Sources of inoculum for Phytophthora ramorum in a redwood forest

ABSTRACT Sources of inoculum were investigated for dominant hosts of Phytophthora ramorum in a redwood forest. Infected trunks, twigs, and/or leaves of bay laurel (Umbellularia californica), tanoak (Lithocarpus densiflorus), and redwood (Sequoia sempervirens) were tested in the laboratory for sporangia production. Sporangia occurred on all plant tissues with the highest percentage on bay laurel leaves and tanoak twigs. To further compare these two species, field measurements of inoculum production and infection were conducted during the rainy seasons of 2003-04 and 2004-05. Inoculum levels in throughfall rainwater and from individual infections were significantly higher for bay laurel as opposed to tanoak for both seasons. Both measurements of inoculum production from bay laurel were significantly greater during 2004-05 when rainfall extended longer into the spring, while inoculum quantities for tanoak were not significantly different between the 2 years. Tanoak twigs were more likely to be infected than bay laurel leaves in 2003-04, and equally likely to be infected in 2004-05. These results indicate that the majority of P. ramorum inoculum in redwood forest is produced from infections on bay laurel leaves. Years with extended rains pose an elevated risk for tanoak because inoculum levels are higher and infectious periods continue into late spring.     

Effect of temperature and host genotype on the production of inoculum by Phytophthora fragariae var. fragariae from the roots of infected strawberry plants

A bioassay was used to monitor the release of inoculum in drainage water from strawberry plants inoculated with zoospores of Phytophthora fragariae var. fragariae. The fungus was detected in drainage water from plants that had been held at temperatures between 2 and 20 C. but not from plants held at 26°C. The lag phase before secondary inoculum was first released, the maximum and total amounts of inoculum released, and the length of time over which inoculum was released were all greater at the lower temperature regimes, especially those below 10 C. The results were consistent with observations on the effect of temperature on zoospore production from agar discs and on zoospore motility: more zoospores were produced at lower temperatures and they remained motile for longer. From this it is concluded that the inoculum detected consists mainly of motile zoospores. In most experiments with standardized suspensions c. 10-15 were sufficient to initiate infection of the plants in the bioassay. In general, more inoculum was produced by host genotype/fungal isolate combinations in which there were marked root rot symptoms than in combinations in which the host was resistant.     

Inheritance of mefenoxam resistance in Phytophthora nicotianae populations from a plant nursery

Three sexual crosses involving isolates of P. nicotianae with differing sensitivity to mefenoxam were established to study the inheritance of mefenoxam resistance. Mefenoxam sensitivity was determined by measuring the mycelial growth on both mefenoxam-amended clarified V8 agar and non-amended agar and then calculating the relative growth. When both parents had the same phenotype (both were resistant or both were sensitive), all F ₁ progeny had the parental phenotype and no segregation for a major effect gene was observed in sensitivity to mefenoxam. However, variations in the mycelial growth of progeny indicated the segregation of minor-effect genes. When the cross involving the mefenoxam-resistant isolate 3A4 and a sensitive parent, the F ₁ progeny segregated for mefenoxam resistance in a ratio of 1:1 (resistant: sensitive), indicating that the mefenoxam resistance is controled by a single dominant gene. Mating type was not linked to the mefenoxam-resistance gene locus. One RAPD marker linked in trans to the MEX locus was obtained by bulked segregant analysis using RAPD markers and was converted to a sequence characterized amplified region marker (SCAR). The SCAR maker identified in this study is a limited but useful tool for differentiating homozygous resistant isolates from sensitive isolates of P. nicotianae.     

