Tomato Leaf Discs Research Articles

Acaricidal Efficacy of Abamectin against Tetranychus urticae Populations When Combined with Entomopathogenic Fungi

Tetranychus urticae (Acari: Tetranychidae) is a widespread and serious mite pest that infests tomato plants and causes economic losses worldwide. We investigated the acaricidal efficacy of two isolates of entomopathogenic fungi (EPF) Metarhizium robertsii (WG-7) and Beauveria bassiana (WG-12) alone and in combination with abamectin when applied topically to tomato leaf discs in the laboratory against T. urticae. We also evaluated the establishment and proliferation of T. urticae mite life stages on tomato plants in the greenhouse after application of each of the above treatments. The combination of abamectin with each EPF caused 100% mortality in T. urticae immatures after 2 days while each EPF or abamectin alone caused moderate mortality, not exceeding 74.2% 3 days post-exposure. Complete (100%) mortality of adults was observed after 5 days in leaf discs treated with M. robertsii plus abamectin whereas B. bassiana plus abamectin caused 100% mortality after 7 days. The mean number of eggs, emerged immatures, and adults were significantly reduced on both sides of the leaves (i.e., abaxial and adaxial sides) after using the combined application of M. robertsii or B. bassiana plus abamectin, compared to abamectin alone and controls. Our results reveal that the acaricidal efficacy of abamectin combined with either EPF was significantly better in managing the T. urticae life stages than either treatment alone under greenhouse conditions.

Impact of Three Entomopathogenic Fungal Isolates on the Growth of Tomato Plants—Ectoapplication to Explore Their Effect on Tetranychus urticae

Tetranychus urticae is an important pest of tomato crops globally, affecting plant yield and growth. Beauveria bassiana and Metarhizium robertsii have the potential to control T. urticae. We investigated the influence of two B. bassiana (i.e., WG-12 and WG-19) isolates and one M. robertsii (WG-02) isolate when colonizing different plant organs (leaves, stems, and roots) and their influence on the growth of tomato plants, through foliar, root-dipping, and seed-soaking application techniques. We also examined the acaricidal activity of the three isolates against T. urticae (female adults), spraying tomato leaf discs with each isolate separately. After 28 days, WG-12 and WG-19 colonized 97 and 91% of the leaves after foliar inoculation, whereas WG-02 exhibited the lowest leaf colonization (76%). The height of the tomato plants, the root length, the number of leaves, and the weight of the biomass above and below the ground were enhanced significantly after inoculation with WG-02 vs. B. bassiana isolates and control. The complete mortality of T. urticae was caused by WG-12 and WG-02 after 10 days, whereas WG-19 killed 94% of the adults. For the effective management of T. urticae, we propose the application of the WG-02 isolate since it provides complete protection and promotes the growth of tomato plants.

Potential of standard strains of Bacillus thuringiensis against the tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

BackgroundThe tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is one of the key pests of tomato worldwide, causing an estimated crop loss of 80 to 100%. This pest has developed resistance to several pesticides due to overuse, resulting in control failures in the field. The use of biological insecticides as Bacillus thuringiensis that expressed insecticidal proteins can be an alternative tool by insecticides to suppress the pest population.Main bodyLaboratory study investigated the efficacy of standard Bacillus thuringiensis (Bt) strains (4D1, 4D4, 4G1, 4K5 and 4XX4) against T. absoluta. Bioassay was conducted using tomato leaf discs treated with spore crystal lysates prepared from the standard strains, and mortality data was subjected to concentration-mortality probit analysis. The LC50 values for Bt 4D1, Bt 4D4 and Bt 4G1 were 6.10, 6.62 and 8.18 μg/ml for the 2nd instar; 9.90, 10.20 and 11.12 μg/ml for the 3rd instar; and 19.82, 23.16 and 24.54 μg/ml for the 4th instar, respectively, while the Bt 4K5 and Bt 4XX4 were not toxic to T. absoluta.ConclusionThis study suggests that Bt strain 4D1 is effective against different larval instars of the pest and can be used in its management.

