Effect of Avocado sunblotch viroid (ASBVd) on avocado yield in Michoacan,Mexico

The total yield of cv. Hass and Mendez avocado trees was evaluated in Grove 1 in Uruapan county: four trees were sunblotch-infected, four asymptomatic (molecularly positive), and four healthy. A further four healthy and four symptomatic trees were evaluated in Grove 2 in Tingambato county. There was a significant 75 % reduction in the total Hass fruit weight from symptomatic trees in Grove 1 (213 kg vs 751 kg in healthy trees) and a 52 % reduction (124 kg vs 255 kg) in Grove 2 (Tukey, p?=?0.05). This reduction was more severe in Mendez: 83 % in Grove 1 (183 kg vs 1,053 kg) and 76 % in Grove 2 (82 kg vs 340 kg). Yield of asymptomatic trees was reduced to 58 % in Mendez and 30 % in Hass. The average weight of 100 fruits was reduced by 13–28 % in Hass and 20–27 % in Mendez in Groves 2 and 1 respectively. The equatorial diameter of 100 symptomatic fruits was 8 % lower in Hass in both groves, and 20–28 % lower in Mendez. The polar diameter decreased by 8–10 % in Hass and 10–11 % in Mendez. The incidence of symptomatic fruits was 46–62 % in Hass and 20–28 % in Mendez. Yield of ASBVd symptomatic Hass and Mendez trees was significantly reduced and fruit morphology negatively affected.     

A list of arthropod pests of avocado and pecan trees in Israel

Lists are given of arthropod pests of avocado and pecan trees in Israel. These include ten new pests of avocado and three of pecan. The pests of economic importance on avocado includeBoarmia (Ascotis) selenaria (Schiff.) (Geometridae, Lepidoptera) andHeliothrips haemorrhoidalis (Bouché) (Thrypidae, Thysanoptera). The pests of importance on pecans includeEmpoasca decedens (Paoli) (Jassidae, Homoptera),Zeuzera pyrina L. (Cossidae, Lepidoptera), andMonellia costalis (Fitch) (Aphididae, Homoptera).     

Evaluation of neonicotinoid, organophosphate and avermectin trunk injections for the management of avocado thrips in California avocado groves

BACKGROUND: Trunk injections of systemic insecticides were evaluated for the management of avocado thrips. Insecticide residues were quantified in leaves to determine when after treatment, and for how long, toxic concentrations of the insecticides were present. Residues in fruit were quantified to determine whether trunk injection of insecticides might present a greater risk than traditional application methods for contaminating fruit. RESULTS: Residues of imidacloprid and dinotefuran were at least tenfold higher in leaves when trees were treated via trunk injection compared with soil application. Dinotefuran uptake was more rapid than imidacloprid, and no residues were detected within fruit. Acephate was also mobilized very rapidly and gave good control of thrips in bioassays; however, residues of acephate and its insecticidal metabolite methamidophos were detected in the fruit for up to 4 weeks after injection. Avermectin uptake was very slow, and it was ineffective against avocado thrips. CONCLUSIONS: Trunk injections of acephate and dinotefuran permitted rapid uptake into avocados, and they are strong candidates as control methods for avocado thrips. However, residues of organophosphates in fruit could necessitate increased preharvest intervals. Residues of neonicotinoids were below detection limits in fruit, suggesting that neonicotinoids may be the more suitable control option of the two chemical classes. Copyright © 2012 Society of Chemical Industry     

Field evaluation of systemic imidacloprid for the management of avocado thrips and avocado lace bug in California avocado groves

BACKGROUND: The efficacy of systemic applications of imidacloprid for the management of avocado thrips and avocado lace bug was determined in field trials. Following insecticide treatment by chemigation, leaves of appropriate age for each insect were sampled over a 6 month period and used for bioassays. Imidacloprid residues were measured by ELISA in leaves used for bioassays to determine concentrations of insecticide that were toxic to both pests. RESULTS: The uptake of imidacloprid into treated trees was extremely slow, peaking in the current year's leaf flush at only 8 ng cm^?2 leaf tissue after 15 weeks. Avocado thrips mortality in bioassays with young flush leaves, the preferred feeding substrate for this insect, was minimal, indicating that imidacloprid concentrations were below threshold levels needed for effective control. Residues present in older leaves, which are preferred by the avocado lace bug, were higher than in young flush leaves, and provided good control of this pest. Probit analysis of bioassay data showed that the avocado lace bug (LC₅₀ = 6.1 ng imidacloprid cm^?2 leaf tissue) was more susceptible to imidacloprid than the avocado thrips (LC₅₀ = 73 ng imidacloprid cm^?2 leaf tissue). CONCLUSIONS: In spite of the slow uptake of imidacloprid into avocado trees, the levels of imidacloprid would be sufficient to control avocado lace bug infestations. In contrast, the slow uptake would be problematic for avocado thrips control because inadequate levels of insecticide accumulate in new flush foliage and would allow avocado thrips populations to build to levels that would subsequently damage developing avocado fruit. Copyright © 2010 Society of Chemical Industry     

