Greenhouse Bioassays Research Articles

Design, Synthesis, and 3D-QASR of Oxazoline Derivatives Containing an S-S Moiety as Potential Acaricide.

To mitigate the detrimental effects of agricultural pest mites on crop yield, an active substructure splicing strategy was employed to modify etoxazole by introducing an S-S moiety. The target products were obtained efficiently via a bilateral disulfurating reagent (DSMO), which was developed by our group. The leaf dip method was used to evaluate the activities of the designed target compounds against the eggs and larvae of the spider mite (Tetranychus cinnabarinus). Most of the target compounds exhibited good efficacy in controlling the larvae and eggs of T. cinnabarinus. Based on these results, a three-dimensional quantitative structure-activity relationship (3D-QSAR) model was established to guide the construction of compound 7l. Notably, compound 7l exhibited a better activity against T. cinnabarinus eggs (LC50 = 0.0035 mg/L) compared to etoxazole (LC50 = 0.2990 mg/L). Greenhouse bioassays indicated that compound 7l exhibits excellent acaricidal activity against egg of T. cinnabarinus, which is better than the etoxazole at 1.0 mg/L. Additionally, some of the compounds showed inhibitory effects against Dickeya zeae (D. zeae), Xanthomonas campestris pv campestris (Xcc), Xanthomonas oryzae pvoryza (Xoo), and Xanthomonas oryzae pvoryzicola (Xoc). Furthermore, compounds 7l not only exhibited relatively potent against Plutella xylostella activities (LC50 = 24.0 mg/L) but also had low toxicity (LC50 > 11.0 μg/bee) to Apis mellifera. In conclusion, the current experimental results suggest that oxazoline derivatives containing an S-S moiety have the potential to serve as lead compounds for the development of novel acaricide agents.

Enhancing garlic propagation through functional biopolymer-based propagules coatings: A bio-nanotechnological strategy

Integrating agricultural, chemical, and technological knowledge is crucial for developing bio-nanotechnologies to improve agricultural production. This study explores the innovative use of biopolymeric coatings, based on sodium alginate and sodium alginate + Laponite® (nanoclay), containing biostimulants (tryptophol and thymol) or not, on garlic cloves. These coatings were analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR-ATR), and scanning electron microscopy (SEM). Greenhouse bioassays showed improvements in garlic shoot plant biomass with both treatments: sodium alginate biopolymer and sodium alginate biopolymer plus Laponite®. In the field experiment, garlic plants treated with sodium alginate, in combination with conventional pesticide treatments, resulted in better quality garlic bulbs, where larger garlics were harvested in this treatment, reducing commercial losses. In tropical garlic crops, obtaining plants with greater initial vigor is essential. Our results highlight the potential of these bio-nanotechnological strategies to enhance garlic propagation, ensuring environmental protection and food security.

Origins of Susceptibility to Insect Herbivores in High-Yielding Hybrid and Inbred Rice Genotypes.

Several studies have reported higher damage from insect herbivores to hybrid compared to inbred (pure line) rice. We used a collection of 20 hybrid and 12 inbred genotypes from diverse origins to test the hypotheses that hybrid rice susceptibility is due to (a) the hybrid plant type and/or (b) rice phylogeny. We challenged the genotypes with Nilaparvata lugans (BPH), Sogatella furcifera (WBPH) and Scirpophaga incertulas (YSB) in greenhouse and screenhouse bioassays and monitored herbivores in field plots. We used single nucleotide polymorphic (SNP) markers to assess genetic similarities between the genotypes and found that the hybrids and inbreds formed two distinct clusters regardless of origin. In the screenhouse, hybrids were more susceptible than inbreds to YSB; however, resistant hybrids and susceptible inbreds were also apparent from both the screenhouse and field plots. Plant biomass was the best predictor of susceptibility to YSB. Plant origin had a greater effect than plant type on susceptibility to BPH and WBPH. WBPH was the most abundant planthopper in the field plots where numbers were highly correlated with planthopper fitness in the greenhouse bioassays. Our results provide evidence that high-yielding hybrids that are relatively resistant to herbivores can be achieved through careful breeding. The avoidance of susceptible genotypes during breeding should remain a key element of integrated rice pest management.

