Survival of endoconidia of Thielaviopsis basicola in soil

Lysis and viability of endoconidia ofThielaviopsis basicola artificially introduced into clay loam and sandy soil were microscopically examined at intervals. Most of the endoconidia remained morphologically unchanged in moist clay loam for more than one year, while in moist sandy soil all had disappeared by lysis within 4 months. One percent of the endoconidia that persisted for 15 months in clay loam germinated when tested with V-8 juice. Endoconidia transformed into chlamydosporelike structures when incubated in phosphate buffer solutions supplemented with glucose and asparagine but not in those without these compounds. The significance of these phenomena for the survival of the pathogen in soil is discussed.Samenvatting Kiemkracht en lysis van endoconidia vanThielaviopsis basicola gedurende een incubatieperiode van maximaal 15 maanden in luchtdroge en vochtige klei- en zandgrond werden microscopisch onderzocht. Het merendeel der endoconidiën in luchtdroge en vochtige kleigrond en in luchtdroge zandgrond onderging geen morfologische verandering gedurende de 10 maanden van incubatie, terwijl in vochtige zandgrond alle endoconidiën reeds binnen 4 maanden door lysis waren verdwenen. Eén procent van de endoconidiën bleek na een 15 maanden durende incubatie in vochtige kleigrond nog te kunnen kiemen. Van de endoconidiën die gedurende een verblijf van tween wintermaanden in zandgrond in het veld geen morfologische verandering ondergingen was eveneens nog 1% kiemkrachtig. Deze waarnemingen doen vermoeden, dat endoconidiën mede verantwoordelijk kunnen zijn voor de overleving vanT. basicola in natuurlijke grond. Omvorming van endoconidiën in chlamydospore-achtige structuren werd waargenomen in fosfaatbuffers waaraan glucose en asparagine was toegevoegd, echter niet in fosfaatbuffers zonder deze verbindingen. De vorming van deze structuren in natuurlijke grond kon niet worden aangetoond.     

Aerial Transmission of Thielaviopsis basicola, a Pathogen of Corn-Salad, by Adult Shore Flies

ABSTRACT Chlamydospores of Thielaviopsis basicola were consistently observed in frass excreted by adults and larvae of shore flies that were collected in the immediate vicinity of naturally infected corn-salad plants obtained from a commercial greenhouse production facility. Approximately 95% of the adult flies and 85% of the larvae were internally infested with the pathogen. Pathogen-free adult shore flies were subsequently shown to acquire the pathogen by ingestion after feeding on naturally infected plants. Viable propagules of the pathogen were excreted by these internally infested adults and were capable of transmitting the pathogen to healthy seedlings, which subsequently became infected.     

土壤中烟草根黑腐病菌的实时定量PCR检测技术研究

 Thielaviopsis basicola is a soil-borne plant pathogen which causes root rot disease in tobacco plants. Detection and monitoring of T. basicolain soil is of great significance to control this disease. Based on the differences in internal transcribed spacer (ITS) sequences of T. basicola and other fungal pathogens, a specific primer pair Tb1/Tb2 for T. basicolawas developed. The results showed that the primer pair gave a single amplicon of 330 bp from T. basicola and revealed no undesirable cross-reaction with other seven soil-borne pathogen isolates and three tobacco rhizosphere dominant fungi isolates. With a series of 10-fold genomic DNA dilutions of T. basicola, the detection limit of 1 pg/μL in conventional PCRand100 fg/μL in real-time quantitative PCR was achieved. With DNA from the soil inoculated with different numbers of T. basicola conidia, the detection limit was 10 conidia per reaction in conventional PCR and 0.4 conidia per reaction in real-time quantitative PCR.     

