CONTENTS AND ABSTRACTS

Volume 1 Number 1 2007

Teresa Bleve-Zacheo, M. Teresa Melillo (Italy), Philippe Castagnone-Sereno (France) The Contribution of Biotechnology to Root-Knot Nematode Control in Tomato Plants (pp 1-16)

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Special Feature: Root-knot nematodes (Meloidogyne spp.) represent a particularly serious pest for tomato crops. These pathogens have evolved a sophisticated interrelationship with the roots of their host where they induce a specific type of nurse cell system, classified as multinucleate giant cells. The structural and physiological transformation of the initial cell to become the nematode feeding site is paralleled by modifications in plant gene expression. The recent characterisation of several parasitism genes specifically expressed within oesophageal gland cells of root-knot nematodes suggests that their products can influence the host cellular metabolism. In plants with genetic disease resistance, these secreted molecules might serve as virulence factors for successful parasitism. The Mi gene, which confers resistance to several species of root-knot nematodes, is present in many modern tomato cultivars. Resistance mediated by Mi is associated with localized necrosis of host tissue at the nematode feeding site and occurs very early after nematode infection. However, how Mi mediates recognition of and resistance to root-knot nematodes is largely unknown. In parallel with the use of such natural resistance, several biotechnological strategies have been experienced to improve tomato resistance. They are mainly based on the over-expression of anti-nematode and/or anti-giant cell genes placed under the control of specific promoters. Here, we review the recent progress in determining the role of signal transduction pathway(s) in tomato responses during both susceptible and resistant interactions, and how such knowledge should allow the development of alternative strategies for engineering durable resistance against root-knot nematodes in tomato.

Bart Lievens (Belgium), Bart P.H.J. Thomma (The Netherlands) Quantification in Multiplex Format as a Challenging Goal for Plant Pathogen Molecular Diagnostic Assays (pp 17-26)

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Invited Mini-Review: Accurate detection and identification of plant pathogens is fundamental to plant disease management. The lack of rapid, accurate and reliable means by which plant pathogens can be detected and identified has been one of the main limitations in plant disease management, and has prompted the development of alternative diagnostic technologies. Increasingly, molecular methods that are based on the detection of nucleic acids are implemented for routine plant pathogen diagnosis. Now that a number of molecular assays have been established, the latest challenge is to be able to quantify pathogen biomass, preferentially in multiplex format, with these assays. However, the development of technology for accurate quantification bears a number of pitfalls that will be highlighted in this review. The ability to perform pathogen quantification will result in a novel challenge; namely to be able to predict disease development based on pathogen densities in a specific environment. Issues that are of relevance to these topics are discussed in this review.

Raymond A. Cloyd (USA) Management of Plant-Feeding Mites in Interior Plantscapes (pp 27-32)

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Invited Mini-Review: Plants grown in greenhouses, conservatories, and interiorscapes are susceptible to many different types of plant-feeding mites. Although there are a diversity of mite species that may feed on ornamental plants grown or used in interior plantscapes this paper focuses on three major species: twospotted spider mite (Tetranychus urticae), broad mite (Polyphagotarsonemus latus), and cyclamen mite (Steneotarsonemus pallidus). These mites are polyphagous and cause damage by withdrawing plant cell contents with their stylet-like mouthparts inducing stippling, bronzing, or leaf distortion, depending on the mite type. Cultural control of mites includes irrigation, fertility, and host plant resistance. The use of biological control has been successful in cut flower greenhouses such as roses (Rosa spp.) using the predatory mites Phytoseiulus persimilis, Neoseiulus californicus, and Amblyseius fallacis. However, the primary method of managing mites, especially in greenhouses, involves applications of miticides. Currently, there are many miticides available for control of twospotted spider mite with variable modes of action, whereas fewer miticides are available for control of broad and cyclamen mite. Due to their biology, genetics, and reproductive capacity, twospotted spider mite can develop resistance to miticides within a short period of time, which means that proper rotation programs, based on mode of action, must be implemented in order to sustain effective miticides. The availability and extensive use of neonicotinoid-based insecticides, in particular imidacloprid, that provide control of phloem-feeding insects such as whiteflies, aphids, and mealybugs may be responsible for the increase in twospotted spider, broad and cyclamen mite populations on many ornamental crops. Although plant-feeding mites have been and continue to be a problem in interior plantscapes, there are several pest management strategies that may be implemented in order to alleviate problems with these mite types.