A device for the rapid removal of tannins from virus infected plant tissues before extraction of inoculum

Samenvatting Sommige plantesoorten bevatten looistoffen, waarvan wordt aangenomen, dat zij de overbrenging met sap van in deze plantesoorten voorkomende virussen verhinderen. In dit artikel wordt een methode beschreven, waarmee deze looistoffen vooraf uit plantemateriaal kunnen worden verwijderd. Het looistofbevattende blad wordt, na snel diepgevroren en gedroogd te zijn, in een gewijzigd Soxhlet-apparaat (Fig. 1) met alcohol of chloroform uitgetrokken. Aldus scheidt men de looistoffen kwantitatief van het virus.Het effect van de extractie der looistoffen of de virusactiviteit werd nagegaan door mengsels van tabaksbladeren, respectievelijk geïnfecteerd met tabaksmozaïekvirus en aardappel-X-virus, en aardbeibladeren volgens de beschreven methode van looistoffen te ontdoen en daarna het infectievermogen van deze virussen ofNicotiana glutinosa, respectivelijkGompherena globosa, te toetsen (Tabellen 1 en 3). Tevens werd de serologische activiteit van de aldus van tannine bevrijde virussen bepaald (Tabellen 2 en 4).Uit de verstrekte gegevens blijkt, dat het tabaksmozaïekvirus en het aardappel-X-virus nagenoeg zonder verlies aan infectievermogen of serologische activiteit uit het mengsel met aardbeiblad kunnen worden geïsoleerd.

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Research carried on at the Instituut voor Plantenziektenkundig Onderzoek, Wageningen, Nederland. Supported in part by a Fellowship from the John Simon Guggenheim Memorial Foundation, New York.

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Approved for publication as Technical Paper No. 939 by the Director of the Oregon Agricultural Experiment Station. Contribution of the Department of Botany and Plant Pathology of this Station, and of the Instituut voor Plantenziektenkundig Onderzoek (I.P.O.), Wageningen.     

Toxic effects of surfactants applied to plant roots

Six surfactants used as additives to pesticide sprays, were applied in aqueous solution to the roots of sorghum plants. After a few hours of exposure to the surfactant solution, ions and amino-acids leaked from the roots into the ambient solution, presumably due to a loss of membrane integrity. After 2-3 days, the plants wilted and, at high concentrations of surfactants, they died. Toxic effects varied with the surfactant and its concentration, but no clear relationship was found between the physical effect of lowering the surface tension, the release of solutes by the roots, and the injury caused to the plant. The results are of significance because of the proposed use of sewage effluents, known to contain detergents, for irrigation purposes in Israel.     

Response of selected South Australian native plant species to Phytophthora cinnamomi

Thirty‐seven South Australian native plant species from 11 families, including 15 threatened species in the state (of which six are listed as threatened under the federal Environment Protection and Biodiversity Conservation Act 1999) were assessed for response to infection by Phytophthora cinnamomi. Seedlings, 3–6 months old and grown in a greenhouse, were inoculated by placing infested pine wood plugs in the potting mix, maintained in moist conditions and assessed for mortality and disease symptoms for between 3 and 10 months. Thirty species were found to be susceptible, of which nine were highly susceptible, 15 moderately susceptible and six slightly susceptible. Three species were found to be resistant and results for four species were inconclusive. Six of the 15 threatened, rare or locally endangered species tested (Eucalyptus viminalis var. viminalis, Correa aemula, C. calycina, Olearia pannosa ssp. pannosa, Pomaderris halmaturina ssp. halmaturina and Prostanthera eurybioides) were moderately susceptible, while two (Allocasuarina robusta and Pultenaea graveolens) were highly susceptible. Significant populations of at least five of the threatened species susceptible to the disease are located close to confirmed or suspected Phytophthora‐infested areas or growing in areas conducive for P. cinnamomi. An effective management strategy is therefore required to avoid extinction of such species due to infection by the phytophthora dieback pathogen.     

