Transfer from Erwinia herbicola to Escherichia coli of a plasmid associated with biocontrol of fire blight

Strains of Erwinia herbicola effective in the biocontrol of fire blight of hawthorn were used to investigate the possibility that the antagonistic activity is coded by plasmid-born genes. Agarose gel electrophoresis of isolated plasmids from four antagonistic Erw. herbicola strains showed a band of a supercoiled 12 kb plasmid in each strain, with a second band greater than 16.2 kb consistently seen in two strains. Erw. herbicola strains showed resistance to penicillin-G, which could be conferred on penicillin-G sensitive Escherichia coli TG1 by transformation with a pure Erw. herbicola plasmid preparation. Transformed strains of Esc. coli appeared to contain the Erw. herbicola 12 kb plasmid, but not the > 16.2 kb plasmid. In an agar plate assay, Esc. coli transformants produced an inhibition zone against Erw. amylovora similar to those produced by the original Erw. herbicola strains. In two biocontrol assays, the transformed Esc. coli strains had a suppressive effect on disease development on infected pear fruit slices and hawthorn blossoms.     

Effects of neemgard on phytophagous and predacious mites and on Spiders

The effects of Neemgard, an acaricidal and fungicidal formulation obtained from neem (Azadirachta indica) seed kernels, on the phytophagous miteTetranychus cinnabarinus, the predacious mitePhytoseiulus persimilis, and the predatory spiderChiracanthium mildei, were investigated in laboratory experiments. Neemgard was highly toxic toT. cinnabarinus but had no toxic effect onC. mildei orP. persimilis. Another neem formulation—the insecticidal Neemix 45—caused conspicuous repellency, but no mortality, inT. cinnabarinus.     

Comparison of two sampling methods for leafhoppers (Homoptera, Cicadellidae) associated with sesame in the east Mediterranean region of Turkey

Yellow sticky-traps and a modified Johnson-Taylor suction-trap were used to index the relative population dynamic of leafhoppers associated with sesame in the east Mediterranean region of Turkey. Comparison of the obtained results signified important differences between both traps. 32 leafhoppers species were caught in the suction-trap while only 18 species were determined on yellow sticky-traps. For most of the leafhopper species, relatively more males were determined on the yellow-traps than in the suction-trap, indicating a higher activity of male leafhoppers during daytime hours. A close relationship between the seasonal flight pattern as indexed by sticky-traps and by suction-trap was only observed forAsymmetrasca decedens (Paoli) andEmpoasca decipiens Paoli. For most other leafhopper species no or only a very poor correlation for the relative population dynamic was determined between both traps. Important leafhopper vector species, e.g.,Circulifer haematoceps (Mulsant et Rey) andOrosius orientalis (Matsumura) were better represented in yellow sticky-trap catches than they were in the suction trap.

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Zusammenfassung  Die relative Populationsdynamik der mit Sesam assozüerten Zwergzikaden wurde mit beleimten Gelbtafeln und einer stationären Johnson-Taylor-Saugfalle an der südöstlichen Mittelmeerküste der Türkei untersucht. Beim Vergleich beider Methoden zeigten sich deutliche Unterschiede zwischen den Fallentypen. In der Saugfalle konnten 32 Zwergzikadenarten erfaßt werden, während dies auf den Gelbtafeln nur 18 Arten waren. Die meisten Zwergzikadenarten zeigten auf den Gelbtafeln ein stark in Richtung der Männchen verschobenes Geschlechterverhältnis, was eine erhöhte Flugaktivität der Männchen während des Tageslichts vermuten läßt. Auch der Verlauf der saisonalen Flugaktivität war für die meisten Zwergzikadenarten zwischen den beiden Fallentypen sehr unterschiedlich, und es konnten zwischen Saug- und Gelbfalle keine deutlichen Korrelationen hergestellt werden. Nur für die beiden zusammen erfaßten ArtenAsymmetrasca decedens (Paoli) undEmpoasca decipiens Paoli wurde ein enger Zusammenhang zwischen der mit der Saugfalle und den gelben Leimtafeln erfaßten relativen Populationsdynamik festgestellt. Wichtige Vektorenarten unter den Zwergzikaden, z. B.Circulifer haematoceps (Mulsant et Rey) undOrosius orientalis (Matsumura) waren auf den Gelbtafeln besser repräsentiert als in der Saugfalle.