利用两种方法检测苹果锈果类病毒

以克隆ASSVd的部分序列,通过RT-PCR成功合成了地高辛标记的cDNA探针,提取苹果和梨树枝条的总RNA,用斑点杂交技术对其进行了检测试验,结果表明,探针具有很高的灵敏度和特异性。地高辛标记的cDNA探针不与阴性对照枝条RNA以及感染PBCVd、AFCVd、ADFVd枝条总RNA发生杂交,仅与感染ASSVd样品的总RNA杂交。     

Comparison of conventional and molecular methods for the detection of Rosellinia necatrix in avocado orchards in southern Spain

White root rot, caused by Rosellinia necatrix , is one of the most important diseases in avocado orchards and is particularly widespread on the Mediterranean seaboard of southern Spain. In this study, the presence of the pathogen in soil samples collected from the base of 47 plants showing different symptoms of canopy decline was assessed with a molecular detection method based on real-time Scorpion PCR. Results were compared with symptoms in the canopy and with the traditional method of isolation of R. necatrix from roots and/or bark. The fungus was isolated from 24 samples by the traditional method and from 37 soil samples by the molecular method (cycle threshold values 25·8 to 47·1), demonstrating the higher sensitivity and reliability of the molecular method. A single real-time PCR amplification was sufficient to detect R. necatrix in naturally infested soils. The avoidance of nested PCR has important practical implications because of the reduced costs and risk of cross contamination. Also, it enables faster sample analysis and is more appropriate for quantitative detection. A modified molecular method was also developed to detect R. necatrix in roots and in soils with very low populations of the pathogen.     

Comparison of bi-directional electrophoresis and molecular hybridization methods to detect potato spindle tuber viroid and chrysanthemum stunt viroid1

A comparison was made of methods for viroid detection. Molecular hybridization using cDNA is a very sensitive method that can handle large quantities of samples at the same time but it has the disadvantage that only small amounts of the sample can be applied to the nitrocellulose filter. The method therefore can only detect viroid in plants when its concentration is 10–20 ng g^-1 of leaves, using ³²P as a marker system. Bi-directional electrophoresis can detect viroid in plants when its concentration is 10 ng g^-1 of leaves, because it uses larger samples. It does not need hazardous chemicals like ³²P and formamide, and the reading of the results of the test is less liable to failures because it is based on two criteria (position and intensity of RNA band). The Dutch Plant Protection Service and the Dutch General Inspection Service for Ornamentals therefore use a modified bi-directional electrophoresis method to detect potato spindle tuber viroid and chrysanthemum stunt viroid, respectively.     

菊花矮化类病毒两种检测方法的建立与比较

菊花矮化类病毒可通过接种寄主植物和电泳方法进行检测。正反向电泳法可从相当于 2 8mg鲜重的菊花样品中检测到菊花矮化类病毒RNA ,并可同时检测10-20个样品材料。生物检测则需要较大的空间、严格的温度条件和较长时间 ,不适合于大规模检测     

A new disease of greenhouse tomatoes in Israel caused by a distinct strain ofTomato apical stunt viroid (TASVd)

Using the sequential PAGE method for detection of small circular RNA molecules we isolated a viroid from greenhouse-grown tomato plants exhibiting severe stunting in Israel. The viroid was transmitted to tomato and to several other solanaceous plants by graft and mechanical inoculation, but only tomato plants showed symptoms of disease. Cloning and sequencing revealed that the viroid RNA is composed of 363 nucleotides, has 92% identity with the type strain (Ivory Coast strain) ofTomato apical stunt viroid (TASVd) and 99% identity with the Indonesian strain of this viroid. The experimental host range of TASVd-Is differs significantly from that of the type strain of TASVd. The possible epidemiological consequences leading to TASVd spread in geographically distant areas are discussed. http://www.phytoparasitica.org posting Sept. 18, 2002. Corresponding author     

Toxicity of systemic neonicotinoid insecticides to avocado thrips in nursery avocado trees

The efficacies of four systemic neonicotinoid insecticides applied to potted avocado trees at manufacturer-recommended rates were assessed against the avocado thrips, Scirtothrips perseae Nakahara. At the time of treatment, fully expanded first-flush young leaves were tagged for identification, and a proportion of these leaves was used in bioassays with second-instar thrips. At 7 weeks post-treatment, a second flush of leaves had fully expanded on the trees, and these leaves were included in additional bioassays comparing avocado thrips mortality on both first- and second-flush leaves. In bioassays with first-flush leaves, imidacloprid (273 mg AI pot(-1)) was the most effective insecticide, providing at least 70% mortality of thrips for 14 weeks. Thiamethoxam (137 mg AI pot(-1)), clothianidin (109 mg AI pot(-1)) and dinotefuran (241 mg AI pot(-1)) provided good control in bioassays that were conducted within 4 weeks of treatment, but thereafter their efficacies were inconsistent. In bioassays with second-flush leaves, imidacloprid provided at least 70% mortality up to 9 weeks after the insecticide application. Thereafter, mortality declined to 30% or lower. Bioassays with second-flush leaves collected from trees treated with thiamethoxam, clothianidin and dinotefuran resulted in unacceptably low thrips mortality. Monitoring of imidacloprid and thiamethoxam residues by ELISA showed that the greater persistence of imidacloprid in both first and second leaf flushes was due to a steadier uptake of this material. Although thiamethoxam residues rose quickly within the first leaf flush, levels had already begun to dissipate by the time the second leaf flush had started to develop.     