Distribution and biological features of Typhlodromus (Anthoseius) recki (Acari: Phytoseiidae) on Tetranychus urticae, T. evansi (Acari: Tetranychidae) and Aculops lycopersici (Acari: Eriophyidae)

The mite family Phytoseiidae contains predatory species used in biological control. However, among the 2,521 valid species, only a few are presently considered for pest management. The study focuses on a species, frequently observed in agrosystems, but whose biology is almost totally unknown: Typhlodromus (Anthoseius) recki. The objectives were to assess its distribution and to determine under laboratory conditions: (i) the development of three populations fed on three tomato pests (Tetranychus urticae, T. evansi, Aculops lycopersici), (ii) the dispersion along the tomato stem, and (iii) the dispersion from mint to infested tomato leaf discs. Based on its distribution, this species seems to be adapted to Mediterranean climate, and is preferentially found on Boraginaceae, Solanaceae, Asteraceae and Lamiaceae. Results show that T. (A.) recki is a generalist predator, with good performance regarding the number of prey consumed. Differences were observed between the populations considered; one population out of the three tested shows even a higher mean consumption of T. urticae than that recorded for Neoseiulus californicus and N. cucumeris. It is attracted by food source and is able to walk along the tomato stem. These results are encouraging enough to consider T. (A.) recki as a good natural enemy candidate for biological control (especially based on biodiversity conservation). Further experiments should be developed to test the predatory ability of this species at larger scale (entire tomato plants and tomato fields or greenhouses).

Management of bacterial spot of tomato caused by copper-resistant Xanthomonas perforans using a small molecule compound carvacrol

Bacterial spot of tomato (BST), caused by Xanthomonas perforans, is one of the most serious diseases in fresh market tomato production in Florida, and currently available management measures are largely ineffective or insufficient. Using small molecule compounds has been shown to be promising in management of BST. Carvacrol is a plant-derived small molecule, which is effective against many human and plant pathogens. In this study, we evaluated the efficacy of carvacrol for control of BST in vitro, in the greenhouse and in field trials. In the laboratory, X. perforans strain used in this study was able to grow on nutrient agar (NA) amended with CuSO4 at 400 mg L−1, which proved that this X. perforans strain was copper resistant. Our results also showed that the minimum inhibitory concentration (MIC) of carvacrol was 32 mg L−1 and its minimum bactericidal concentration (MBC) was 64 mg L−1. Carvacrol increased the sensitivity of the copper-resistant X. perforans strain to copper. In the leaf disc assay, carvacrol combined with copper reduced recovery of X. perforans from tomato leaf discs. Seed priming with carvacrol at 32 mg L−1 was found to be effective in promoting seed germination and seedling vigor of tomato. In greenhouse assays, carvacrol foliar applied alone or in combination with copper significantly (P < 0.05) reduced BST severity. Moreover, carvacrol at 32 mg L−1 combined with copper at 76.8 mg L−1 was most effective in reducing BST severity, which was significantly greater than either treatment alone and also greater than copper at 153.6 mg L−1. In field trials during 2018 and 2019, control efficacy of carvacrol at 32 mg L−1 was significantly greater than copper. Results from this study indicate that carvacrol significantly reduces BST severity and enhances the efficacy of copper against copper resistant X. perforans. There is potential for the small molecule compound carvacrol to be integrated into BST management programs for copper resistant X. perforans and provide a more environmentally sustainable approach for controlling BST.

A Robust Functional Genomics Approach to Identify Effector Genes Required for Thrips (Frankliniella occidentalis) Reproductive Performance on Tomato Leaf Discs.

Thrips (Frankliniella occidentalis) is a persistent plant pest that is able to vector pathogenic viruses. Natural plant resistance to thrips has become a prominent breeding target in commercial crops. The main reason for this is the shift toward banning key pesticides used for controlling thrips infestations and the lack of effective alternatives. Despite this urgent need for crop plants that are resistant, or tolerant, to thrips infestation, the toolbox for studying genetic resistance to this insect is still underdeveloped. Essentially, there is a lack of robust protocols for the screening and identification of thrips genes relevant to its performance on crop plants. To bridge this gap, we have developed a functional analysis screening method. Our approach relies on the, Agrobacterium tumefaciens-mediated, homogeneous, and transient ectopic expression of thrips genes in large tomato leaf discs followed by the assessment of thrips reproductive performance. The setup is designed to maintain gene expression during the course of the assay, where GFP signal in the control treatment is used as a reporter of expression. The screen is conducted in a climate box under controlled settings. As a result, multiple genes can be screened for their effect on thrips reproductive performance in a single experiment and in a relatively small space, without the need for generating stable transgenic plants. The method also eliminates the need for a greenhouse equipped to accommodate the combination of A. tumefaciens-infiltrations and thrips infestations. It is not only flexible and convenient for screening genes encoding putative thrips effectors but also for plant resistance genes or effector-targets of host plants and can be adapted for other crop plants, or other herbivorous arthropods.

