Mise en œuvre d'un réseau d'information des risques de tavelure en moyenne vallée du Rhône par la mesure et l'utilisation raisonnée de facteurs climatiques1

La mise au point à Stuttgart (RFA) en 1974 d'un appareil électronique simple permettant d'intégrer la température, l'humidité relative et l'humectation a permis de mettre en valeur des courbes de Mills, ce qui a facilité la prévision des attaques de tavelure sur pommiers. Les données fournies par les thermohumectographes Bazier et KIT-INRA ont été utilisées en 1975–1976 pour les prévisions de tavelure, dans la moyenne vallée du Rhône. Etant donné que les résultats pratiques se sont révélés satisfaisants, tant sur le plan de l'efficacité que sur celui du coût, il a paru intéressant en 1977 d'établir dans les départements de la Drôme et de l'Ardèche un réseau d'information reposant sur 15 stations d'observations recouvrant environ 4000 ha de vergers de pommiers et de poiriers. Un système amélioré de prévisions qui s'inspire du modèle de Strizyk est à l'étude en 1982.     

Understanding the site of action of photosystem II inhibitors

It is believed that the different classes of compound which interfere with photosynthesis system II (PS 11) must act by binding at different sites, because they appear to be structurally so dissimilar. However, it can be argued that some of the classes of compound of diverse structural type share very similar external surface features. Now that details about the binding oj PSII inhibitors are becoming available, it will be possible to see how many of the different compound classes actually bind similarly. In future, increasingly detailed knowledge of the structures of potential sites of action will be available. QSAR methods will need to be used together with molecular modelling to be effective tools for agrochemical design.     

Note on the Control of Olive Fly (Dacus oleae [Gmel.]) by Means of Low and Ultra-low Volume Bait-spraying

In 1967, 1968 and 1969 the efficacy of aerial low volume and ultra-low volume bait-spraying against Dacus oleae (Gmel.) was compared in Greece. Results were mainly assessed by periodical trapping and by post-treatment countings of the percentage of attack in sampled olives. No difference between the effect of the two methods became apparent. It is deemed necessary, however, to repeat the experiments under conditions of heavier infestation.     

The absolute configuration of chiral organophosphorus anticholinesterases

Contrary to an earlier report in this journal by Wustner and Fukuto (1), bovine erythrocyte acetylcholinesterase is inhibited preferentially by the same (S)_P-isomers of the two closely related anticholinesterases O-2-butyl S-2-(dimethylammonium)-ethyl ethylphosphonothioate hydrogen oxalate(I) and O-isopropyl S-2-(trimethylammonio)ethyl methylphosphonothioate iodide(II).     

The uptake of metabolites of permethrin by plants grown in soil treated with [14C]permethrin

Sugar beet, wheat, lettuce and cotton were grown in soil treated with [¹⁴C]permethrin, the crops being sown at intervals of 30, 60 and 120 days after treatment of the soil. The uptake of radioactive residues into these crops was measured. Low radioactive residues (up to 0.86 μg g^?1) were detected in the mature plants sown 30 days after soil treatment, and this uptake declined significantly as the interval between soil treatment and sowing increased. Metabolites derived from the acid moiety of the permethrin molecule were shown to constitute the greater part of the residue transferring from the soil to the crops. (1RS)-cis- and (1RS)-trans-3-(2,2-dichlorovinyl)- 2,2-dimethylcyclopropanecarboxylic acid and 3-(2,2-dichlorovinyl)-1-methylcyclopropane-1,2-dicarboxylic acid were identified as the major acidic metabolites. The latter compound is a metabolite of permethrin which has not previously been identified in soil or plants.     

THE MOVEMENT OF PARAQUAT IN PLANTS

Summary. A qualitative study of the movement of the herbicide paraquat from droplets applied to leaves of tomato plants, using ¹⁴C-methyl-labelled and ¹⁴C-ring-labelled paraquat dichloride and di(methylsulphate), has shown that it moves in the xylem with the transpiration stream. The chemical is as well transported from young leaves as from mature ones, and will move through a steam-ringed petiole. The enhancement of the amount of paraquat transported from the treated leaves which occurs when treated plants are kept in darkness for a period following treatment and then exposed to light, is probably due to the greater movement into the xylem through undamaged tissue which can occur in the dark. Once the chemical has been absorbed into treated leaves, light-induced damage is required for significant movement through the rest of the plant to take place, but the damage then inhibits further entry of paraquat into the xylem. The movement of paraquat in broad bean and maize is essentially similar, though the enhancement of movement by a period of darkness after application is much less marked.
La migration du paraquat dans les plantes     

Tumours of Begonia and some other ornamentals,induced by Corynebacterium fascians

