacentor variabilis ticks, a robust tick capable of vectoring human diseases, in a no-human horizontal Petri dish assay. For comparison, we also tested the active ingredients currently recommended by the CDC and EPA as personal repellents for use against ticks. Of the 16 oil components tested, three performed significantly better than N,N-diethyl-meta-toluamide (DEET) in our assay. These compounds were myristicin and safrole found in the nutmeg oil, and terpinolene found in nutmeg oil and as a minor (<1%) constituent of rosemary oil. The current market natural product, 2-undecanone, also performed strongly in our assay. Our assay focused on comparing active ingredients as potential repellents and found that many natural products can elicit a strong response from ticks. Terpinolene is the most promising active ingredient identified, owing to human health concerns regarding myristicin and safrole. Our results from examining individual terpenoids from two essential oils suggest that there remain unexploited natural compounds that could be further developed for new personal tick repellents. © 2020 Society of Chemical Industry.

Volatiles of the entomopathogenic fungus, Metarhizium brunneum, attract and kill plant parasitic nematodes

Root knot nematodes (RKNs) cause significant crop losses. Although RKNs and entomopathogenic fungi, such as Metarhizium brunneum, are associated with plant roots, very little is known about the interactions between these two organisms. This study showed that conidia and VOCs of Me. brunneum influenced the behaviour of M. hapla. The response was dependent on the fungal strain, VOC, concentration of both VOC and conidia, and time. Tomatoes planted in soil treated with the highest doses of conidia usually had a higher number of nematodes than untreated control plants. This was particularly obvious for Me. brunneum strain ARSEF 4556, 7 and 14-days post-treatment. The VOCs, 1-octen-3-ol and 3-octanone, lured M. hapla to plants when used at low doses and repelled them at high doses. In Petri dish assays. the VOCs 1-octen-3-ol and 3-octanone, caused 100% mortality of M. hapla at the highest dose tested (20 µl). Very few live M. hapla were recovered from soil treated with the VOC 1-octen-3-ol, especially at the highest doses tested.

An inexpensive, high-throughput μPAD assay of microbial growth rate and motility on solid surfaces using Saccharomyces cerevisiae and Escherichia coli as model organisms.

Many microbial phenotypes are differentially or exclusively expressed on agar surfaces, including biofilms, motility, and sociality. However, agar-based assays are limited by their low throughput, which increases costs, lab waste, space requirements, and the time required to conduct experiments. Here, we demonstrate the use of wax-printed microfluidic paper-based analytical devices (μPADs) to measure linear growth rate of microbes on an agar growth media as a means of circumventing the aforementioned limitations. The main production materials of the proposed μPAD design are a wax printer, filter paper, and empty pipet boxes. A single wax-printed μPAD allowing 8 independent, agar-grown colonies costs $0.07, compared to $0.20 and $9.37 for the same number of replicates on traditional microtiter/spectrophotometry and Petri dish assays, respectively. We optimized the μPAD design for channel width (3 mm), agar volume (780 μL/channel), and microbe inoculation method (razor-blade). Comparative analyses of the traditional and proposed μPAD methods for measuring growth rate of nonmotile (Saccharomyces cerevisiae) and motile (flagellated Escherichia coli) microorganisms suggested the μPAD assays conferred a comparable degree of accuracy and reliability to growth rate measurements as their traditional counterparts. We substantiated this claim with strong, positive correlations between the traditional and μPAD assay, a significant nonzero slope in the model relating the two assays, a nonsignificant difference between the relative standard errors of the two techniques, and an analysis of inter-device reliability. Therefore, μPAD designs merit consideration for the development of enhanced-throughput, low-cost microbial growth and motility assays.

Identification of a non-host semiochemical from miniature pinscher, Canis lupus familiaris, that repels Rhipicephalus sanguineus sensu lato (Acari: Ixodidae)

