Anatomy of cranberry stem gall and localization of bacteria in galls

ABSTRACT Cranberry stem gall is characterized by tumors that girdle stems, thereby killing all distal leaves, flowers, and fruit. Bacteria that produce high levels of the plant growth hormone indole-3-acetic acid (IAA) are associated with and believed to cause cranberry stem gall. The anatomy of naturally occurring galls on woody cranberry plants and galls caused by inoculation of micropropagated cranberry plants with Pantoea agglomerans strain 4/99 was consistent with elevated levels of IAA in plants. Field galls exhibited hypertrophy and hyperplasia of tissue external to the vascular cambium, resulting in extensive stem swelling and splitting of the periderm. Similarly, galls on micropropagated plants contained enlarged cortical parenchyma cells. The current year's xylem vessels in field galls were narrow and dense compared with xylem vessels of healthy stems. Curved xylem elements apparently developed de novo within field galls and galls on inoculated plants. Cavities and fissures in both types of galls contained dense aggregates of bacteria. Treatment of micropropagated plants with synthetic IAA caused hypertrophy of cortical parenchyma and formation of adventitious roots. The results support the hypothesis that IAA-producing bacteria cause cranberry stem gall.     

Occurrence of indole-3-acetic Acid-producing bacteria on pear trees and their association with fruit russet

ABSTRACT A relatively high percentage of epiphytic bacteria on pear leaf and fruit surfaces had the ability to produce indole-3-acetic acid (IAA) in culture media supplemented with tryptophan. While over 50% of the strains produced at least small amounts of IAA in culture, about 25% of the strains exhibited high IAA production as evidenced by both colorimetric and high-performance liquid chromatography analysis of culture supernatants. A majority of the strains that produced high amounts of IAA were identified as Erwinia herbicola (Pantoea agglomerans), while some strains of Pseudomonas syringae, Pseudomonas viridiflava, Pseudomonas fluorescens, Pseudomonas putida, and Rahnella aquaticus that produced high amounts of IAA also were found on pear. Fruit russeting was significantly increased in 39 out of 46 trials over an 8-year period in which IAA-producing bacteria were applied to trees compared with control trees. A linear relationship was observed between fruit russet severity and the logarithm of the population size of different IAA-producing bacteria on trees in the 30 days after inoculation, when normalized for the amount of IAA produced by each strain in culture. On average, the severity of fruit russet was only about 77% that on control trees when trees were treated at the time of bloom with Pseudomonas fluorescens strain A506, which does not produce IAA. Both total bacterial populations on pear in the 30-day period following full bloom and fruit russet severity varied greatly from year to year and in different commercial orchards over a 10-year period. There was a strong linear correlation between the logarithm of total bacterial population sizes and fruit russet severity.     

Production of Indole-3-acetic Acid and Tryptophol by Pythium ultimum and Pythium Group F: Possible Role in Pathogenesis

Pythium group F is a minor pathogen which induces symptomless infections that occur frequently and results in yield losses in tomato soilless cultures. To elucidate the mode of action of this microorganism, the influence of culture filtrates of Pythium group F on tomato growth was investigated and compared to that of the pathogen Pythium ultimum. Depending on metabolite production by the fungus, marked differences were observed in plant response. Pythium group F crude culture filtrates or low molecular weight fractions (< 500) caused swelling behind the root tip and reduced root growth; the cohesion and adherence of cells within the cortical area were also affected. These symptoms were similar to those observed on plants treated with indole-3-acetic acid. By contrast, P. ultimum filtrates caused a marked distortion of cell shape accompanied with folding of host cell walls, particularly in the cortical area. These symptoms were characteristic of the activity of toxic compound(s) on host cells. Chemical analysis of the filtrates demonstrated that indole-3-acetic acid and tryptophol were produced by Pythium group F and P. ultimum. However, Pythium group F took up and metabolized more indole-3-acetic acid precursors, especially tryptophan, a key amino acid in the pathways leading to indole-3-acetic acid synthesis. The fact that Pythium group F and P. ultimum transformed tryptamine and indole-3-acetaldehyde into indole-3-acetic acid and tryptophol confirms the existence of a tryptamine pathway within both fungi. These results support the hypothesis that auxins facilitate Pythium group F infections. On the other hand, toxin(s) and hydrolytic enzymes are likely involved in P. ultimum pathogenesis.     