Efficacy of some biorational insecticides against Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) under laboratory and greenhouse conditions in Kuwait

AbstractThe tomato leafminer, Tuta absoluta, is one of the most destructive pests of tomato worldwide. Management of the pest is mainly based on chemical insecticides. Reliance on insecticides is difficult to sustain because of unintended long‐term adverse effects on the environment and human health. Consequently, there is a need to develop pest management strategies that ensure the production of high‐quality products, while at the same time ensuring environmental sustainability and maximum consumer protection. We evaluated the efficacy the biopesticides: Azadirachtin, Bacillus thuringiensis, Steinernema feltiae and Beauveria bassiana individually and in combination against T. absoluta under laboratory and greenhouse conditions. When second instar larvae were exposed to tomato leaf discs treated with Azadirachtin (3 g/L), B. thuringiensis (0.5 g/L) or B. bassiana (1.5 g/L), 70%–86%, 55%–65%, and 45.5%–58.5% mortality was observed, respectively. Steinernema feltiae (1,000 IJs/ml) was the least effective biopesticide, with 26%–42% mortality. In the greenhouse trials on tomato, pest infestation (mines/10 leaves/plant) and fruits damaged were significantly lower on plants treated with Azadirachtin + B. thuringiensis or Azadirachtin + B. bassiana compared to plants treated with Azadirachtin, B. thuringiensi, B. bassiana or S. feltiae alone. Azadirachtin + B. thuringiensis and Azadirachtin + B. bassiana resulted in 90% and 81% reduction in fruits damaged in the summer experiments, respectively, and 96% and 91% in winter. The most severe pest infestation was observed on plants treated with S. feltia. The results indicate that the biopesticides, except S. feltia, can contribute to T. absoluta control in greenhouse tomato crops. In particular, the combined use of Azadirachtin with B. thuringiensis or B. bassiana provided the highest level of control of the pest. The potential for including these biopesticides in an overall sustainable integrated pest management programme for T. absoluta is discussed.

Functional response of Neoseiulus cucumeris (Oudemans) (Acari: Phytoseiidae) to Bemisia tabaci (Gennadius) on tomato leaves

ABSTRACTBemisia tabaci (Gennadius) is an important invasive pest of vegetables and other horticultural plants worldwide. In this study, the functional response of Neoseiulus cucumeris (Oudemans) to different stages of immature B. tabaci was evaluated under laboratory conditions. Predation experiments were conducted on tomato leaf discs (2.5 cm diameter) over a 24-h period at 26 ± 1°C and 65 ± 5% relative humidity with a L16:D8 photoperiod. The prey densities ranged from 5 to 90 immature stages (eggs and first- to fourth-instar nymphs) of B. tabaci per leaf disc. The results showed that the egg stage of B. tabaci was the most susceptible prey stage and that the mated female adult mite (3-day-old) was a more effective predator than the male adult mite. The functional response of adult N. cucumeris followed a Type II trend curve as shown in a logistic regression model. Adult N. cucumeris exhibited different predation tendencies towards prey in different stages of immaturity. The daily maximum number of eggs, first-, second- and third-instar nymphs of B. tabaci killed by a single female over a 24-h period (26 ± 1°C, 65 ± 5% RH and L16:D8 photoperiod) were 8.5, 5.2, 3.0 and 2.1, respectively, whereas the number killed by a single male was 6.0, 4.0, 2.3 and 1.8, respectively. The results of this study could help determine an effective B. tabaci biocontrol measure that employs a natural predator.

Drought-Stressed Tomato Plants Trigger Bottom-Up Effects on the Invasive Tetranychus evansi.

