Phytophthora root and crown rot of raspberry in Bulgaria

Root and crown rot of raspberry (Rubus idaeus L.) was observed in a plantation at the experimental station of small fruits in Kostinbrod, Bulgaria. Isolates ofPhytophthora spp. were obtained from diseased plants. Colony morphology, growth rates, features of asexual and sexual structures were studied and as a result twoPhytophthora species were identified:Phytophthora citricola Saw. andPhytophora citrophthora (R.E. Sm. & E.H. Sm.) Leonian. Their pathogenicity was confirmed in artificial inoculation experiments. The isozyme (-esterase) patterns ofP. citrophthora andP. citricola isolates from raspberry and from the collection of the CBS, Baarn the Netherlands were compared, using micro-gel electrophoresis. Both species are reported for the first time as pathogens of raspberry in Bulgaria. This is only the second report in phytopathological literature ofP. citrophthora on raspberry, the first being from Chile [Latorre and Munoz, 1993].     

Collar rot caused byPhytophthora citrophthora on pear trees in Greece

A severe crown rot of pear trees of cultivar ‘Kondoula’ grafted on quince rootstock was observed in Greece. Isolations from the affected tissues repeatadly yielded aPhytophthora sp. that was determined by morphological and physiological characteristics to beP. citrophthora. The pathogenicity of two of theP. citrophthora isolates was tested by inoculating trunks of 2-year-old pear trees by mycelial agar disks. Thirty-two days after inoculation all inoculated trees were infected. Although the pear isolates could not be differentiated from isolates ofP. palmivora orP. nicotianae based on isozyme profiles of α-esterase or lactate dehydrogenase, RAPD profiles with one selected primer differentiated the pear isolates from the other species and revealed an electrophoretic banding pattern similar to that of aP. citrophthora standard. This is the first report ofP. citrophthora on pear trees in Greece.     

<Emphasis Type="Italic">Pythium</Emphasis> and <Emphasis Type="Italic">Phytophthora</Emphasis> species associated with root and stem rots of kalanchoe

Pythium and Phytophthora species were isolated from kalanchoe plants with root and stem rots. Phytophthora isolates were identified as Phytophthora nicotianae on the basis of morphological characteristics and restriction fragment length polymorphism (RFLP) analysis of the rDNA-internal transcribed spacer regions. Similarly, the Pythium isolates were identified as Pythium myriotylum and Pythium helicoides. In pathogenicity tests, isolates of the three species caused root and stem rots. Disease severity caused by the Pythium spp. and Ph. nicotianae was the greatest at 35°–40°C and 30°–40°C, respectively. Ph. nicotianae induced stem rot at two different relative humidities (60% and >95%) at 30°C. P. myriotylum and P. helicoides caused root and stem rots at high humidity (>95%), but only root rot at low humidity (60%).     

Molecular and Pathogenicity Characteristics of Phytophthora nicotianae Responsible for Root Necrosis and Wilting of Pepper (Capsicum annuum L.) in Tunisia

Isolates of Phytophthora from pepper, produced in Tunisia, were characterised according to molecular and pathogenicity criteria. Polymerase chain reaction amplification of the ITS1 region in the ribosomal DNA resulted in different sized fragments. The pepper isolates and P. nicotianae yielded a fragment of 310bp that distinguished it from P. capsici with a fragment of 270bp. The ribosomal RNA gene amplicons of both internal transcribed spacers and the 5.8 S of the pepper Phytophthora and P. nicotianae were digested with 8 endonucleases. The patterns generated, with the 2 enzymes that cut, were identical for both taxa. This molecular analysis corroborated the morphological and biological characteristics and suggests strongly that the isolates of Phytophthora from pepper belong to the species P. nicotianae. Inoculation of pepper, tomato, eggplant and tobacco plants with the isolates of P. nicotianae from pepper showed they were highly pathogenic on pepper but not on tobacco, while their pathogenicity was weak on tomato and eggplant and was associated with atypical symptoms not observed in the field. These pathogenicity tests suggest that pepper isolates of P. nicotianae are particularly adapted to their host and may thus constitute a forma specialis of P. nicotianae.     

