Rozprawy doktorskie na temat „Suppressive soils”

Root-knot nematodes (RKN), Meloidogyne spp., are the most economically important genus of plant parasitic nematodes that cause considerable damage and yield losses of horticultural crops worldwide. RKN management strategies tend to reduce chemical nematicides by encouraging alternative control methods like the use of plants bearing resistance genes (R-genes) and/or by microbe-inducing plant resistance, and the antagonistic potential of soils. In the thesis, two biological control approaches of Meloidogyne spp. were evaluated: 1) the application of selected nematode antagonists, the fungus Pochonia chlamydosporia and the bacteria Bacillus firmus I-1582 (Bf I-1582), to know its ability to induce plant resistance, and 2) the level of soil suppressiveness of vegetable production sites conducted under organic or integrated standards. Regarding the ability of P. chlamydosporia and Bf I-1582 to induce plant resistance, the results of this thesis provide evidence that two out of five P. chlamydosporia isolates (M10.43.21 and M10.55.6) and Bf I-1582 are able to induce systemic resistance against M. incognita in the susceptible tomato (Solanum lycopersicum) cv. Durinta but not in the cucumber (Cucumis sativus) cv. Dasher II in split-root experiments. In addition, the cardinal temperatures for the Bf I-1582 growth and biofilm formation were determined in order to improve its use in field conditions. Moreover, Bf I-1582 was transformed with GFP to study its effect on nematode eggs and on tomato and cucumber root colonization. In tomato, the number of egg masses and the number of eggs per plant were reduced by M10.43.21 and M10.55.6 P. chlamydosporia isolates and by Bf I-1582. P. chlamydosporia isolates colonized both tomato and cucumber roots, being the M10.43.21 and the M10.55.6 isolates the best root colonizers in tomato and cucumber, respectively. In the case of Bf I-1582, the bacteria colonized endophytically roots of both plants, but highest values were recorded in tomato. The dynamic regulation of genes related to jasmonic acid (JA) and salicylic acid (SA) was determined by RT-qPCR at three different times after nematode inoculation (dani). Bf I-1582 primed tomato plants by both SA and JA at all the times in tomato, but only SA at 7 dani in cucumber. Regarding P. chlamydosporia, isolate M10.43.21, induced the expression of the SA pathway in tomato at 0, 7 and 42 dani. The JA pathway was also up regulated at 7 dani. These results show the similar model of dynamic regulation of these plant hormone pathways related to plant defense mechanisms against the nematode. Also, Bf I-1582 grew and formed biofilm between 15 and 45 ºC, being 35 ºC the optimal temperature. Bf I-1582GFP was adhered to the egg shell and inside the eggs. Also, Bf I-1582GFP colonized root hairs and epidermal cells and some bacteria were found inside the tomato root. In cucumber, few bacteria were observed on epidermal cells and the bacteria were no found inside the root. In relation to the level of soil suppressiveness of vegetable production it was carried out a study in four organic and two integrated vegetables production standards sites located in north-eastern Spain. The fluctuation both of Meloidogyne population density and fungal egg parasitism were determined during the rotation sequences in two years (2015-2016). Five out of six of these sites were suppressive soils to Meloidogyne spp. The percentage of fungal egg parasitism ranged from 11.2 to 55 % and P. chlamydosporia was the only fungal species isolated from the eggs. In parallel, two tomato pots experiments were carried out using sterilized and non-sterilized soils from each site and inoculated with second-stage juveniles (J2) to achieve a rate of 1 J2 cm-3 of soil. In both, in five of them the number of nematode eggs per plant was reduced in all nonsterilized soils compared to the sterilizes ones. Also, P. chlamydosporia was the only fungal species isolated from parasitized nematode eggs.
Meloidogyne spp. (RKN) es el género de nematodos fitopatógenos que causan las mayores pérdidas económicas y que más afectan al rendimiento de cultivos hortícolas a nivel mundial. Las estrategias de manejo de RKN tienden a sustituir la utilización de nematicidas químicos por medidas de control alternativas como son el uso de plantas con genes de resistencia (genes R) y/o mediante la utilización de microorganismos inductores de resistencia, y el potencial antagónico del suelo. En esta tesis, se han evaluado dos enfoques de control biológico: 1) la aplicación de microorganismos antagónicos, el hongo Pochonia chlamydosporia (Pc) y la bacteria Bacillus firmus I-1582 (Bf I-1582) para evaluar su capacidad de inducir mecanismos de resistencia, y 2) el nivel de supresividad del suelo de diferentes lugares bajo estándares de producción orgánica e integrada. Con respecto a la capacidad de Pc y Bf I-1582 para inducir resistencia, los resultados de esta tesis muestran que dos (M10.43.21 y M10.55.6) de los cinco aislados de Pc utilizados y la bacteria Bf I-1582 inducen resistencia sistémica frente a M. incognita en el tomate susceptible (Solanum lycopersicum) cv. Durinta pero no en el pepino (Cucumis sativus) cv. Dasher II usando el modelo split-root. En el caso de Bf I-1582, se determinaron las temperaturas cardinales para el crecimiento y la formación de biofilms de Bf I-1582 con el fin de mejorar su utilización en condiciones de campo y se transformó con la GFP para estudiar su efecto sobre los huevos de RKN y sobre la colonización radicular. Los aislados M10.43.21 y M10.55.6 de Pc y Bf I-1582 redujeron el número de masas de huevos y el número de huevos por planta en tomate. Todos los aislados de Pc colonizaron raíces de tomate y pepino, siendo los aislados M10.43.21 y M10.55.6 los mejores colonizadores en tomate y pepino, respectivamente. En el caso de Bf I-1582, la bacteria colonizó endofíticamente las raíces de ambas plantas, pero los valores más altos se registraron en tomate. La expresión de los genes relacionados con el ácido jasmónico (JA) y el ácido salicílico (SA) se determinó a tres tiempos tras la inoculación de nematodos (dani). En plantas de tomate inoculadas con Bf I-1582 la expresión de los genes relacionados con SA y JA aumentaron en los tres puntos, pero en pepino solo se observó un incremento de expresión en el gen relacionado con la ruta de SA a los 7 dani. Con respecto a Pc, el aislado M10.43.21, indujo la expresión de la vía SA en tomate a los 0, 7 y 42 dani. La vía JA también aumentó su expresión a los 7 dani. Además, Bf I-1582 creció y formó biofilms entre 15 y 45 ºC, siendo 35 ºC la temperatura óptima. Bf I-1582GFP se adhirió a la cubierta y al interior de los huevo de M. incognita. Además, Bf I-1582GFP en tomate colonizó los pelos radiculares, así como las células epidérmicas y se encontraron algunas bacterias en el interior radicular. En el pepino, se observó un menor número de bacterias en las células epidérmicas y no se encontraron bacterias en el interior radicular. En relación con el nivel de supresión del suelo, se realizó un estudio en cuatro lugares de producción hortícola orgánica y dos de producción integrada en el noreste de España. Durante la secuencias de rotación en 2015-2016 se determinó la fluctuación tanto de la densidad de población de Meloidogyne en suelo como del parasitismo de huevos de nematodos. Cinco de estos sitios resultaron ser supresivos a Meloidogyne spp. Paralelamente, se llevaron a cabo dos experimentos en macetas con suelo esterilizado y no esterilizado de cada sitio donde las plantas de tomate se inocularon con juveniles (J2) para lograr una tasa de 1 J2 cm-3 de suelo. En cinco de ellos, el número de huevos de nematodos por planta se redujo en todos los suelos no esterilizados en comparación con los esterilizados. Respecto al parasitismo, Pc fue la única especie aislada de los huevos de Meloidogyne spp. p