It is already known that the beagle breed of domestic dogs produces semiochemicals capable of repelling the brown dog tick, Rhipicephalus sanguineus sensu lato (s.l.). With a view to discovering new non-host semiochemicals as tick repellents, we compared the semiochemicals produced by a putative tick-resistant breed of dog, miniature pinscher, with known tick-resistant (beagle) and tick-susceptible (English cocker spaniel) breeds. Two non-host compounds produced by beagles, i.e. 2-hexanone and benzaldehyde, were shown to be present in samples collected from all three breeds. Furthermore, two compounds, 6-methyl-5-hepten-2-one and 1,2,4-trimethylbenzene, were found in higher amounts in samples collected from miniature pinscher dogs. The mean amounts of benzaldehyde, 2-hexanone and 1,2,4-trimethylbenzene were similar for beagles and miniature pinschers (P > 0.05) and higher than the means observed for cocker spaniels (P < 0.05), whereas the mean amount of 6-methyl-5-hepten-2-one produced by miniature pinschers was significantly higher (P < 0.05) than for the other breeds of dogs. In Petri-dish assays with adult R. sanguineus s.l., 6-methyl-5-hepten-2-one was repellent for all observation periods evaluated for the two highest concentrations (0.100 and 0.200 mg.cm−2, P < 0.01). The obtained results support our hypothesis that miniature pinschers are a tick-resistant dog breed and agree with previous observations of miniature pinschers being the breed least parasitized by ticks. Furthermore, the non-host semiochemical 6-methyl-5-hepten-2-one has potential to be developed for use as a repellent for the protection of susceptible dogs from R. sanguineus s.l. ticks.

Control of postharvest grey spot rot of loquat fruit with Metschnikowia pulcherrima E1 and potential mechanisms of action

In the present study, the biocontrol efficacy of Metschnikowia pulcherrima E1 against grey spot rot (Pestalotiopsis vismiae) on loquat fruits was assessed and along with potential mechanisms of action. Results indicated that decay incidence and lesion diameter were both significantly reduced by treatment of fruits with the yeast, M. pulcherrima E1. M. pulcherrima E1 quickly colonized wounds in loquat fruit stored at either 20 °C or 4 °C. Scanning electron microscopy revealed that the yeast formed a biofilm on the wound surface in loquat fruit which inhibited the invasion of pathogenic fungi. M. pulcherrima E1 also competed with the pathogen for nutrients (iron) and space. Results of dual-culture petri dish assay indicated that M. pulcherrima E1 produces volatile antifungal compounds that inhibit the growth of P. vismiae. SPME-GC–MS analysis revealed that 3-methyl-1-butanol, phenylethyl alcohol and 1-Hexanol are the main volatile organic compounds produced by M. pulcherrima E1 and that had a significant inhibitory effect on the growth of fungal mycelia. M. pulcherrima E1 induced a higher level of defense-related enzyme activity in loquat fruit, including polyphenol oxidase, peroxidase, catalase, ascorbate peroxidase, and phenylalanine ammonia-lyase. Collectively, the results of the present study indicate that M. pulcherrima E1 has good potential to be used as a biocontrol agent against postharvest grey spot rot on loquats. The different mechanisms of action exhibited by M. pulcherrima E1 enhances its ability to control P. vismiae.

Volatile Organic Compounds From Lysobacter capsici AZ78 as Potential Candidates for Biological Control of Soilborne Plant Pathogens.

The genus Lysobacter includes several bacterial species which show potential for being used in biological control of plant diseases. It was shown recently that several Lysobacter type strains produce volatile organic compounds (VOCs) which controlled the growth of Phytophthora infestans in vitro when the bacteria were grown on a protein rich medium. In the present study, Lysobacter capsici AZ78 (AZ78) has been tested for its potential to produce VOCs that may contribute to the bioactivity against soilborne plant pathogens. To this end, split Petri dish assays of bacterial cultures have been combined with GC-MS measurements with the aim to reveal the identity of the VOCs which inhibit the growth of Pythium ultimum Rhizoctonia solani, and Sclerotinia minor. While AZ78 completely suppressed the growth of P. ultimum and S. minor, the growth of R. solani was still reduced significantly. The GC-MS analysis revealed 22 VOCs to be produced by AZ78, the majority of which were (putatively) identified as mono- and dialkylated methoxypyrazines. Based on additional cultivation and GC-MS experiments, 2,5-dimethylpyrazine, 2-ethyl-3-methoxypyrazine and 2-isopropyl-3-methoxypyrazine were selected as presumable bioactive compounds. Further bioassays employing indirect exposure to standard solutions (1–10 mg per Petri dish) of the synthetic compounds via the gas phase, revealed that each of these pyrazines was able to suppress the growth of the pathogens under investigation. The results of this study highlight the possible future implementation of pyrazine derivatives in the control of soilborne plant diseases and further support the biocontrol potential of L. capsici AZ78.