Characterization of the Suppressiveness of Hairy Vetch-Amended Soils to Thielaviopsis basicola

ABSTRACT Factor(s) involved in soil suppressiveness to Thielaviopsis basicola when hairy vetch was used as a green manure were studied in a cotton production system. Soil suppressiveness was assessed in vitro at hairy vetch amendment levels of 0, 0.25, and 0.75% (wt/wt) by observing chlamydospores, using a nylon fabric technique. Chlamydospore germination in all soils was below 5%, and microscopic examination showed no germ tube lysis or visible propagule destruction. Viability (chlamydospore germination on T. basicola-carrot-etridiazol-nystatin [TB-CEN] medium) was reduced by 29% within 48 h after hairy vetch amendment. Viability also was reduced in atmospheres of amended soils, suggesting that the suppressiveness was due to a volatile factor. In a field study, chlamydospore viability in amended soils was reduced by 16%. T. basicola hyphal growth was more sensitive to ammonia than Rhizoctonia solani or Pythium ultimum, and chlamydospore mortality of T. basicola was 100% in petri dish atmospheres with 0.4 ppm of ammonia (50% lethal dose = 0.15 ppm). Soil atmospheric ammonia was 0.08 and 0.10 ppm for 0.25 and 0.75% amendment levels, respectively, both at 3 and 7 days after incorporation. In the field, 0.11 and 0.14 ppm of ammonia were detected in soil atmospheres 3 and 7 days after incorporation, respectively. The levels of ammonia detected were sufficient to account for the loss in T. basicola chlamydospore viability, indicating that ammonia is responsible for the suppressiveness observed.     

Reassessment of the Role of Saprophytic Activity in the Ecology of Thielaviopsis basicola

ABSTRACT The ability of Thielaviopsis basicola to survive saprophytically in soil was investigated using root tissue from susceptible hosts as organic substrates. Inoculum densities were lower in soils amended with root tissue than in nonamended controls after 2 and 4 weeks of incubation. The greatest decrease occurred in soils containing the highest concentration of root tissue or in soils in which root tissue included the soluble components of the living root. Reproduction by T. basicola also was examined in axenic media containing either killed root pieces or various carbohydrates as the sole carbohydrate source. T. basicola utilized killed root tissue as a carbohydrate source in axenic media, particularly in cultures in which root tissue included the soluble components. Enzymatic activities of T. basicola, however, did not result in maceration of the root tissue. T. basicola utilized sucrose and cellobiose, but did not utilize structural carbohydrates such as cellulose, hemicellulose, or pectin. Based on the absence of significant saprophytic ability, T. basicola should be classified ecologically as an obligate parasite.     

Ultrastructure of the Penetration and Infection of Pansy Roots by Thielaviopsis basicola

ABSTRACT Transmission electron microscopy was used to study the penetration and infection of pansy roots by Thielaviopsis basicola. Events observed in 7- to 10-day-old roots produced on moist filter paper differed slightly from those in roots from 4-week-old plants washed free of potting media prior to inoculation. By 3 h postinoculation (PI), epidermal cells of roots produced on filter paper exhibited aggregated cytoplasm and papilla formation in response to germ tube tips. The presence of callose in papillae was demonstrated using immunogold labeling. Papilla formation was not effective in preventing host cell penetration. A slender infection hypha emerged from a germ tube tip and grew through a papilla. Its tip then expanded to form a globose infection vesicle. By 6 h PI, infection hyphae emerged from infection vesicles, and invaded host cells showed signs of necrosis. By 8 h PI, infection hyphae had grown into cortical cells in spite of papilla formation in these cells. By 24 h PI, distinctive intracellular hyphae were present in necrotic cortical cells. In washed roots, most epidermal cells failed to respond to invasion. Hyphae simply grew through these cells and contacted cortical cells that exhibited aggregated cytoplasm and papillae formation. Infection structures similar to those produced in epidermal cells from roots grown on filter paper then formed in cortical cells of washed roots. The fact that T. basicola formed infection structures only in cells that responded to invasion suggests that T. basicola has a more complex relationship with its host than would be expected in a nectrotrophic pathogen. We believe that T. basicola is best described as a necrotrophic hemibiotroph.     

The occurrence in Denmark of black root rot of pea caused by Thielaviopsis basicola

Thielaviopsis basicola has been shown to be a root pathogen of pea of considerable importance in Denmark. The fungus is only found in fields with one or more previous pea crops in the field history. In the dry and warm growing season of 1989 the fungus was found in 0·6% and 3·2% of the fields in two separate areas in Denmark. In the fields where T. basicola was detected the average disease severity index in plant samples was 51·8, whereas the average disease severity index in plant samples without the fungus was 27·0. The average yield of green peas was reduced from 5167 to 4171 kg/ha when T. basicola was present. For detection and isolation of T. basicola it is important to use a technique combining microscopic examination, a semi-selective medium and a dilution plate method.     