Cotton plants overexpressing the Bacillus thuringiensis Cry23Aa and Cry37Aa binary-like toxins exhibit high resistance to the cotton boll weevil (Anthonomus grandis)

The cotton boll weevil (CBW, Anthonomus grandis) stands as one of the most significant threats to cotton crops (Gossypium hirsutum). Despite substantial efforts, the development of a commercially viable transgenic cotton event for effective open-field control of CBW has remained elusive. This study describes a detailed characterization of the insecticidal toxins Cry23Aa and Cry37Aa against CBW. Our findings reveal that CBW larvae fed on artificial diets supplemented exclusively with Cry23Aa decreased larval survival by roughly by 69%, while supplementation with Cry37Aa alone displayed no statistical difference compared to the control. However, the combined provision of both toxins in the artificial diet led to mortality rates approaching 100% among CBW larvae (LC50 equal to 0.26 PPM). Additionally, we engineered transgenic cotton plants by introducing cry23Aa and cry37Aa genes under control of the flower bud-specific pGhFS4 and pGhFS1 promoters, respectively. Seven transgenic cotton events expressing high levels of Cry23Aa and Cry37Aa toxins in flower buds were selected for greenhouse bioassays, and the mortality rate of CBW larvae feeding on their T0 and T1 generations ranged from 75% to 100%. Our in silico analyses unveiled that Cry23Aa displays all the hallmark characteristics of β-pore-forming toxins (β-PFTs) that bind to sugar moieties in glycoproteins. Intriguingly, we also discovered a distinctive zinc-binding site within Cry23Aa, which appears to be involved in protein-protein interactions. Finally, we discuss the major structural features of Cry23Aa that likely play a role in the toxin’s mechanism of action. In view of the low LC50 for CBW larvae and the significant accumulation of these toxins in the flower buds of both T0 and T1 plants, we anticipate that through successive generations of these transgenic lines, cotton plants engineered to overexpress cry23Aa and cry37Aa hold promise for effectively managing CBW infestations in cotton crops.

Comparative effectiveness of carbon nanoparticles and biochar in alleviating copper stress in corn (Zea mays L.)

The application of carbon nanoparticles (CNPs) and biochar in agriculture for improving plant health and soil quality and alleviating metal stress offers alternative approaches to meet the ever-increasing demand for food. However, poor understanding of their roles in improving crop production under Cu stress represents a significant obstacle to their wide application in agriculture. To clarify how CNPs and biochar affect corn (Zea mays L.) seed germination, seedling growth, plant health, and nutrient uptake under different Cu stress levels, soil-less Petri-dish and greenhouse soil-based bioassays were conducted. The results revealed that CNPs and biochar stimulated corn seed germination and seedling growth. Besides, they were effective in immobilizing Cu2+ sorption in sandy soil and alleviating Cu stress for plant growth, as shown by the increased plant height and dry biomass. The plant nutrient uptake efficiency (NUE) was significantly increased by CNPs, with a maximum increase of 63.1% for N and 63.3% for K at the highest Cu2+ stress level (400 mg Cu2+ L−1). In contrast, non-significant effects on NUE were observed with biochar treatments regardless of Cu stress levels. Interestingly, CNPs significantly increased plant uptake of Cu in the Petri dish test, while biochar inhibited plant uptake of Cu under both experimental conditions. Principle component analysis (PCA) and Pearson correlation analysis indicated that CNPs mitigated Cu stress mainly by elevating antioxidant enzyme activities, enhancing plant photochemical efficiency, and increasing plant uptake of N and K, while biochar was more likely to reduce bioavailability and uptake of Cu in the plant. These findings have great implications for the application of CNPs and biochar as plant growth stimulators and de-toxicity agents in agriculture.

Causal agents of Stemphylium-induced foliar diseases of tomatoes and other Solanaceae hosts in Brazil.