Widespread Detection of Phytophthora Taxon Salixsoil in the Littoral Zone of Lake Constance, Germany

An unnamed ITS clade 6 Phytophthora was frequently isolated from rhizosphere soil of reed (Phragmites australis) growing on the littoral zone of Lake Constance. The isolates closely resembled P. gonapodyides, having internally proliferating, non-papillate sporangia, a rather high temperature optimum for growth (30 °C), and being sexually sterile. ITS sequence analysis revealed that they were identical to the as yet unnamed Phytophthora taxon Salixsoil, originally isolated from Salix roots in the UK and Alnus debris in Denmark. The taxon was readily isolated from permanently as well as occasionally flooded reed sites using standard baiting procedures, indicating a wide distribution in the Lake Constance littoral zone. In an in vitro leaf inoculation assay P. taxon Salixsoil proved to be more aggressive towards Salix alba than P. gonapodyides. The new taxon may be of significance as a root pathogen of woody plants in moist or flooded situations occurring in alluvial forest/plant communities. We propose that due to its close resemblance to P. gonapodyides the taxon might have passed unnoticed in the past, and possibly is much more widely distributed than previously recognised.     

A comparison of morphology,pathogenicity and restriction fragment patterns of mitochondrial DNA among isolates of Phytophthora porri Foister

Thirteen strains ofPhytophthora porri from five different hosts were compared with respect to their morphology, cardinal temperatures for growth, pathogenicity to leek and cabbage and restriction fragment patterns of mitochondrial DNA. Morphology of vegetative growth was rather similar in most isolates. Those characters which differed among isolates showed overlapping variability and could not be used to distinguish groups, with the exception of production of oogonia and sporangia and the antheridium type. Considerable differences were found in restriction patterns of mitochondrial DNA, isolates from the same host mostly showing identical patterns. Isolates from differentAllium species showed relatively similar restriction patterns if compared to the other isolates. Isolates fromBrassica oleracea proved to be a homogeneous group, quite different from the others with respect to restriction patterns, production of sporangia, production of oogonia, antheridium type and pathogenicity. One isolate, CBS 366.59, isolated from and pathogenic toA. porrum, deviated in many characters from the other isolates. It showed the restriction patterns ofPhytophthora nicotianae and also the high cardinal temperatures for growth typical for this species. The sporangia, however, were distinctly non-papillate and the majority of antheridia was of the paragynous type.     

Observations of Phytophthora spp. in Water Recirculation Systems in Commercial Hardy Ornamental Nursery Stock

Samples of water and sediment were taken from drains, reservoirs and wells from four commercial hardy ornamental nurseries with water recirculation systems. The samples were taken on seven different dates throughout a single year from August 1994 to July 1995. The samples were screened for Phytophthora species using five different methods: direct plating, three bait tests (using lupin seedlings, apples and Rhododendron leaves) and a DAS-ELISA (double-antibody sandwich enzyme-linked immunosorbent-assay) with two antisera. In the nurseries with old water recirculation systems, Phytophthora species were detected in the drains and in the reservoirs. In the nursery with a new recirculation system, the pathogens were only present in the drains. None of the water samples from wells in any of the nurseries were contaminated. Phytophthora species were present in the water as well as in the sediment samples from drains and reservoirs. They were detected in the water recirculation systems irrespective of the season. The number of isolates increased about sevenfold between late summer and spring. At least 12 different Phytophthora species were identified: some isolates were previously unrecorded species. The epidemiology of the pathogens in outdoor water recirculation systems as well as the importance of the results for commercial nurseries is discussed.     

Testing variability in pathogenicity ofPhytophthora cactorum, P. citrophthora andP. syringae to apple, pear, peach, cherry and plum rootstocks

The relative virulence ofPhytophthora cactorum andP. syringae originating from almond trees, and ofP. citrophthora originating from citrus, to apple, pear, peach, cherry and plum rootstocks, was studiedin vivo andin vitro. Results of the different experiments were in good agreement. All testedPhytophthora isolates showed little virulence to pear rootstocks-causing only minor crown rot symptoms - and no virulence at all to apple rootstocks. In contrast, they were highly virulent to stone fruit rootstocks, causing crown rot disease. The non-pathogenicity of these isolates to pome rootstocks could be interpreted as strict host specificity.     

