Studies on plant growth-promoting rhizobacteria (PGPR) and fungi (PGPF) as biostimulants have shown significant positive effects on plant health, fruit yield, or pest management. However, very few published studies to date have been specific regarding their effects on strawberries (Fragaria × ananassa), particularly on soilborne disease prevalence in organically grown strawberries. Empirical data on the results of using these products in commercial growing applications under various conditions would be highly valuable, especially for organic growers who have limited synthetic chemical pesticides, herbicides and fertilizers registered for use. The objective of this study is to evaluate the efficacy of biostimulant supplementation on strawberries for improving fruit yield, fruit quality, and plant health in both high-tunnel, open-sided ‘hoophouse’ and field conditions. This study consisted of two research projects. The first project investigated the effects of commercially available PGPR-based biostimulant products on strawberry plant health. The three products contained differing proprietary combinations of PGPR, primarily from the Bacillus and Lactobacillus genera. Plants were grown in two different soil types: sandy and clay, in order to investigate the effects of biostimulant supplementation in different soil conditions. In fall of 2018, 160 ‘Monterey’ strawberry plants were grown in an outdoor hoophouse in 3-gallon pots. Plants were either treated monthly with a single bacterial biostimulant product (EM-1, Accomplish LM, or Armory), or left untreated as a control. Plants were grouped into 20 blocks, each block comprised of 8 plants (each of the four treatments replicated in both soil types). Fruit yield (g), fruit sugar content (Brix), and leaf SPAD absorbance levels were measured weekly from January 27 to June 26, 2019. The treatments tested had no significant effects on fruit yield, leaf SPAD absorbance or Brix; soil type, however, did significantly impact fruit yield, with higher yields in sandy soil. The second project was a field trial beginning in spring of 2020, in collaboration with Rutiz Farms in Arroyo Grande, CA, involving a total of 480 ‘Chandler’ strawberry plants. The farm is organically managed and has a history of soilborne diseases, including Verticillium dahliae. These plants were either treated monthly with one of three microbial biostimulant products: a product containing a proprietary strain of Trichoderma harzianum biocontrol fungus (TrichoSym), and two of the same PGPR-based products used the previous year (Accomplish LM and Armory); or left untreated as a control. The experiment was laid out in a randomized complete block design with four blocks, with each block consisting of 4 plots for each of the 4 treatments; each plot contained 30 plants. Fruit yield (g) per plot was measured weekly throughout the 2020 growing season and phenotypic disease incidence was measured biweekly. Soil samples were taken at three different points throughout the season, cultured on selective media, and analyzed to obtain estimates of V. dahliae colony-forming units (CFU) per gram soil. The treatments tested had no significant effect on fruit yield, phenotypic disease incidence, or V. dahliae CFU/g soil. The results are inconclusive as to whether this lack of effect is due to viability of the products themselves, ineffective application techniques resulting in lack of rhizosphere colonization, or some combination of these. Further research is needed to determine whether or not supplementation with microbial biostimulants can produce reliable, beneficial results in strawberries.

No description available.

