Resistance Management for San Jose Scale (Hemiptera: Diaspididae).

The San Jose scale Diaspidiotus perniciosus Comstock is one of the most important pests of deciduous fruit trees. The major cause of recent outbreaks in apple orchards is thought to be the development of insecticide resistance, specifically organophosphates. The first report was given in North America, and now, in Chile. In the present study, San Jose scale populations collected from two central regions of Chile were checked for their susceptibility to different mode of action insecticides in order to establish alternatives to manage this pest. No evidence of cross resistance between organophosphates insecticides and acetamiprid, buprofezin, pyriproxyfen, spirotetramat, sulfoxaflor, or thiacloprid was found. Baselines of LC50-LC95 for different life stages of San Jose scale are given, as reference to future studies of resistance monitoring. The systemic activity of acetamiprid, spirotetramat, and thiacloprid was higher than the contact residue effect of these compounds. For sulfoxaflor, both values were similar. Program treatments including one or more of these compounds are compared in efficacy and impact on resistance ratio values. In order to preserve new insecticides as an important tool to control San Jose scale, resistance management programs should be implemented, considering insecticide mode of action classes alternated or mixed.

First Report of Alfalfa mosaic virus Infection in Viburnum tinus in Chile.

Viburnum tinus L., commonly known as laurustinus, is an ornamental shrub that is widely used as a garden plant and flower crop. V. tinus is popular because of its desirable characteristics such as evergreen foliage, tolerance to pruning, winter blooms, and its adaptation to cold temperate zones. It is also relatively easy to grow and is commonly used as a windbreak. Infection of this ornamental species by Alfalfa mosaic virus (AMV) has been associated with yellow mottling or variegated leaf coloring, including light green and white, and has been referred to as the "Viburnum Calico" (1,4). In April 2011, at the onset of winter in the Southern Hemisphere, intense yellow spotting and mottling was observed on V. tinus leaves in the San Joaquin Campus at Pontificia Universidad Catolica de Chile. Presence of Aphis spiraecola Patch was observed on the shrubs, however, in the area it is also common to find other aphid species such as Toxoptera aurantii (Boyer de Fonscolombe) and A. fabae Scopoli. Leaf tissue samples from 10 asymptomatic and 10 symptomatic plants were examined for the presence of AMV by tissue-blot immunoassay with a commercially available polyclonal antibody (Agdia Inc., Elkhart, IN) along with the Goat affinity purified anti-rabbit IgG conjugated (Whole Molecule) (Molecular Probes, Invitrogen Corp., Carlsbad, CA). First-strand cDNA synthesis and PCR were performed with specific primers CP-AMV1 and CP-AMV2 (3). AMV was detected in all symptomatic leaves and also in two of the asymptomatic tissue analyzed by tissue blot assay. Reverse transcription (RT)-PCR produced 753-bp amplicons in all samples that were positive to AMV by tissue printing. No amplification product was observed when water control or seronegative samples were used as templates in the RT-PCR assays. Two amplicons were directly sequenced in both directions to confirm the identification of AMV in the leaf samples. The sequences obtained were homologous and BLASTN analysis of the submitted sequence (GenBank Accession No. JN040542) showed 99% nucleotide sequence identity to an AMV isolate described from Nicotiana tabacum L. (GenBank Accession No. FJ527749). These results demonstrate the presence of AMV in V. tinus in Chile. This pathogen has also been described to be affecting V. tinus in France (1) and V. lucidum Mill. in Spain (2). In Chile, V. tinum is increasingly grown as an ornamental plant. Therefore, care should be taken to ensure that the propagative materials of V. tinum are devoid of AMV infection to prevent further spread of this virus. References: (1) L. Cardin et al. Plant Dis. 90:1115, 2006. (2) M. Cebrián et al. Plant Dis. 92:1132, 2008. (3) M. Finetti-Sialer et al. J. Plant Pathol. 79:115, 1997. (4) H. E. Williams et al. Phytopathology 61:1305, 1971.

First Report of Nothofagus macrocarpa Dieback Caused by Phytophthora citrophthora and P. nicotianae in Chile.