棉铃疫病生防细菌筛选、鉴定及制剂防治效果

为有效防治由苎麻疫霉Phytophthora boehmeriae引起的棉铃疫病,采用平板对峙培养法、离体试验和田间小区试验对棉花、玉米、番茄、黄瓜等作物根围细菌进行筛选,结合形态学观察、16S rDNA序列分析及Biolog微生物自动鉴定系统对筛选出的生防细菌进行分类鉴定,并通过离体试验对优秀生防菌2种制剂的防治效果进行评价。拮抗细菌初筛试验结果表明,在供试的1 250株作物根围细菌中,399株细菌菌株有良好的抑菌能力,其中40株拮抗细菌菌株抑菌率在80.00%以上,菌株HMB22922抑菌能力突出,对棉铃疫病菌的抑菌率为85.71%,抑菌带宽10.0 mm。室内筛选试验结果表明,菌株HMB22922、HMB23917和HMB21405的病情指数显著低于空白对照,与化学药剂对照间差异不显著,人工接种苎麻疫霉5 d和7 d后,3株菌株对棉铃疫病的防治效果分别为73.92%、69.58%、56.54%和81.34%、66.67%、64.60%。田间筛选试验结果表明,菌株HMB22922培养液对棉铃疫病的田间防治效果为47.12%～58.64%,优于其它2株供试菌株,与化学药剂的防治效果相当且防治效果稳定。生防菌株HMB22922经形态学观察、序列分析和和微生物鉴定系统被鉴定为萎缩芽胞杆菌Bacillus atrophaeus。人工接种苎麻疫霉5、7和12 d时,以菌株HMB22922为有效成分的2.5′109 CFU/mL萎缩芽胞杆菌悬浮剂的防治效果分别为86.33%、78.66%和64.44%,均优于其相同菌量培养液的防治效果。     

Occurrence and distribution of <Emphasis Type="Italic">Phytophthora</Emphasis> species in European chestnut stands,and their association with Ink Disease and crown decline

The Phytophthora complex associated with Castanea sativa Mill. was investigated in five European countries in 35 regions and with respect to various domestication levels. Annual precipitation and length of drought season were the main parameters that regulated the presence of Phytophthora species in the chestnut stands. Seven species of Phytophthora were detected; three of these, P. megasperma, P. cryptogea and P. syringae had not been previously reported on sweet chestnut. P. cinnamomi. P. cambivora and P. citricola were most frequently isolated. P. cinnamomi and P. cambivora were the species significantly associated with declining trees with symptoms of Ink Disease. P. cinnamomirequired distinct ecological conditions compared to the other species. P. cinnamomi was never detected in sites characterized by minimum temperatures below 1.4 °C, maximum temperature above 28 °C, or soil pH below 5.4. The results obtained provide useful information for modeling the probability of Ink Disease, crown decline and associated Phytophthora species in chestnut groves in global climatic change scenarios.     

Evaluation of morphology of infection structures in distinguishing between different Allium rust fungi

Fifteen isolates of rust fungi were collected in the United Kingdom and in the Netherlands from severalAllium species. The samples represented three putative rust species. The morphology of the telia, teliospores and urediniospores was investigated. From urediniospores infection structures were induced on leek, and their morphology was described. Telia and teliospores were not available on every sample. Morphology of the infection structures clearly differentiated between ‘leek’ type and ‘chive’ type isolates. The morphology of infection structures ofPuccinia mixta is very similar to that ofUromyces ambiguus, but clearly distinct fromPuccinia allii sensu Jennings from leek. Quantitative differences in urediniospore characters differentiated between the putative species, but there was overlap between the taxa. We conclude that morphology of infection structures of urediniosporelings is a useful trait for identification of rust isolates fromAllium. This is especially true where more than one rust species may occur on the same host species, as withAllium fistulosum.     

Associations betweenFrankliniella spp. andOrius niger populations in cotton

The distribution of theFrankliniella speciesF. occidentalis (Pergande) andF. intonsa (Trybom) (Thysanoptera: Thripidae), and of the predatory bugOrius niger (Wolff) (Hemiptera: Anthocoridae), in various organs of the cotton plant, as well as prey — predator interactions between thrips andO. niger, were investigated over 6 years in cotton fields in the eastern Mediterranean region of Turkey. The highest number of larvae ofFrankliniella spp. were found inhabiting bolls, whereas the adults colonized mainly flowers. The majority of predatory bug nymphs were present on leaves, followed by bolls, whereasO. niger adults visited mostly flowers. The thrips larvae were most likely preyed upon on flowers and squares, and bolls were safe plant parts for thrips, with a low predation rate. An intermediate but relatively high predation rate occurred on cotton leaves. In further field experiments, the effects of insecticide treatment on the relationships betweenO. niger andFrankliniella spp. were investigated. These trials revealed that a higher correlation existed between the numbers of adultO. niger in flowers andFrankliniella spp. in non-treated cotton fields than in insecticide-treated fields. The proportions of prey/predator in flowers ranged from 1.53 to 19.28 and were below four thrips per predator at most sampling dates in some of the non-treated cotton fields. It is concluded thatO. niger is an effective predator that can play an important role in suppressing population increase ofFrankliniella spp. in cotton. http://www.phytoparasitica.org posting May 12, 2006.     