Plant endophytes promote growth and alleviate salt stress in Arabidopsis thaliana

Plant growth promoting rhizobacteria (PGPR) are a functionally diverse group of microbes having immense potential as biostimulants and stress alleviators. Their exploitation in agro-ecosystems as an eco-friendly and cost-effective alternative to traditional chemical inputs may positively affect agricultural productivity and environmental sustainability. The present study describes selected rhizobacteria, from a range of origins, having plant growth promoting potential under controlled conditions. A total of 98 isolates (ectophytic or endophytic) from various crop and uncultivated plants were screened, out of which four endophytes (n, L, K and Y) from Phalaris arundinacea, Solanum dulcamara, Scorzoneroides autumnalis, and Glycine max, respectively, were selected in vitro for their vegetative growth stimulating effects on Arabidopsis thaliana Col-0 seedlings with regard to leaf surface area and shoot fresh weight. A 16S rRNA gene sequencing analysis of the strains indicated that these isolates belong to the genera Pseudomonas, Bacillus, Mucilaginibacter and Rhizobium. Strains were then further tested for their effects on abiotic stress alleviation under both Petri-plate and pot conditions. Results from Petri-dish assay indicated strains L, K and Y alleviated salt stress in Arabidopsis seedlings, while strains K and Y conferred increases in fresh weight and leaf area under osmotic stress. Results from subsequent in vivo trials indicated all the isolates, especially strains L, K and Y, distinctly increased A. thaliana growth under both normal and high salinity conditions, as compared to control plants. The activity of antioxidant enzymes (ascorbate peroxidase, catalase and peroxidase), proline content and total antioxidative capacity also differed in the inoculated A. thaliana plants. Furthermore, a study on spatial distribution of the four strains, using either conventional Petri-plate counts or GFP-tagged bacteria, indicated that all four strains were able to colonize the endosphere of A. thaliana root tissue. Thus, the study revealed that the four selected rhizobacteria are good candidates to be explored as plant growth stimulators, which also possess salt stress mitigating property, partially by regulating osmolytes and antioxidant enzymes. Moreover, the study is the first report of Scorzoneroides autumnalis (fall dandelion) and Solanum dulcamara (bittersweet) associated endophytes with PGP effects.

Antifungal Activity of Volatile Organic Compounds Produced by Bacillus methylotrophicus and Bacillus thuringiensis against Five Common Spoilage Fungi on Loquats

Loquat fruit is one of the most perishable fruits in China, and has a very limited shelf life because of mechanical injury and microbial decay. Due to an increasing concern about human health and environmental security, antagonistic microorganisms have been a potential alternative for fungicides to control postharvest diseases. In this work, the antifungal effect of volatile organic compounds (VOCs) produced by Bacillus methylotrophicus BCN2 and Bacillus thuringiensis BCN10 against five postharvest pathogens isolated from loquat fruit, Fusarium oxysporum, Botryosphaeria sp., Trichoderma atroviride, Colletotrichum gloeosporioides, and Penicillium expansum were evaluated by in vitro and in vivo experiments. As a result, the VOCs released by BCN2 and BCN10 were able to suppress the mycelial growth of all targeted pathogens according to inhibition ratio in the double petri-dish assay as well as disease incidence and disease diameter on loquat fruits. The main volatile compounds were identified by solid-phase microextraction (SPME)-gas chromatography. These VOCs produced by the two strains played complementary roles in controlling these five molds and enabled loquat fruits to keep fresh for ten days, significantly. This research will provide a theoretic foundation and technical support for exploring the functional components of VOCs applicable in loquat fruit preservation.

Management of seed-borne Sirococcus conigenus on Norway spruce by fungicide seed treatment

Seedling blight caused by Sirococcus conigenus was recently reported on Norway spruce (Picea abies) from Norwegian forest nurseries. The inoculum source was found to be infected seeds. In a Petri dish assay, the fungicide fludioxonil + difenoconazole was, among other fungicides, found to inhibit mycelial growth of S. conigenus. This fungicide is formulated as a seed treatment and registered for cereals in Norway, and was chosen for an experiment to control S. conigenus on Norway spruce seeds. Samples from two naturally infected seed lots were treated with half, normal and double dose of the recommended rate for cereals. Together with untreated control samples, treated seeds were tested in the laboratory for efficacy against S. conigenus on potato dextrose agar (PDA) in Petri dishes and for germination potential on filter paper. We also recorded seed emergence in soil of one of the seed lots in a growth chamber and in a forest nursery. On agar, the fungus was not detected after seed treatment with fludioxonil + difenoconazole at any of the three dosages, but it was present in the control. Germination on filter paper and emergence in soil was high in both treated and untreated control seeds with no signs of detrimental effects from any of the three fungicide doses.