An extensive survey was done to clarify the prevalent Stemphylium species on Solanaceae plants across Brazil, and their host ranges. Eighty nine (89) Stemphylium isolates were obtained from naturally infected tomatoes as well as S. paniculatum, potato, eggplant, scarlet eggplant (Solanum aethiopicum var. gilo), Physalis angulata, and Capsicum species. Phylogenetic analyses encompassing the ITS-5.8S rDNA and glyceraldehyde-3-phosphate dehydrogenase genomic regions placed the isolates into two distinct groupings with either Stemphylium lycopersici or S. solani. Isolates of S. lycopersici (n=81) were obtained infecting tomato, potato, eggplant, S. paniculatum, and P. angulata. Isolates of S. solani (n=8) were detected in natural association with scarlet eggplant and tomato. Two isolates of S. lycopersici displayed a wide experimental host range in greenhouse bioassays, infecting accessions of 12 out of 18 species. Ocimum basilicum (Lamiaceae) was the only experimental host outside the Solanaceae family.

Evaluating cover crop tolerance to corn residual herbicides using field-treated soil in greenhouse bioassay

AbstractMore growers across the U.S. Midwest are considering interseeding or overseeding cover crops into corn for soil health purposes. One challenge of this practice is the potential injury from soil residual herbicides applied preemergence (PRE) for weed control in corn to the interseeded and overseeded cover crop species. Field-treated soil was collected in 2021 and 2022 at Janesville, WI, and Lancaster, WI, to investigate the impact of PRE residual herbicides on establishment of interseeded and overseeded cover crops via greenhouse bioassay. Soil samples (0 to 5 cm depth) were collected from field experiments at 0, 10, 20, 30, 40, 50, 60, and 70 days after treatment (DAT). Treatments consisted of 14 single and multiple sites of action (SOAs) PRE herbicides plus a nontreated check (NTC). Four bioindicator cover crop species were used in the greenhouse bioassay: annual ryegrass, cereal rye, radish, and red clover. Cover crop biomass was collected 28 d after bioassay seeding. Cover crop species responded differently across herbicide treatments. Annual ryegrass and cereal rye were sensitive to treatments containing herbicide Group 15, whereas Groups 2, 4, 5, 14, and 27 had minimal impact on their establishment when field soil was collected at 30 DAT (interseeding scenario) and 70 DAT (overseeding scenario) compared to the NTC. Radish and red clover were sensitive to herbicide Groups 2, 4, and 27, whereas Groups 5, 14, and 15 had minimal impact on their establishment. Annual ryegrass, radish, and red clover were more sensitive to PRE herbicides containing two and three SOAs than to herbicides with a single SOA. On the basis of these greenhouse bioassay results, cover crop species should be carefully selected depending on the soil residual herbicide when interseeded and overseeded into corn. Field studies will be conducted to validate these results and support recommendations to growers interested in this system.

Toxicity of Bacillus sp. (Bacillales: Bacillaceae) on the fungus gnats, Bradysia aff. ocellaris larvae (Diptera: Sciaridae)

Bacillus thuringiensis (Bt) Berliner has potential for use in insect management. Its use can be an alternative for the management of Bradysia aff. ocellaris (Comstock), considered one of the main strawberry pests in a soilless system. Therefore, the objective of this work was to evaluate the toxicity of different bacteria on B. aff. ocellaris in laboratory and greenhouse bioassays. The following isolates were used in the experiments: Bacillus circulans (Bc), B. thuringiensis var. oswaldo cruzi (Bto) or B. thuringiensis var. israelensis (Bti) and B. thuringiensis var. kurstaki (Btk) In the laboratory, B. aff. ocellaris larvae showed high susceptibility to Bti isolate (92 % mortality) 14 days after treatment exposure (DAET). In contrast, the isolates Bc, Bto, and Btk showed less than 32 % mortality, not differing from the control treatment (water – 22 % mortality). According to the concentration-response curves the values of lethal concentration LC50 and LC90 were 4 x 106 CFU.mL-1 and 4 x 1015 CFU.mL-1. By applying Bti (4 × 1012 CFU.mL-1) at the base of strawberry plants growing in plastic pots containing commercial plant substrate, a reduction of 26 % in the emergence of B. aff. ocellaris was observed. According to these results, the Bti isolate is considered promising for the formulation of bioinsecticides based on Bt for the management of B. aff. ocellaris in strawberry culture.

