Characterization of phytoplasmas detected in Chinaberry trees with symptoms of leaf yellowing and decline in Bolivia

Polymerase chain reaction (PCR) assays were used to detect phytoplasmas in foliage samples from Chinaberry ( Melia azedarach ) trees displaying symptoms of yellowing, little leaf and dieback in Bolivia. A ribosomal coding nuclear DNA (rDNA) product (1·8 kb) was amplified from one or more samples from seven of 17 affected trees by PCR employing phytoplasma-universal rRNA primer pair P1/P7. When P1/P7 products were reamplified using nested rRNA primer pair R16F2n/R16R2, phytoplasmas were detected in at least one sample from 13 of 17 trees with symptoms. Restriction fragment length polymorphism (RFLP) analysis of P1/P7 products indicated that trees CbY1 and CbY17 harboured Mexican periwinkle virescence (16SrXIII)-group and X-disease (16SrIII)-group phytoplasmas, respectively. Identification of two different phytoplasma types was supported by reamplification of P1/P7 products by nested PCR employing X-disease-group-specific rRNA primer pair R16mF2/WXint or stolbur-group-related primer pair fSTOL/rSTOL. These assays selectively amplified rDNA products of 1656 and 579 bp from nine and five trees with symptoms, respectively, of which two trees were coinfected with both phytoplasma types. Phylogenetic analysis of 16S rDNA sequences revealed Chinaberry yellows phytoplasma strain CbY17 to be most similar to the chayote witches'-broom (ChWBIII-Ch10) agent, a previously classified 16SrIII-J subgroup phytoplasma. Strain CbY1 resembled the Mexican periwinkle virescence phytoplasma, a 16SrXIII-group member. The latter strain varied from all known phytoplasmas composing group 16SrXIII. On this basis, strain CbY1 was assigned to a new subgroup, 16SrXIII-C.     

Purification and some properties of Papaya meleira virus, a novel virus infecting papayas in Brazil

'Meleira', or 'sticky disease', is currently the most damaging papaya disease in the mid-eastern Brazilian growing regions. Consistent disease transmission via latex injection, presence of similar isometric particles in the laticiferous vessels of diseased plants, and detection of double-stranded DNA in naturally and experimentally infected papaya trees suggest that a virus is the causal agent. Conclusive evidence for viral aetiology was previously lacking, mostly because every attempt to purify the putative virus from infected papayas had failed. Following the successful purification and partial characterization of the meleira virus, healthy papaya seedlings injected with purified virus particles later developed typical symptoms of the disease. Negatively stained, isometric, full and 'empty' purified virus particles measured 42 and 38 nm, respectively. The viral genome was a single dsRNA molecule of about 12 kbp. Several capsid proteins, ranging in size from 14·4 to 45 kDa, were consistently revealed by PAGE. Papaya meleira virus (PMeV) appears to represent a novel group of viruses, with no known similar counterpart among known plant-, vertebrate-, invertebrate- or prokaryote-infecting viruses.     

Decision support systems used in the Netherlands for reduction in the input of active substances in agriculture

Since the middle of the 1980s, Dutch farmers have been using decision support systems (DSS) as an aid in the control of pests. This started with EPIPRE, then weather-related potato blight warning systems were developed (Prophy and Plant-Plus). In the 1990s, many weather-based DSS were developed against pests of orchards, flower bulbs, arable crops and field-produced vegetables. Also, a DSS was developed to predict and check the effect of meteorological conditions on the effectiveness of application timing of plant protection products (GEWIS). The use of these systems resulted in more sustainable crop protection: sustainable because the use of DSS led to a lower risk of crop damage and, in many cases, to a lower input of active substances, by optimization of the product and dose to actual phytosanitary and meteorological conditions. The use of GEWIS to ensure application at the right time of day further reduced the input of active substances and increased efficacy.     

The Pacific Pest List Database for agricultural trade facilitation

The Pest List Database for the Pacific is a user-friendly database that provides information on agricultural pest occurrences within a country as required to facilitate trade in terms of the International Plant Protection Convention and International Standards For Phytosanitary Measures. Its main outputs are: (a) a pest list for any specified crop intended for export and (b) a list of pest incursions detected on imported goods from any selected country. The system is designed for use by the 22 Pacific Island countries and territories that the Secretariat of the Pacific Community serves and is so far installed in five countries with a new one being delivered every 3–4 months. It is typically delivered with a few thousand known pest occurrence records of that country, and look-up lists of several thousand Pacific pests and a few hundred crops.     

Development and use of a forecasting model for Cydia pomonella*

For more than 10 years, a forecasting model for Cydia pomonella in apple orchards, worked out by the French NPPO, has described the development of emergence cohorts in spring, and followed their development and descent, through the whole agricultural season. In homogeneous areas, this tool, still under development, can be used to define periods for effective treatment (ovicides, larvicides, mating disruption) and the tolerance for codling moth levels in various situations. Alternation of insecticides is provided for, so as to manage resistance phenomena. The reliability of the model is based on rigorous continuous biological checks on the forecasts made by the algorithm, on scientific surveillance by INRA and on regular collaboration between the advisers involved and the agrometeorological services. The model forms part of a wider decisional scheme, or expert system, in which the fruit grower and his adviser provide observations on the changes which cannot be provided by the model: installation of hail protection nets, night lights, fruit spreading. More parameters will be incorporated in future and the geographical validity of the model will be extended, particularly to more northerly areas.