Root Drench Research Articles

Evaluation of plant defence activators for the potential control of Pseudomonas syringae pv. aesculi

Glasshouse trials were conducted using tobacco (Nicotiana benthamiana) to assess the efficacy of five plant defence activators (PDAs), namely harpin protein, potassium phosphite, salicylic acid analogue, silicon phosphite and a plant hormone–vitamin complex against the bacterial pathogen Pseudomonas syringae pv. aesculi (Pae), the causal agent of Pseudomonas bleeding canker of horse chestnut. PDAs were applied preventatively, i.e. before Pae inoculation of plants and therapeutically, i.e. after Pae inoculation of plants and as both as a foliar spray (FS) and root drench (RD). Irrespective of mode of application (i.e. FS, RD) or whether applied preventatively or therapeutically, PDAs containing salicylic acid analogues, plant hormone–vitamin complex and harpin protein possessed limited efficacy as Pae protectant and/or eradication compounds. Only application of potassium and silicon phosphite induced positive effects on plant vitality [increased leaf chlorophyll content, leaf chlorophyll fluorescence (Fv/Fm)], enhanced defensive enzyme activity (β-1,3-glucanase, peroxidase) and reduced Pae lesion size, the main proxy of Pae success or aggressiveness. Preventative rather than therapeutic phosphite application resulted in greater reductions in Pae severity. Little significance of mode of application was demonstrated, indicating that phosphites can be applied as either a FS or RD resulting in similar degrees of Pae control. Significant reductions in Pae severity recorded in this study give credence to the potential of phosphites as an alternative or complement conventional bactericides for Pae control.

Pre-harvest treatment of spinach with Ascophyllum nodosum extract improves post-harvest storage and quality

Fresh spinach (Spinacia oleracea L.) leaves contain high concentrations of beneficial phytochemicals. However, spinach does not store well and is highly perishable especially during handling and post-harvest storage. In this study, we investigated the effect of pre-harvest root-treatment of spinach with Ascophyllum nodosum extract (ANE) at different concentrations (0, 0.1, 1.0, or 5.0gL−1) on post-harvest quality of fresh-cut spinach over a 35-day storage period. At the time of harvest there was no significant difference in dry weight, chlorophyll, ascorbate and lipid peroxidation between ANE-treated and non-treated plants. However, the loss in fresh weight and visual quality (color and turgor) of spinach leaves during storage was reduced by pre-harvest application of ANE. Lipid peroxidation was significantly reduced in ANE-treated leaves. The total chlorophyll content and ascorbate content in the control and treated leaves was however identical over the storage period and decreased at a similar rate. A negative correlation was observed between visual quality and lipid peroxidation. The results show that pre-harvest ANE application through root drench, especially at 1.0gL−1, enhanced post-harvest storage quality of spinach leaves.

Enhanced root uptake of acibenzolar-S-methyl (ASM) by tomato plants inoculated with selected Bacillus plant growth-promoting rhizobacteria (PGPR)

The combination of plant growth-promoting rhizobacteria (PGPR) and plant resistance inducers is an alternative crop protection approach in modern agricultural systems. Despite the numerous reports regarding the improved suppression of plant pathogens by their combined application, little is known about the interactions among these components. In the present study, the persistence behavior of the plant activator acibenzolar-S-methyl (ASM) in the rhizosphere of tomato plants and its root uptake as well as systemic translocation ability in aboveground parts after combined use with certain Bacillus PGPR strains (B. amyloliquefaciens IN937a, B. pumilus SE34, B. subtilis FZB24 and GB03) were investigated. Additionally, the population dynamics of the PGPR strain B. subtilis GB03 at the tomato root system and rhizosphere soil applied with or without the pesticide were studied. The results showed that the addition of PGPR inocula did not affect the dissipation rate of ASM in rhizosphere soil. Also, the formation of its major metabolite CGA 210007 in soil was rapid, since it was detected one hour after root drench and it was maintained at high levels during the sampling period without considerable variations among the bacterial treatments compared to the control. The uptake and systemic translocation of ASM and its metabolite CGA 210007 from root to shoot was rapid and maximum concentrations were observed at 48–96 h after its application. It was revealed that in plants treated with the PGPR strains B. subtilis GB03 and B. pumilus SE34 the uptake and systemic translocation of ASM and CGA 210007 in the aerial parts of the tomato plants was significantly higher compared to the control receiving no bacterial treatment. Also, the populations of the strain B. subtilis GB03 showed high colonizing ability in the root system and the rhizosphere soil. PGPR strains that lead to enhanced pesticide uptake by plants should be further evaluated as components in integrated management systems.