Soil amendment by composted plant wastes reduces the Verticillium dahliae abundance and changes soil chemical properties in a bell pepper cropping system

Organic amendments can be effective at controlling some soil-borne pathogens. This work entailed two parts; the first involved two field experiments that investigated the effects of four different composts derived from agricultural wastes on soil load of Verticillium dahliae in organic and conventional bell pepper (Capsicum annuum L.) systems. The composts were prepared using dairy and horse manure (DC), grape pomace (GC), olive pomace-dairy manure mix (ODC) or mixed crop residue (CRC). For each system, one 25 t ha−1 compost application was made in May 2018 before bell pepper planting. Soil samples were taken before application and four times after application, approximately every six weeks. Plant growth and yield were also monitored. The second part involved lab experiments that tested the effects of extracts of the above composts on the growth of V. dahliae on selective media in Petri dishes. All four compost treatments significantly suppressed soil pathogen populations in June, two weeks after the application of treatments, with plant-based amendments presenting greater effects than DC. These suppressive effects disappeared within eight weeks (for DC) or 14 weeks (for GC, ODC and CRC) after application. The effects of composts on soil chemical properties, V. dahliae abundance and bell pepper growth and yield parameters were generally similar in both organic and conventional fields. In the Petri dish assays, plant composts reduced V. dahliae growth by 40–60 %, especially during the first week after application.

Control of Filth Flies, Cochliomyia macellaria (Diptera: Calliphoridae), Musca domestica (Diptera: Muscidae), and Sarcophaga bullata (Diptera: Sarcophagidae), Using Novel Plant-Derived Methyl Ketones.

Filth flies live in close proximity to humans and livestock and transmit pathogens. Current control relies on chemical insecticides, and flies can develop resistance to these insecticides. The public is also interested in natural and safer insecticides. Therefore, alternative pesticides compatible with the synanthropic nature of flies are needed. Four plant aliphatic methyl ketones were evaluated for control of adult house flies, Musca domestica L., blow flies, Cochliomyia macellaria (F.), and gray flesh flies, Sarcophaga bullata (Parker). In sealed petri dish assays, 2-heptanone, 2-octanone, 2-nonanone, and 2-undecanone exhibited fumigant activity against house flies with 24-h LC50s of 6.9, 7.5, 8.0, and 9.2 µg/cm3, respectively. Further research focused on undecanone (a U.S. EPA-registered biopesticide). When tested in larger enclosures at 1.7, 2.3, and 2.8 µg/cm3, undecanone provided 60.4, 82.2, and 94.4% house fly mortality; 56.9, 75.6, and 92.5% flesh fly mortality; and 62.1, 84.5, and 97.9% blow fly mortality, respectively, after a 2-h exposure. In a two-choice behavioral assay with 194.6 µg/cm2 of the test compound on the treatment versus an untreated surface of the same area, the overall mean repellencies for blow flies were 84.7% for undecanone versus 87.6% for N,N-diethyl-meta-toluamide (DEET). For house flies, mean repellencies were 80.7% for undecanone and 84.9% for DEET. The house fly topical LD50 for undecanone was 58.1 µg per fly. Undecanone was far less expensive for filth fly control than the gold standard for insect fumigation, methyl bromide.

A Petri dish test for detection of flumetsulam and MCPA resistance in giant buttercup (Ranunculus acris subsp. acris)

ABSTRACT A quick test to enable early detection of flumetsulam and MCPA resistance in Ranunculus acris L. subsp. acris was developed in a series of Petri dish assays and pot trials. Initial experiments used seeds (Experiment 1) or cotyledonary seedlings (Experiment 2) from two R. acris populations of known past herbicide exposure, in Petri dishes containing broad ranges of herbicide concentrations. A further seedling assay (Experiment 3) was carried out using refined ranges of herbicide concentrations and four populations of R. acris of known past herbicide exposure. Percent germination, numbers of new true leaves, root length and green biomass were recorded at intervals after treatment. Results were compared with the LD50 values calculated from dose response pot trials carried out concurrently using the same R. acris populations and herbicides (Experiment 4), in order to validate the results. Percent green biomass 29 DAT at 5 µM for flumetsulam and 28 DAT at 25–50 µM for MCPA, gave accurate detection of resistant populations, as shown by high correlations with LD50 values obtained in the pot trials and consistency with results from previous studies.