An in-situ baiting bioassay for detecting Phytophthora species in irrigation runoff containment basins

Experiments were conducted in irrigation runoff containment basins to assess the effects of bait species ( Camellia japonica , Ilex crenata or Rhododendron catawbiense ), bait type (whole leaf vs. leaf disc), baiting duration (1, 2, 7 or 14 days), baiting depth and growth media (modified PARP-V8 or PARPH-V8) on the recovery of Phytophthora species. A two-rope, flexible bait-deployment system was compared with a one-rope fixed system for bait stability at designated locations and depths. A total of 907 Phytophthora isolates were subjected to PCR-based single-strand conformation polymorphism (PCR-SSCP) analysis to identify to species level. Seven distinct SSCP patterns representing six morphospecies: P. citricola (Cil I), P. citrophthora (Cip I), P. hydropathica (Hyd), P. insolita (Ins), P. megasperma (Meg I & II) and an unidentified Phytophthora species were identified. Irrespective of culture medium, 7 days of baiting with rhododendron leaves consistently resulted in the recovery of the greatest diversity and populations of Phytophthora species with minimum interference from Pythium species. The flexible bait-deployment system was superior to the fixed system, minimizing the risk of bait loss and dislocation of baiting units and allowing baits to remain at designated depths from the surface under inclement weather.     

Pathogenicity and infectivity of Phytophthora ramorum vary depending on host species,infected plant part,inoculum potential,pathogen genotype,and temperature

A total of 25 ornamental plant species representing 10 families were inoculated using three genotypes, each representing one of the genetic lineages NA1, NA2, and EU1 of the pathogen Phytophthora ramorum. Leaves were inoculated using suspensions with two zoospore concentrations and exposure at three temperatures, while stems were inoculated using agar plugs colonized by mycelia. Susceptibility was determined by measuring either the success of pathogen reisolation or lesion length caused by the pathogen. Infectivity was determined by counting sporangia in washes of inoculated leaves or stems. Results from all three pathogen genotypes combined were used to rank each of the 25 plant species for susceptibility and infectivity, while pooled results per genotype from all 25 hosts combined were employed for a preliminary comparison of pathogenicity and infectivity among genotypes. Statistical analyses showed that leaf results were affected by the concentration of zoospores, temperature, plant host, pathogen genotype, and by the interaction between host and pathogen genotype. Stem results were mostly affected by host and by the interaction between host and pathogen genotype. Hosts ranked differently when looking at the various parameters, and differences in rankings were also significant when comparing stem and leaf results. Differences were identified among the 25 hosts and the three pathogen genotypes for all parameters: results can be used for decision-making regarding regulations or selection of plants to be grown where infestations by P. ramorum are an issue.     

Infectivity,inoculum density and germination of Spongospora subterranea resting spores: a solution-culture test system1

Spongospora subterranea, causal agent of powdery scab of potatoes and vector of potato mop-top furovirus, survives in the soil as balls of resting spores (cystosori). So far, the factors affecting longevity, germination and infectivity of cystosori have not been investigated. A rapid and versatile bioassay with tomatoes as bait plants has been developed to quantify the infectivity of cystosorus inoculum or infested soil. The intensity of root infection, as a measure of infectivity, was determined by evaluating the quantity of zoosporangia present in epidermal cells and root hairs of the whole, stained root system. A correlation was obtained between the intensity of root infection and the cystosorus inoculum density in nutrient solution. Sterile soil suppressed the inoculum potential of pure cystosori. Infectivity of untreated soil decreased with increasing time of storage. Root infection was not influenced by the pH level of the nutrient solution.     

