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1.
Wood-based mulches are used in avocado production and are being tested on Fraser fir for reduction of Phytophthora root rot, caused by Phytophthora cinnamomi. Research with avocado has suggested a role of microbial cellulase enzymes in pathogen suppression through effects on the cellulosic cell walls of Phytophthora. This work was conducted to determine whether cellulase activity could account for disease suppression in mulch systems. A standard curve was developed to correlate cellulase activity in mulches with concentrations of a cellulase product. Based on this curve, cellulase activity in mulch samples was equivalent to a cellulase enzyme concentration of 25 U ml(-1) or greater of product. Sustained exposure of P. cinnamomi to cellulase at 10 to 50 U ml(-1) significantly reduced sporangia production, but biomass was only reduced with concentrations over 100 U ml(-1). In a lupine bioassay, cellulase was applied to infested soil at 100 or 1,000 U ml(-1) with three timings. Cellulase activity diminished by 47% between 1 and 15 days after application. Cellulase applied at 100 U ml(-1) 2 weeks before planting yielded activity of 20.08 μmol glucose equivalents per gram of soil water (GE g(-1) aq) at planting, a level equivalent to mulch samples. Cellulase activity at planting ranged from 3.35 to 48.67 μmol GE g(-1) aq, but no treatment significantly affected disease progress. Based on in vitro assays, cellulase activity in mulch was sufficient to impair sporangia production of P. cinnamomi, but not always sufficient to impact vegetative biomass. 相似文献
2.
ABSTRACT A series of samples were taken from mulched and unmulched trees starting at the surface of mulch or soil to a 15 cm soil depth, forming a vertical transect. Saprophytic fungi isolated from the soil samples on rose bengal medium and surveyed visually were most abundant in mulches and at the interface of mulch and soil (P < 0.05). Microbial activity as assayed by the hydrolysis of fluorescein diacetate was significantly greater in mulch layers than in soils. Cellulase and laminarinase enzyme activities were greatest in upper mulch layers and rapidly decreased in soil layers (P < 0.05). Enzyme activities against Phytophthora cinnamomi cell walls were significantly greater in mulch than in soil layers. When Phytophthora cinnamomi was incubated in situ at the various transect depths, it was most frequently lysed at the interface between soil and mulch (P < 0.001). Roots that grew in mulch layers were significantly less infected with Phytophthora cinnamomi than roots formed in soil layers. In mulched soil, roots were commonly formed at the mulch-soil interface where Phytophthora populations were reduced, whereas roots in unmulched soil were numerous at the 7.5 cm depth where Phytophthora cinnamomi was prevalent. Enzyme activities were significantly and positively correlated with each other, microbial activity, and saprophytic fungal populations, but significantly and negatively correlated with Phytophthora recovery. 相似文献
3.
Unwounded and wounded periderm tissue of 1-year old stems of Eucalyptus marginata were infected and lesioned after 5 days'exposure to either mycelium or motile zoospores of Phytophthora cinnamomi. Lesions produced by P. cinnamomi were longer in wounded than in unwounded stems. The inclusion of non-sterile mine site soil with inocula in the unwounded treatments did not affect the rate or extent to which P. cinnamomi colonized E. marginata stem tissue. The ability of P. cinnamomi zoospores to infect unwounded suberized woody tissue of E. marginata , has important implications for mine site rehabilitation in P. cinnamomi infested areas. This is the first study to demonstrate clearly that zoospores of P. cinnamomi can infect and invade unwounded suberized tissue. 相似文献
4.