Indole-3-acetic acid biosynthesis in <Emphasis Type="Italic">Aciculosporium take</Emphasis>, a causal agent of witches' broom of bamboo

 Aciculosporium take (Ascomycota; Clavicipitaceae) is a causal agent of witches' broom of bamboo plants. The symptoms of this disease are believed to be induced by plant hormones, particularly auxins. Indole-3-acetic acid (IAA) was identified in cultures of this fungus in an l-tryptophan-supplemented liquid medium. IAA production was confirmed on 30 isolates of A. take from various hosts and locations at levels up to 1 mg/l. The biosynthetic pathway of IAA in A. take culture was examined by analyzing intermediate products and by feeding experiments. The results showed that the indole-3-pyruvic acid pathway (l-tryptophan → indole-3-pyruvic acid → indole acetaldehyde → IAA) was the dominant pathway in A. take. Received: June 3, 2002 / Accepted: July 25, 2002     

Cross-reactions of Corynebacterium sepedonicum antisera with soil bacteria associated with potato tubers

The occurrence of low numbers of fluorescing coryneform bacteria located by immunofluorescence microscopy (IF) in heel-end extracts of healthy potatoes was demonstrated to be a normal phenomenon. The number of bacteria found was highly dependent on the antiserum dilution. Bacteria isolated from other healthy potato material also cross-reacted, mostly at low antiserum dilutions compared with homologous isolates or bacteria of the same species, which reacted at a dilution of 11280. Only relatively small differences were found between the antisera tested. Failure to recognize the occurrence of cross-reacting unknown soil bacteria, indicated by the data presented in this paper, can only increase the dangers of incorrect interpretation of IF results.Samenvatting Het optreden van lage aantallen fluorescerende, coryneforme bacteriën gevonden met behulp van immuno fluorescentiemicroscopie in extracten van naveleinden van genzonde aardappelen, bleek een normaal verschijnsel te zijn. Het aantal gevonden bacteriën was sterk afhankelijk van de verdunning van het antiserum. Bacteriën die geïsoleerd werden van ander gezond aardappelmateriaal vertoonden ook kruisreacties, meestal bij lage verdunningen van het antiserum in vergelijking met homologe isolaten of bacteriën van dezelfde soort, die beide nog reageerden bij een verdunning van 11280. Tussen de getoetste antisera bleken slechts geringe onderlinge verschillen te bestaan. De gegevens in dit artikel onderstrepen het gevaar van een onjuiste interpretatie van IF-resultaten, wanneer het voorkomen van kruisreagerende, onbekende bodembacteriën over het hoofd wordt gezien.     

Hymenoptera wasps associated with the Asian gall wasp of chestnut (Dryocosmus kuriphilus) in Calabria,Italy

The parasitoid complex of the Asian chestnut gall wasp Drycosmus kuriphilus Yasumatsu was studied in Calabria (Italy). A total of 14 different species of parasitoids were collected, of which three are recorded on the Asian gall wasp for the first time. The composition of the parasitoid complex collected in Calabria was compared with that reported from Italy and from Europe. The altitude of the sites of collection seemed to have an effect on the distribution and abundance of the single species of parasitoids.     

New subgroup 16SrIII-Y phytoplasmas associated with false-blossom diseased cranberry (Vaccinium macrocarpon) plants and with known and potential insect vectors in New Jersey

The identity of the presumed phytoplasmal pathogen associated with cranberry false-blossom disease has never been fully clarified. In the present study a molecular-based procedure was employed to determine the identity of the phytoplasma. Tissues of cranberry plants exhibiting cranberry false-blossom symptoms were collected from multiple bogs on each of three randomly selected commercial cranberry farms in New Jersey. Leafhoppers, including the known vector Limotettix vaccinii (Van Duzee) (=Scleroracus vaccinii, Euscellis striatulus) and the sharp-nosed leafhopper Scaphytopius magdalensis (Provancher), a known vector of blueberry stunt disease, were collected from two different farms in New Jersey. Nested PCR assays and RFLP analysis of 16S rRNA gene sequences were employed for the detection and identification of the associated phytoplasmas. All of 20 cranberry plants sampled and five out of 14 batches of leafhoppers tested positive for phytoplasma. Virtual RFLP and sequence analyses revealed that all the associated phytoplasmas were members or variants of a new subgroup, 16SrIII-Y. Phylogenetic analysis of 16S rRNA sequences indicated that cranberry false-blossom phytoplasma strains represented a lineage distinct from other 16SrIII subgroups. This is the first report confirming that a new phytoplasma (designated as a new subgroup 16SrIII-Y) is associated with cranberry false-blossom disease and associated with both leafhopper species in New Jersey.     