A novel strategy to reduce overwintering inoculum of Monilinia laxa

Brown rot on cherry and plum, caused by Monilinia laxa, is an important disease, for which overwintered mummified fruit is a significant inoculum source for infection of flowers and fruit in the spring. Experiments were conducted to assess the potential of applying plant protection products in winter and/or early spring to suppress sporulation on mummified fruit. Products tested included Indar 5 EW (a commercial fungicide, a.i. fenbuconazole), Aureobasidium pullulans Y126 [a candidate biocontrol agent (BCA)]), Bacillus sp. B91 (a candidate BCA) and Serenade (a commercially formulated BCA of Bacillus subtilis strain QST 713) in addition to control treated with tap water. Indar and A. pullulans Y126 significantly reduced sporulation when applied once in winter. Overall, a single treatment in early spring (February) was slightly more effective than single treatment in winter (November). Application of all products in both winter and early spring led to significant reduction in sporulation. Indar had the highest efficacy, reducing the number of spores from 9?×?10⁵ to 5?×?10³ per mummified plum when applied twice. Of the three BCAs applied on both occasions, A. pullulans Y126 had the highest efficacy, reducing the number of spores from 9?×?10⁵ to 5?×?10⁴ per mummified plum. There were no synergistic but additive effects between the two applications in winter and early spring based on the Bliss independence test. These results suggest that reducing overwintering inoculum in dormant season is effective and may be part of an integrated management strategy for brown rot on stone fruit.     

加强基层植保工作促进植保可持续发展--郓城县在新形势下走出一条做好基层植保工作的路子

基层植保工作是农技推广体系的重要组成部分，是农业发展、农民增收的重要支撑。新形势下，植保工作中面临着诸多困难和挑战，表现为植保推广体系不健全，队伍建设不稳定，信息传递手段落后，技术入户率低，缺乏相应的领导支持等。尽管植保工作面临许多困难，各级植保人员大都能够以高度的责任感和强烈的事业心，真抓实干，为农业安全生产保驾护航，并涌现出一批好的典型。菏泽市郓城植保站走出了一条新形势下切实做好基层植保工作的路子。１加强体系建设，发挥网络优势郓城自１９９５年开始注重加强植保技术推广体系的建设。首先争取领导的…     

Evaluation of resistance to Phytophthora cinnamomi in seed-grown trees and clonal lines of Eucalyptus marginata inoculated in lateral branches and roots

Seed-grown trees and six clonal lines of 3·5–4·5-year-old Eucalyptus marginata (jarrah) growing in a rehabilitated bauxite mine site in the jarrah forest were underbark-inoculated on lateral branches (1995) or simultaneously on lateral branches and lateral roots (1996) with isolates of Phytophthora cinnamomi in late autumn. Individual seedlings from which the clonal lines were derived had previously been assessed as either resistant (RR) or susceptible (SS) to P. cinnamomi . At harvest, the acropetal lesion and colonization lengths were measured. Overall, the length of colonization in roots and branches was more consistent as a measure of resistance than lesion length, because colonization length recorded the recovery of P. cinnamomi from macroscopically symptomless tissue ahead of the lesion which, on some occasions, was up to 6 cm. In both trials, one RR clonal line was able to contain the P. cinnamomi isolates consistently, as determined by small lesion and colonization lengths in branches and roots. In contrast, the remaining two RR clonal lines used in both trials were no different from the SS line in their ability to contain lesions or colonization. These latter two RR lines may therefore not be suitable for use in rehabilitation of P. cinnamomi -infested areas. Differences in lesion and colonization lengths among P. cinnamomi isolates occurred only in the 1995 trial. Colonization and lesion lengths in branches were up to eight times greater in 1996 than in 1995, but the relative rankings of clonal lines were consistent between trials. Although colonization was always greater in branches than roots, the relative rankings of the lines were similar between branch and root inoculations. Branch inoculations are a valid option for testing the resistance and susceptibility of young jarrah trees to P. cinnamomi .     