Phytophthora cinnamomi was the species isolated most frequently from soil associated with dead or dying proteaceous plants in the Adelaide region of South Australia. The association of P. citricola with diseased Banksia species in South Australia is reported for the first time. The response of a range of Banksia species to inoculation with P. cinnamomi and P. citricola was assessed. P. cinnamomi was generally more pathogenic than P. citricola . Inoculation of 10-month-old seedlings with colonized millet seed or zoospores showed that B. hookeriana and B. ashbyi were the most susceptible of the species tested, whereas B. coccinea , B. menziesii and B. prionotes were moderately susceptible. B. ericifolia , B. serrata , B. spinulosa var. collina and B. lemanniana showed tolerance. Similarly, 2–3-week-old seedlings of B. ericifolia , B. serrata and B. spinulosa var. collina inoculated in vitro showed little disease 6 and 12 days after inoculation, whereas B. baueri, B. baxteri , B. coccinea and B. solandri , as well as B. hookeriana and B. ashbyi , showed severe symptoms of disease after 6 days. Results suggested that the in vitro assay may have potential in the evaluation of breeding material. Development of infection was studied microscopically in 2–3-week-old seedlings of B. coccinea , B. menziesii , B. serrata and B. spinulosa var. collina inoculated in vitro with zoospores of P. cinnamomi . Roots of B. coccinea and B. menziesii were colonized rapidly and root tips became necrotic within 24 h and hypocotyls by day 5. Penetration was delayed in B. spinulosa var. collina , and callose deposition was delayed in B. coccinea . Necrosis of roots of B. serrata and B. spinulosa var. collina began 3 days after inoculation but rarely extended more than half way up the root by 9 days. 相似文献
5.
Plants of the eucalypt. Eucalyptus marginata. selected through a glasshouse screening procedure for resistance or susceptibility to Phytophthora cinnamomi , were established in tissue culture and micropropagated. After inoculation with P. cinnamomi , root lesions in clonal lines selected as resistant (RR) to P. cinnamomi were restricted and became contained within four days after inoculation while lesions in roots of those lines susceptible (SS) to P. cinnamomi continued to extend rapidly. Activity of phenylalanine ammonialyase (PAL) was increased above controls in root segments of the RR lines 48 h after inoculation with P. cinnamomi while activity in unselected seedlings and the SS lines was reduced or unchanged. After inoculation, lignin concentration was increased and reached high levels compared with uninoculated control levels in roots of the two RR lines tested. Constitutive levels of phenolics in roots of the RR lines were up to 94% higher than in seedling roots and levels were further increased after inoculation. Levels of phenolics in the other lines and seedlings were unaltered by inoculation. A line derived from resistant seedlings from a susceptible family (RS) had the highest constitutive levels of lignin, which were further increased after inoculation. Resistance to P. cinnamomi in clonally propagated E. marginata seedlings is based on similar mechanisms to those of field resistant species. 相似文献
6.
Excised shoot and root assays were evaluated for routine screening for Phytophthora resistance or tolerance in a Banksia breeding programme. An excised root assay provided useful information on the response of 15 Banksia species to Phytophthora cinnamomi and P. citricola . Roots were excised from 9- to 12-month-old plants, inoculated with plugs of mycelium, and sampled to establish the extent of colonization. Species susceptibility, expressed as the extent of root colonization at day 8, gave good agreement with previously published results obtained for plants inoculated in a shadehouse containment facility. This assay also showed differences in susceptibility among individual plants of B. baxteri and B. coccinea . An excised shoot assay was considered unsuitable for routine screening because lesion development in 16 species was found to be inconsistent when performed over 3 years. Preliminary evaluation of an assay using micropropagated shoots is reported. 相似文献
7.
The pathogenicity of five species of Phytophthora to English walnut was studied in a greenhouse experiment. Phytophthora cinnamomi was the most aggressive species, causing severe root rot and seedling mortality. The other species tested, P. cambivora , P. citricola , P. cactorum and P. cryptogea , did not induce visible crown symptoms on seedlings 2 months after inoculation. Some strains of P. cambivora and P. cactorum also caused taproot damage to seedlings. All except one of the tested isolates caused significant necrosis of fine roots and a significant reduction of root weight compared with noninoculated seedlings. Reduction of above-ground plant development was not statistically significant. While P. cinnamomi is well known as an aggressive primary pathogen of English walnut, the other species of Phytophthora may act as predisposing factors to walnut decline, affecting root system development and increasing host vulnerability to environmental stress. 相似文献
8.