First Report of Dickeya dianthicola Causing Blackleg on Potato (Solanum tuberosum) in Bulgaria.

Potato (Solanum tuberosum) is an important and widespread crop in Bulgaria. A new disease was observed on a single potato plot (Plovdiv region) without a history of potato cultivation in the spring of 2011. Initially, single lower leaves wilted on recently emerged plants (approx. 15% incidence) with subsequent desiccation of the leaf margins. The wilting progressed over time and eventually the whole stem became desiccated. A blackleg-like necrosis was noticed at the stem base when symptomatic plants were uprooted. Most diseased stems remained green above ground but pith tissue was heavily macerated and some of the stems became hollow as the pith dried out. Mother tubers were partially or entirely macerated. In most cases, the decay was initiated from the stolon end. Bacterial strains were obtained from symptomatic stems and tubers by dilution plating on King's B medium. The strains produced indigoidin pigment and induced a hypersensitive response 24 h after infiltration into tobacco and Sedum hybridum leaves (2). The strains were identified as Dickeya spp. by the production of the PCR amplicon of the pectate lyase ADE gene cluster (3) and of the pectate lyase I gene (4). The partial sequence of the fliC PCR amplicon (1) of strain SB2589 (GenBank Accession No. KF442436) displayed 100% homology with four whole genome shotgun sequences of Dickeya dianthicola in GenBank. Pectinolytic activity was demonstrated by inoculation of surface disinfested potato tubers of cv. Kondor. Conical core tissue was removed at the apical end and 100 μl bacterial suspension (107 CFU in sterile 10 mM phosphate buffer) was deposited in the cavity. The cap was reattached to the tuber and immobilized by Parafilm. Positive control tubers were inoculated with D. dianthicola reference strain GBBC 2039 (LMG 25864) and negative control tubers were inoculated with sterile 10 mM phosphate buffer. All tubers were incubated for 48 h at 28°C under micro-aerobic conditions reducing the air pressure to 90 mb in a vacuum incubator. The D. dianthicola reference strain and Bulgarian strains produced maceration of tuber tissue. Maceration was not observed in the negative control tubers. Potato plants cv. Kondor were grown from minitubers in sandy soil in plastic nursery containers. The plants were inoculated by root drenching (one application of cell suspension at 109 CFU/liter) when the stems were 15 to 20 cm high (tuber initiation stage). Plants were incubated at 25 to 28°C with regular watering. Wilting symptoms developed within 10 days of inoculation, followed by necrosis of the pith. Strains obtained from the inoculated stems were confirmed as D. dianthicola as described above. Based on the disease symptoms, the cultural, molecular, and pathological features of the strains, we conclude that the disease was caused by D. dianthicola and to our knowledge this is the first report of the pathogen on potato in Bulgaria. Furthermore, this incident warrants further surveys of pectinolytic bacteria causing blackleg-like symptoms in potato crops in Bulgaria.