Climate change will bring more drought periods that will have an impact on the irrigation practices of some crops like tomato, from standard water regime to deficit irrigation. This will promote changes in plant metabolism and alter their interactions with biotic stressors. We have tested if mild or moderate drought-stressed tomato plants (simulating deficit irrigation) have an effect on the biological traits of the invasive tomato red spider mite, Tetranychus evansi. Our data reveal that T evansi caused more leaf damage to drought-stressed tomato plants (≥1.5 fold for both drought scenarios). Mite performance was also enhanced, as revealed by significant increases of eggs laid (≥2 fold) at 4 days post infestation (dpi), and of mobile forms (≥2 fold and 1.5 fold for moderate and mild drought, respectively) at 10 dpi. The levels of several essential amino acids (histidine, isoleucine, leucine, tyrosine, valine) and free sugars in tomato leaves were significantly induced by drought in combination with mites. The non-essential amino acid proline was also strongly induced, stimulating mite feeding and egg laying when added to tomato leaf disks at levels equivalent to that estimated on drought-infested tomato plants at 10 dpi. Tomato plant defense proteins were also affected by drought and/or mite infestation, but T. evansi was capable of circumventing their potential adverse effects. Altogether, our data indicate that significant increases of available free sugars and essential amino acids, jointly with their phagostimulant effect, created a favorable environment for a better T. evansi performance on drought-stressed tomato leaves. Thus, drought-stressed tomato plants, even at mild levels, may be more prone to T evansi outbreaks in a climate change scenario, which might negatively affect tomato production on area-wide scales.

Efficacy of entomopathogenic nematodes against larvae of Tuta absoluta in the laboratory.

Previous studies have indicated the control potential of entomopathogenic nematodes (EPNs) against Tuta absoluta. Here, the potential of Steinernema feltiae, S. carpocapsae and Heterorhabditis bacteriophora is studied when applied against larvae of T. absoluta inside leaf mines in tomato leaf discs by means of an automated spray boom. The studied EPN species were effective against all four larval instars of T. absoluta but caused higher mortality in the later instars (e.g. fourth instar: 77.1-97.4% mortality) than in the first instars (36.8-60.0% mortality). Overall, S. feltiae and S. carpocapsae yielded better results than H. bacteriophora. Steinernema carpocapsae and H. bacteriophora performed better at 25 °C (causing 55.3 and 97.4% mortality respectively) than at 18 °C (causing 12.5 and 34.2% mortality respectively), whereas S. feltiae caused 100% mortality at both temperatures. Under optimal spraying conditions and with the use of Addit and Silwet L-77 adjuvants, a reduced dosage of 6.8 infective juveniles (IJs) cm(-2) yielded equally good control as a recommended dosage of 27.3 IJs cm(-2) . Under laboratory conditions, S. feltiae and S. carpocapsae showed good potential against the larvae of T. absoluta inside tomato leaf mines. Results need to be confirmed in greenhouse experiments. © 2015 Society of Chemical Industry.

Toxicity and Residual Activity of Insecticides Against Tamarixia triozae (Hymenoptera: Eulophidae), a Parasitoid of Bactericera cockerelli (Hemiptera: Triozidae).

Bactericera cockerelli (Sulc) (Hemiptera: Triozidae) is one of the most economically important pests of potato, tomato, and peppers in Central America, Mexico, the United States, and New Zealand. Its control is based on the use of insecticides; however, recently, the potential of the eulophid parasitoid Tamarixia triozae (Burks) (Hymenoptera: Eulophidae) for population regulation has been studied. Because T. triozae is likely to be exposed to insecticides on crops, the objective of this study was to explore the compatibility of eight insecticides with this parasitoid. The toxicity and residual activity (persistence) of spirotetramat, spiromesifen, beta-cyfluthrin, pymetrozine, azadirachtin, imidacloprid, abamectin, and spinosad against T. triozae adults were assessed using a method based on the residual contact activity of each insecticide on tomato leaf discs collected from treated plants growing under greenhouse conditions. All eight insecticides were toxic to T. triozae. Following the classification of the International Organization of Biological Control, the most toxic were abamectin and spinosad, which could be placed in toxicity categories 3 and 4, respectively. The least toxic were azadirachtin, pymetrozine, spirotetramat, spiromesifen, imidacloprid, and beta-cyfluthrin, which could be placed in toxicity category 2. In terms of persistence, by day 5, 6, 9, 11, 13, 24, and 41 after application, spirotetramat, azadirachtin, spiromesifen, pymetrozine, imidacloprid, beta-cyfluthrin, abamectin, and spinosad could be considered harmless, that is, placed in toxicity category 1 (<25% mortality of adults). The toxicity and residual activity of some of these insecticides allow them to be considered within integrated pest management programs that include T. triozae.