Effect of Temperature on and Histopathology of the Interaction Between Meloidogyne incognita and Thielaviopsis basicola on Cotton

ABSTRACT Controlled environments were used to study the relationship between the root-knot nematode (Meloidogyne incognita) and Thielaviopsis basicola on cotton. Temperature treatments were continuous 20, 24, and 28 degrees C or two cyclic linear regimes with ranges of 14 to 32 or 18 to 28 degrees C over 24 h. Cotton seeds were planted in fumigated soil infested with T. basicola, M. incognita, or both. After 42 days, pathogen effects on plant growth and pathogen development were evaluated. Histology was conducted on roots collected 14, 28, and 42 days after planting in the continuous 24 degrees C treatment. Reductions in plant height-to-node ratio and total fresh weight were observed for soils infested with both pathogens compared with the control or with soils infested with either pathogen, except for M. incognita-infested soil at 28 degrees C. T. basicola reduced root galling and reproduction of the nematode at all temperatures. Vascular discoloration caused by T. basicola was greater in the presence of M. incognita compared with that by T. basicola alone. At 2 and 4 weeks, histological studies showed that plants grown in all T. basicola-infested soils contained chlamydospore chains on the root surface and in cortical cells. The fungus was not observed inside the vascular cylinder. Roots from 4-week-old plants from soils infested with T. basicola and M. incognita showed fungal sporulation in vascular tissue and localized necrosis of vascular tissue adjacent to the nematodes. At 6 weeks, plants grown in soil infested with T. basicola alone exhibited no remaining cortical tissue and no evidence of vascular colonization by the fungus. Six-week-old plants grown in T. basicola + M. incognita-infested soils exhibited extensive vascular necrosis and sporulation within vascular tissue. These studies suggest that coinfection expands the temperature ranges at which the pathogens are able to cause plant damage. Further, M. incognita greatly increases the access of T. basicola to vascular tissue.     

Interactions between the biocontrol agent Pseudomonas fluorescens CHA0 and Thielaviopsis basicola in tobacco roots observed by immunofluorescence microscopy

Pseudomonas fluorescens CHA0 protects plants from damage caused by several soilborne fungi. In this work, immunofluorescence microscopy was used to investigate the colonization of tobacco roots by CHA0 and its physical relationship with the black root rot fungus Thielaviopsis basicola . The pseudomonad colonized the rhizoplane shortly after planting of tobacco seedlings in sterile soil microcosms, in which it had been introduced as soil inoculant. CHA0 was found between and inside cells in the epidermis and the cortex, as well as in the xylem vessels, within 4–7 days after planting of seedlings. The presence of CHA0 delayed the colonization of the interior of tobacco roots by T. basicola compared with the treatment in which only the fungus had been inoculated. Likewise, the pseudomonad reduced the extent of black root rot from 82% to 28%. However, CHA0 was seldom found in contact with the mycelium of T. basicola or in its vicinity, indicating that direct colonization of the mycelium of T. basicola by CHA0 was not required for protection of tobacco against black root rot. Overall, the results suggest that the interior of the root is a key site for implementation of the strain's biocontrol activity against soilborne plant-pathogenic fungi.     

Comparison of Soil Receptivity to Thielaviopsis basicola, Aphanomyces euteiches, and Fusarium solani f. sp. pisi Causing Root Rot in Pea