Staphylococcus microbes in the bovine skin microbiome attract blood-feeding stable flies

The human skin microbiome reportedly contributes to the attraction of mosquitoes to human hosts. We tested the hypothesis that bovine skin microbes affect the attraction of blood-feeding stable flies, Stomoxys calcitrans, to their bovine hosts. Microbes were collected from a calf and adult cow, and subsequently isolated and identified by mass spectrometry and genetic sequencing. Separate groups of (i) four Staphylococcus congeners (S. chromogenes, S. sciuri, S. simulans, S. succinus) and (ii) three bacterial heterogeners (Glutamicibacter protophormiae, Corynebacterium stationis, Wautersiella sp.) grown on agar, each attracted flies in still-air olfactometers, as did each Staphylococcus congener singly. The four Staphylococcus microbes also attracted flies in room bioassays. In greenhouse bioassays with paired black barrels as visual (surrogate host) stimuli, the treatment barrel baited with S. sciuri on agar induced significantly more fly alighting responses than the control barrel with sterile agar. This treatment effect could not be demonstrated on a cattle farm, possibly because of chemically and visually complex surroundings. Ammonia emitted by Staphylococcus microbes attracted flies, and a synthetic blend of microbe odorants enhanced the attractiveness of ammonia. Optimal attraction of stable flies to bovine microbes likely requires the integration of multimodal host cues.

Lyophilized biopolymeric beads of chitosan-xanthan with edible fungus Laccaria laccata (Scop.) Cooke as forest ectomycorrhizal biofertilizers

Objective: To evaluate whether or not the spores of the edible fungus Laccaria laccata (Scop.) Cooke encapsulated in a lyophilized biopolymeric matrix of chitosan-xanthan can cause ectomycorrhization in Pinus greggii Englem. trees under greenhouse conditions. Methodology: Spores of the edible ectomycorrhizal fungus L. laccata were encapsulated in beads made with the chitosan-xanthan biopolymer. The embedded spores were analyzed using scanning electron microscopy to evaluate possible structural damage. Next, these beads were used as biofertilizers in a greenhouse bioassay using Pinus greggii plants to evaluate their ability to be ectomycorrhized. The bioassay lasted 270 days. Subsequently, stereoscopic and bright field microscopy was used to determine if the roots of the pines had been subjected to an ectomycorrhizal colonization. Additionally, the growth of inoculated plants was evaluated compared to non-inoculated plants, 180 and 270 days after sowing. Results: The spores of L. laccata encapsulated in the biopolymeric matrix formed ectomycorrhizae in the roots of P. greggii. The percentages of ectomycorrhizal colonization in the plants ranged from 80 to 90%, demonstrating that the production of chitosan-xanthan biopolymeric beads can maintain the viability of the spores of the ectomycorrhizal fungus evaluated and extensively colonize the roots of Pinus greggii. Study Limitations/Implications: The biopolymeric matrix beads that contain spores of the fungus L. laccata can induce ectomycorrhization in trees of forest importance. Conclusions: The spores of an edible ectomycorrhizal fungus encapsulated in the chitosan-xanthan biopolymer have potential as a forest biofertilizer, which opens the opportunity to scale its use up to an industrial level.

Mutations in the acetolactate synthase (ALS) enzyme affect shattercane (Sorghum bicolor) response to ALS-inhibiting herbicides