藜麦黑茎病拮抗细菌的筛选及与杀菌剂协同防治作用

为安全高效防治藜麦黑茎病,减少化学药剂施用量,筛选出对藜麦黑茎病菌Ascochyta caulina有良好抑制作用的拮抗细菌,分别采用平板对峙法和菌丝生长速率法测定拮抗细菌及杀菌剂对藜麦黑茎病菌的室内毒力;初步筛选出抑菌效果良好的拮抗菌和杀菌剂,采用稀释涂布平板法测定不同杀菌剂与拮抗细菌的相容性,并采用Horsfall法确定最佳复配比例,以确定的最佳复配比例进行田间防效测定。试验初步筛选出2株对A.caulina具有较好抑菌活性的拮抗细菌LS3和LS10,及室内毒力较高的2种杀菌剂戊唑醇和咪鲜胺。经过生物相容性试验最终选出戊唑醇和拮抗细菌LS3为最佳组合,其中,戊唑醇对A.caulina的EC₅₀为1.78μg/mL,LS3菌株对其EC₅₀为2.37×10⁵ cfu/mL,LS3初步鉴定为芽胞杆菌Bacillus sp.;在各自EC₅₀浓度下戊唑醇和LS3体积比为6∶4复配时对A.caulina抑制率达59.24%,IR值为1.003,具有加和作用,为最佳复配比例。以筛选出的0.5%木质素磺酸钠作为...     

大豆根瘤菌抗性菌株的筛选及鉴定

从陕西西安、杨凌两地采摘的大豆根瘤中分离出32株菌,采用形态学方法筛选出11株菌进行实验.对供试菌株进行了5种有机试剂的抗性筛选、5种病原真菌拮抗性筛选,得到YR3和YR6两株优势菌株,进行分子生物学鉴定.结果表明:菌株XR3,YR3,YR6,YR7对二甲苯、苯酚、丙酮、丙烯酰胺、氟磺胺草醚抗药性较强;YR3,YR6两株菌对病原真菌拮抗性较强,生理生化研究和16S rDNA鉴定最后确定,菌株YR3应为Rhizobium leguminosarum U29386,菌株YR6应为Sinorhizobium americanum AF506513.     

16s rDNA文库法分析番石榴果实蝇共生菌组成

[目的]探索分析番石榴果实蝇[ Bactrocera correcta (Bezzi)]的共生菌组成,为进一步探索共生菌的生理功能以及与宿主的协同进化关系奠定基础.[方法]构建番石榴果实蝇室内种群共生菌的16s rDNA文库,BLAST分析其共生菌的组成以及丰度.[结果]室内雄虫共生菌主要为Pseudomonas aeruginosa和Lactococcus lactis,雌虫共生菌主要为Enterobacter属的细菌.[结论]本研究结果证明番石榴果实蝇存在多种共生菌.     

Pectinolytic bacteria associated with potato soft rot and blackleg in South Africa and Zimbabwe

Soft rot and blackleg can cause severe economic losses in potato production in South Africa and Zimbabwe depending on climatic conditions. The aim of the study was to identify the predominant bacteria causing potato soft rot and blackleg in these countries. Samples, comprising of stems and tubers from potato plants with blackleg and soft rot symptoms were collected from 2006?C2009 from potato production areas where disease outbreaks occurred. The isolates from these plants and tubers yielded Gram negative, pectinolytic bacteria on crystal violet pectate and inoculated tubers. Identification was based on biochemical and phenotypic characteristics, rep-PCR, Amplified Fragment Length Polymorphisms and sequences of gyrB and recA genes. Isolates from Zimbabwe were identified as Pectobacterium carotovorum subsp. brasiliensis (Pcb) (21 isolates), Dickeya dadantii subsp. dadantii (Dd) (20 isolates), P. c. subsp. carotovorum (Pcc) (16 isolates) and P. atrosepticum (Pa) (4 isolates). Pcb, Pcc and Dd subsp. dadantii were isolated from samples collected from all the regions, while Pa was isolated from Nyanga the coolest region in Zimbabwe. In South Africa, however, Pcb was the most common causal agent of soft rot and blackleg. P. atrosepticum was the only pathogen isolated from samples collected in Nyanga, Zimbabwe, and was not isolated from any South African samples. AFLP analysis separated the Pcb strains into 12 clusters, reflecting subdivision in terms of geographic origin, and Pcc isolates were clearly differentiated from Pcb isolates. A large degree of DNA polymorphism was evident among these 12 clusters. The study identified all the pathogens associated with the blackleg/soft rot disease complex.     