Effect of Beauveria bassiana and Metarhizium anisopliae on the Trialeurodes vaporariorum-Encarsia formosa system

The virulence of three strains of Beauveria bassiana and one of Metarhizium anisopliae was tested against Trialeurodes vaporariorum and its parasitoid Encarsia formosa in laboratory assays. These strains were previously selected for their virulence against Galleria mellonella and Tenebrio molitor. The commercial B. bassiana strain ATCC 74040, both as pure fungal culture and formulated myco-insecticide (Naturalis), was included in the assays as positive control. First, the entomopathogenic fungal strains were tested for their virulence against T. vaporariorum nymphs on tomato leaf disks. Then, the E. formosa development was evaluated under treatment with the entomopathogenic fungal strains at five different time points from the parasitization of T. vaporariorum nymphs. The virulence of our entomopathogenic fungal strains was superior to that of ATCC 74040, although not significantly, resulting in a cumulative mortality (CM) of T. vaporariorum nymphs 7 days after inoculation (DAI) greater than 86 %. Our M. anisopliae strain CIST8 was the most effective (96.6 % CM 7 DAI), even superior to the myco-insecticide Naturalis (94.2 %), which was more effective than the ATCC 74040 pure strain (85.6 %). The entomopathogenic fungal strains, and especially Naturalis, negatively affected E. formosa development and its parasitization activity of T. vaporariorum nymphs. This effect was more pronounced when the fungal strains were applied before parasitization. Results suggest that the application of entomopathogenic fungi is incompatible with E. formosa release on crops.

Effects ofTomato zonate spot virusInfection on the Development and Reproduction of Its VectorFrankliniella occidentalis(Thysanoptera: Thripidae)

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is the main vector of Tomato Zonate Spot Virus (TZSV) in Yunnan, China. We investigated the life history parameters of F. occidentalis on tomato and pepper leaves either with or without TZSV infection. The total duration of the immature stages of F. occidentalis reared on TZSV-infected leaves was significantly shorter than the total duration of those reared on uninfected leaves. Also the survival rates of the instars and prepupae on TZSV-infected tomato and pepper leaf disks were significantly higher than those on uninfected tomato and pepper leaf disks. The F. occidentalis populations reared on TZSV-infected tomato and pepper leaf disks respectively increased 11.97- and 10.64-fold in 1 generation, while those reared on uninfected tomato and pepper leaf disks increased only 8.10- and 6.45-fold, respectively. These results demonstrated that TZSV infection improved the fitness and host suitability of its vector, F. occidentalis. Also our findings suggest that TZSV-infection is likely to induce larger field populations of F. occidentalis, thereby increasing the probability of TZSV transmission. Los trips occidental de las flores, Frankliniella occidentalis, (Pergande) (Thysanoptera: Thripidae), es el principal vector del Virus de la Mancha Zonada del Tomate (VMZT) en Yunnan, China. Se investigo los parametros del ciclo de vida de F. occidentalis sobre hojas de tomate y pimiento con o sin infeccion por VMZT. La duracion total de las etapas inmaduras de F. occidentalis criadas en las hojas infectadas por el VMZT fue significativamente mas corta que la duracion total de las criadas en las hojas no infectadas. Tambien, las tasas de sobrevivencia de los instares y prepupas sobre discos de hojas de tomate y pimiento infectadas por VMZT fueron significativamente mas altas que las tasas sobre discos de hojas de tomate y pimiento no infectadas. Las poblaciones del F. occidentalis criadas sobre discos de hojas de tomate y pimienta infectados por VMZT, incrementaron 11.97 y 10.64 veces, respectivamente en 1 generacion, mientras que las criadas sobre discos de hojas de tomate y pimienta no infectadas incrementaron solo 8.10 y 6.45 veces, respectivamente. Estos resultados demostraron que la infeccion por VMZT mejoro el estado fisico e idoneidad de su vector, F. occidentalis. Tambien nuestros hallazgos sugieren que es probable que la infeccion por VMZT induzca poblaciones de campo de F. occidentalis mas grandes y con ello incrementando la probabilidad de transmision de VMZT. View this article in BioOne