BackgroundShattercane [Sorghum bicolor (L.) Moench ssp. Arundinaceum (Desv.)] is a competitive weed in North America's corn, soybean, sorghum, and other agronomic crops. Control of shattercane with POST herbicides in corn became possible with the introduction of acetolactate synthase (ALS)-inhibiting herbicides in the 1980s, and their extensive use resulted in the evolution of ALS-inhibitors resistant shattercane.ResultsShattercane seeds were collected from 16 south-eastern and south-central Nebraska fields that were treated with primisulfuron for three consecutive years. Three resistant plants were found in greenhouse evaluations of more than 30,000 plants. Results from a greenhouse bioassay conducted to assess the response of each shattercane biotype to ALS-inhibiting herbicides showed a differential response to ALS inhibitors within and between chemical classes. Biotype P8-30 was resistant or partially resistant to all ALS-inhibiting herbicides applied and displayed a unique amino acid sequence substitution (Trp574 to Leu) relative to the other two resistant biotypes, P2-205 and P9-102. Whole plant dose–response studies confirmed a 4- to the 12-fold level of primisulfuron resistance in three shattercane biotypes compared with the known primisulfuron-susceptible shattercane biotype. The ALS gene was sequenced using primers designed from the corn ALS sequence to identify mutations in the ALS gene that confer resistance. A total of seven nucleotide substitutions were detected in the three herbicide-resistant biotypes P2-205, P8-30, and P9-102. These biotypes are being crossed to adapted sorghum lines (grain, sweet, and forage) to broaden germplasm with resistance to ALS-inhibiting herbicides.ConclusionThe discovery of these mutants should accelerate the development of sorghum genotypes that tolerate ALS-based herbicides, which provide additional choices for sorghum farmers to control weeds, especially grasses, in their fields.

Dose-response of five weed species to indaziflam and oxadiazon

AbstractIndaziflam and oxadiazon are efficacious preemergence herbicides used in warm-season turfgrass because of their persistence and residual activity. It is beneficial to quantify effective concentrations for preemergence control of summer annual weeds and determine whether these concentrations are maintained throughout weed emergence periods. Therefore, greenhouse bioassays were conducted with barnyardgrass, broadleaf signalgrass, doveweed, large crabgrass, and purple nutsedge. Treatments included indaziflam at 0, 4, 8, 12, 17, 21, 25, 29, 33, and 37 g ai ha−1 or oxadiazon at 0, 420, 841, 1,260, 1,681, 2,102, 2,354, 2,942, 3,363, and 3,783 g ha−1. Although preemergence herbicides are not used to control perennial weeds, purple nutsedge was included to investigate the effect of selected herbicides on its growth. Herbicide EC50, EC80, and EC90 for seedling emergence inhibition and shoot and root mass reduction were quantified from log-logistic dose–response curves. Herbicide concentration that remains from a preemergence application during the regional species-specific periodicity of emergence was predicted using first-order kinetics equations. Indaziflam and oxadiazon controlled seedling emergence 14 d after treatment (DAT) in the evaluated annual weeds and shoot and root mass in all species 84 DAT. Indaziflam applied in mid-March at 33 g ha−1 may provide up to 90% seedling emergence inhibition in large crabgrass and signalgrass; up to 80% in barnyardgrass; and up to 50% in doveweed. Oxadiazon applied in mid-March at 3,363 g ha−1 may provide up to 80% seedling emergence inhibition in all species. Indaziflam and oxadiazon may control up to 80% shoot mass and up to 50% root mass, respectively, in purple nutsedge and 80% to 90% shoot or root mass in other species. Such information is useful in evaluating adequacy of herbicide management practices for season-long weed control, and it aids turfgrass managers in applying preemergence herbicides at optimal timing based on target weed species.

Evaluation of Coffea arabica Cultivars for Resistance to Meloidogyne konaensis

Coffee is an important agricultural crop for the State of Hawaii. Developing new coffee cultivars with resistance to damaging pests and diseases is crucial for improving production and maintaining the profitability of the industry. With the recent discovery of Hemileia vastatrix, coffee leaf rust (CLR), to Hawaii there is a strong interest in replanting with CLR-resistant germplasm. However, when selecting an appropriate cultivar for replanting, susceptibility to other pathogens, such as plant-parasitic nematodes, should be taken into consideration. Meloidogyne konaensis, the Kona coffee root-knot nematode, causes severe destruction of the root system, reducing the yield and causing the mortality of susceptible Coffea arabica cv. Typica trees. Fortunately, resistance to root-knot nematodes has been found in some C. arabica germplasm. In this study, accessions of wild Ethiopian C. arabica and two CLR-resistant C. arabica cultivars, Tupi-HI and Obata, were evaluated for resistance to M. konaensis in a greenhouse bioassay. All Ethiopian accessions retained high levels of resistance, resulting in reproductive factors (Rfs) lower than 1.0, and low root-rot ratings. Tupi-HI was highly susceptible to M. konanensis, with an Rf value of 7.12, whereas Obata was slightly susceptible, with an Rf value of 2.33. Both cultivars had high root-rot ratings, suggesting intolerance to the nematode. Hybridizing Ethiopian C. arabica with Tupi-HI or Obata may result in new elite cultivars, resistant to both H. vastatrix and M. konaensis.