Pectobacterium spp. associated with bacterial stem rot syndrome of potato in Canada

Pectobacterium atrosepticum, P. carotovorum subsp. brasiliensis, P. carotovorum subsp. carotovorum, and P. wasabiae were detected in potato stems with blackleg symptoms using species- and subspecies-specific polymerase chain reaction (PCR). The tests included a new assay for P. wasabiae based on the phytase gene sequence. Identification of isolates from diseased stems by biochemical or physiological characterization, PCR, and multi-locus sequence typing (MLST) largely confirmed the PCR detection of Pectobacterium spp. in stem samples. P. atrosepticum was most commonly present but was the sole Pectobacterium sp. detected in only 52% of the diseased stems. P. wasabiae was most frequently present in combination with P. atrosepticum and was the sole Pectobacterium sp. detected in 13% of diseased stems. Pathogenicity of P. wasabiae on potato and its capacity to cause blackleg disease were demonstrated by stem inoculation and its isolation as the sole Pectobacterium sp. from field-grown diseased plants produced from inoculated seed tubers. Incidence of P. carotovorum subsp. brasiliensis was low in diseased stems, and the ability of Canadian strains to cause blackleg in plants grown from inoculated tubers was not confirmed. Canadian isolates of P. carotovorum subsp. brasiliensis differed from Brazilian isolates in diagnostic biochemical tests but conformed to the subspecies in PCR specificity and typing by MLST.     

Diversity of cultivable endophytic bacteria associated with halophytes in Xinjiang of China and their plant beneficial traits

Endophytic bacteria from halophytes have a wide range of application prospects in various fields, such as plant growth-promoting, biocontrol activity and stress resistance. The current study aimed to identify cultivable endophytic bacteria associated with halophytes grown in the salt-affected soil in Xinjiang Uygur Autonomous Region, China and to evaluate their plant beneficial traits and enzyme-producing activity. Endophytic bacteria were isolated from Reaumuria soongorica (PalL Maxim.), Artemisia carvifolia (Buch.-Ham. ex Roxb. Hort. Beng.), Peganum harmala L. and Suaeda dendroides (C. A. Mey. Moq.) by using the cultural-dependent method. Then we classified these bacteria based on the difference between their sequences of 16S rRNA (16S ribosomal RNA) gene. Results showed that the isolated bacteria from R. soongorica belonged to the genera Brucella, Bacillus and Variovorax. The bacteria from A. carvifolia belonged to the genera Micromonospora and Brucella. The bacteria from P. harmala belonged to the genera Paramesorhizobium, Bacillus and Peribacillus. The bacteria from S. dendroides belonged to the genus Bacillus. Notably, the genus Bacillus was detected in the three above plants, indicating that Bacillus is a common taxon of endophytic bacteria in halophytes. And, our results found that about 37.50% of the tested strains showed strong protease-producing activity, 6.25% of the tested strains showed strong cellulase-producing activity and 12.50% of the tested strains showed moderate lipase-producing activity. Besides, all isolated strains were positive for IAA (3-Indoleacetic acid) production, 31.25% of isolated strains exhibited a moderate phosphate solubilization activity and 50.00% of isolated strains exhibited a weak siderophore production activity. Our findings suggest that halophytes are valuable resources for identifying microbes with the ability to increase host plant growth and health in salt-affected soils.     

Anastomosis groups and pathogenicity of binucleate Rhizoctonia isolates associated with stem canker of potato in China

Potato stem canker caused by Rhizoctonia solani commonly occurs in potato-growing regions around the world, but little is known about whether binucleate Rhizoctonia (BNR) can incite this disease on potato plants in China. In the present study, a total of 69 BNR isolates were recovered from cankered subterraneous stems of potato collected from 17 provinces, autonomous regions, and municipalities of China. Based on the morphological characteristics and sequence analysis of the internal transcribed spacers of the ribosomal DNA, 48 isolates were classified as anastomosis group (AG)-A with a ratio of 69.56 %, 15 isolates (21.74 %) were AG-K, four isolates (5.80 %) were AG-F, one isolate (1.45 %) was AG-I and one isolate (1.45 %) was AG-U. Pathogenicity tests under glasshouse conditions revealed that all BNR isolates, except for the AG-I isolate, could induce symptoms of stem canker on potato plants with disease incidence ranging from 5.26 to 55.56 % and disease index ranging from 1.32 to 13.89, respectively. To our knowledge, this is the first detailed report about BNR AGs causing stem canker on potato plants in China.