Els nematodes formadors de gal·les, Meloidogyne spp., és el gènere més important nematodes fitoparàsits que causen danys considerables i generen pèrdues econòmiques en cultius hortícoles arreu del món. Les estratègies actuals de gestió de Meloidogyne solen reduir l’ús dels nematicides químics fomentant mètodes de control alternatius com l’ús de plantes amb gens de resistència (gens R) i/o l’ús de la resistència vegetal induïda per microorganismes, i el potencial antagonista dels sòls. En la present tesis, dos aproximacions al control biològic de Meloidogyne spp. van ser estudiades: 1) l’aplicació d’antagonistes dels nematodes: el fong Pochonia chlamydosporia i el bacteri Bacillus firmus aïllat I-1582 i es a avaluar la seva capacitat per induir resistència vegetal, i 2) el nivell de supressivitat de sòls de producció vegetal orgànica o integrada. Respecte a la capacitat de P. chlamydosporia i B. firmus I-1582 (Bf I-1582) a induir resistència vegetal, els resultats d’aquesta tesis van donar evidències que dos de cinc aïllats de P. chlamydosporia (M10.43.21 i M10.55.6) i Bf I-1582 induien resistència sistèmica enfront M. incognita en tomàquet susceptible (Solanum lycopersicum) cv. Durinta però no en cogombre (Cucumis sativus) cv. Dasher II en experiments “split-root”. A més, les temperatures cardinals de creixement i de formació de biofilm de Bf I-1582 van ser determinades per tal de millorar el seu ús en condicions de camp. A més, el bacteri va ser transformat amb GFP per estudiar el seu efecte sobre els ous del nematode i la seva colonització sobre les arrels de tomàquet i cogombre per microscopia de rastreig làser confocal. En tomàquet, tant el nombre de masses d'ou com el nombre d'ous per planta es va veure reduït quan s’aplicaven tant els aïllats fúngics com el bacteri. Els aïllats de P. chlamydosporia colonitzaven les arrels de tomàquet i cogombre, però diferien en el nivell de colonització. L’aïllat M10.43.21 va ser el millor colonitzador de les arrels de tomàquet mentre que l’aïllat M10.55.6 ho va ser per cogombre. En el cas de Bf I-1582, el bacteri va ser capaç de colonitzar endofíticament les arrels de les dues plantes, però es va trobar un 61% més de densitat d’ADN de bacteri en arrels de tomàquet. La regulació dinàmica dels gens relacionats amb l’àcid jasmònic (JA) i l’àcid salicílic (SA) a tres temps diferents van ser avaluats: 7 dies després de la inoculació de l’antagonista i just després de la inoculació del nematode (0 dani), 7 dies desprès de la inoculació del nematode (7 dani) i 40 dies desprès de la inoculació del nematode (40 dani). Les dues vies SA (gen PR-1) i JA (gen Lox D) van ser sobre-expressades plantes de tomàquet a 0 dani, reduint el nombre de masses d’ou al final de l’experiment “split-root” quan es va inocular amb Bf I-1582. No obstant, no hi va haver diferencies en l’expressió dels gens relacionats SA (PR 1) i JA (Lox D) en cogombre inoculat amb el bacteri com tampoc en el nombre de masses d’ou produïdes en les arrels de cogombre. A 7 dani, el gen relacionat amb el JA (Lox D) estava sobre-expressat en tomàquet i podria afectar el desenvolupament del nematode i la seva reproducció. En cogombre, la via del SA (Pal I) estava sobre-expressada tant en les plantes inoculades amb M. incognita com en les co-inoculades amb el bacteri i el nematode. A 40 dani, quan va començar l’eclosió dels ous i es van produir noves infeccions a l’arrel, les plantes de tomàquet co-inoculades amb els nematode 2 i Bf I-1582 tenia reprimit el gen relacionat amb el JA (Lox D), mentre que el gen relacionat amb la via del SA (PR 1) estava sobre-expressat en plantes co-inoculades i també amb només Bf I-1582, però va ser reprimit en plantes inoculades només amb el nematode. En cogombre, les dues vies, JA i SA, van ser reprimides en plantes inoculades amb M. incognita però només la JA en plantes co-inoculades. Respecte l’aïllat de P. chlamydosporia M10.43.21, va induir l’expressió de la via del SA en arrels de tomàquet a 0, 7 i 42 dani. La via del JA va ser també sobre-expressada a 7 dani. Per tant, alguns aïllats de P. chlamydosporia i l’aïllat Bf I-1582 poden induir resistència sistèmica envers al nematode, encara que depèn de l’espècie vegetal. Aquests resultats han demostrat el model similar de regulació dinàmica d’aquestes vies d’hormones vegetals relacionades amb mecanismes de defensa de les plantes contra el nematode. El bacteri Bf I-1582 va créixer en el rang de temperatures des de 15 ºC a 45 ºC, sent 35 ºC la temperatura òptima de creixement tant en medi sòlid com en líquid, però no a 10 ºC i 50 ºC. Igualment, es va observar la formació de biofilm entre 15 ºC i 45 ºC però tampoc a 10 ºC ni a 50 ºC, sent més gruixut i uniforme a 35 ºC. La degradació de la closca del nematode i la colonització dels ous per Bf I-1582 GFP va mostrar que a 3 dies desprès de la seva inoculació (dai) el bacteri estava envoltant i degradant l'ou del nematode; a 5 dai, colònies de bacteri es van adherir a la closca de l’ou i es van trobar alguns bacteris dins de l’ou; a 10 dai, el bacteri era completament adherit a la closca de l’ou i dins de l’ou. A més, Bf I-1582GFP va colonitzar les pèls radiculars i cèl·lules epidèrmiques a 5 dai; es van observar colònies de bacteris en pèls radiculars de tomàquet i alguns bacteris dins de l’arrel a 10 dai. En cogombre, es van observar pocs bacteris a les cèl·lules epidèrmiques a 5 dai i no es va trobar el bacteri dins de l’arrel a 10 dai. En relació al nivell de supressivitat del sòl, es va realitzar un estudi a sis parcel·les de producció d’hortalisses localitzades al nord-est d’Espanya. Quatre realitzaven producció orgànica (M10. 16, M10.41, M10.55, i M10.56) i dues (M10.43 i M10.45) producció integrada. La fluctuació de la densitat de població de Meloidogyne i el parasitisme d’ous per part de fongs van ser determinats durant la seqüència de rotació de cultius durant dos anys (2015-2016). Cinc dels sols estudiats eren sòls supressius a Meloidogyne spp. El percentatge de parasitisme d’ous va variar de 11.2 a 55 % i P. chlamydosporia va ser l'única espècie fúngica aïllada dels ous. En paral·lel, dos experiments es van dur a terme utilitzant sòl de cada parcel·la. Una part de cada sòl es va esterilitzar i es va barrejar amb sorra estèril, i una altre part no es va esterilitzar i es va barrejar també amb sorra estèril amb una relació 1:1 i es va col·locar en testos de 3-l. El cultivar susceptible de tomàquet Durinta es va trasplantar en cada test i es va inocular amb juvenils de segon estadi (J2) amb un nivell de 1 J2 cm-3 de sòl. En els dos experiments en testos, els nombre d’ous per planta es va reduir (P<0.05) en tots els sòls no esterilitzats comparats amb els estèrils, excepte en el M10.45. També, P. chlamydosporia va la única espècie fúngica aïllada d’ous parasitats de nematodes. P. chlamydosporia és el fong més freqüent i més prevalent amb una alta plasticitat capaç d’adaptar-se a les pràctiques agronòmiques en un sistema de producció vegetal molt pertorbat.