Chemical profiling of Artemisia herba-alba, Cuminum cyminum, Cinnamomum camphora, and Salvia rosmarinus essential oils and assessment of their insecticidal potential to control the wild cochineal Dactylopius opuntiae (Cockerell)

The wild cochineal, Dactylopius opuntiae (Hemiptera: Dactylopiidae), has become a serious pest of prickly pear Opuntia ficus-indica L. in the Mediterranean region. The present study investigated the insecticidal activity of four essential oils, namely Cuminum cyminum, Cinnamomum camphora, Artemisia herba-alba, and Salvia rosmarinus against D. opuntiae nymphs and adult females in laboratory and greenhouse bioassays. Laboratory tests showed that at a concentration of 2.5%, C. cyminum oil was the most effective (inducing 100% nymph mortality at 3 h after treatment), followed by C. camphora, A. herba-alba and S. rosmarinus oils which recorded comparable mortality rates ranging from 89.40 to 100%, while S. rosmarinus and C. cyminum oils induced the highest mortality rates on adult females (88% and 86%, respectively) 8 days after treatments. Under greenhouse conditions, the combined application of C. cyminum oil (2.5%) and black soap (10 g/L) showed the highest nymphs’ mortality (100%) at 3 days after application. Adult female mortality in the greenhouse was lower than in the laboratory bioassay for all tested oils, with S. rosmarinus inducing 47% mortality at 2.5% at 14 days after the second spray. Eucalyptol was the main constituent of S. rosmarinus (41.20%) and C. camphora (56.47%) oils, and thujon-camphor was the major chemotype of A. herba-alba (30.55%/28.16%), while cuminaldehyde was the main compound of C. cyminum oil seeds (32.53%). These findings showed that the compounds of the two essential oils S. rosmarinus and C. camphora potential sources of insecticidal compounds and warrant further investigation.

Characterizing atrazine, mesosulfuron‐methyl, and topramezone bioavailability in North Carolina soils using greenhouse bioassays

AbstractHerbicide carryover injury to rotational crops can vary in severity depending on the influence of soil properties on herbicide bioavailability. Greenhouse bioassays were conducted with soybean, radish, and canola to evaluate differences in the bioavailability of three herbicides with carryover risk, atrazine, mesosulfuron‐methyl, and topramezone. Bioassays were conducted in three varying regional soil types with nine herbicide treatment rates including a control. Plant visual injury was evaluated weekly, and aboveground dry biomass was weighed after harvest of soybean 28 days after emergence (DAE) and radish and canola 21 DAE. A log‐logistic dose–response regression model was used to quantify herbicide‐effective concentrations for 30% (EC30), 50% (EC50), and 80% (EC80) visual injury and aboveground dry biomass reduction in each soil type. Relative herbicide‐soil bioavailability was determined through comparisons of herbicide‐effective concentrations among soil types. Pearson correlation revealed that atrazine, mesosulfuron‐methyl, and topramezone EC30 for all species were positively correlated to soil organic matter (OM) content (r = 0.56, 0.48, and 0.40, respectively) and cation exchange capacity (CEC) (r = 0.43, 0.41, and 0.45). Topramezone EC80 for soybean and radish was positively correlated to soil clay content (r = 0.51) and silt content (r = 0.51) and negatively correlated to sand content (r = −0.51) and pH (r = −0.52). Decreased atrazine, mesosulfuron‐methyl, and topramezone bioavailability in soil with high OM and CEC, decreased topramezone bioavailability in coarse‐textured soil and at high soil pH, and differential herbicide sensitivity of crop species can inform grower decisions on herbicide selections and rotational crop plans.