In 1975 many tumours were observed in plants ofBegonia Schwabenland grown in Aalsmeer. Submersion of the roots ofNicotiana megalosiphon seedlings in a homogenate of tumorous tissue, induced tumours after two weeks. Short periods of submergence yielded results similar to those obtained after longer periods. Tumour homogenates lost their infectivity after ten min at 50°C. Aphids transmitted the infectious agent.Treatment with propylene oxide did not inhibit infectivity completely. Filtration through a 450 nm filter removed the infectious agent.Tobacco tumor virus or a viroid could not be isolated. Cultures ofCorynebacterium fascians, isolated from tumours ofN. megalosiphon were highly infectious and induced tumours in healthyN. megalosiphon andBegonia. Tumorous tissue homogenates ofPelargonium zonale, Dahlia sp.,Gladiolus sp., andLilium sp. also caused tumours inN. megalosiphon, from whichC. fascians was isolated. It was not possible to produce tumours inN. megalosiphon with homogenates from roses with symptoms of bud proliferation.Samenvatting In 1975 werden vele tumoren waargenomen inBegonia Schwabenland op Aalsmeerse bedrijven (Fig. 1). De infectiositeit van tumorweefsel kon goed en snel worden vastgesteld door de wortels van zaailingen vanNicotiana megalosiphon in een homogenaat van tumorweefsel te dompelen. Tumoren ontstonden na twee weken, de eindbeoordeling geschiedde na een maand (Fig. 2). Ook verschillende andereNicotiana spp.,Melilotus officinalis (Fig. 3) enPisum odoratum (Fig. 4) werden aangetast.Bij de infectiositeitstoets gaven zeer korte dompeltijden even goede resultaten als langere (Tabel 1). Infectieus sap verloor zijn infectievermogen na 10 min verhitting bij 50°C. Bladluizen brachten de smetstof over. Propyleenoxide verminderde de infectiositeit wel, doch onderdrukte deze niet totaal. Bij filtratie door een 450 nm filter bleef het infectieuse agens op het filter achter. Het tumor-inducerende agens was ook aanwezig in die delen van planten met tumoren welke gezond leken en het ging voor een gering deel over met zaad (Tabel 2).Uit tumoren konden wij geen tabakstumorvirus of een viroïde isoleren. Culturen vanCorynebacterium fascians, geïsoleerd uit tumoren vanN. megalosiphon bleken zeer infectieus en veroorzaakten tumoren inN. megalosiphon enBegonia. Homogenaten van tumorweefsel vanPelargonium zonale, dahlia (Fig. 5), gladiool (Fig. 6) enLilium Mid Century Hybrid Enchantment (Fig. 7) veroorzaakten ook tumoren opN. megalosiphon, waaruitC. fascians werd geïsoleerd. Met sap van kroeskopzieke rozen konden wijN. megalosiphon niet besmetten.     

Pathogenicity of the root-knot nematode Meloidogyne javanica on potato

Host–parasite relationships and pathogenicity of Meloidogyne javanica on potatoes (newly recorded from Malta) were studied under glasshouse and natural conditions. Potato cvs Cara and Spunta showed a typical susceptible reaction to M. javanica under natural and artificial infections, respectively. In potato tubers, M. javanica induced feeding sites that consisted of three to four hypertrophied giant cells per adult female. Infection of feeder roots by the nematode resulted in mature large galls which usually contained at least one mature female and egg mass. In both tubers and roots, feeding sites were characterized by giant cells containing granular cytoplasm and many hypertrophied nuclei. Cytoplasm in giant cells was aggregated alongside the thickened cell walls. Stelar tissues within galls appeared disorganized. The relationship between initial nematode population density ( P ) [0–64 eggs + second-stage juveniles (J2s) per cm³ soil] and growth of cv. Spunta potato seedlings was tested under glasshouse conditions. A Seinhorst model [ y = m  + (1 −  m ) z ^{( P − T )}] was fitted to fresh shoot weight and shoot height data of nematode-inoculated and control plants. Tolerance limits ( T ) for fresh shoot weight and shoot height of cv. Spunta plants infected with M. javanica were 0·50 and 0·64 eggs + J2s per cm³ soil, respectively. The m parameter in that model (i.e. the minimum possible y -values) for fresh shoot weight and shoot height were 0·60 and 0·20, respectively, at P  = 64 eggs + J2s per cm³ soil. Root galling was proportional to the initial nematode population density. Maximum nematode reproduction rate was 51·2 at a moderate initial population density ( P  = 4 eggs + J2s per cm³ soil).     

Note: Comparison of three laboratory methods to evaluate the pathogenicity and virulence of tenPseudomonas syringae pv.syringae strains on apple, pear, cherry and peach trees

The pathogenicity and virulence of ten GreekPseudomonas syringae pv.syringae strains from different hosts (citrus, pear, apple, peach and cherry) were evaluated using three different laboratory methods, which produced results in good agreement. All ten strains were virulent on apple, pear, cherry and peach trees. The extent of tissue colonized varied considerably among strains and cultivars. On excised shoots and twigs of apple and pear, strains BPI 176, BPI 203, PI 2 and PI 14 were the most virulent and strains BPI 689, BPI 992, BPI 4, BPI 20, PI 18 and PI 19 were the least virulent. On excised shoots and twigs of peach and cherry, strains BPI 176, BPI 203, PI 2, PI 14, PI 18 and PI 19 were the most virulent and strains BPI 4 and BPI 20 were the least virulent. Moderate virulence was evinced by strains BPI 689 and BPI 992. These pathogenicity assays are proposed as rapid and reproducible screening systems to evaluate the susceptibility of apple, pear, cherry and peach cultivars to this bacterial pathogen.     

Perceptions of risk, risk aversion, and barriers to adoption of decision support systems and integrated pest management: an introduction

Rational management of plant diseases, both economically and environmentally, involves assessing risks and the costs associated with both correct and incorrect tactical management decisions to determine when control measures are warranted. Decision support systems can help to inform users of plant disease risk and thus assist in accurately targeting events critical for management. However, in many instances adoption of these systems for use in routine disease management has been perceived as slow. The under-utilization of some decision support systems is likely due to both technical and perception constraints that have not been addressed adequately during development and implementation phases. Growers' perceptions of risk and their aversion to these perceived risks can be reasons for the "slow" uptake of decision support systems and, more broadly, integrated pest management (IPM). Decision theory provides some tools that may assist in quantifying and incorporating subjective and/or measured probabilities of disease occurrence or crop loss into decision support systems. Incorporation of subjective probabilities into IPM recommendations may be one means to reduce grower uncertainty and improve trust of these systems because management recommendations could be explicitly informed by growers' perceptions of risk and economic utility. Ultimately though, we suggest that an appropriate measure of the value and impact of decision support systems is grower education that enables more skillful and informed management decisions independent of consultation of the support tool outputs.