Les bactéries du sol produisant des antifongiques comme le 2,4-diacétylphloroglucinol(DAPG) protègent les racines des plantes vis-à-vis des champignons phytopathogènes. Néanmoins, les conditions de fonctionnement de ces populations bactériennes dans le sol restent très mal connues. Dans certains sols, dits résistants aux maladies, ces bactéries phytoprotectrices sont présentes à des effectifs importants et leur activité est suffisante pour protéger la plante malgré la présence du pathogène. L'objectif de cette thèse a été de comprendre la relation entre la résistance des sols à la maladie de la pourriture noire des racines de tabac, et la fonction de synthèse du DAPG chez les bactéries du genre Pseudomonas. Dans la situation de référence de Morens (Suisse), les sols résistants diffèrent des sols sensibles par la présence de vermiculite, argile capable de relarguer du fer. On sait que la présence de vermiculite améliore la phytoprotection assurée par les Pseudomonas producteurs de DAPG, mais les mécanismes moléculaires sous-jacents restent inconnus. Dans un premier temps, la quantification de ces bactéries par une nouvelle méthode de PCR quantitative développée ici, a confirmé que leurs effectifs sont élevés dans les sols résistants, mais aussi dans les sols sensibles, suggérant que la résistance puise plutôt dépendre d'une plus forte expression de la fonction de synthèse du DAPG. Dans un second temps, l'étude de l'expression des gènes de synthèse du DAPG en système de sol artificiel, à l'aide de la souche rapportrice P. protegens phlA-gfp, a montré que la présence de vermiculite dans le sol se traduit par une plus forte biodisponibilité du fer pour les Pseudomonas, induisant une plus forte expression des gènes de synthèse du DAPG et la protection du tabac. En conclusion, la résistance des sols de Morens à la maladie de la pourriture noire des racines est conditionnée par plusieurs facteurs abiotiques et biotiques, dont la biodisponibilité du fer qui régule l'expression des gènes de synthèse du DAPG chez Pseudomonas
Soil bacteria producing antimicrobial compounds like 2,4-diacetylphloroglucinol (DAPG) protect plants from soil-borne phytopathogens. Nevertheless, the functioning of these bacterial populations in the soil is largely unknown. In certain soils, termed disease- suppressive soils, these bacteria are present at high numbers and their activity is sufficient to assure effective plant protection in the presence of the pathogen. The aim of this thesis was to understand the relation between soil suppressiveness towards black root rot of tobacco, and the 2,4-diacetylphloroglucinol synthesis ability of certain Pseudomonas. In Morens region (Switzerland), suppressive soils differ from conducive soil by the presence of vermiculite, an iron-releasing clay. It is known that DAPG-producing Pseudomonas provide better plant protection in the presence of vermiculite, but the molecular basis of this interaction is still unknown. First, the quantification of these bacteria, through a new real-time PCR method developed here, confirmed that high numbers of DAPG-producing Pseudomonas occur in suppressive soils, as well as in conducive ones, raising the possibility that suppressiveness depends rather on a higher expression of DAPG synthetic genes. Second, expression studies of DAPG synthetic genes using a P. protegens ph/A- gfp reporter strain and artificial soil systems, confirmed that the presence of vermiculite in the soil can translate into higher iron bioavailability for Pseudomonas, triggering higher expression of DAPG synthetic genes and effective plant protection. In conclusion, black root rot suppressiveness of Morens soils is determined by several abiotic and biotic factors, among which iron bioavailability regulating the expression of DAPG synthetic genes in plant-protecting Pseudomonas

Take-all, caused by the soilborne fungus, Gaeumannomyces graminis var. tritici (Ggt), is an important root disease of wheat that can be reduced by take-all decline (TAD) in successive wheat crops, due to general and/or specific suppression. A study of 112 New Zealand wheat soils in 2003 had shown that Ggt DNA concentrations (analysed using real-time PCR) increased with successive years of wheat crops (1-3 y) and generally reflected take-all severity in subsequent crops. However, some wheat soils with high Ggt DNA concentrations had low take-all, suggesting presence of TAD. This study investigated 26 such soils for presence of TAD and possible suppressive mechanisms, and characterised the microorganisms from wheat roots and rhizosphere using polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE). A preliminary pot trial of 29 soils (including three from ryegrass fields) amended with 12.5% w/w Ggt inoculum, screened their suppressiveness against take-all in a growth chamber. Results indicated that the inoculum level was too high to detect the differences between soils and that the environmental conditions used were unsuitable. Comparison between the Ggt DNA concentrations of the same soils collected in 2003 and in 2004 (collected for the pot trial), showed that most soils cropped with 2, 3 and 4 y of successive wheat had reduced Ggt DNA concentrations (by 195-2911 pg g-1 soil), and their disease incidences revealed 11 of the 29 test soils with potential take-all suppressiveness. Further pot trials improved the protocols, such that they were able to differentiate the magnitudes of suppressiveness among the soils. The first of the subsequent trials, using 4% w/w Ggt inoculum level, controlled conditions at 16°C, 80% RH with alternate 12 h light/dark conditions, and watering the plants twice weekly to field capacity (FC), screened 13 soils for their suppressiveness against take-all. The 13 soils consisted of 11 from the preliminary trial, one wheat soil that had been cropped with 9 y of wheat (considered likely to be suppressive), and a conducive ryegrass soil. The results revealed that 10 of these soils were suppressive to take-all. However, in only four of them were the effects related to high levels of microbial/biological involvement in the suppression, which were assessed in an experiment that first sterilised the soils. In a repeat trial using five of the soils H1, H3, M2, P7 (previously cropped with 3, 3, 4 and 9 y successive wheat, respectively) and H15 (previously cropped with 5 y of ryegrass), three of them (H1, H3 and M2) had reduced Ggt DNA concentrations (>1000 pg g-1 soil reductions), and were confirmed to be suppressive to take-all. A pot trial, in which 1% of each soil was transferred into a γ-irradiated base soil amended with 0.1% Ggt inoculum, indicated that soils H1 and H3 (3 y wheat) were specific in their suppressiveness, and M2 (4 y wheat) was general in its suppressiveness. The microbial communities within the rhizosphere and roots of plants grown in the soils, which demonstrated conduciveness, specific or general suppressiveness to take-all, were characterised using PCR-DGGE, and identities of the distinguishing microorganisms (which differentiated the soils) identified by sequence analysis. Results showed similar clusters of microorganisms associated with conducive and suppressive soils, both for specific and general suppression. Further excision, re-amplification, cloning and sequencing of the distinguishing bands showed that some actinomycetes (Streptomyces bingchengensis, Terrabacter sp. and Nocardioides sp.), ascomycetes (Fusarium lateritium and Microdochium bolleyi) and an unidentified fungus, were associated with the suppressive soils (specific and general). Others, such as the proteobacteria (Pseudomonas putida and P. fluorescens), an actinomycete (Nocardioides oleivorans), ascomycete (Gibberella zeae), and basidiomycete (Penicillium allii), were unique in the specific suppressiveness. This indicated commonality of some microorganisms in the take-all suppressive soils, with a selected distinguishing group responsible for specific suppressiveness. General suppressiveness was considered to be due to no specific microorganisms, as seen in soil M2. An attempt to induce TAD by growing successive wheat crops in pots of Ggt-infested soils was unsuccessful with no TAD effects shown, possibly due to variable Ggt DNA concentrations in the soils and addition of nutrients during the experiment. Increasing numbers of Pseudomonas fluorescens CFU in the rhizosphere of plants, during successive wheat crops was independent of the Ggt DNA concentrations and disease incidence, suggesting that increases in P. fluorescens numbers were associated with wheat monoculture. This study has demonstrated that TAD in New Zealand was due to both specific and general suppressiveness, and has identified the distinguishing microorganisms associated with the suppression. Since most of these distinguishing microorganisms are known to show antagonistic activities against Ggt or other soilborne pathogens, they are likely to act as antagonists of Ggt in the field. Future work should focus on validating their effects either individually, or interactively, on Ggt in plate and pot assays and under field conditions.