Sylvaine Simon, Benoît Sauphanor, Pierre-Eric Lauri (France) Control of Fruit Tree Pests through Manipulation of Tree Architecture (pp 33-37)

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Invited Mini-Review: Although chemical aspects of plant-insect relationships are largely studied, the effect of within-plant structure on insects is seldom investigated, especially in perennial crops. In fruit production, the manipulation of tree architecture is generally considered to be involved in pest development through considerations of “tree vigour” or branching density. However, both physiological and physical aspects of tree architecture (i.e., canopy height, width and shape, fruiting and vegetative shoot distribution, branching, connectivity, growth rhythmicity) affect the distribution and abundance of both phytophagous arthropods and natural enemies. Tree architecture can affect arthropod pests by modifying: (a) the attractiveness of the host-plant; (b) the within-plant life conditions including microclimate, availability and accessibility of resources and reproduction sites, and enemy-free spaces; (c) the efficiency of chemical or alternative pest control methods (including the use of pheromones). Despite seasonal effects and variability in species biology, modelling and experimental approaches have shown that a more complex architecture favours phytophagous insects and is detrimental to the foraging of most natural enemies. Orchards are permanent habitats, in which the manipulation of tree architecture is potentially a powerful tool for pest regulation, through the implementation of innovating training systems.

G. Christopher Cutler, Cynthia D. Scott-Dupree (Canada) Novaluron: Prospects and Limitations in Insect Pest Management (pp 38-46)

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Invited Mini-Review: Biorational insecticides are a valuable insect pest management option for growers and pest management practitioners. Novaluron is a recently developed benzoylphenyl urea insecticide with excellent activity against several important insect pests. Through inhibition of chitin synthesis, larval insect stages are targeted with death from abnormal endocuticular deposition and abortive molting. This physiological specificity lends novaluron well to integrated pest management (IPM) programs, as toxicity to mammals, birds and other vertebrates is low, and adult beneficial insects, including predators, parasitoids and pollinators, are generally unaffected. Foliar applications have demonstrated prolonged persistence, providing long-lasting control for growers, and the mode of action of novaluron, completely different from that of commonly used neurotoxic insecticides, makes it a useful alternative insecticide for resistance management. However, there are several obstacles, many inherent to IPM, which may hinder the utility of novaluron. While its narrow spectrum of activity is a key attribute, paradoxically this may be a significant detractor for growers who prefer broad-spectrum control of multiple pests. As an insect growth regulator, timing of novaluron applications is often more restrictive and delayed insecticidal activity usually occurs. The purchase price of benzoylphenyl ureas is generally greater than that of conventional insecticides, which may limit the appeal of novaluron. Further, studies have shown that some beneficial organisms are susceptible to novaluron. Knowledge reviewed here will facilitate continued development and use of biorational compounds for IPM.

Roman Pavela (Czech Republic) Possibilities of Botanical Insecticide Exploitation in Plant Protection (pp 47-52)

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Mini-Review: In this article three types of botanical insecticides are shown: products of neem oil from seeds of Azadirachta indica Juss., pongam oil from Pongamia pinnata L. and essential oils from some aromatic plants. Their effective use against common greenhouse pests such as whitefly (Trialeurodes vaporariorum West, Bemisia tabaci Gennad.), two-spotted spider mite (Tetranychus urticae Koch), aphids and caterpillars is demonstrated. The capacity to use botanical insecticides as effective pest-controlling agents, as well as some of their limitations, are also discussed.

Marlinda Lobo de Souza, Maria Elita Batista de Castro, William Sihler (Brazil), Ewelina Krol, Boguslaw Szewczyk (Poland) Baculoviruses: A Safe Alternative in Pest Control? (pp 53-60)

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Invited Mini-Review: Broad spectrum chemical pest control agents have been widely regarded as ecologically unacceptable. Due to this opinion, there is the increased social pressure to reduce their use in the future and gradually replace them by biopesticides. Viruses of a few families are known to infect invertebrates, but only those belonging to the family Baculoviridae have been used for biocontrol of pests. They are safe to people and wildlife, their specificity is usually very narrow. Their application as bioinsecticides was limited until recently because of their slow killing action and technical difficulties for in vitro commercial production. Successful protection of over 2 million hectares of soybean in Brazil revived the hopes for using baculoviruses as effective biopesticides. Wider application of baculoviruses for pest control is very likely to be implemented in the future and two approaches for improvements of baculovirus killing properties can be foreseen. In countries where the use of genetically modified organisms (GMOs) is restricted, the improvements will be mainly at the level of in vitro production, diagnostics, and changes in biopesticide formulations. In countries that have fewer concerns towards GMOs, the killing activity of baculoviruses may be augmented by genetic modifications of the baculovirus genome. It is expected that baculoviruses improved by genetic modifications will compete successfully with other methods of pest control in many regions of our globe, especially in most densely populated countries of the world.

S.E. Brown, B. O Been, W.A. McLaughlin (West Indies) The Lethal Yellowing (16SrIV) Group of Phytoplasmas (pp 61-69)

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Invited Mini-Review: Lethal yellowing (LY) is the single most important threat to world coconut palm production. Molecular based tools, and sensitive detection procedures developed over the past decade have permitted great advances in the detection and characterization of the LY phytoplasma. The practice of RFLP analyses of PCR-amplified 16S rRNA sequences with selected restriction endonucleases has resulted in the accurate identification of different strains of the LY group of phytoplasmas associated with plants and insects. The LY phytoplasmas are currently classified as members of the 16SrIV group of phytoplasmas. This progress has facilitated studies on the epidemiology of LY phytoplasma-associated diseases and has made it possible to study LY phytoplasma ecology in greater detail. Here we present an overview of the current status of the LY disease, with emphasis on its geographical distribution, socio-economic impact, vector status, methods of control as well as current advances that have been made in the past decade in the characterization of this group.