An assessment was made of the effects of several fungicides on the formation of zoosporangia, the release of zoospores from zoosporangia, zoospore motility, germ tube formation and mycelial growth, by Phytophthora cinnamomi Rands. Compounds active against mycelial growth (such as metalaxyl and furalaxyl), as well as those active against zoospores (such as captafol and zineb), could be detected by a lupin (Lupinus angustifolius L.) assay which has been developed. This assay may be useful as a screening procedure to detect new fungicides. 相似文献
9.
烟草疫霉是重要的病原真菌,但在人工培养条件下难以培养、产孢以及释放游动孢子.作者对烟草疫霉培养、产孢、接种方法进行了研究.芝麻培养基、黑麦培养基、燕麦培养基可用来培养烟草疫霉,烟草疫霉在三种培养基上平均每天生长量为1.10、0.78、0.86cm;芝麻培养基、黑麦培养基为烟草疫霉产孢子囊较好的培养基,产孢能力强,分别为2.52×104、2.07×104个孢子囊/cm2.而且孢子囊释放率高,分别为43.0%、32.1%.游动孢子囊悬浮液灌根接种和注射接种都能使烟草发病,但不同的接种方法和接种浓度下,病情指数不同. 相似文献
10.
Rapid detection of Phytophthora cinnamomi using PCR with primers derived from the Lpv putative storage protein genes 总被引：1，自引：1，他引：1
Phytophthora cinnamomi is an ecologically and economically important pathogen. In this study, PCR assays were developed with primer pair LPV2 or LPV3 for rapid detection and identification of this organism. Both primer pairs were selected from putative storage protein genes. The specificity of these primer pairs was evaluated against 49 isolates of P. cinnamomi , 102 isolates from 30 other Phytophthora spp., 17 isolates from nine Pythium spp. and 43 isolates of other water moulds, bacteria and true fungi. PCR with both primer pairs amplified the DNA from all isolates of P. cinnamomi regardless of origin. The LPV3 primers showed adequate specificity among all other species tested. The LPV2 primers cross-reacted with some species of Pythium and true fungi, but not with any other Phytophthora species. PCR with the LPV3 primers detected the pathogen at levels of a single chlamydospore or 10 zoospores in repeated tests. The PCR assay was at least 10 times more sensitive than the plating method for detection of the pathogen from artificially infested soilless medium, and, to a lesser extent, from naturally infected plants. PCR with LPV3 primers can be a useful tool for detecting P. cinnamomi from soilless media and plant tissues at ornamental nurseries, whereas the LPV2 primers can be an effective alternative for identification of this species from pure culture. Applications of these assays for detection of P. cinnamomi in other environments were also discussed. 相似文献
11.
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 . 相似文献
12.
Pieter van de Graaf Alison K. Lees Danny W. Cullen James M. Duncan 《European journal of plant pathology / European Foundation for Plant Pathology》2003,109(6):589-597
A sensitive real-time polymerase chain reaction (PCR) assay was developed for the quantification of Spongospora subterranea, the cause of powdery scab and root galling in potato, and the vector of Potato mop top virus. A specific primer pair and a fluorogenic TaqMan® probe were designed to perform a quantitative assay for the detection of S. subterranea in soil, water and plant tissue samples. The assay was tested using DNA from cystosori, zoospores, plasmodia and zoosporangia of the pathogen. DNA was extracted directly from cystosori suspended in water and from clay soil with varying levels of added cystosori. DNA obtained from zoospores released into nutrient solution by cystosori in the presence of tomato bait plants was also tested, as was DNA from plasmodia and zoosporangia in infected tomato roots. In many cases, detection was successful even at low inoculum levels. This specific quantitative assay could therefore be a useful tool for studying the biology of S. subterranea, and for the optimisation of disease avoidance and control measures. 相似文献
13.