Leguminous cover crops are promising as Meloidogyne spp. suppressants but where populations of mixed species occur, their potential remains uncertain. When inoculated with a Meloidogyne arenaria-incognita-javanica complex in a glasshouse experiment, Mucuna pruriens and Crotalaria spectabilis, were poor or non-hosts, did not gall and plant height and shoot biomass were not affected. However, Dolichos lablab was highly susceptible. The root system of D. lablab stimulated population increase but the leaf eluant proved lethal. Thus, different parts of a plant contain different active ingredients or concentrations of compounds. In ancillary experiments, M. pruriens, C. retusa and C spectabilis inhibited hatching of eggs, caused juvenile mortality, decreased population density and roots were either not invaded by juveniles or invasion was minimal.

Use of known antagonists and antagonistic, endophytic bacteria was investigated to screen a successful antagonist for the fungal strains R. solani AG 2-1, R. solani AG 4 and R. solani AGSL01.   Reputed antagonists used in the study; Bacillus subtilis MBI 205,  B. subtilis MBI 600, Pseudomonas fluorescens B5 and P. corrugate R. 117 were capable of suppressing the fungus in dual cultures. Manipulation of soil factors to reduce pre-plant density of R. solani sclerotia involved a laboratory experiment followed by two field experiments.  In the laboratory study, the effect of constant soil temperatures was investigated by incubating sclerotia at 30, 35, 40, 45 and 50°C.  Sclerotia were counted into lots of 100, placed in polyester mesh bags (85 μm pore size, 10 x 10 cm dimension) at depths of 5 and 10 cm in rice field soils contained in plastic containers (20x20x18 cm).  Total loss of viability was observed on day 1, day 8 and day 28 at 45°C, 40°C and 35°C, respectively.  Loss was even detected within 6.00 h at 50oC. Field experiments of soil solarization (carried out at The Regional Agricultural Research Institute (RARI), Bombuwela, Sri Lanka) were conducted during the fallow periods between the two main cropping seasons in 2003.  During the trials, the effect of polythene mulching, straw incorporation and their combined effect on the viability of sclerotia were investigated.  Sclerotia (lots of 100) were buried at depths of 5 and 10 cm and the soil temperature was recorded at 8.00, 11.00, 14.00 and 17.00h daily at both depths.  During the field trials, at both depths, the effect of treatment over time was noted on percentage recovery and viability of sclerotia (p<0.001).  The results showed a drop in mean percentage recovery of less than 50% during the first week of both trials.  Germination was markedly reduced to less than 10% by the first week in all the treatments.  Depth of burial and straw incorporation had no effect.  In solarized plots, a significant increase in soil temperature at both soil depths was observed between 14.00 and 17.00h.  Average temperatures of 40°C and 34°C were observed for solarized and non-solarized plots, respectively.  The study therefore has identified a practical, low cost and environmentally friendly method of control, and the use of polythene five weeks prior to rice seed sowing is recommended to minimise sheath blight and other diseases caused by similar soil-borne fungal pathogens.

The objective of this study was to evaluate the effect of various organic amendment on weed suppression, soil content and yield components of sweet com (Zea mays L.) grown under organic or sustainable agriculture regimes. Field experiments were conducted during 2004, 2005 and 2006 to study the effect poultry manure, cow manure and barley mulch, used at three rates (half, recommended. double). Sweet com ({Zea mays L.) was planted. Two experiments were conducted each year. Experiment I was in combination with nitrogen fertilization (nitrogen was added in each treatment according to the nitrogen content of each amendment; the amount added was equal to that needed to bring all treatments to the rate of 240 kg N/ha). Experiment II was purely organic.