La verticilliose est une maladie vasculaire des plantes dont les symptômes typiques sont un flétrissement des parties aériennes, des feuilles chlorosées puis séchées, et dans les cas de maladie grave la mort de la plante. Au niveau des racines on observe une coloration brune du tissu conducteur. Cette maladie est causée par un champignon du sol du genre Verticillium. Les espèces majeures V. dahliae et V. albo-atrum sont responsables de pertes importantes de rendement sur de nombreuses cultures. Le champignon entre dans la racine par des blessures ou par des fissures au niveau de sites d’émergence de racines latérales, puis il avance vers le cylindre central et envahit les vaisseaux du xylème. Sa croissance reste pendant longtemps limitée aux vaisseaux qu’il colonise en avançant vers les parties aériennes de la plante. Aux stades tardifs, le champignon sort du cylindre central et colonise les autres tissus. En Europe, V. albo-atrum constitue l’une des principales causes de maladies chez la luzerne pérenne et est à l’origine de pertes économiques très importantes. La capacité de V. albo-atrum de survivre dans le sol ainsi que sa localisation protégée dans le cylindre centrale des plantes infectées en font un pathogène difficile à combattre, la lutte génétique par sélection de variétés tolérantes apparaissant comme une approche prometteuse. Cependant, la capacité des microorganismes pathogènes de s’adapter rapidement à des nouvelles plantes hôtes est une menace bien connue de la durabilité des variétés résistantes. Au laboratoire, des travaux ultérieurs ont établi que la plante modèle des légumineuses Medicago truncatula, une espèce sauvage proche de la luzerne cultivée, peut être utilisée pour étudier les mécanismes de résistance et sensibilité vis-à-vis de V. alboatrum. Une lignée résistant et une lignée sensible ont été identifiées et l’étude de la descendance d’un croisement entre ces deux lignées a permis d’identifier un locus majeur (Quantitative trait locus, QTL) contrôlant la résistance à une souche de V. albo-atrum isolée de la Luzerne (Ben et al., 2013 ; Negahi en 6e co-auteur). Ce travail a également montré qu’il existait une grande biodiversité au sein de l’espèce M. truncatula par rapport à la réponse à cette souche de V. albo-atrum. / Verticillium wilt, caused by Verticillium albo-atrum (Vaa) and Verticillium dahliae (Vd), is responsible for yield losses in many economically important crops. The capacity of pathogenic fungi to adapt to new hosts is a well-known threat to the durability of resistant crop varieties. Medicago truncatula is a good model for studying resistance and susceptibility to Verticillium wilt in legume plants. Phenotyping a population of inbred lines from a cross between resistant parent line A17 and susceptible parent F83005.5 contributed to the identification of a first QTL controlling resistance to an alfalfa strain of Vaa in M. truncatula. Then, 25 M. truncatula genotypes from a core collection and six Vaa and Vd strains were used to study the potential of non-host Verticillium strains isolated from different plant species to infect this legume plant, and the plant’s susceptibility to the pathogens. The experiment was arranged as factorial based on a randomized complete block design with three replications. The wilt symptoms caused by Vaa and Vd were scored on a disease index scale from 0 to 4, during 30 days after inoculation of ten day-old plantlets. Disease severity was quantified by the parameters Maximum Symptom Scores (MSS) and Areas Under the Disease Progress Curves (AUDPC). Highly significant differences were observed among plant genotypes and fungal strains, and their interaction was also significant. The correlation between MSS and AUDPC was 0.86 and highly significant. The most severe symptoms were caused by the alfalfa strain Vaa-V31-2 and the least severe by Vd-JR2, as shown by mean values obtained on the 25 genotypes. M. truncatula genotype TN8.3 was identified as the most susceptible genotype by mean values obtained with the 6 fungal strains, whereas F11013-3, F83005.9 and DZA45.6 were highly resistant to all strains studied. The results were used to choose parents for studying the genetics of resistance in M. truncatula to a nonalfalfa Verticillium strain. So, in the second part of this work, genotype A17 which was susceptible and genotype F83005.5 which was resistant to the potato strain Vaa-LPP0323 and recombinant inbred lines (RILs) from a cross between these genotypes were selected in order to study the genetic control of resistance to this strain of the pathogen. Our experimental design was a randomized complete blocks with 116 RILs and three replications. High genetic variability and transgressive segregation for resistance to Vaa-LPP0323 were observed among RILs. A total of four QTLs controlling resistance to Vaa-LPP0323 were detected for the parameters MSS and AUDPC. The phenotypic variance explained by each QTL (R2) was moderate, ranging from 3 to 21%. A negative sign of additive gene effects showed that favourable alleles for resistance come from the resistant parent.