ABSTRACT Soil receptivity as a quantifiable characteristic ranging from conduciveness to suppressiveness to soilborne pea pathogens Thielaviopsis basicola and Aphanomyces euteiches was determined by analysis of differences in disease response curves obtained by artificial introduction of inoculum into natural field soil samples. Several parameters, including maximum root rot severity, the area under the health index curve, scores on the first axis of a principal component analysis (PCA) on dose responses, and Weibull model fitting were used to describe the disease responses. In all cases, the Weibull model gave satisfactory fits. PCA yielded a first axis that comprised 86% of the variance found when using Weibull predicted responses for T. basicola and 74% of the variance found for A. euteiches. This PCA axis essentially represented the average increase in disease severity due to the addition of increasing doses of inoculum to the soil. The Weibull scale parameter B, which represents the amount of inoculum necessary to increase root rot severity by 63% with respect to the level caused by pathogens naturally present in the soil, is another means of quantifying the receptivity of soils to these plant pathogens. Weibull parameter B, maximum root rot severity, the areaunder the health index curve, and the scores on the first PCA axis were strongly correlated for each of the pathogens tested individually. To compare the extent and behavior of soil receptivity responses to different pathogens, Weibull parameters B and C (slope at dose B) were chosen because of their universal definition, in contrast to PCA scores. Comparison of the average levels of Weibull parameters B and C indicated significant differences between the pathogens. Yet, no significant similarity in the ranking of the soils was found for the three pathogens, demonstrating that individual soils may interact with different pathogens in totally different ways. In general, soils were suppressive to T. basicola but conducive to A. euteiches, whereas their response to Fusarium solani f. sp. pisi ranged from conducive to suppressive. Therefore, risk assessment of soils prior to planting may require different strategies for each pathogen. Bioassays with soil samples taken before the last pea crop in 1987 and 1991 revealed a significant increase in the natural inoculum potential of soils that mainly was accounted for by A. euteiches and Pythium spp. These results strongly indicate that A. euteiches must be considered one of the most threatening pathogens to pea crops in the Netherlands.     

Interaction of root-lesion nematodes, Pratylenchus thornei and P. crenatus, with the fungus Thielaviopsis basicola and a grey sterile fungus on roots of pea (Pisum sativum)

Pratylenchus thornei invaded excised pea roots in agar in greater numbers and penetrated the cortex more deeply than P. crenatus . Both species fed on the roots ectoparasitically and displaced root cells into the surrounding medium. The cytoplasm of cortical cells near cither nematode became granulated, with enlarged vacuoles and nuclei. P. thornei also caused these responses in the endodermis. Infection of the root surface with a grey sterile fungus inhibited invasion by P. crenatus and P. thornei . Infection by Thielaviopsis basicola inhibited P. thornei invasion but encouraged penetration by P. crenatus and the hyphae were found deeper in the cortex when P. crenatus was present.     

The perfect stage ofPhloeosporella padi,the causal fungus of cherry leaf spot,in the Netherlands

Samenvatting Blumeriella jaapii (Rehm) v. Arx, het perfecte stadium vanPhloeosporella padi (Lib.) v. Arx, werd in het voorjaar van 1964 gevonden op bladeren van morel (Prunus cerasus), die afkomstig waren uit een boomgaard bij St. Odiliënberg (Limburg). Dit is waarschijnlijk de eerste vermelding van dit perfecte stadium op gekweekte kersen in West-Europa.     

Microbial dysbiosis together with nutrient imbalance cause the replant problem of upper six flue-cured tobacco in Central Henan

Journal of Plant Diseases and Protection - Replant problem in agriculture is popular and has restricted the development of tobacco industry. To identify the key soil factors affecting replant...     

Female age as a factor determining the patterns of tree canopy utilisation by the European cherry fruit fly,Rhagoletis cerasi

The European cherry fruit fly, Rhagoletis cerasi is a univoltine, oligophagous pest of cultivated sweet cherries. The pest is closely associated with the canopy of its host tree, and its on-farm behaviour and mobility are determined by the crop structure and spatial arrangement of the farm. However, in spite of its relevance to integrated pest management, little is known about the within-canopy behaviour of R. cerasi, or the role of host and non-host canopy traits in local pest translocations. This paper reports the results of our exploratory studies, which reveal the modulating role of female age on various aspects of R. cerasi on-farm behaviour, such as diurnal and lifetime patterns of canopy utilisation and within-canopy activity, the propensity to undertake local explorative errands and the response to volatiles emanating from host and non-host canopies. The potential implications of our findings on the development of site-optimised IPM and/or pest-resilient agro-landscapes were also discussed.     

R/Rle de Fusarium oxysporum dans Ǐéquilibre du complexe parasitaire du pied du haricot associant Fusarium solani f. sp. phaseoli,Thielaviopsis basicola et Fusarium oxysporum1