Different feeding behaviours in a single predatory mite species. 2. Responses of two populations of Phytoseiulus longipes (Acari: Phytoseiidae) to various prey species, prey stages and plant substrates

Tritrophic studies involving several populations of the predatory mite Phytoseiulus longipes showed distinct life history traits depending on the prey offered and/or the plant substrate. In order to better understand the biology of this predator, the response to several combinations of prey species (Tetranychus evansi and Tetranychus urticae), prey stages (eggs and mobile stages) and plant substrates (bean and tomato leaf discs) has been assessed for two populations of P. longipes. Unlike what was found for life history traits, both populations displayed similar behaviour: they went and stayed more on tomato than on bean, they preferred T. urticae over T. evansi and mobile stages over eggs. Combining the previous life history data with the present results suggests that P. longipes may display host-plant mediated specialization on a prey species, T. evansi. Possible underlying mechanisms are discussed, as well as directions for future work.

Comparative antifeedant activities of polygodial and pyrethrins against whiteflies (Bemisia tabaci) and aphids (Myzus persicae)

Polygodial, a sesquiterpene dialdehyde of the drimane family, has been shown to have deterrent and antifeedant effects on various insect species, including Myzus persicae (Sulzer), Spodoptera spp. and Leptinotarsa decemlineata (Say). This compound may have potential as a broad-spectrum biocontrol agent, similar to pyrethrins, given that it was previously reported to improve yield when sprayed on barley fields. This study compares the deterrent effect of polygodial and pyrethrins against the silverleaf whitefly Bemisia tabaci (Gennadius) and the green peach aphid M. persicae in dual-choice assays using compound-coated tomato leaf discs. B. tabaci adults were deterred by polygodial at an ED50 (effective dose at which 50% of the insects are deterred) of about 25 µg g(-1) fresh weight (FW), and green peach aphids at about 54 µg g(-1) FW. Bioassays were benchmarked with pyrethrins that had a 20-fold lower ED50 of approximately 1.4 µg g(-1) FW against whiteflies, but only a twofold lower ED50 (about 28 µg g(-1) FW) against peach aphids. Polygodial showed moderate phytotoxic effects (score of 2 on a scale of 1-5) on tomato leaves at concentrations above the ED50 concentrations (≥ 90 µg g(-1) FW). The sesquiterpene dialdehyde polygodial is 2-20 times less deterrent than pyrethrins, depending on the insect species, but it could provide a useful complement to pyrethrin sprays as it has a different mode of action, is food grade and has low volatility. However, a formulation that reduces the risks of phytotoxic effects should be developed.

Nitric oxide and reactive oxygen species regulate the accumulation of heat shock proteins in tomato leaves in response to heat shock and pathogen infection

Heat shock proteins (HSP) are produced in response to various stress stimuli to prevent cell damage. We evaluated the involvement of nitric oxide (NO) and reactive oxygen species (ROS) in the accumulation of Hsp70 proteins in tomato leaves induced by abiotic and biotic stress stimuli. A model system of leaf discs was used with two tomato genotypes, Solanum lycopersicum cv. Amateur and Solanum chmielewskii, differing in their resistance to fungal pathogen Oidium neolycopersici. Leaf discs were exposed to stress factors as heat shock and pathogen infection alone or in a combination, and treated with substances modulating endogenous NO and ROS levels. Two proteins of Hsp70 family were detected in stressed tomato leaf discs: a heat-inducible 72kDa protein and a constitutive 75kDa protein. The pathogenesis and mechanical stress influenced Hsp75 accumulation, whereas heat stress induced mainly Hsp72 production. Treatment with NO donor and NO scavenger significantly modulated the level of Hsp70 in variable manner related to the genotype resistance. Hsp70 accumulation correlated with endogenous NO level in S. lycopersicum and ROS levels in S. chmielewskii. We conclude NO and ROS are involved in the regulation of Hsp70 production and accumulation under abiotic and biotic stresses in dependence on plant ability to trigger its defence mechanisms.