DL-β-Aminobutyric Acid-Induced Resistance in Soybean against Aphis glycines Matsumura (Hemiptera: Aphididae)

Priming can improve plant innate capability to deal with the stresses caused by both biotic and abiotic factors. In this study, the effect of DL-β-amino-n-butyric acid (BABA) against Aphis glycines Matsumura, the soybean aphid (SA) was evaluated. We found that 25 mM BABA as a root drench had minimal adverse impact on plant growth and also efficiently protected soybean from SA infestation. In both choice and non-choice tests, SA number was significantly decreased to a low level in soybean seedlings drenched with 25 mM BABA compared to the control counterparts. BABA treatment resulted in a significant increase in the activities of several defense enzymes, such as phenylalanine ammonia-lyase (PAL), peroxidase (POX), polyphenol oxidase (PPO), chitinase (CHI), and β-1, 3-glucanase (GLU) in soybean seedlings attacked by aphid. Meanwhile, the induction of 15 defense-related genes by aphid, such as AOS, CHS, MMP2, NPR1-1, NPR1-2, and PR genes, were significantly augmented in BABA-treated soybean seedlings. Our study suggest that BABA application is a promising way to enhance soybean resistance against SA.

Enhanced Salt Tolerance of Tomatoes by Exogenous Salicylic Acid Applied Through Rooting Medium

In Tunisia, like in the other countries of the Mediterranean, tomato is ranked among the important vegetables in the economic sphere. Tunisia ranks as the first consumer of this vegetable in the world. However, tomatoes are exposed to multiple environmental stresses. In particular, salinity is the most stressful limiting factor to productivity. Salt tolerance of the tomato is susceptible to be ameliorated by genetic and physiologic ways. Salicylic acid (SA), a plant phenolic, is now considered as a hormone-like endogenous regulator, and its role in the defense mechanisms against biotic and abiotic stressors has been well documented. So, the aim of this study was to investigate the impact of exogenous application of SA (0.01 mM) on growth, nutritional behavior, and some metabolic parameters (total chlorophyll, soluble sugars, proline, and proteins) of tomato plants cv. Moneymaker exposed to NaCl (100 mM). Our results showed that the application of 0.01 mM SA to tomato plants via root drenching attenuate the depressive effect of salinity on plants. This amelioration results in stimulation of growth and development of plant. Under stress conditions, SA-treated plants exhibited more accumulation of photosynthetic pigments and K(+) contents. Thus, SA induces an increase in soluble sugars in roots and leaves; also, we noted the increase of proteins only in roots. Overall, the adverse effects of salt stress tomato plants were alleviated by the exogenous application of SA at vegetative stage, which upregulated nutrition and the accumulation of some organic solutes and osmoprotectors such sugars, proline, and proteins. So salicylic acid can be greatly used to enhance salt tolerance of tomato plants.

Saccharin-induced systemic acquired resistance against rust ( Phakopsora pachyrhizi) infection in soybean: Effects on growth and development

We examined the effect of saccharin on the systemic acquired resistance (SAR) response of soybean to the fungus Phakopsora pachyrhizi, the causal agent of soybean rust. Plants were grown hydroponically in half-strength Hoagland’s solution and were challenged with the pathogen 1, 5, 10 and 15 d after treatment with 3 mM saccharin applied either as a foliar spray or a root drench at the 2nd trifoliate (V3) and early reproductive (R1) stages. Plants were destructively harvested and assessed for visible rust symptoms 2 wk after inoculation. Mode of saccharin application was a significant factor influencing the severity of rust infection. Saccharin applied as a root drench was more effective than the foliar spray treatment at inducing SAR, with increased resistance observed 1 d after application. Systemic protection against rust infection was still apparent 15 d after application of saccharin as a root drench. In contrast, foliar treatment with saccharin did not increase systemic protection until 15 d after treatment. When systemic protection was induced by the application of saccharin in either manner, there was no significant reduction of plant growth, except when plants were inoculated 15 d after the saccharin application as a root drench at the R1 stage of development.

The effects of a plant defence priming compound, β-aminobutyric acid, on multitrophic interactions with an insect herbivore and a hymenopterous parasitoid

Biocontrol of aphids by natural enemies is utilized in many organic and integrated pest management schemes. β-aminobutyric acid (BABA), a non-protein amino acid, is a plant defence primer that suppresses growth of some insect herbivores when applied as a root drench. This investigation examined how applying BABA to host plants via the roots may impact on a parasitoid wasp of aphids. Female Aphidius ervi (Haliday) did not discriminate against pea aphids (Acyrthosiphon pisum (Harris)) reared on BABA-treated beans (Vicia faba L.) or show any modified responses to volatiles released from BABA-treated plants. BABA reduced the size of emerging wasps, primarily by inhibiting the growth of the host aphid. Metabolomic analysis revealed BABA in both aphids and emergent wasps indicating some potential for direct physiological inhibition to have occurred. Survival of the parasitoids was only reduced at doses of BABA likely to produce phytotoxic effects in many plant species, thus there may be potential to incorporate plant defence primers like BABA into integrated pest management practices. However, the precise mechanisms of BABA-inhibition of insects still require elucidation.