Osmar Nickel, Cristiane de Jesus Barbosa, Hermes Peixoto Santos-Filho, Orlando Sampaio Passos, Francisco Ferraz Laranjeira (Brazil) Bahia Bark Scaling of Citrus: A Disease of Unknown Etiology (pp 70-75)

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Invited Mini-Review: In the 1960’s a bark scaling disorder was identified in sweet orange and grapefruit trees in Brazil. It is characterized by yellow-beige to light brown scaling lesions on the trunk or on small branches on the upper part of the plant and followed by a significant exudation of water soluble gum. The disease affects all sweet oranges and some mandarins but it is especially severe on grapefruit varieties. Because of its regional occurrence in the states of Bahia and Sergipe, and being symptomatically very similar to psorosis A, this disease was initially referred to as Bahia type psorosis (tBa). However, accumulated data on inoculated indicator plants, histopathological studies as well as attempts of RT-PCR and molecular hybridization showed that it was a novel disease. The etiology of the disorder is still not elucidated and its nature remains unknown. Nevertheless, experimental data on its epidemiology showed that it is naturally transmitted, citrus diseased plants are the main inoculum source and its progress and spread is consistent with a disease vectored by an insect of limited dispersion ability. Currently the work is aiming at the identification of the pathogen and its vector.

Blanka Kokošková, Roman Pavela (Czech Republic) Effectiveness of Plant Essential Oils on the Growth of Erwinia amylovora, the Causal Agent of Fire Blight Disease (pp 76-80)

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Original Research Paper: Erwinia amylovora [(Burr.) Winslow et al. 1920], the causative agent of fire blight disease, threatens some species of the Rosaceae family. In chemical control, preparations based on copper compounds are most frequently applied, but these can be phytotoxic and not effective enough, hence other alternatives need to be considered. In our experiment, thirty-four essential oils obtained from different plants were tested for their antimicrobial effectiveness against the fire blight pathogen. Screening was conducted in vitro on agar plates contaminated by E. amylovora. The strongest inhibitory effect (i.e. complete bacterial inhibition) was shown by essential oils from Mellisa officinalis, Mentha arvensis, Origanum compactum, O. vulgare and Thymus vulgaris. An inhibitory effect more than 50% higher than the standard was shown by essential oils from Eugenia caryophyllata, Mentha pulegium, and Nepeta cataria. An inhibitory effect up to 50% higher than the standard was found in essential oils from Artemisia absinthium, Citrus aurantifolia, Lavandula latifolia, Melaleuca quinqunervia, Mentha citrata, M. spicata, Ocimum basilicum, Pelargonium graveolens, P. roseum, Rosmarinus officinalis, Salvia sclarea, Thuja occidentalis and Tsuga canadensis. An antimicrobial effect comparable to the standard was found in essential oils from Amyris balsamifera, Citrus limonum, Juniperus communis, J. virginiana, Origanum majorana, Salvia officinalis, Tagetes bipinata and Thymus matschiana. Standard employed was oxychloride-Cu 84% (0.84 μg/μl), it had a weak inhibitory effect. The essential oils from Acorus calamus, Lavandula angustifolia and Zingiber officinale had a lower inhibitory effect than the standard. The essential oils of two plant extracts from Abies siberica and Pogostemon cablin had no effect on the growth of E. amylovora. Five of the most effective essential oils appear promising for the development of potential bio-pesticides.

Roman Pavela (Czech Republic) The Feeding Effect of Polyphenolic Compounds on the Colorado Potato Beetle [Leptinotarsa decemlineata (Say)] (pp 81-84)

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Original Research Paper: Colorado Potato Beetle, Leptinotarsa decemlineata (Say) is a serious pest of potato plants and devastates additional crops such as eggplant, tomato, pepper, and tobacco by its voracious feeding. Plants of the Lamiaceae family produce a large number of polyphenols with insecticidal activity. In this study we tried to identify if some of these compounds could be used as antifeedants and if there is any influence of these compound on food conversion by the Colorado Potato Beetle whose 3^rd instar larvae were fed food contaminated with quercetin, naringenin, vanillin, p-coumaric acid, catechin, caffeic acid, vanillin acid, rutin and phloroglucinol in 1.33, 0.66 and 0.11 mg/cm^-2 doses. Several compounds remarkably decreased larval growth and inhibited their feeding. The flavonoids were almost ineffective, having little or no effect on growth and/or food deterrence of the larvae, whereas phenols and phenolic acid demonstrated a very high efficiency.