Efficacy of ethanolic seed extracts of Annona spp. against Aphis glycines

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an important pest that can cause significant economic damage to soybean. Synthetic insecticides are currently employed as the main management strategy to control A. glycines; however, over-use of these products has stimulated research in the development of alternative management methods, including botanical derivatives. In this study, we evaluated the bioactivity of Annona mucosa and A. muricata seed extracts and a formulation based on acetogenins (Anosom® 1 EC, 10,000 ppm) compared to the pyrethroid insecticide lambda-cyhalothrin (Warrior II®) on A. glycines. Initially, the insecticidal effect was assessed in vial bioassays and the concentration-response curves were estimated (LC50/LC90 for A. muricata 305.721 ppm/1290.3 ppm and A. mucosa 134.229 ppm/487.890 ppm, respectively). In the systemic effect bioassay, the same extracts were used (at 100, 500, 1,000, 5000 and 10,000 ppm), showing a reduction in the number of insects on the trifoliates. Both extracts at LC50 and LC90 were used in a behavior test, indicating that they are repellent and Warrior II® was attractive for the insects. The LC90 rates were also used in lethal time (LT) and in greenhouse bioassays. The LT50 for A. mucosa and A. muricata extracts was around 20 h. All treatments showed insect mortality rates above 65%, reaching 100% for Warrior II®, followed by the LC90 of A. mucosa (92.1%). The results demonstrate the potential of Annona spp. derivatives for the management of A. glycines in soybean, and these Annonaceae-derived seed extracts could likely serve as an additional IPM tool to improve A. glycines control strategies in organic farming systems.

Suppression of Meloidogyne incognita by co-application of chitin and Streptomyces nigrescens (AMV1033)

ABSTRACT Root-knot nematodes, Meloidogyne spp., are among the most polyphagous and ubiquitous plant-parasitic nematodes. Among other management strategies, organic soil amendments and biological control agents are proposed. In this study, potential synergistic benefits of co-application of chitin and Streptomyces nigrescens (AMV1033) against M. incognita were determined. Hypothetically, chitinolytic activity of these microbes deteriorates nematode eggshells reducing nematode numbers. Additional chitin could enhance actinobacteria activity for nematode suppression. In in vitro and greenhouse bioassays, suppressive capacities of M. incognita by chitin amendment at 50 mg/g of soil (chitin-low) and at 500 mg/g of soil (chitin-high; only tested in the greenhouse), Streptomyces nigrescens (AMV1033) and the co-application of AMV1033 with the two chitin rates were tested. After four weeks of in vitro egg incubation, the number of extractable second-stage juveniles (J2s) was significantly reduced after co-application of chitin-low plus AMV1033, and less so after sole application of AMV1033. In a similar 2-week in vitro assay with M. incognita egg masses, the numbers of J2s were similarly reduced after the same treatments. In a watermelon greenhouse bioassay with M. incognita, root infection was decreased after co-application of AMV1033 plus chitin-high or chitin-low compared to the non-treated control. After these treatments, plants grew similarly as in the control, whereas sole chitin-high addition led to severe plant damage. Some amelioration of phytotoxicity of chitin-high by the co-application of AMV1033 was found. The results of the study demonstrated the potential to enhance suppression of M. incognita by S. nigrescens by co-application of chitin.

Interactions Among Heterodera glycines, Macrophomina phaseolina, and Soybean Genotype.