     

Biological and molecular characterization of Tomato spotted wilt Virus in Israel

Received April 24, 1997; received in final form June 29, 1997. Symptoms resembling tomato spotted wilt virus (TSWV) infections were documented among ornamental and vegetable crops in commercial greenhouses and open fields in Israel. Plants exhibiting these symptoms were collected from January 1992 to December 1996. Among cultivated plants analyzed for TSWV by enzyme-linked immunosorbent assay (ELISA), 19 species representing five families were found to be infected; natural infection was also recorded in six plant species of weeds. Virus identity was characterized by host range, serology and electron microscopy. Serological reaction with the isolates, found in Israel, using antisera from different sources as well as the sequence analysis of the nucleocapsid gene, demonstrated that the Israeli isolates of TSWV are a member of tospovirus serogroup I, type I (BR-01 strain). No virus transmission was found in seeds collected from virus-infected vegetable and ornamental crops. A non-radioactive molecular probe derived from the cloned nucleocapsid isolate enables specific detection of the virus in crude sap from infected plants. The detection of TSWV in Israel constitutes a severe potential threat to the ornamental and vegetable industry.     

Abscisic acid is a potent inhibitor of growth and sporidial formation inneovossia indica cultures: Dual mode of actionvia loss of polyamines and cellular turgidity

The inhibition of polyamine biosynthesis inNeovossia indica (Mitra) Mundkur by D,L— α-difluoromethylornithine (DFMO) caused an effective reduction of mycelial growth and sporidial production underin vitro conditions, which was reversed by ornithine application. Abscisic acid proved to be similarly effective, not only in inhibiting mycelial growth and sporidial formation but also the germination of teliospores, which constitute the primary inoculum of the pathogen. ABA-mediated inhibition resulted in decreased polyamine levels and loss of cellular turgidity of mycelial cultures. Scanning electron microscopy of ABA-treated cultures revealed extremely shrunken hyphae, in marked contrast to the turgid controls. It is suggested that the manipulation of ABA levels and/or tissue sensitivity in wheat could be a strategy to combat ‘Karnal’ bunt, the disease caused byN. indica.     

Effects of the host, the pathogen, the environment and their interactions, on fusarium wilt in carnation

Fusarium oxysporum f.sp.dianthi causes severe wilting in carnation (Dianthus caryophyllus L.) worldwide. The pathogen is present in the soil profile in which carnation roots are distributed and may infect the plants at any time during the growing season. To minimize the losses induced by Fusarium wilt, growers use carnation cuttings free ofFusarium spp. and fumigate the soil with methyl bromide prior to planting. The severity of epidemics and the resulting losses are governed by the main and interacting effects of the three components of the disease syndrome: the host, the pathogen and the environment. Host variables include the type and the degree of cultivar resistance (i.e., complete, partial or tolerance); pathogen variables include the race, its virulence and infectivity, and the amount of initial inoculum; environmental variables include solar radiation intensity, photoperiod, temperature and the growth substrate. In the present review the information available on the effect of the host, the pathogen and the environment, and their interactions, on Fusarium wilt in carnation is summarized.     

Biological control and plant health in the UK1

The protected crop environment has long been recognized as offering particularly good opportunities for the application of biological control and this is reflected in the predominance of integrated pest management programmes and the wide range of biological control agents available. The introduction of new pest species of quarantine concern can often occur in glasshouse crops, as a result of international trade in plant material, and can have a highly disruptive impact upon well established, integrated pest management programmes. The use of biological control agents against quarantine pests is discussed, including both the use of exotic species and those established in the UK. The relevant legislation in the UK is outlined in relation to the introduction of non-native species, including both plant protection and conservation interests. Environmental safety aspects such as the impact of such introductions on non-target species and issues of quality control to prevent the introduction of contaminants are noted as of particular plant health interest.     

Auxins increase the occurrence of leaf-colour variants in Caladium regenerated from leaf explants

Leaf explants of Caladium ‘Pink Cloud’ were cultured in vitro on MS medium containing various auxins (NAA, IBA, IAA, 2,4,5-T and 2,4-D) in combination with cytokinin (BA). NAA gave the most vigorous in vitro propagation of this plant, and only 15% of the plants were leaf-colour variants on the medium containing 0.5 μmol NAA. Leaf colour variation was observed in all plants regenerated on the medium containing 2,4-D at 0.5–4.5 μmol. In hormone-free medium, only a few leaf-colour variants (6%) occurred, but the rate of plant regeneration was very low. Application of 0.5 μmol NAA together with 4.5 μmol BA seemed to be the most appropriate for in vitro propagation of Caladium ‘Pink Cloud’ with only a few leaf-colour variants.