Trichoderma atroviride promotes growth and enhances systemic resistance to Diplodia pinea in radiata pine (Pinus radiata) seedlings

SummaryRoot drench application of Trichoderma atroviride isolates R32, R33, R40 and R84 promoted the growth of potted radiata pine seedlings. After 6 weeks, seedlings treated with R33 and R84 had thicker stems and greater stem and root biomass (p < 0.05) than untreated controls. Treatment with R32 increased seedling root biomass whilst R40 increased stem diameter. None of the isolates affected seedling height. One isolate, R33, induced systemic resistance to stem inoculation with Diplodia pinea and reduced dieback incidence by 20% compared with untreated controls. To our knowledge, this is the first report of systemic induced resistance by Trichoderma in a pine species. Furthermore, seedlings that were treated with R33 (root drench) plus foliar application of methyl jasmonate (MeJA) expressed elevated peroxidase activity in their stems 2 weeks later, compared with seedlings treated only with MeJA. Because R33 itself did not affect peroxidase activity, this may be indicative of treatment synergy or defence potentiation by R33. Curiously, R33 + MeJA induced terpenoids but suppressed phenylalanine ammonia‐lyase activity suggesting possible trade‐offs between phenolic and terpenoid defence pathways in the treated seedlings.

A root drench in unsaturated hydrogel solution reduced stress in transplanted Eucalyptus pilularis cuttings but was ineffective for seedlings: a glasshouse experiment

Summary Available soil moisture and quality of planting material are two important criteria affecting survival during plantation establishment. It has been observed that in northern NSW most seedling deaths occur within the first four weeks of planting. Reducing the rate that plants become stressed is important as less-stressed plants are more capable of exploiting available soil moisture required for survival beyond this four-week period. The health (leaf gas exchange, visual symptoms of leaf and stem wilt) and survival of Eucalyptus pilularis Smith seedlings and cuttings were examined following the application of water in the form of either a hydrogel solution or as irrigation. The main findings were that the rate at which stress developed was slower for cuttings than for seedlings; and that supplying more water, either as hydrogel or irrigation, reduced transplant stress and prolonged survival. Differences in morphology between seedlings and cuttings may explain why cuttings developed stress more slowly than did seedlings. Compared with seedlings, cuttings had reduced leaf area, an increased root: shoot ratio and lower leaf area: root dry mass ratio, all of which are traits that enhance water uptake and reduce water loss. The most effective treatments for reducing stress of seedlings and cuttings were either removing individual seedlings or cuttings from nursery trays and dipping the root ball into a 100% saturated hydrogel solution which coated it with a layer of saturated hydrogel, or supplying the equivalent volume of water as irrigation when transplanting the plants. Drenching nursery trays in 25% and 50% unsaturated hydrogel solutions prior to the removal of the plants delayed stress of transplanted cuttings to a similar extent as the 100% saturated hydrogel solution, but these solutions were ineffective in delaying stress in seedlings. It is thought the more open structure of the soil medium used for cuttings allowed the unsaturated hydrogel solutions to enter the root-ball during root drenching, and because the hydrogel solutions are more viscous than water the drainage of the solutions after removing the nursery trays from the root drench was reduced.