The genus Nothofagus, family Nothofagaceae, comprises 36 species of trees that are native to the Southern Hemisphere. N. macrocarpa (DC.) F.M. Vásquez & R.A. Rodríguez (Roble de Santiago) is an important deciduous tree, endemic to central Chile (32 to 35°S), and found above 800 m altitude. There is an increasing interest in N. macrocarpa as an ornamental. However, a general dieback (40 to 50% prevalence) was observed at a commercial nursery in Santiago in 2009, limiting its multiplication. Symptoms are wilting, partial defoliation, reddish brown cankers on the crowns, and root necrosis. The purpose of this work was to study the etiology of the dieback in nurseries. Phytophthora was isolated from the roots and cankers of symptomatic plants (n = 3) and soil samples (using apples and avocados as baits) on amended corn meal agar (3) at 20°C for 5 days in the dark. Morphologically, P. citrophthora (Smith & Smith) Leonian, and P. nicotianae Breda de Haan were identified (2). On V8 juice agar (V8) (1), P. citrophthora formed petaloid colonies, grew between 5 and 30°C (optimum of 25°C), and produced deciduous, mono- or bipapillated sporangia of (28.1) 45.0 to 64.1 × (18.8) 32.0 to 39.2 µm. On V8, P. nicotianae produced cottony colonies, grew between 10 and 30°C (optimum of 25°C), and produced spherical, intercalary chlamydospores (mean diameter of 19.6 µm) and persistent, papillate, spherical to ovoid, ellipsoid, obpyriform sporangia of (33.2) 47.5 to 67.6 × (24.1) 30.0 to 48.9 µm. Isolates of P. citrophthora were sexually sterile, but P. nicotianae formed oogonia with amphigenous antheridia in dual cultures with P. cinnamomi (A2 compatibility type). BLAST analysis of the internal transcribed spacer (ITS) region of rDNA of isolates identified as P. citrophthora (IMI 399056 and IMI 399054, GenBank Accession Nos. JF699756 and JF699755) and P. nicotianae (IMI 399055, Accession No. JF699757), amplified by PCR using ITS universal primers (4), revealed 100% similarity with reference isolates of P. citrophthora (Accession Nos. GU259324.1 and GU259317.1) and P. nicotianae (Accession No. GU983635.1). P. citrophthora (n = 2) and P. nicotianae (n = 1) were pathogenic when wounded detached twigs (n = 5) of N. macrocarpa and N. obliqua were inoculated with 20 µl of a mycelial suspension (106 CFU/ml) of either Phytophthora spp. Twigs were placed in a moist chamber at 20°C for 12 days prior to determine the length of the necrotic lesions that developed. An equal number of noninoculated twigs were left as control. Reisolation of P. citrophthora and P. nicotianae from inoculated material was 100%. The length of the necrotic lesions (13 to 80 mm) from inoculated N. macrocarpa and N. obliqua was significantly greater (P < 0.05) compared with the controls. Regardless of Phytophthora isolates, necrotic lesions (53.9 ± 15.8 mm) in infected N. macrocarpa were significantly longer than in N. obliqua (28.6 ± 13.1 mm) (P < 0.0001). To our knowledge, this is the first report of P. citrophthora and P. nicotianae associated with dieback on N. macrocarpa in Chile. Therefore, there is a potential risk of Phytophthora dieback in N. macrocarpa in nature. References: (1) J. Ampuero et al. Plant Dis. 92:1529, 2008. (2) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (3) B. A. Latorre and R. Muñoz. Plant Dis. 77:715, 1993. (4) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990.

Systemic induction of phloem secondary metabolism and its relationship to resistance to a canker pathogen in Austrian pine.

The mechanisms and conditions affecting expression of systemic induced resistance (SIR) in pine are not clearly understood. Two hypotheses were tested here: that SIR against a pathogen induced by either a pathogen or an insect involves coordinated shifts in phloem secondary metabolism; and that fertility affects the production of these compounds. To test these hypotheses, a tripartite system was used comprising Austrian pine (Pinus nigra) grown under three different fertility regimes, the fungal pathogen Diplodia pinea, and the defoliator Neodiprion sertifer. Fungal induction led to systemic accumulation of lignin, phenolic glycosides and stilbenes, whereas insect defoliation led to an increase in germacrene D concentration in branch phloem. Fertility affected the concentrations of only the phenolic glycosides. Multivariate analyses showed coregulation of compounds within at least three consistent groupings: phenolic glycosides, stilbenes and monoterpenes. As groups and as individual compounds, accumulation of phenolic glycosides and stilbenes was negatively correlated with disease susceptibility. The experimental manipulation of the phenolics and terpenoids metabolic networks achieved in this study by biotic induction and changes in nutrient availability suggests that lignin, phenolic glycosides and stilbenes are important biochemical factors in the expression of SIR against the pathogen in this system.