Characterization of a new viroid strain from hops: evidence for viroid speciation by isolation in different host species

A new viroid was detected in hops cultivated in Akita Prefecture, Japan where it is prevalent in many hops fields. In a survey of hop samples collected during the 1986–2002 growing seasons, the new viroid was present in the major Japanese hop-cultivating areas as early as the 1980s. A single-stranded circular RNA of 368–372 nucleotides that assume a highly basepaired, stable, rod-like secondary structure, shares 93%–98% sequence homology with Apple fruit crinkle viroid (AFCVd) isolated from apple and 85%–87% with Australian grapevine viroid (AGVd) isolated from grapevine. Taking into account the present concept of viroid species, we conclude that the viroid is AFCVd. Circumstantial evidence suggests that AFCVd from apples and hops were endemic in Japan only where cultivation of the two host plants overlapped, thereby strongly supporting the possibility that AFCVd (or an ancestral viroid) was transmitted across the species barrier from apples to hops or hops to apples somewhere in the region. Phylogenetic analysis of AFCVd from hops, AFCVd from apples, and AGVd together with the other members of the genus Apscaviroid revealed that the Akita isolates of AFCVd from hops (AFCVd-hop) formed a cluster that is distinct from AFCVd-apple and AGVd. Accumulation of host-specific sequence variation following their isolation in different host species may be leading to the formation of two viroid species from a common ancestor.     

Evaluation of local and imported fire blight warning systems in Israel

ABSTRACT The possibility of using local and imported warning systems for the management of fire blight (caused by the bacterium Erwinia amylovora) in pears was tested in Israel from 1997 to 2000. Three imported systems (MARYBLYT 4.3, BIS95, and Cougarblight 98C) and one local system (Fire Blight Control Advisory [FBCA]) were used. All systems were tested in simulation experiments; MARYBLYT 4.3 and FBCA were also tested in orchard experiments under natural infections. Simulation experiments included 193 orchard-plots in which the time of disease onset enabled us to determine the date of infection. Thirty-five experiments were conducted in commercial orchards; in 10 of these, fire blight developed naturally. The performance of the imported warning systems was too variable to be accurately used under Israeli conditions. In the simulation experiments, the success rate (i.e., the capacity of the systems to predict the exact date of the occurrence of infection episodes) of the imported systems was low (3 to 55%) with considerably large variability among years (CV = 30 to 67%). Similar results were obtained in the orchard experiments for MARYBLYT 4.3: in only two of five experiments where plots were managed according to that system was disease severity significantly lower than that recorded in untreated control plots. In comparison, the local system, FBCA, predicted most infection episodes in the simulation experiments with low variability (99%, CV = 1.0%). In the orchard experiments, adequate disease suppression was achieved in all eight experiments in which FBCA recommendations were followed. We concluded that it was not possible to import and successfully implement fire blight warning systems in Israel that have been developed in regions with dissimilar environmental conditions.     

Genetic diversity and pathogenicity of potato spindle tuber viroid and chrysanthemum stunt viroid isolates in Russia

European Journal of Plant Pathology - To investigate the current status of viroid infection in potato fields in Russia, potato spindle tuber viroid (PSTVd) and chrysanthemum stunt viroid (CSVd)...     

Incidence and genetic diversity of Peach latent mosaic viroid and Hop stunt viroid in stone fruits in Serbia

Tissue-imprint hybridization (TIH) assay was validated for large-scale detection of Peach latent mosaic viroid (PLMVd) and Hop stunt viroid (HSVd). All 72 collected leaves (100%) from 2 PLMVd- and 2 HSVd-infected trees were positive in TIH, regardless of the geographic orientation of the scaffold, level of the canopy and position of the leaf in the shoot. In a large-scale survey in Serbia, we tested by TIH 871 trees of stone fruits, representing 602 cultivars from fruit collections in Belgrade, Čačak and Novi Sad. PLMVd was detected in 185 (50%) peach trees or 95 (54%) cultivars and HSVd in 2 apricot trees and cultivars (2%). The occurrence of HSVd is a new report for Serbia. No viroid infection was found in European plums, sweet cherries, sour cherries and wild Prunus spp. PLMVd-infected peach cultivars originated from the world’s main breeding centres of this crop. Western European and Asian cultivars were the most infected (58%) followed by those originating from North America (50%). Nine PLMVd and two HSVd isolates were sequenced and analyzed. All showed PMLVd sequences clustered together in the previously reported phylogenetic group III. Both HSVd isolates were found to be derived from recombinant events, but that of the cv. Saturn represented a putative new phylogenetic group of HSVd.