This thesis includes two studies. The first study examined changes in soil characteristics as a result of prolonged conifer dominance in successional aspen-conifer forests. Changing disturbance patterns in aspen-conifer forests appear to be altering successional dynamics that favors conifer expansion in aspen forests. The primary objective of this paper was to identify how increasing conifer dominance that develops in later successional stages alters forest soil characteristics. Soil measurements were collected along a stand composition gradient: aspen dominated, aspen-conifer mix, conifer dominated and open meadow, which includes the range of conditions that exists through the stages of secondary succession in aspen-conifer forests. Soil chemistry, moisture content, respiration, and temperature were measured. There was a consistent trend in which aspen stands demonstrated higher mean soil nutrient concentrations than adjacent meadows, mixed or conifer stands. Soil moisture was significantly higher in aspen stands and meadows in early summer. Soil respiration was significantly higher in aspen stands than conifer stands or meadows throughout the summer. The results indicate that soil resource availability and respiration peak within aspen dominated stands that are present during early succession and then decrease as conifer abundance increases along our stand composition gradient, representative of stand characteristics present in mid to late successional stages. Emerging evidence from other studies suggest that these observed changes in soil characteristics with increasing conifer dominance may have negative feedbacks on aspen growth and vigor. The second study examined the facilitation effect between aspen and subalpine fir establishment. In subalpine forests, conifer species are often found intermixed with broadleaf species. However, few if any studies have explored the existence and influence of facilitation between broadleaf tree species and conifers. We have observed the general establishment of subalpine fir seedlings at the base of aspen trees in a subalpine forest, indicating that a facilitative relationship may exist. To explore the potential facilitative relationship during secondary succession in subalpine forests, subalpine fir seeds were planted across a stand composition gradient (aspen dominated → mixed → conifer dominated stands) at six study sites in the Fishlake National Forest. Seeds were placed during the fall of 2010, at distances of 0 cm and 25 cm in each cardinal direction at the base of mature aspen and subalpine fir trees in each of the three stand types. Seeds were also planted within stand interspaces and in adjacent meadows. Seedling emergence was recorded at the beginning of the summer of 2011 and seedling mortality was recorded in October 2011. Soil moisture content was measured at the position that seeds were placed during the summers of 2009 and 2011. Aspen dominated stands had subalpine fir germination that was on average 11 times greater than mixed or conifer dominated stands. Germination was 2.3 fold greater at the base of aspen trees than fir trees and two fold greater at the base of aspen trees than interspaces. Seedling mortality was lower in aspen stands but was not significantly influenced by position relative to mature trees. Soil moisture was highest in aspen dominated stands, with better soil moisture conditions at the base of aspen trees and in interspaces compared to the base of fir trees. Few if any studies regarding conifer facilitation have provided evidence for facilitation at the germination life stage, rather they focus on seedling survival. However, our study illustrates a strong facilitative interaction in which both aspen dominated stands and aspen trees increase the likelihood of subalpine fir seedling establishment by drastically increasing rates of subalpine fir germination. Because of aspen's primary role in initiating secondary succession through post-disturbance sucker regeneration, and the subsequent dependence of conifers on aspen for establishment, aspen mortality via competition with conifers under longer fire cycles, droughts, or intensive ungulate browsing may result in a loss of aspen-conifer forest communities in some locales.

Compost can suppress soilborne plant pathogens that cause significant damage on globally important food crops. However, reports of plant pathogen suppression are inconsistent likely because there are no established standards for feedstock material, application rate, and maturity age upon application. Excellent results can be achieved in greenhouse trials, but field applications are much less reliable. Disease suppression occurs through the activity of biocontrol organisms (direct antagonism), and general microbial competition. Biocontrol species are hypothesized to colonize the pile during the curing phase, but single species may not be as important as microbial consortia. Substrate composition during maturation may give rise to a suppressive microbial community. More research is needed to understand the relationships between feedstock, maturity, and production process on compost microbial ecology. The thesis had two main objectives: 1) identify biological indicators in compost that could (a) characterize maturity, process, and feedstock, and (b) predict disease suppression against R. solani, and 2) identify bacterial and fungal community composition and/or structure that is associated with suppression of soilborne disease. Rhizoctonia solani is a facultative saprophytic fungus and soilborne plant pathogen that attacks many globally important food crops and turfgrass. Prior research suggests that managing carbon quality and compost maturity will alter relative competition between biological control microbes and the R. solani pathogen. The pathogen is responsible for economic losses to organic vegetable production in Vermont and there are no available methods to manage the disease that meet organic certification. R. solani on radish was chosen as a model system given its global importance, competitiveness affected by carbon quality, and lack of disease management options for organic production. Compost samples were most abundant in the bacterial phyla Proteobacteria and Bacteroidetes, and known biocontrol species were not detected in abundance. Compost samples did not differ significantly in fungal community composition, suggesting a dominance effect from the native soil fungal community. Overall, anaerobic digestate and vermicompost were most suppressive against R. solani. Thermophilic composts were not very suppressive overall, though a specially made hardwood bark compost was comparable to the suppressiveness of vermicompost application. Ecoenzyme analysis was able to integrate information on environmental substrate composition, microbial nutrient acquisition, and microbial community metabolism, offering the best view of current ecological conditions in compost. Ecoenzyme analysis showed that the most suppressive composts, anaerobic digestate and vermicompost, were most nutrient limited. All compost samples were severely nitrogen (N) limited, and anaerobic digestate and vermicompost were severely limited in both N and phosphorus (P). The additional P limitation may support non-pathogenic species to outcompete R. solani. The key to disease suppression may lie in matching up the ecology of the plant pathogen with the ecology of biocontrol, which may be engineered in compost.

Soil spectroscopy is a promising technique for soil analysis, and has been successfully utilized in the laboratory. When it comes to space, the presence of vegetation significantly affects the performance of imaging spectroscopy or hyperspectral imaging on the retrieval of topsoil properties. The Forced Invariance Approach has been proven able to effectively suppress the vegetation contribution to the mixed image pixel. It takes advantage of scene statistics and requires no specific a priori knowledge of the referenced spectra. However, the approach is still mainly limited to lithological mapping. In this case study, the objective was to test the performance of the Forced Invariance Approach to improve the estimation accuracy of soil salinity for an agricultural area located in the semi-arid region of Northwest China using airborne hyperspectral data. The ground truth data was obtained from an eco-hydrological wireless sensing network. The relationship between Normalized Difference Vegetation Index (NDVI) and soil salinity is discussed. The results demonstrate that the Forced Invariance Approach is able to improve the retrieval accuracy of soil salinity at a depth of 10 cm, as indicated by a higher value for the coefficient of determination (R2). Consequently, the vegetation suppression method has the potential to improve quantitative estimation of soil properties with multivariate statistical methods.

The influence of soil water repellency (WR) on vegetation recovery after a fire is poorly understood. This dissertation presents strategies to broaden opportunities for enhanced post-fire rangeland restoration and monitoring of burned piñon and juniper (P-J) woodlands by: 1) mapping the extent and severity of critical and subcritical WR, 2) determining the influence of WR on soil ecohydrologic properties and revegetation success, and 3) evaluating the suitability of a wetting agent composed of alkylpolyglycoside-ethylene oxide/propylene oxide block copolymers as a post-fire restoration tool for ameliorating the effects of soil WR and increasing seedling establishment. Results indicate that: • Post-fire patterns of soil WR were highly correlated to pre-fire P-J woodland canopy structure. Critical soil WR levels occurred under burned tree canopies while sub-critical WR extended out to approximately two times the canopy radius. At sites where critical soil WR was present, infiltration rate, soil moisture, and vegetation cover were significantly less than at non-hydrophobic sites. These parameters were also reduced in soils with subcritical WR relative to non-hydrophobic soils (albeit to a lesser extent). Aerial photography coupled with feature extraction software and geographic information systems (GIS) proved to be an effective tool for mapping P-J cover and density, and for scaling-up field surveys of soil WR to the fire boundary scale. • Soil WR impairs seed germination and seedling establishment by decreasing soil moisture availability by reducing infiltration, decreasing soil moisture storage capacity, and disconnecting soil surface layers from underlying moisture reserves. Consequently, soil WR appears to be acting as a temporal ecological threshold by impairing establishment of desired species within the first few years after a fire. • Wetting agents can significantly improve ecohydrologic properties required for plant growth by overcoming soil WR; thus, increasing the amount and duration of available water for seed germination and seedling establishment. Success of this technology appears to be the result of the wetting agent increasing soil moisture amount and availability by 1) improving soil infiltration and water holding capacity; and 2) allowing seedling roots to connect to underling soil moisture reserves.