La maladie du pied du haricot est causée par deux agents pathogénes: Fusarium solani f.sp. phaseoli et Thielaviopsis basicola. La mycoflore des racines associée à ces deux espèces est principalement constituée de souches de Fusarium oxysporum (90%), non pathogènes sur haricot. Ces trois espèces fongiques sont associées dans 50% des cas de maladie et forment un complexe parasitaire. En confrontation sur boîte de Petri, F. oxysporum a inhibé la croissance des deux agents pathogénes. En inoculation artificielle, ces interactions étaient modulées et dépendaient principalement des rapports de densité entre les populations du saprophyte et des pathogènes. En aucun cas F. oxysporum n'a favorisé la maladie. Bien que F. oxysporum colonise souvent les tissus du haricot avant les agents pathogènes, aucun phénomène de prémunition n'a pu être mis en évidence. Ainsi, la compétition entre les deux espèces pathogènes et F. oxysporum doit avoir lieu dans le sol, et plus précisément dans la rhizosphère. ?équilibre du complexe parasitaire détermine en partie le niveau de réceptivité des sols à la maladie.     

Elucidation of the microbial complex having a causal role in the development of apple replant disease in washington

ABSTRACT Systematic studies were conducted to elucidate the role of different soil microbial groups in the development of apple replant disease. Populations of targeted microorganisms were reduced by the application of semiselective biocides and soil pasteurization. Bacteria were not implicated in the disease, because application of the antibiotic chloramphenicol reduced soil populations of bacteria but failed to improve growth of apple transplants, while enhanced growth was achieved at pasteurization temperatures that did not alter attributes of the bacterial community recovered from apple roots. Populations of Pratylenchus penetrans were below the damage threshold level in eight of nine orchards surveyed, and nematicide applications failed to enhance apple growth in four of five replant soils tested, indicating that plant parasitic nematodes have a minor role or no role in disease development. Application of the fungicide difenconazole or metalaxyl enhanced growth of apple in all five replant soils, as did fludioxinil in the two soils tested. Soil pasteurization enhanced growth of apple and resulted in specific changes in the composition of the fungal community isolated from the roots of apple seedlings grown in these treated soils. Cylindrocarpon destructans, Phytophthora cactorum, Pythium spp., and Rhizoctonia solani were consistently isolated from symptomatic trees in the field and were pathogenic to apple. However, the composition of the Pythium and Rhizoctonia component and the relative contribution of any one component of this fungal complex to disease development varied among the study orchards. These findings clearly demonstrate that fungi are the dominant causal agents of apple replant disease in Washington state.     

北京怀柔地区樱桃上发现李属坏死环斑病毒

 李属坏死环斑病毒(Prunus necrotic ringspot virus,PNRSV)属雀麦花叶病毒科(Bromoviridae)等轴不稳环斑病毒属(Ilarvirus),是我国二类检疫性有害生物。PNRSV主要危害李属和蔷薇属植物。如,樱桃、桃、李、月季等。春季感染PNRSV的樱桃早期幼叶会出现深棕色坏死斑和线纹,叶片展开期坏死斑脱落造成穿孔症状。受PNRSV危害后,果树树势减弱,产量降低,甚至死树。我国学者调查陕西、辽宁和山东等省的果树病害时发现并报道了该病毒^[1~3]。     

Assessment of the inheritance of resistance and tolerance in cherry (Prunus sp.) to Blumeriella jaapii,the causal agent of cherry leaf spot

Cherry leaf spot (CLS), caused by Blumeriella jaapii, is a serious fungal disease of sour cherry (Prunus cerasus). Cultivar Montmorency, the major cultivar grown in the United States, is highly susceptible to CLS. As many as 10 fungicide sprays can be required each growing season to combat this disease; therefore, developing CLS‐resistant cultivars is a top breeding priority. Germplasm previously reported to be resistant or tolerant to CLS was acquired and incorporated into the sour cherry breeding programme at Michigan State University (MSU) and included three cherry species: sour cherry, sweet cherry (P. avium), and the wild species P. canescens. This study aimed to: (i) compare the CLS disease progression profile of the susceptible cultivar Montmorency with those of the resistant and tolerant germplasm; and (ii) gain an understanding of the inheritance of these resistance and tolerance traits by evaluating the host response of progeny individuals belonging to families derived from this germplasm. Significant differences were observed between the susceptible Montmorency and the tolerant and resistant accessions in their response to CLS and its progression during the growing season. Evaluation of the CLS host responses of progeny individuals derived from this germplasm supported a dominant two‐gene model for P. canescens‐derived resistance and a recessive gene model for sweet cherry‐derived tolerance. These insights into disease progression and trait inheritance improve the efficiency and potential success of breeding sour cherry cultivars with durable resistance to CLS.