Commercial extract from the brown seaweed Ascophyllum nodosum reduces fungal diseases in greenhouse cucumber

This study examined the effects of Stimplex™, a marine plant extract formulation from Ascophyllum nodosum, on some common cucumber fungal pathogens. Greenhouse cucumber plants were sprayed and/or root drenched using Stimplex™ at 0.5% or 1% concentration twice at 10-day intervals. Treatments also included application of fungicide (chlorothalonil, 2 g L−1) alternating with Stimplex™ application. Treated plants were inoculated with four cucumber fungal pathogens including Alternaria cucumerinum, Didymella applanata, Fusarium oxysporum, and Botrytis cinerea. Stimplex™ application resulted in a significant reduction in disease incidence of all the pathogens tested. The disease control effect was greater for Alternaria and Fusarium infection, followed by Didymella and Botrytis. Combined spray and root drenching with Stimplex™ was more effective than either spray or root drenching alone. The alternation of one fungicide application, alternated with Stimplex™ application, was highly effective and found to be the best treatment in reducing the disease ratings. Plants treated with Stimplex™ showed enhanced activities of various defense-related enzymes including chitinase, β-1,3-glucanase, peroxidase, polyphenol oxidase, phenylalanine ammonia lyase, and lipoxygenase. Altered transcript levels of various defense genes, including chitinase, lipoxygenase, glucanase, peroxidase, and phenylalanine ammonia lyase were observed in treated plants. Cucumber plants treated with Stimplex™ also accumulated higher level of phenolics compared to water controls. These results suggest that seaweed extracts enhance disease resistance in cucumber probably through induction of defense genes or enzymes.

Biological control of take-all in wheat by endophytic Bacillus subtilis E1R-j and potential mode of action

The bacterial strain E1R-j, isolated as an endophyte from wheat roots, exhibited high antifungal activity to Gaeumannomyces graminis var. tritici ( Ggt). Strain E1R-j was identified as Bacillus subtilis based on morphological, physiological and biochemical methods as well as on 16S rDNA analysis. This strain inhibited mycelium growth in vitro of numerous plant pathogenic fungi, especially of Ggt, Coniothyrium diplodiella, Phomopsis sp . and Sclerotinia sclerotiorum. In greenhouse experiments, soil drenches with cell densities of 10 6, 10 9 and 10 12 CFU ml −1 E1R-j reduced significantly take-all disease, caused by Ggt, in wheat seedling by 62.6%, 68.6% and 70.7%, respectively, compared to the inoculated control, 4 weeks after sowing. Growth parameters such as lengths and fresh weights of roots and shoots of Ggt-inoculated control plants were significantly lower compared to Ggt-inoculated and E1R-j treated plants. Field experiments in the season 2006/2007, heights of wheat plants in the Ggt inoculated plots were significantly reduced compared to the non inoculated treatments. Yield parameters such as kernels per head and thousand kernel weight (TKW) in inoculated control plants were lower compared to the other treatments. In the experimental year 2007/2008, independent treatments with the bacterial strain E1R-j and the fungicide Triadimefon reduced take-all disease in wheat roots by 55.3% and 61.9%, compared to the inoculated control plants. In this season plant height in inoculated control was significantly lower and also the yield parameters seeds per head and especially TKW were drastically reduced compared to the other treatments. E1R-j treatment alleviated the detrimental effects of take-all on grain yield parameters to a similar extent as Triadimefon application. SEM studies revealed that in the presence of E1R-j, hyphae of Ggt showed leakage, appeared ruptured, swollen and shriveled. Following root drench, strain E1R-j was able to colonize endophytically roots and leaves of wheat seedlings. While the population of the bacterial strain in wheat roots steadily increased from the second to the fourth leaf stage, in the leaf tissue the population of the strain rapidly declined. TEM studies also showed that cells of E1R-j were present in roots of wheat seedlings and effectively retarded infection and colonization of Ggt in root tissue; suppression of Ggt by E1R-j was accompanied by disintegration of hyphal cytoplasm. In addition, in the presence of E1R-j cells in Ggt-infected root tissue morphological defense reactions were triggered such as formation of wall appositions and papillae. The results presented indicate that the endophytic strain E1R-j of B. subtilis meets demands required for biocontrol of take-all.