一种植物线虫的快速分离方法

目前 ,我国口岸检验检疫机关对于检疫性植物线虫的分离 ,大多数仍然采用贝尔曼漏斗法。该方法的优点是灵敏度高 ,分离物杂质少 ;缺点是分离时间较长 ,大约需要1 0～ 2 4ｈ ,分离效果才达到最佳 ,而且仅限分离活动性的蠕虫形线虫 ,对死虫、不活动的线虫 (如胞囊线虫和根结线虫的雌虫 )则是无效的。我们经过长期的研究与探索 ,找出了一种植物线虫的快速分离方法。将植物线虫的分离时间缩短至 40ｍｉｎ ,并且分离线虫的数量与贝尔曼漏斗法 1 0～ 2 4ｈ的分离数量接近。这种方法适用于目前检疫对象名单上所有的检疫性的线虫分离 ,满足了口岸植物…     

植保有害生物风险分析理论体系的探讨

植保有害生物风险分析需要正确地收集大量数据。并急需建立实用的或可操作的有害生物风险分析体系，针对这种情况，本文将风险相关因素归纳为天气，地理和生物3大类，提出了有害生物的天气-地理-生物复合体系。该体系以生态网为出发点，对有害生物风险条件，事件及风险种类按层次和等级进行风险因子划分，然后进行风险因子模拟，风险分析和计算，实现有害生物的多因子调控管理。从而在风险分析，风险预测和风险决策的基础上，完成从风险确定，风险评价，风险管理到风险交流的风险全过程管理。     

Evaluation of a method for quantification of Pythium aphanidermatum in cucumber roots at different temperatures and inoculum densities

Journal of Plant Diseases and Protection - A method for the quantification of Pythium aphanidermatum density in cucumber roots based on an indirect enzyme-linked immunosorbent assay (Elisa) was...     

Results and experiences from the first EU proficiency test for the detection of Phytophthora ramorum1

The Crop Protection unit of the Institute for Agricultural and Fisheries Research offers plant disease diagnostic services through its ‘Diagnostic Centre for Plants’ (ILVO‐DCP). ILVO‐DCP has requested accreditation (ISO 17025) for a number of diagnostic detection methods in bacteriology, mycology, entomology and nematology. Accreditation forms an essential part of quality control programs such as ISO17025, which can in part be realized by proving the laboratory's competence in inter‐laboratory proficiency or ring tests. In 2006, ILVO‐DCP organized such a proficiency test for the detection of Phytophthora ramorum. The protocol was developed using the standard ILAC‐G13:2000, and defined rules for participation, sample preparation and transport, communication, fraud prevention and reporting. Eight European diagnostic centres participated in the proficiency test including ILVO‐DCP. Each participant received one set of 10 coded samples, each sample consisting of either leaves or stems that were artificially inoculated with either the target or an alternative organism. Participants could use one or more methods listed in the EPPO diagnostic protocol PM 7/66. They had to report within a specific timeframe and received a detailed report of their performance. The success rate of the proficiency test was 100%. This paper lists some of the experiences gained from organising this type of proficiency test.     

Gene expression profiling of Medicago truncatula roots in response to the parasitic plant Orobanche crenata

Orobanche crenata is a root parasitic weed that is a major constraint for grain and forage legume cultivation in Mediterranean and West Asia. Only moderate to low levels of incomplete resistance of complex inheritance has been identified so far in legume crops, which has hampered genetic and genomic analysis. In the present study, we provide a gene expression profile of roots of the model legume Medicago truncatula in response to infection by O. crenata . M. truncatula accessions SA27774 (complete resistance acting at early penetration stages) and SA4087 (incomplete late acting resistance mediated by necrosis of parasite tubercle) were inoculated with O. crenata seeds in a semi-sterile dish system. Roots were harvested at 15 (first contacts of the parasitism structures with the host roots), 21 (initial stage of parasite tubercle formation on SA4087) and 35 (prior necrosis of well-developed parasite tubercle of on SA4087) days post-inoculation. Array hybridisations revealed several hundred genes up-regulated in response to O. crenata infection. Gene expression patterns suggest that resistance mechanisms activated in both genotypes are temporally and spatially different and resemble those associated with plant resistance to microbial pathogens. Regulated genes identified here represent a comprehensive resource that can be used as a support to breeding strategies for resistance.