Real-time detection of <Emphasis Type="Italic">Phytophthora nicotianae</Emphasis> and <Emphasis Type="Italic">P. citrophthora</Emphasis>in citrus roots and soil

Two primers, specific for Phytophthora nicotianae (Pn6) and P. citrophthora (Pc2B), were modified to obtain Scorpion primers for real-time identification and detection of both pathogens in citrus nursery soils and roots. Multiplex PCR with dual-labelled fluorogenic probes allowed concurrent identification of both species ofPhytophthora among 150 fungal isolates, including 14 species of Phytophthora. Using P. nicotianaespecific primers a delayed and lower fluorescence increase was also obtained from P. cactorumDNA. However, in separate real-time amplifications, the aspecific increase of fluorescence from P. cactorum was avoided by increasing the annealing temperature. In multiplex PCR, with a series of 10-fold DNA dilutions, the detection limit was 10 pg l^-1 for P. nicotianaeand 100 pg l^–1 for P. citrophthora, whereas in separate reaction DNA up to 1 pg l^-1 was detected for both pathogens.Simple and rapid procedures for direct DNA extraction from soil and roots were utilised to yield DNA whose purity and quality was suitable for PCR assays. By combining these protocols with a double amplification (nested Scorpion-PCR) using primers Ph2-ITS4 amplifying DNA from the main Phytophthora species (first round) and PnB5-Pn6 Scorpion and Pc2B Scorpion-Pc7 (second round), it was possible to achieve real-time detection of P. nicotianaeand P. citrophthora from roots and soil. The degree of sensitivity was similar to that of traditional detection methods based on the use of selective media. The analyses of artificially and naturally infested soil showed a high and significant correlation between the concentration of pathogen propagules and the real-time PCR cycle threshold.     

Effects of inoculum density,plant age and temperature on disease severity caused by pythiaceous fungi on several plants

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.     

疫霉菌对霜脲氰抗性遗传及对霜脲氰和甲霜灵的交互抗性

就疫霉菌对霜脲氰抗性的产生和遗传，以及疫霉菌对霜脲氰和甲霜灵的交互抗性进行了研究。结果表明，苎麻疫霉容易对霜脲氰产生抗药性突变，但抗性在连续３代单游动孢子分离过程中逐渐丧失。大雄疫霉对霜脲氰不易产生抗性突变，恶疫霉、大雄疫霉和苎麻疫霉对甲霜灵和霜脲氰不存在交互抗性     

Phytophthora lateralis discovered in an old growth Chamaecyparis forest in Taiwan

The geographic origins of the invasive Phytophthora species, P. lateralis and P. ramorum are unknown. In 2008 soil samples were collected in an old growth yellow cedar (Chamaecyparis obtusa var. formosana) stand in the Ma‐kau Ecological Park in north eastern Taiwan and subjected to Phytophthora baiting procedures at 18°C. Cedar needle baits yielded isolates of a slow growing Phytophthora culture from one soil sample, together with P. cinnamomi. Phytophthora bisheria sp. nov. was obtained from another sample. The slow growing isolates conformed closely to P. lateralis in the morphology of their sporangia and chlamydospores, growth–temperature relationships, absence of gametangia and their ITS and cox II sequences. The isolates’ sporangia were partially caducous, with short pre‐formed pedicels of ca. 3–5 μm, a highly unusual feature in a non‐papillate Phytophthora. The isolates also produced multicellular stromata on cedar decoction agar. Small morphological and molecular differences were observed between the Taiwan‐isolates and Oregon‐control isolates. Taiwan may lie within the geographic centre of origin of P. lateralis. By analogy Japan may also lie within the natural range of P. lateralis; and Japan, along with Taiwan and Yunnan, could be an origin for the closely related P. ramorum.     

Natural occurrence of and inoculation experiments withConidiobolus coronatus andConidiobolus sp. in glasshouse populations ofBemisia tabaci

Bemisia tabaci (Gennadius), the sweetpotato whitefly, has only one known entomophthoralean pathogen,Erynia radicans (Entomophthoraceae). Two new pathogens have been isolated recently from a glasshouse population of this pest:Conidiobolus coronatus and another, undescribed species ofConidiobolus (Entomophthorales: Ancylistaceae). Artificial inoculation experiments revealed that eggs ofB. tabaci are practically immune to infection by either species. Second-instar larvae are highly resistant, only high doses of conidia causing between <1% and 4.6% mortality. Adults were found to be much more susceptible. Doses of 60 conidia/mm² ofC. coronatus caused average mortalities ofca 95%. The maximum mortality of adults caused byConidiobolus sp. was much lower,ca 30%, at a dose of 210 conidia/mm². The incubation period (inoculation to death) for both species, under our experimental conditions, is very short: 18–24 h forC. coronatus and 30 h forConidiobolus sp. Both fungi produced loricoconidia (conidia metamorphosed into resting spores) on cotton leaves and other dry surfaces. This ability allowedConidiobolus sp. to remain viable for 17–21 days on cotton leaves, in glasshouse conditions and in the absence of hosts, whileC. coronatus persisted for 10–14 days.     