Sucrose-Induced Tolerance to and Recovery from Deicing Salt Damage in Containerized Ilex aquifolium L. and Quercus robur L.

Two outdoor experiments were conducted using containerized trees of the species holly (Ilex aquifolium L.) and English oak (Quercus robur L.) to determine the effectiveness and feasibility of sucrose to improve tolerance to and recovery from deicing salt (sodium chloride [NaCl]) damage. In experiment one, sucrose plus a water-only control was applied as a root drench to containerized stock. Seventy-two hours later, NaCl was applied to both tree species as a root drench. At day 15 after NaCl application, effects on leaf chlorophyll a and b, carotenoid (lutein, β-carotene, neoxanthin, α-carotene), xanthophyll (zeaxanthin, antheraxanthin, violaxanthin) concentration, leaf necrosis, and chlorophyll fluorescence (Fv/Fm) were measured. In experiment 2, NaCl was applied as a root drench. At day 14 after NaCl application, plants were root drenched with sucrose plus a water-only control and recovery rates monitored by recording leaf necrosis, leaf chlorophyll concentration, and chlorophyll fluorescence over the proceeding 8 weeks. At week 8 after sucrose application, effects on tree growth were recorded. Sucrose was found to confer to both tree species a useful degree to tolerance to NaCl and improve recovery from salt-induced damage with promotion of photoxidative antioxidant pigments (carotenoids, xanthophylls) and chlorophylls strongly indicated as significantly contributing to the induction of NaCl tolerance.

Citrus abscission and Arabidopsis plant decline in response to 5‐chloro‐3‐methyl‐4‐nitro‐1H‐pyrazole are mediated by lipid signalling

ABSTRACTThe compound 5‐chloro‐3‐methyl‐4‐nitro‐1H‐pyrazole (CMNP) is a pyrazole‐derivative that induces abscission selectively in mature citrus (Citrus sinensis) fruit when applied to the canopy and has herbicidal activity on plants when applied to roots. Despite the favourable efficacy of this compound, the mode of action remains unknown. To gain information about the mode of action of CMNP, the effect of application to mature citrus fruit and Arabidopsis thaliana roots was explored. Peel contact was essential for mature fruit abscission in citrus, whereas root drenching was essential for symptom development and plant decline in Arabidopsis. CMNP was identified as an uncoupler in isolated soybean (Glycine max) mitochondria and pea (Pisum sativum) chloroplasts and an inhibitor of alcohol dehydrogenase in citrus peel, but not an inhibitor of protoporphyrinogen IX oxidase. CMNP treatment reduced ATP content in citrus peel and Arabidopsis leaves. Phospholipase A2 (PLA2) and lipoxygenase (LOX) activities, and lipid hydroperoxide (LPO) levels increased in flavedo of citrus fruit peel and leaves of Arabidopsis plants treated with CMNP. An inhibitor of PLA2 activity, aristolochic acid (AT), reduced CMNP‐induced increases in PLA2 and LOX activities and LPO levels in citrus flavedo and Arabidopsis leaves and greatly reduced abscission in citrus and delayed symptoms of plant decline in Arabidopsis. However, AT treatment failed to halt the reduction in ATP content. Reduction in ATP content preceded the increase in PLA2 and LOX activities, LPO content and the biological response. The results indicate a link between lipid signalling, abscission in citrus and herbicidal damage in Arabidopsis.

Use of Sugars to Improve Root Growth and Increase Transplant Success of Birch (Betula Pendula Roth.)