Graduation date: 1994

Verticillium wilt is a serious disease in a wide range of economic crops worldwide. Verticillium wilt of potato is caused, primarily, by the fungus Verticillium dahliae. Disease management requires understanding of V. dahliae pathogenesis and interactions with potato, which was the main objective of this study. A differential potato-V. dahliae pathosystem was established where pathogenicity of four V. dahliae isolates with different levels of aggressiveness was evaluated on two potato cultivars, Kennebec (susceptible) and Ranger Russet (moderately resistant). External and internal symptoms and growth measurements revealed that isolates Vd1396-9 and Vs06-14 are highly and weakly aggressive, respectively. These two isolates were selected for transcriptomics and proteomics investigations to identify pathogenicity-related factors. Transciptomics analysis was conducted in both isolates after elicitation by root extracts from either Kennebec or Ranger Russet using a combinational approach involving subtractive hybridization and cDNA-AFLP. A total of 573 differentially expressed transcripts were detected in one or the other isolate. Among them, 185 transcripts of interest were recovered, re-amplified, sequenced and searched against NCBI and the Broad Institute V. dahliae genome databases for identification. The two contrasting-aggressiveness isolates were used for a comparative proteomics investigation. The first proteomic map of V. dahliae was established. The proteomics analysis was carried out using 2-Dimentional electrophoresis and mass spectrometry. Twenty five proteins were differentially expressed and identified in one or the other isolate. Many of the identified genes/proteins showed potential involvement in pathogenesis of V. dahliae or other fungi. Genes of stress response regulator A (oxidative stress tolerance factor), isochorismatase hydrolase (potential plant defense suppressor) and tetrahydroxynaphthalene reductase (involved in melanin and microsclerotia formation) were isolated from both isolates and cloned. Sequence analysis of these genes showed many differences that may explain their differential expression in the two isolates. Given that some of the identified genes/proteins are potentially involved in overcoming and suppressing plant defense, phenolics were profiled in Kennebec-inoculated with Vd1396-9 or Vs06-14 isolate. Chlorogenic, caffeic, ferulic acids, cis-jasmone and rutin accumulation showed variations after inoculation. The results obtained from this study will help understanding the V. dahliae-potato interactions and develop efficient strategies to control Verticillium wilt disease.

In Manitoba, potato fields have been found to be infested with Verticillium dahliae, which can produce Vertcillium wilt disease severity of up to 90% and reduce yield. Potato producers have then an increased interest on use of green manures and organic amendments to control Verticillium wilt. The objectives of this research were to evaluate selected green manure and organic amendments for their ability to reduce propagule density of V. dahliae in soil, incidence and severity of Verticillium wilt, and to enhance potato yield in Manitoba. In addition, a second study was conducted for the purpose of studying the potential of mustard green manure and seed meal to inhibit the germination of microsclerotia. Findings suggest that composted-cattle-manure and oriental mustard seed-meal amendments have promise as an alternative strategy for the control of V. dahliae. However, only composted beef cattle manure reduced disease, increased potato yield and improved nutrient availability (P) in soil

Verticillium wilt, caused by Verticillium dahliae Kleb, is one of the most economically important diseases of woody hosts such as ash (Fraxinus spp.), sugar maple (Acer saccharum), and redbud (Cercis canadensis). The causal agent has a broad host range, including not only woody hosts but also important vegetable and field crops, and it is distributed worldwide. Diagnosis of V. dahliae in infected woody hosts is often based on the occurrence of vascular discoloration and time-consuming isolation. However, not all woody hosts exhibit vascular discoloration symptoms, and not all vascular discoloration symptoms are due to infection by V. dahliae. In this study, real-time PCR-based assays were evaluated and employed for rapid and accurate detection of V. dahliae in different woody hosts. DNA was extracted in large quantities from presumptively infected woody hosts by collecting drill-press shavings from sample tissue, bead-beating, and extracting using a CTAB method. Six published primer sets were evaluated against genomic DNA of V. dahliae as well as selected negative controls, and two sets (VertBt-F/VertBt-R and VDS1/VDS2) showed promise for further evaluation using DNA extracts from field samples. The VertBt primers amplified a species-specific 115-bp fragment of the expected size, while the VDS primers amplified the expected specific 540-bp fragment. However, the VertBt primer set exhibited higher sensitivity in detection of V. dahliae even in asymptomatic trees. The PCR-based methods developed here could be used as rapid tools for pathogen detecting and monitoring, thus informing plant pathogen management decisions.