Action of the fungicide phosphite on Eucalyptus marginata inoculated with Phytophthora cinnamomi 总被引：1，自引：1，他引：0
Although phosphite has been effective in the control of P. cinnamomi in E. marginata (jarrah) , the biochemical mechanisms behind phosphite protection are poorly understood. Using an aeroponics system, jarrah clones with moderate resistance to P . cinnamomi were treated with foliar applications of phosphite (0 and 5 g L−1 ). The roots were inoculated with zoospores of P. cinnamomi at 4 days before and 0, 2, 5, 8 and 14 days after phosphite treatment. Root segments were then analysed for activity of selected host defence enzymes (4-coumarate coenzyme A ligase [4-CL], cinnamyl alcohol dehydrogenase [CAD]) and the concentration of soluble phenolics and phosphite. Lesion development was most effectively reduced when phosphite concentrations within the roots were highest (i.e. days 8–14). During this time, the levels of host defence enzymes remained relatively unchanged. Lesion development was also effectively restricted when phosphite concentrations within the roots were lowest (i.e. days 2 and 5); a significant increase in host defence enzymes was associated with this decrease in lesion development. It was concluded from these studies that the effect of phosphite in controlling the pathogen is determined by the phosphite concentration at the host–pathogen interface. When phosphite concentrations within the roots are low, phosphite interacts with the pathogen at the site of ingress to stimulate host defence enzymes. At high phosphite concentrations, phosphite acts directly on the pathogen to inhibit its growth before it is able to establish an association with the host, and the host defences remain unchanged. 相似文献
14.
Rapid and sometimes extensive mortality and decline of oak, principally Quercus suber and Q. ilex , has occurred in parts of southern Spain and Portugal in recent decades. We report here isolation of the aggressive root pathogen Phytophthora cinnamomi from roots of diseased oaks or from soil at eleven out of thirteen decline foci examined. It is proposed that the introduction and spread of P. cinnamomi may be a major factor in the Iberian oak decline, interacting with drought and other site factors, and leading to stress-related attacks by insects and other fungi. By analogy, it may also be involved in the similar oak declines occurring elsewhere on the Mediterranean. 相似文献
15.
利用mariner转座子对产酶溶杆菌Lysobacter enzymogenes OH11进行转座诱变,构建菌株OH11的突变体文库.筛选到1株4种胞外酶(蛋白酶、纤维素酶、几丁质酶和β-1,3-葡聚糖酶)产生均减少的突变株D-11.通过亚克隆,鉴定转座子的插入位点,涉及1个羧基末端蛋白酶(carboxy-terminal protease)编码基因ctp.通过同源重组的方法对该基因进行敲除,对缺失突变体Δctp表型分析发现:(1)Δctp与野生型OH11在营养丰富型(2YT)与营养缺陷型(MMX)培养基中生长速率基本一致;(2)Δctp降低了蛋白酶、纤维素酶和β-1,3-葡聚糖酶的产生,但不影响几丁质酶的产生;(3)Δctp生物膜的产生量明显减少.研究还表明,突变体基本不改变其对油菜菌核病菌Sclerotinia sclerotiorum、水稻纹枯病菌Rhizoctonia solani和辣椒疫霉病菌Phytophthora capsici的拮抗能力.互补菌株均恢复了野生型的相关功能. 相似文献
16.
Alfalfa, maize, sorghum and sugarbeet plants were inoculated with zoospores ofPhytophthora andPythium species in order to assess the effects of inoculum density, plant age and temperature on disease severity. Seedlings were
grown axenically in test tubes and inoculated with zoospore suspensions. Disease severity was assessed by measuring the root
growth and discoloration of treated and control seedlings. The incremental root length of all plants decreased and root discoloration
increased as inoculum concentration of the pathogen increased. Changes were more intensive among low levels of zoospore concentrations
and no significant differences in disease severity were found for inoculum densities higher than 104 zoospores ml-1. Disease severity was negatively related to plant age. Disease development on sugarbeet seedlings infected withPythium andPhytophthora species was affected by temperature, but the pattern of response was determined by the pathogen’s temperature preferences.
The incremental root length decreased as temperature increased up to 25°C. The effect ofPythium dissimile andPhytophthora cactorum on root length was significantly lower at 35°C than at 25°C, whereasPythium aphanidermatum andPhytophthora nicotianae caused significant damage to roots even at 35°C.
http://www.phytoparasitica.org posting Dec. 3, 2001. 相似文献
17.