Two field trials undertaken in 1999 and 2003 investigated the influence of a range of sugars applied as a root drench at 25, 50, and 70 g/L (3.4, 6.8, and 10.3 oz/gal) of water on root and shoot growth, chlorophyll fluorescence, photosynthetic rates, and leaf carotenoid and chlorophyll concentrations of birch (Betula pendula Roth.). Irrespective of concentration and year, the sugars galactose and rhamnose had no significant effects on tree growth or leaf photosynthetic properties. Application of the sugar maltose increased shoot and root dry weight in the 1999 trial but had no effect in the 2003 trial. Sucrose, fructose, and glucose increased shoot and root dry weight in both 1999 and 2003 trials; however, growth responses were influenced by the concentration of sugar applied. In many cases, sugar application increased the number of new roots formed by week 6 but had no significant effects on the length of existing roots or shoot growth. By week 24, increases in both root and shoot growth were recorded. Sugar feeding at 25 g/L (3.4 oz/gal) of water had no significant effect on leaf chlorophyll fluorescence, photosynthetic rates, or carotenoid and chlorophyll concentrations; however, sugar feeding at 50 and 75 g/L (6.8 and 10.3 oz/gal) of water reduced these values by week 6. At the cessation of the experiment, maximal increase in root and shoot growth was associated with a root drench of sucrose at a concentration of 70 g/L (10.3 oz/gal) of water in both 1999 and 2003 trials. Lower mortality rates recorded in sugar-treated trees indicate applications of sugars would aid in the survival of young birch trees following transplanting.

Inducible double-stranded RNA expression activates reversible transcript turnover and stable translational suppression of a target gene in transgenic tobacco

A binary vector amenable to high-throughput cloning was constructed for ethanol-inducible expression of double-stranded RNA (dsRNA) in plants. Silencing of a transgene encoding β-glucuronidase ( GUS) was then examined at RNA and protein levels in tobacco. Transient gene silencing could be effectively achieved in plants with higher expression levels of alcR (the ethanol sensor) after single application of 1% ethanol (v/v) through root drenching. GUS activities showed more dramatic pattern of loss and recovery in young leaves than in older leaves. Repeated ethanol treatment resulted in extended gene suppression and increased loss of GUS activities. Interestingly, recovery of GUS transcript level is dramatically earlier than that of GUS protein levels as measured by enzyme assays. These observations indicate that dsRNA-mediated gene silencing may occur through more stable translational inhibition in addition to reversible targeted RNA degradation.

THE INFLUENCE OF BIOSTIMULANTS ON GROWTH AND VITALITY OF THREE URBAN TREE SPECIES FOLLOWING TRANSPLANTING

Summary Four commercially available, biostimulants sold under the trade names ‘Generate’, ‘Crop Set’, ‘Fulcrum’ and ‘Redicrop 2000’ were applied either as a root drench or foliar spray to three transplant-sensitive tree species, red oak(Quercus rubra), birch(Betula pendula) and beech (Fagus sylvatica) post transplanting. The short and long-term efficacy of the biostimulants on growth was quantified by recording root and shoot vigour at week 8 and 20. In addition, improvements in tree vitality were assessed by measurement of a chlorophyll a performance index based on leaf chlorophyll fluorescence emissions. Irrespective of species, no significant effect of mode of application (foliar spray versus root drench) was recorded on growth and vitality. The biostimulants Generate and Fulcrum increased growth of all three tree species. No significant effects on growth and chlorophyll fluorescence of birch and beech were recorded following applications of the biostimulants Crop Set and Redicrop 2000, however, significant increase in growth of red oak was recorded. Only the biostimulant Generate increased chlorophyll fluorescence values of all test species. Results show use of biostimulants can improve root and shoot vigour following transplanting. However, selection of an appropriate biostimulant is critical as effects on growth and vitality can vary widely between tree species possibly as a result of the differing active ingredient used in the formulation of the product.

Relative effects of the insecticide thiamethoxam on the predator Podisus nigrispinus and the tobacco whitefly Bemisia tabaci in nectaried and nectariless cotton.