This study focuses on the soil- and water-borne plant pathogen Phytophthora cinnamomi Rands and the phenomenon of P. cinnamomi suppressive soil. In particular, this thesis reports on the outcome of field surveys and glasshouse assays undertaken to locate P. cinnamomi suppressive soils and to confirm the involvement of biological processes in suppression. The potential role of cellulase and laminarinase in suppression was investigated and a molecular technique known as length heterogeneity PCR (LH-PCR) was used to analyse the structure and diversity of bacterial and fungal communities in avocado orchard soils that were suppressive and conducive to P. cinnamomi. Four avocado orchards with P. cinnamomi suppressive soils were identified and soils were ã-irradiated to destroy their suppressive capacity, thus confirming biological suppression. Suppression was also partially transferred to ã-irradiated and conducive soils by mixing with 10% suppressive avocado soils. Cellulase and laminarinase activities measured in avocado orchard soils inoculated with P. cinnamomi were not associated with disease severity in lupin seedlings during glasshouse assays involving the same soil samples. Minor shifts in bacterial and fungal community structure were observed in response to mixing conducive and irradiated soils with suppressive soils. This was associated with decreased disease severity in avocado seedlings in these treatments. The shift in bacterial community structure was partially determined by the appearance and increased abundance of several bacterial 16S rDNA sequences, which were unique to the suppressive soils, in the mixed soil treatments. It is suggested that the bacteria and fungi from which these sequences originated may be involved in suppression and further work should be undertaken to determine their identity and confirm their potential role in the development and maintenance of P. cinnamomi suppressive soils.
Doctor of Philosophy (PhD)

This study focuses on the soil- and water-borne plant pathogen Phytophthora cinnamomi Rands and the phenomenon of P. cinnamomi suppressive soil. In particular, this thesis reports on the outcome of field surveys and glasshouse assays undertaken to locate P. cinnamomi suppressive soils and to confirm the involvement of biological processes in suppression. The potential role of cellulase and laminarinase in suppression was investigated and a molecular technique known as length heterogeneity PCR (LH-PCR) was used to analyse the structure and diversity of bacterial and fungal communities in avocado orchard soils that were suppressive and conducive to P. cinnamomi. Four avocado orchards with P. cinnamomi suppressive soils were identified and soils were ã-irradiated to destroy their suppressive capacity, thus confirming biological suppression. Suppression was also partially transferred to ã-irradiated and conducive soils by mixing with 10% suppressive avocado soils. Cellulase and laminarinase activities measured in avocado orchard soils inoculated with P. cinnamomi were not associated with disease severity in lupin seedlings during glasshouse assays involving the same soil samples. Minor shifts in bacterial and fungal community structure were observed in response to mixing conducive and irradiated soils with suppressive soils. This was associated with decreased disease severity in avocado seedlings in these treatments. The shift in bacterial community structure was partially determined by the appearance and increased abundance of several bacterial 16S rDNA sequences, which were unique to the suppressive soils, in the mixed soil treatments. It is suggested that the bacteria and fungi from which these sequences originated may be involved in suppression and further work should be undertaken to determine their identity and confirm their potential role in the development and maintenance of P. cinnamomi suppressive soils.