Riboflavin induces resistance against Botrytis cinerea in bean, but not in tomato, by priming for a hydrogen peroxide-fueled resistance response

Riboflavin (vitamin B2) can act as an activator of plant resistance against biotic stress. Here, we demonstrate the effect of exogenous application of riboflavin on bean and tomato resistance against Botrytis cinerea. In bean, riboflavin applied at a concentration of 10 up to 1000 μM reduced the number of spreading lesions by approximately 25% compared to control plants. In tomato, however, riboflavin was not able to control the pathogen at any concentration tested. Hydrogen peroxide accumulation was detected in bean leaf discs of riboflavin-treated plants as early as 4 h post inoculation (hpi) while in tomato leaf discs, no hydrogen peroxide accumulation was detected prior to 48 hpi irrespective of riboflavin treatment. Stimulation of lipoxygenase activity was observed in bean, but not in tomato plants treated with riboflavin, while jasmonate could trigger lipoxygenase activity and resistance to B. cinerea in both bean and tomato. Riboflavin may prime bean plants for earlier accumulation of hydrogen peroxide and prompt activation of the lipoxygenase pathway when challenged with B. cinerea.

Cuscuta reflexa invasion induces Ca2+ release in its host

Cuscuta reflexa induces a variety of reaction in its hosts. Some of these are visual reactions, and it is clear that these morphological changes are preceded by events at the molecular level, where signal transduction is one of the early processes. Calcium (Ca(2+)) release is the major second messenger during signal transduction, and we therefore studied Ca(2+) spiking in tomato during infection with C. reflexa. Bioluminescence in aequorin-expressing tomato was monitored for 48 h after the onset of Cuscuta infestation. Signals at the attachment sites were observed from 30 to 48 h. Treatment of aequorin-expressing tomato leaf disks with Cuscuta plant extracts suggested that the substance that induced Ca(2+) release from the host was closely linked to parasite haustoria.

Predação por coccinelídeos e crisopídeo influenciada pela teia de Tetranychus evansi

O objetivo deste trabalho foi avaliar o efeito da teia produzida por Tetranychus evansi (Acari: Tetranychidae) na eficiência de predação por coccinelídeos Cycloneda sanguinea e Eriopis connexa e pelo crisopídeo Chrysoperla externa. A eficiência em predar as fêmeas de T. evansi na presença e na ausência de sua teia em discos de folhas de tomateiro com ácaros foi avaliada para cada instar das diferentes espécies de predadores. Foi observado efeito negativo da teia produzida por T. evansi na eficiência de predação do segundo e do terceiro instar de C. externa. Quanto à E. connexa, somente a predação pelo último instar foi influenciada negativamente pela presença da teia. A predação pelas larvas de primeiro e terceiro instar de C. sanguinea foi significativamente menor na presença da teia; no entanto, o resultado foi contrário para o quarto instar. O efeito da teia de T. evansi como mecanismo de defesa varia conforme a espécie e o estágio de desenvolvimento do predador.

Effects of crop type on Bacillus thuringiensis toxicity and residual activity against Trichoplusia ni in greenhouses

Abstract:We assessed the efficacy and persistence of a Bacillus thuringiensiskurstaki (Btk) formulation (Dipel) against Trichoplusia ni (Hubner) (Lep., Noctuidae), the cabbage looper, on three greenhouse vegetable crops (tomato, bell pepper and cucumber). First, T. ni larvae were fed leaf discs treated with Btk to assess how Btk toxicity varies with host plant. Secondly, T. ni larvae were fed leaf discs harvested from plants that had been sprayed with Btk 1, 5 and 9 days previously to assess the residual activity of Btk toxicity in greenhouse environments. Mortality of T. ni larvae fed tomato leaf discs was significantly higher than T. ni fed cucumber or pepper leaf discs. The toxicity of Btk had declined by less than 50% after 9 days, which suggests that Btk persistence is lengthy in greenhouse environments. No crop effects on the residual activity of Btk were found. These results demonstrate that the greenhouse environment and the crop should be considered when using Btk for insect management on greenhouse crops.