The predaceous stinkbug Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) feeds on plants as well as on arthropod prey. The question arises whether feeding on plants might expose the predator to systemic insecticide via ingestion of the active ingredient or its metabolites through plant sap of treated plants. This interaction was investigated with nectaried and nectariless cotton plants cropped in pots and treated with the systemic insecticide thiamethoxam at 0.5, 1.0 and 2.0 mg per plant as a root drench. Development of P. nigrispinus fed on prey and on treated nectaried and nectariless cotton plants and confined at 15, 30 and 45 days after insecticide application, and adult reproduction from nymphs caged 30 days after treatment were determined. Podisus nigrispinus life history traits were unaffected by the type of cotton plant, nectaried or nectariless, but were significantly affected by insecticide dose and time after application. Developmental time was extended and fresh adult body weight was reduced by feeding on prey and treated plants. Nymphs caged on treated plants with the highest thiamethoxam concentration at 15 days after application produced only 13.2% of adults. Females emerged from nymphs caged on both plants and at all thiamethoxam concentrations at day 30 after application presented similar reproductive characteristics, except for age of first oviposition, which was delayed on plants treated with the highest thiamethoxam concentration. Thiamethoxam at 0.5 mg per plant restrained tobacco whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) colonization only during the first 15 days after application to either cotton plant, and similar immature densities were sampled at day 35 after application on treated and untreated plants. However, plants treated with 1.0 and 2.0 mg per plant as a drench and cropped in pots were protected from tobacco whitefly for up to 45 days after exposure to a whitefly colony.

Ambiol, spermine, and aminoethoxyvinylglycine prevent water stress and protect membranes in Pinus strobus L under drought

The ability of antistress compounds to enhance the drought tolerance of conifer seedlings was tested by feeding plant growth regulators (PGRs) to 1-year-old white pine (Pinus strobus L.), which were then subjected to either a moderate (11 day) or a more severe (16 day) drought. The following PGRs were either fed directly into the xylem or applied as a root drench: the antioxidant Ambiol (2-methyl-4-[dimethylaminomethyl]- 5-hydroxybenzimidazole dihydrochloride), the polyamine, spermine, an anti-ethylene agent, aminoethoxyvinylglycine (AVG), and the inhibitor, abscisic acid (ABA). Leaf water potentials (Ψl) declined in untreated seedlings when they were exposed to drought. Preconditioning with PGRs postponed water deficits and prevented membrane leakage under drought. The specific physiological adjustments observed were found to vary, depending on the type of compound. Ambiol, AVG and spermine caused transpirant rates to decline under drought. Although the antitranspirant effects of Ambiol and spermine would explain the increase in water use efficiency under drought, spermine also enhanced photosynthesis. The same compounds promoted osmotic adjustment, which would help to maintain turgor under drought. This was shown by the decline in osmotic potential at full turgor, and at zero turgor, in Ambiol and spermine-treated seedlings. Seedlings treated with Ambiol and ABA could sustain a greater water loss before turgor declined to zero. The possibility that preconditioning may help to maintain leaf physiological functioning under drought by reducing water stress and stress-ethylene production is discussed.

Effect of chitin on biological control activity of Bacillus spp. and Trichoderma harzianum against root rot disease in pepper (Capsicum annuum) plants

Two bacterial isolates and one strain of Trichoderma harzianum were tested alone and in combination with chitin for efficacy in control of root rot disease caused by Phytophthora capsici and Rhizoctonia solani in pepper plants under greenhouse conditions. These bacteria (Bacillus subtilis HS93 and B. licheniformis LS674) were isolated from repeatedly washed roots of pepper plants. In in vitro assays, HS93, LS674 and T. harzianum were antagonistic against P. capsici and R. solani and produced high levels of chitinase. Seed treatment and root drenching with bacterial suspensions of HS93 with 0.5% chitin was more effective against Phytophthora and Rhizoctonia root rot than addition of the organisms without chitin. LS674 and T. harzianum reduced Rhizoctonia but not Phytophthora root rot. In two greenhouse tests, seed treatment and root drenching with HS93 amended with chitin enhanced its biocontrol activity against P. capsici but not on R. solani. The effects of LS674 and T. harzianum against R. solani were significantly enhanced when they were used as suspensions with 0.5% chitin for root drenching, but this had no effect on P. capsici. In both greenhouse experiments, the use of 0.5% chitin alone for root drenching reduced Rhizoctonia root rot. Reduction of root rot disease was accompanied by increased yield. These results show that the antagonistic activity of HS93, LS674 and T. harzianum may be stimulated by chitin resulting in significant improvements in their effectiveness against pathogens.