Rhizoctonia solani AG8 is a significant soil-borne pathogen of cereal roots in semi-arid Mediterranean regions of Australia and the Pacific North West region in the United States of America, causing severe productivity and economic losses to farmers. During the past twenty years the conversion of many farming systems to conservation tillage has meant that the mycelial network of the pathogen is no longer seasonally disturbed by cultivation which has subsequently increased the potential for greater incidence of Rhizoctonia root rot. There has been some success in reducing incidence by using modifications to direct drill seeding equipment enabling some disturbance to Rhizoctonia at sowing. However, a long term sustainable solution with both economic and environmental benefit, as concluded from a review of the literature (Chapter 1) is to harness the potential for biological control of the disease via natural or induced suppression in soils. Biological suppression to specific disease organisms in soil has been reported worldwide from a range of environments. Further, the development of biological soil-borne suppression to Rhizoctonia root rot has been described for one specific agricultural location (Avon) in South Australia following a decade of stubble retention together with higher than average nutrient inputs (Chapter 1). The studies in this thesis investigate soilborne suppression to Rhizoctonia in agricultural soils from a semi-arid region of South Australia called Eyre Peninsula (EP) that produces 40% of the State’s grain. The context is that historically in Eyre Peninsula farming systems crop residue inputs to soil are inherently low, as are fertiliser N and P inputs. However, recent intensification of these systems with the implementation of continuous cereals and minimum or zero tillage has resulted in greater inputs of stubbles and fertilisers. Rhizoctonia root disease is prevalent in the mainly coarse textured alkaline soils of the region, and the reduction in cultural control associated with adoption of reduced till systems has highlighted a need for alternative control measures. In a broad context, the key question addressed in this thesis is whether the soil ecology to suppress Rhizoctonia is present or can develop in these soils from a region considered an extremely harsh environment climatically as well as edaphically. Specific key questions will be addressed in the discussion section of each chapter. The thesis, through a series of controlled environment studies, examines abiotic-biotic interactions between the soil, the Rhizoctonia solani pathogen and wheat seedlings. The work assesses how the soil organisms involved in disease suppression (both the pathogen Rhizoctonia solani AG8 organism and other antagonists or competitors) are influenced by cereal stubbles and fertilizer inputs to the system. Through a series of preliminary experiments (Chapter 3) the important variables of soil moisture and amount of pathogen inoculum (e.g. number of pathogen infected agar plugs) suitable for a bioassay method were standardised, and used throughout the rest of the work described in this thesis. Two controlled environment bioassay experiments (Chapter 4) were undertaken surveying soils from six sites across the region differing in physico-chemical and biological properties to elucidate the influence of abiotic and biotic factors on plant-soil-pathogen interactions and the potential for suppression of Rhizoctonia. A comparison was made with soil from the long term study site in SA (Avon) reported to be suppressive to Rhizoctonia. Studies growing wheat seedlings in sterilised soils demonstrated that the soils assessed were intrinsically different in terms of the growth supported by the abiotic matrix. Greatest shoot and root dry weight was observed in the soil from a region outside the EP (i.e. Avon) and the least was in an EP soil with extremely high calcium carbonate content (e.g. Streaky Bay) – a clear example of plant-soil abiotic interaction. Avon soil was confirmed as suppressive to Rhizoctonia root rot since the Avon soil inoculated with its own biotic component reduced root infection to 50% from more than 70% in the sterilised abiotic control. Whereas, for plants in the two EP soils with low calcium carbonate root infection was similar in the sterilised abiotic matrix to that in the soils inoculated with their biotic component, suggesting they were not biologically suppressive. Further evidence of the suppressive capability of the biotic component of Avon soil was obtained where it was inoculated into the two EP soils with higher carbonate and reduced root infection in plants grown in these two soils, although not in the lower carbonate content abiotic matrix of Minnipa, another EP soil. Surprisingly, considering the hostile edaphic conditions, root infection was reduced in the high calcium carbonate soil inoculated with its own biotic component, suggesting it was suppressive but not to the same extent as Avon. It was hypothesised this was possibly related to the organic C content in that soil being similar to Avon and higher than the other two EP soils. Shifts in soil organism community structure were observed when plants were grown in sterilised soils inoculated with the biotic component from another soil (i.e. rhizosphere soil from plants grown in another non-sterile matrix). Overall this work suggested there was some biotic potential for suppression in EP soils but low organic C was likely to be a constraint. EP soils were not as suppressive as Avon and abiotic constraints were highly likely, for example, the high carbonate reducing availability of P due to chemical fixation. A long term glasshouse study (Chapter 5) was undertaken to measure the effect of carbon addition to two EP soils, as stubble or young root residues, on the potential to suppress Rhizoctonia. Other measurements in this experiment were microbial biomass carbon and quantitative PCR for DNA of pathogen and other specific micro-organisms implicated as contributing to disease suppression. C input to EP soils suppressed Rhizoctonia infection in wheat seedlings (despite abiotic constraints). C input as young roots increased DNA of Rhizoctonia solani and beneficial soil organisms Microbacterium spp. and Pantoea agglomerans. C input as stubble increased the populations of the beneficial soil organism, Trichoderma spp. A further bioassay experiment (Chapter 6) investigated the effect of N and P fertiliser inputs on plant growth and Rhizoctonia suppression in two EP soils. The bioassay further investigated the interaction of these fertiliser nutrients with added available C in these two EP soils, one of which was highly calcareous. There was a positive plant growth response to added ammonium–N in both soils but no effect on Rhizoctonia infection. Addition of fertilizer P to the highly calcareous soil increased shoot and root growth and also Rhizoctonia infection without compromising effects on plant growth. Addition of available C (sucrose) with P fertiliser in the highly calcareous soil markedly suppressed Rhizoctonia infection. Two final experiments focussed on measuring the changes in pathogen and other microbial communities in response to inputs of fertiliser and C in a highly calcareous EP soil, since Rhizoctonia root rot impacts are considered a particularly big issue in this soil type. In the first experiment (Chapter 7) it was hypothesised that fertiliser P may affect suppression of Rhizoctonia root rot not only via increasing plant growth but also by altering microbial community composition. Results showed that virulence of Rhizoctonia solani was unaltered by P addition although pathogen DNA in soil and plant root infection increased. The effect of P fertiliser on plant growth compensated for the effect of P on increased pathogen population and root infection. Whilst fertiliser P increased microbial activity no shifts were detected in communities so the effects of P on soil organisms involved in suppression of Rhizoctonia root rot were not conclusive. However, in the last experiment (Chapter 8) there were measured shifts in populations of organisms resulting from addition of fertiliser P in conjunction with stubble. The known suppressive soil organisms Pantoea agglomerans and Microbacterium spp. increased whereas Rhizoctonia solani (DNA) remained constant and hence Rhizoctonia infection decreased. In summary, some soils from the EP region of South Australia expressed a degree of suppression to Rhizoctonia root rot via their biotic component in pot culture experiments. Furthermore, some of the soils, although not necessarily the same ones, contained soil micro-organisms implicated by other studies in suppression of Rhizoctonia root rot. The biotic component from some of the EP soils, whilst not suppressive in the soil matrix it was extracted from did demonstrate the potential to suppress Rhizoctonia root rot when transferred into another soil matrix, indicating an abiotic constraint to suppression. It is postulated that important abiotic properties in these EP soils were calcium carbonate content, with organic carbon and to a lesser extent mineral N and P also important since these latter properties bridge the abiotic to biotic divide. Important biotic properties are likely to be microbial activity, microbial community structure and the population of the pathogen, Rhizoctonia solani AG8. Results from this thesis work suggest that suppression to Rhizoctonia root rot can occur in EP soils despite abiotic and biotic constraints of limited C and P. Improvement and maintenance of a high suppressive capacity in soils in this semi-arid environment will require integrated agronomy aimed at maintaining a healthy crop using fertilisers, particularly P. Available carbon appears to be the most limiting constraint to microbe based biological disease suppression of Rhizoctonia root rot in these soils. Therefore it is essential that adequate available C is supplied via stubble input to develop and maintain a highly functioning soil biota. Although these results highlight that disease suppression to Rhizoctonia root rot is indeed possible in the constrained soils of the EP, the time required to develop this suppressive capacity in a field situation remains to be investigated.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2013

This research has examined the effects of soil compaction, and common agricultural management strategies used to overcome soil compaction, on soil bacterial and fungal activity and diversity. Soil microbial communities, bacteria and fungi in particular, play essential roles in the maintenance of soil health, where high soil microbial diversity might strongly contribute to the natural disease suppression. The activity and diversity of soil microbial communities is, however, strongly dependent on other soil characteristics, especially soil physical parameters. Soil compaction indicated by increased bulk density is the most soil physical parameter that directly modifies soil environment where crops and diseases exist in, but it might also indirectly cause more disease by affecting the composition of soil microbial communities in the soil. Many strategies have been used to attempt to overcome compaction in temperate environments, but they have been poorly studied/less successful in tropical and subtropical environments. This thesis, therefore, looks at the impact of compaction, and methods used to reduce compaction, on the soil microbial profile, and its capacity to resist introduced diseases.

碩士
國立中興大學
植物病理學系
89
This study was aimed at verifying the suppressiveness of soil collected from a cucumber cultivation field at Hualian, determining the suppressive factor(s), screening the beneficial nonpathogenic Fusarium oxysporum and bacterial antagonists, and their application on biological control the Fusarium wilt of cucumber caused by F. oxysporum f. sp. cucumerinum. Fusarium wilt is an important limiting factor of cucumber cultivation in Taiwan. Typical wilt symptoms in cucurbits, resulting in mortality are manifested in both young and mature plants and when infection occurs at the seedling stage. The Hualian soil was proved to be a suppressive soil to Fusarium wilt of cucumber with soil infestation method in greenhouse. The possible suppressive factor(s) in Hualian soil Fusarium wilt of cucumber might be biological agents. An isolate of nonpathogenic Fusarium oxysporum (Fo-366) was screened and used to protect cucumber plants from Fusarium wilt up to harvest time by using peat moss infestation method. Moreover, if several isolates of nonpathogenic Fusarium oxysporum were applied at the same test, the protection effect would be much better. Cucumber seeds coated with strains of plant growth promoting rhizobacteria (PGPR) supplied by (Soilborne Disease lab National Chung Hsing University.), the result showed fail to protect plants from Fusarium wilt, but they were effective on promoting plant growth. The pathogenic and nonpathogenic Fusarium oxysporum produced different pigmentations and could be distinguished from each other easily when grown on a modified PCNB medium (using 2% galactose instead of 1.5% peptone). This differential medium was very useful for studying the possible mechanisms involved in the cross protection of cucumber wilt by using nonpathogenic Fusarium oxysporum. Competition of infection site was proved to be one of the protection mechanisms. Ageing of cucumber plants showed more susceptible to Fusarium wilt; the physiological changes of cucumber plants might be one of factors for the disease development.