安徽省大豆疫霉根腐病菌的鉴定及rDNA-ITS序列分析

为明确安徽省夏大豆疫霉根腐病的病原菌种类,对采集自涡阳、怀远、固镇3个县的夏大豆病株及土样分离纯化后获得28株菌株,选取6株代表性菌株,通过形态学观察及核糖体DNA-ITS序列分析对其进行鉴定,并测定了其致病型。结果表明,6株菌株在利马豆培养基上菌落白色,质地均匀;菌丝无隔,致密,具近直角分枝;在10%V8C培养液中,游动孢子囊顶生,不脱落,卵形至椭圆形,无明显乳突,有内层出现象,长宽比大于1.6∶1;同宗配合,在利马豆培养基上单株培养产生大量卵孢子,藏卵器球形,雄器大多侧生;接种合丰35大豆品种后出现典型的大豆疫霉根腐病症状。r DNA-ITS序列分析表明,6株菌株与Gen Bank中大豆疫霉Phytophthora sojae的ITS序列同源性高达100%;菌株GY4、GY8、HY11、HY16、GZ10、GZ21的毒力公式分别为1b,2,3a,3b,4,5,6,7;1b,1d,3a,3b;1d,3a,3b,3c,4,5,6,7;2,3c,4,5,6,7;1b,3a,3c,5,8;3a,3b,5,6,7,8;属于6个不同的致病型。研究表明,这6株菌株均为大豆疫霉。     

Natural occurrence of citrinin in rice grains and its biocontrol byTrichoderma hamatum

Paddy rice was sampled from El-Sharkia, El-Gharbia, El-Dakahlia and Kafr El-Shekh governorates, Egypt. Of the 30 samples taken, ten were contaminated with the mycotoxin citrinin. An average of 6.79 × 10⁴ fungal spores per gram rice was found. The isolated fungi represented 47 species and 28 genera. The predominant genera wereAspergillus, Cladosporium andPenicillium. Aspergilli were represented by 22 species;Aspergillus niger andA. flavus had the highest occurrence.Penicillium viridicatum produced the highest amount of citrinin on glucose ammonium nitrate salts broth and rice grains, and hence this isolate was selected as a good producer of citrinin in this study. The presence ofTrichoderma hamatum reduced the amount of citrinin produced byP. viridicatum compared with its respective control. The excessive growth ofT. hamatum onP. viridicatum was increased with time. Viability ofP. viridicatum conidia decreased byT. hamatum with an increase in the incubation period. Chitinases and 1,3-β-glucanase enzyme activity ofT. hamatum increased with extending the incubation period onP. viridicatum mycelia up to maximum values at 72 and 84 h, respectively.T. hamatum led to a decrease in the production of citrinin byP. viridicatum on rice grains compared with the respective control values. http://www.phytoparasitica.org posting Dec. 19, 2004.     

复合微生物菌剂对苹果再植病害的生防效果测定及拮抗菌株鉴定

为探究复合微生物菌剂对苹果再植病害的生防效果，以苹果砧木实生海棠幼苗为试材，通过盆栽试验测试了木美土里复合微生物菌剂对苹果再植病害的防治效果及对再植海棠的促生作用，然后对该菌剂的可分离微生物进行了分离纯化，并以尖孢镰刀菌Fusarium oxysporum菌株HS2为靶标菌，测试分离获得的10株菌株的拮抗效果，并对拮抗效果显著的1株真菌菌株和2株细菌菌株进行种类鉴定。结果表明，木美土里复合微生物菌剂对苹果再植病害的防治效果达87.78%；经该菌剂处理后，再植海棠苗的株高、茎粗、鲜重、干重及叶面积分别是对照处理的1.51、2.00、5.74、5.21和2.83倍，表明该菌剂有显著的促生作用。木美土里复合微生物菌剂对菌株HS2的抑制率达到68.59%，并从中分离到7株真菌菌株，3株细菌菌株。其中，拮抗效果高于80.00%的真菌菌株有1株，细菌菌株有2株。经鉴定，真菌菌株MMTL-1为哈茨木霉Trichoderma harzianum；细菌菌株BM-01和BM-03均为解淀粉芽胞杆菌Bacillus amyloliquefaciens。