The soil-borne plant pathogen Phytophthora cinnamomi is widely distributed in the jarrah ( Eucalyptus marginata ) forest of Western Australia. Infested areas of the forest are mined for bauxite and the presence of the pathogen could after the survival of trees re-established after mining. Monitoring of 21 revegetated bauxite mined areas found that survival of jarrah and marri ( Eucalyptus calophylla ) trees was high (85–92% and 93–99%, respectively) after 5–7 years but P. cinnamomi was recovered from dead trees. To identify trees for more detailed study, plant symptoms of stress such as suppressed growth, wilting, yellowing of crown, coppice and epicormic growth and visible stem lesions were used. Over a period of 15 months, 30 E. marginata and 28 E. calophylla were carefully excavated and examined for lesions and the presence of P. cinnamomi. P. cinnamomi was consistently isolated from the lignotuber and collar regions of both hosts but never from the roots alone, except in one instance from E. calophylla where it was isolated from a non-lesioned root. In E. calophylla , the lignotuber appears to be very susceptible to invasion by P. cinnamomi in contrast to the roots which appear resistant. The invasion of the pathogen into the lignotuber and collar regions of both species was consistently associated with ponding of water around the plants. This ponding persists for many hours to days after rain and appears to provide an infection court for P. cinnamomi. Development of rehabilitation procedures to reduce this ponding will minimize the risk of tree deaths caused by this pathogen. 相似文献
18.
ABSTRACT A microbioassay was developed for the discovery of compounds that inhibit Phytophthora spp. This assay uses a 96-well format for high-throughput capability and a standardized method for quantitation of initial zoospore concentrations for maximum reproducibility. Zoospore suspensions were quantifiable between 0.7 and 1.5 x 10(5) zoospores per ml using percent transmittance (620 nm). Subsequent growth of mycelia was monitored by measuring optical density (620 nm) at 24-h intervals for 96 h. Full- and half-strength preparations of each of three media (V8 broth, Roswell Park Memorial Institute mycological broth [RPMI], and mineral salts medium) and four zoospore concentrations (10, 100, 1,000, and 10,000 zoospores per ml) were evaluated. Both full- and half-strength RPMI were identified as suitable synthetic media for growing P. nicotianae, and 1,000 zoospores per ml was established as the optimum initial concentration. The assay was used to determine effective concentration values for 50% growth reduction (EC(50)) for seven commercial antifungal compounds (azoxystrobin, fosetyl-aluminum, etridiazole, metalaxyl, pentachloronitrobenzene, pimaricin, and propamocarb). These EC(50) values were compared with those obtained by measuring linear growth of mycelia on fungicide-amended medium. The microbioassay proved to be a rapid, reproducible, and efficient method for testing the efficacy of compounds that inhibit spore germination in P. nicotianae and should be effective for other species of Phytophthora as well. The assay requires relatively small amounts of a test compound and is suitable for the evaluation of natural product samples. 相似文献
19.
恶疫霉有性杂交后代的生物学研究 总被引：1，自引：1，他引：1
将2个带有不同抗药性标记的恶疫霉菌株配对,培养36 d后诱导其卵孢子萌发,从3760个单卵孢株中,获得50株带有双亲标记的杂交个体。对其中32株杂交个体的生长速率、有性和无性繁殖能力、卵孢子和游动孢子萌发率、致病力及对高温的耐受力等生物学性状进行测定。结果显示,测试的32株杂交个体在LBA培养基上均能较好地生长,有24株的杂交个体的生长速率介于2亲本之间;在LBA和SL培养基上,大多数杂交个体均能产生较大数量的卵孢子,有37%的杂交个体在SL培养基上产卵孢子能力显著大于双亲,仅有1个杂交个体不产生卵孢子;在人工培养条件下,大多数供试杂交个体可以产生较大数量的孢子囊,其中15株杂交个体产孢子囊能力处于双亲之间;被测的杂交个体产生的卵孢子或游动孢子均可以萌发形成有效的单孢株,有22株的杂交个体的卵孢子萌发率大于50%;被测的杂交个体接种在苹果上都有较强的致病力,有16株杂交个体的致病力显著大于双亲。表明在群体水平上恶疫霉有性杂交后代具有较强的生活能力,提示同宗配合恶疫霉不同菌株间的有性重组,对该种的群体遗传多样性可能具重要作用。 相似文献