Heterodera glycines, the soybean cyst nematode (SCN), and fungal pathogen Macrophomina phaseolina are economically important soybean pathogens that may coinfest fields. Resistance remains the most effective management tactic for SCN, and the rhg1-b resistance allele derived from plant introduction 88788 is most commonly deployed in the northern United States. The concomitant effects of SCN and M. phaseolina on soybean performance, as well as the effect of the rhg1-b allele in two different genetic backgrounds, were evaluated in three environments (during 2013 to 2015) and a greenhouse bioassay. Within two soybean populations, half of the lines had the rhg1-b allele, and the other half had the susceptible allele in the backgrounds of the cultivars IA3023 and LD00-3309. Significant interactions between soybean rhg1-b allele and M. phaseolina-infested plots were observed in 2014. In all experiments, initial SCN populations (Pi) and M. phaseolina in roots were associated with reduced soybean yield. SCN reproduction factor (RF = final population/Pi) was affected by SCN Pi, rhg1-b, and genetic background. A background-by-genotype interaction on yield was observed only in 2015, with a stronger rhg1-b effect in the LD00-3309 background, which suggested that the susceptible parent 'IA3023' is tolerant to SCN. SCN female index from greenhouse experiments was compared with field RF, and Lin's concordance and Pearson's correlation coefficients decreased with increasing field SCN Pi in soil. In this study, both SCN and M. phaseolina reduced soybean yield asymptomatically, and the impact of SCN rhg1-b resistance was dependent on SCN virulence but also population density.

A New Method of Preparing Aurone by Marine Actinomycetes and Its Potential Application in Agricultural Fungicides.

A strain of marine actinomycetes was isolated from an intertidal zone and identified as Streptomyces cinereoruber. Through the fermentation of this strain, a compound with fungicidal activity was extracted and purified. Using mass spectrometry (MS) and nuclear magnetic resonance (NMR) data, the metabolite was determined to be an aurone. The toxicity of the aurone toward four kinds of tumor cells-SH-SY5Y, HepG2, A549, and HeLa cells-was verified by the MTT method, delivering IC50 values of 41.81, 47.19, 63.95, and 51.92 μg/mL, respectively. Greenhouse bioassay showed that the aurone exhibited a high fungicidal activity against powder mildew (Botrytis cinerea), cucurbits powder mildew (Sphaerotheca fuliginea (Schlecht ex Ff.) Poll), and rice blast (Pyricularia oryzae).

Factors influencing successful establishment of exotic Pinus radiata seedlings with co-introduced Lactarius deliciosus or local ectomycorrhizal fungal communities.

An introduction of exotic or non-native trees may fail due to a lack of suitable fungal partners. We planted exotic Pinus radiata in Xifeng, Guizhou Southwest China. Strategies to introduce P. radiata seedlings either colonized with an ectomycorrhizal fungus (EcMF), Lactarius deliciosus, or expect them to form familiar/new associations with local EcMF in a new habitat were studied to know how P. radiata could be successfully established over a period of 2.5 years. Plant height and needle nutrient acquisition, the persistence of the co-introduced L. deliciosus, and fungal community composition in rhizosphere soil and root tips were analyzed. In addition, a greenhouse bioassay experiment of local soil to assess the differences in the EcMF community between exotic and native pine seedlings was also conducted. The current results demonstrated that P. radiata could establish in the Xifeng plantation with or without co-introduced L. deliciosus. The co-introduced L. deliciosus might be naturalized with P. radiata in the new area since it has been fruited for 2 years with high relative abundance in mycorrhizosphere soil. L. deliciosus pre-colonization significantly altered the mycorrhizosphere fungal composition and it had a positive correlation with nitrogen acquisition of P. radiata. Host identity had no effect on fungal composition since exotic P. radiata and native P. massoniana recruited similar local fungal communities in early establishment or in plantation. The cosmopolitan species Suillus placidus, with high relative abundance, formed a familiar association with P. radiata. The greenhouse bioassay experiment further showed that Suillus sp. contributed relatively higher total extracellular enzymes by forming ectomycorrhizas with P. radiata and the same type of ectomycorrhiza of P. radiata and P. massoniana showed different enzymatic functions. Our study indicated that exotic P. radiata could be a suitable tree capable to get established successfully in the Xifeng plantation either by interaction with the co-introduced L. deliciosus or with a local EcMF, but we should be cautious about large-scale planting of P. radiata. L. deliciosus persisted in plantation and more attention should be paid to local EcMF community changes induced by the introduced L. deliciosus.