Laboratory and field tests of predation on the cereal leaf beetle, Oulema melanopus (Coleoptera: Chrysomelidae)

ABSTRACTThe cereal leaf beetle (CLB), Oulema melanopus (L.) (Coleoptera: Chrysomelidae), is an invasive pest in North America recently reported in the Canadian Prairies. We performed a series of laboratory assays to identify potential predators and a field study to quantify predation of CLB eggs. In no-choice Petri dish assays, ground beetles (Carabidae), rove beetles (Staphylinidae), and several common lady beetle species (Coccinellidae) were the most consistent predators of eggs and larvae. Nabis spp. (Hemiptera: Nabidae) and wolf spiders (Araneae: Lycosidae) consumed many larvae, but did not consume eggs. Hippodamia spp., Coccinella septempunctata (L.) (Coleoptera: Coccinellidae), and Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) also fed on CLB eggs on potted plants when an alternative food source was available, Sitobion avenae (Fabricius) (Hemiptera: Aphididae). In our field study, we found an average of 24.5% of sentinel eggs disappeared over a 24 h period, likely due to predation. Our results suggest that generalist predators can play an important role in the biological control of CLB, and warrant further study.

Aqueous Leaf Extract of Duranta repens Promotes Seed Germination and Seedling Growth of Salinity-Stressed Solanum lycopersicum Seedlings.

Aqueous extract of Duranta repens leaves was investigated for its allelopathic effect on Solanum lycopersicum seedlings germinated and grown under salinity condition. The study was carried out using both laboratory petridish and pot assays to simulate the plant’s immediate environmental conditions. The experiment consisted of 5 groups (1-5) each containing 4 replicates (of 10 seeds). Group 1 was treated with distilled water; Group 2 was treated with 5 mM NaCl; Group 3 was treated with Duranta repens aqueous leaf extract, Group 4 was treated with a mixture of 5 mM NaCl and the extract (2:1 v/v) and Group 5 was treated with a mixture of 5 mM NaCl and the extract (1:2 v/v). Results from the studies revealed that treatment with NaCl caused significant (p &lt; 0.05) reduction in percentage germination and growth parameters (plumule and radicle lengths) of S. lycopersicum seedlings, when compared to those treated with distilled water and D. rupens aqueous leaf extract. NaCl treatment (Group 2) also caused an increase in malondialdehyde (MDA) and also increased the activities of superoxide dismutase (SOD) and catalase (CAT) while reducing chlorophyll concentration of the plants. However, in the presence of the extract, the adverse effects of the NaCl were attenuated, implying that the extract improved tolerance of S. lycopersicum seedlings. In conclusion, the findings of this study indicate that the constituents of the extract may play a positive role in plant survival under saline conditions and could be employed in the management of soil salinity problem in agriculture.

Interaction between Triticum aestivum plants and four fusarium head blight species on the level of pathogenicity: Detected in an in vitro Petri-dish assay

The interaction between bread wheat (Triticum aestivum L.) plants and four filamentous species of the Fusarium genus (the causal agent of Fusarium head blight, FHB) was analyzed in an in vitro Petri-dish assay. Pathogenicity criteria as well as germination rate reduction, standardized area under disease progress curve (AUDPCstandard), and coleoptile length reduction were investigated in seeds and six-day-old seedlings showing a moderately level of quantitative resistance, after inoculations with 16 FHB isolates. AUDPCstandard did differentiate FHB isolates and the other two pathogenicity criteria did not. It was not possible to cluster the isolates based on their species origins because of similarity in pathogenic level among the 16 fungal isolates. Cultivar-specific pathogenicity has been detected. The values of disease incidence and disease severity involved in previous artificial head and floret inoculations showed significant correlation with AUDPCstandard: r=0.653** and r=0.559*, respectively. AUDPCstandard could be of potential use in evaluating the pathogenicity of FHB in adult wheat plants.