Root-lesion nematodes, Pratylenchus spp., are serious pathogens of potato plants worldwide. Several management practices can control Pratylenchus spp.; however, they all have shown some limitations. Therefore, environmentally-safe, low-cost, and effective control strategies are needed as possible alternative to currently used strategies. This thesis was designed to assess if liquid hog manure (LHM) holds such potential. The objectives of this thesis were to determine: (i) the prevalence and identity of species of Pratylenchus spp. in Manitoba potato fields, (ii) if short-chain volatile fatty acids (VFA) in LHM are the constituents responsible for the manure’s toxicity to Pratylenchus spp. using solution exposure experiments (iii) the effectiveness of LHM in killing Pratylenchus spp. in soil, and (iv) the impact of LHM on nematode communities. Pratylenchus spp. were detected in 39% of 31 potato fields surveyed in Manitoba with population densities ranging, for positive fields, from 45 to 631 nematodes kg-1 fresh soil. Morphometrics of female nematodes and molecular diagnosis (using species-specific PCR primers) showed that the species of Pratylenchus present in the potato fields to be P. neglectus. Potato, cv. Russet Burbank, showed to be a poor host to two populations of Pratylenchus spp. from Manitoba potato fields. Accordingly, P. neglectus does not seem to be a limitation to potato production in Manitoba; thus, P. penetrans, the most widely spread and damaging species to potato was used in the successive studies of assessing the use of LHM to control Pratylenchus spp. in potato fields. VFA (acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, and n-caproic acids) accounted for the majority of the lethal effect of LHM to P. penetrans under acidic conditions. VFA in LHM killed Pratylenchus spp. in soil and acidification seemed to enhance its ability when VFA concentration in the manure is low. LHM did not act as a soil fumigant eliminating soil trophic interactions but increased bottom-up food web interactions. VFA in LHM persisted in the soil for four days with biological degradation being their mode of loss. In conclusion, LHM is potentially an effective and low-cost strategy to control Pratylenchus spp. and its efficacy can be improved by acidification.
October 2009

碩士
國立臺北科技大學
土木與防災研究所
100
Mercury is receiving a major focal among many of the heavy metals due to its unique characteristics, such as its high toxicity, volatility and ability to bioaccumulate. Mercury has been recognized as a toxic hazard for centuries. Both inorganic and organic mercury can cause serious health effects. Organic forms of mercury are generally more toxic than inorganic forms, but it is possible for inorganic mercury to be biologically transformed into organic mercury. Therefore, it is important to control inorganic mercury leaching from mercury containing wastes. In this study, cement solidification accompanied with chemically modified activated carbon was used to inhibit the dissolution of mercury（Hg）from the contaminated soil. The research parameters for examining the leachability of Hg via the toxicity characteristic leaching procedure （TCLP）tests included the cement adding amount, the curing duration（seven days and 28 days）, the addition of chemically modified activated carbon (bromine and sulfur treated), and the water / cement ratio. The TCLP leaching concentration of Hg, for the original soil without added cement and carbon adsorbent was 2.54×10-1 mg / L, which exceeded Taiwan''s regulation standard （i.e., 0.2 mg / L）. The leaching concentrations for soil samples after adding cement and carbon complied with the regulation standard, but 28 day curing caused a greater leaching concentration than 7 day curing. It may be explained that the increasing pH, after 28 day curing led to the enhancing dissolution of Hg from the contaminated soil. Additionally, the reducing water / cement ratio may also cause an increase in Hg leaching. Future approach in suppressing the release of Hg from contaminated soil should be focused on lower the pH and operating the solidification under ab appropriate water / cement ratio to avoid re-dissolution of Hg.

碩士
國立中央大學
土木工程研究所
93
Abstract Vibration caused by transportation vehicles pass through viaduct or bridge may be transmitted from piers to pile foundations. This vibration may generate waves in deep layer. The wave propagation from the bearing stratum may cause damages to the adjacent structures or high-tech production facilities. The purpose of this research is to investigate the wave propagation in soil layers and the method for reducing these vibrations. To reduce the vibration that may cause some detrimental effects to the residences, adjacent structures or high-tech production facilities, this research designed two model piles. One of the model piles, a spring is set on the pile head as the vibration suppression, and the other one is the original pile with no treatment. A series of model pile tests were carried out in laboratory to investigate the effects of vibration mitigation, behavior of the attenuation of wave propagation around model pile in the soil and the relationships among vertical displacement of model pile, impact energy and From the results of experiments, it was revealed that the impact energy generated vibrations by means of pile tip and transmitted to the bearing stratum then generated waves. If the waves transmitted to the interface layer between the bearing stratum and the loose sand stratum, parts of energy would be transmitted outward by the interface layer. For the two kinds of model piles, the behaviors of attenuation of wave propagation approach to a similar curve and attenuate in proportion of distance. For the stiffness ratio lower than 1.6, the vibration energy generated by the pile tip of vibration suppression is decreased to 50% of that generated by the original model pile. It is revealed also that the wave propagation transmitted by bearing stratum and the interface layer had predominant vibration mitigation.

碩士
國立虎尾科技大學
生物科技系碩士在職專班
107
In order to cope with the possible shortage of food caused by the increase in population, all countries in the world are working hard to increase food production. However, how to achieve a balance between food production and environmental and ecological systems is the goal of national agricultural policy efforts, such as promoting organic agriculture is one of its policies. Biological control is recognized as one of the important means to replace or reduce chemical pesticide use in the future. Therefore, this thesis is conducted to isolate antagonistic microorganisms from organic tea garden and test their disease control ability, in order to develop bio-pesticide in the future. The experimental fields were selected in the Fenghuang Nature Education Areas of the Experimental Forest National Taiwan University to explore the differences in the composition of soil microbial phase structure in tea gardens under the management of organic farming methods and conventional farming methods, and to screen for beneficial microorganisms from their soils and to detect anthracnose disease control of chinese cabbage caused by Colletotrichum higginsianum and the pathogen growth. According to soil microbial survey, the average number of fungi in organic tea gardens (59.82×103 cfu/g) is generally higher than that of conventional tea gardens (18.86×10^3 cfu/g); similarly, the average number of Trichoderma spp. is in organic tea gardens (23.72×10^3 cfu/g) is also about 4 times higher than the conventional tea garden (5.78×10^3 cfu/g). For bacteria and actinomycetes number investigations, the results showed no significant difference between organic tea gardens and conventional tea gardens. Comparing the number of microbial populations with the annual rainfall and temperature, it was found that the number of fungi and actinomycetes was positively correlated with the amount of rainfall in the area, but the number of all microorganisms was not significantly correlated with temperature. For dual culture of pathogen and antagonists on medium, 8 strains of Trichoderma spp. which had better growth inhibition of C. higginsianum were screened out, and to control anthracnose disease of chinese cabbage was detected in the greenhouse. The results showed that the 8 selected strains of antagonists were effective to reduce the anthracnose disease of chinese cabbage about 32~53% compared with the untreated control, among which strain O1-5-3 was the best. This strain O1-5-3 was identified by gene sequencing and assigned as Trichoderma virens.