Verticillium wilt is a serious disease in a wide range of economic crops worldwide. Verticillium wilt of potato is caused, primarily, by the fungus Verticillium dahliae. Disease management requires understanding of V. dahliae pathogenesis and interactions with potato, which was the main objective of this study. A differential potato-V. dahliae pathosystem was established where pathogenicity of four V. dahliae isolates with different levels of aggressiveness was evaluated on two potato cultivars, Kennebec (susceptible) and Ranger Russet (moderately resistant). External and internal symptoms and growth measurements revealed that isolates Vd1396-9 and Vs06-14 are highly and weakly aggressive, respectively. These two isolates were selected for transcriptomics and proteomics investigations to identify pathogenicity-related factors. Transciptomics analysis was conducted in both isolates after elicitation by root extracts from either Kennebec or Ranger Russet using a combinational approach involving subtractive hybridization and cDNA-AFLP. A total of 573 differentially expressed transcripts were detected in one or the other isolate. Among them, 185 transcripts of interest were recovered, re-amplified, sequenced and searched against NCBI and the Broad Institute V. dahliae genome databases for identification. The two contrasting-aggressiveness isolates were used for a comparative proteomics investigation. The first proteomic map of V. dahliae was established. The proteomics analysis was carried out using 2-Dimentional electrophoresis and mass spectrometry. Twenty five proteins were differentially expressed and identified in one or the other isolate. Many of the identified genes/proteins showed potential involvement in pathogenesis of V. dahliae or other fungi. Genes of stress response regulator A (oxidative stress tolerance factor), isochorismatase hydrolase (potential plant defense suppressor) and tetrahydroxynaphthalene reductase (involved in melanin and microsclerotia formation) were isolated from both isolates and cloned. Sequence analysis of these genes showed many differences that may explain their differential expression in the two isolates. Given that some of the identified genes/proteins are potentially involved in overcoming and suppressing plant defense, phenolics were profiled in Kennebec-inoculated with Vd1396-9 or Vs06-14 isolate. Chlorogenic, caffeic, ferulic acids, cis-jasmone and rutin accumulation showed variations after inoculation. The results obtained from this study will help understanding the V. dahliae-potato interactions and develop efficient strategies to control Verticillium wilt disease.

In Manitoba, potato fields have been found to be infested with Verticillium dahliae, which can produce Vertcillium wilt disease severity of up to 90% and reduce yield. Potato producers have then an increased interest on use of green manures and organic amendments to control Verticillium wilt. The objectives of this research were to evaluate selected green manure and organic amendments for their ability to reduce propagule density of V. dahliae in soil, incidence and severity of Verticillium wilt, and to enhance potato yield in Manitoba. In addition, a second study was conducted for the purpose of studying the potential of mustard green manure and seed meal to inhibit the germination of microsclerotia. Findings suggest that composted-cattle-manure and oriental mustard seed-meal amendments have promise as an alternative strategy for the control of V. dahliae. However, only composted beef cattle manure reduced disease, increased potato yield and improved nutrient availability (P) in soil

Die bodenbürtigen, pflanzenpathogenen Pilze der Verticillium Familie sind über die ganze Welt verteilt. Bislang gibt es keine Fungiszide, die einen Befall der Wirtspflanzen verhindern können. Auf infizierten Feldern ist dem Pilz für viele Jahre ein Überleben im Boden in sogenannten Dauerformen (Mikrosklerotien, melanisierte Hyphen) möglich. Auch nach langer Zeit können diese auskeimen und der Pilz dann die Wirtspflanzen befallen, was ihn zu einem wirtschaftlichen Problem macht. Die Infektion der Wirtspflanzen erfolgt durch die Wurzeln; und nachdem der Pilz in die Xylemgefäße der Pflanze eingedrungen ist, wächst er innerhalb dieser vasculären Leitungsbahnen. Die infizierten Pflanzen zeigen Infektionssymptome wie frühzeitige Chlorose der Blätter, absterbendes Gewebe sowie verfärbte Gefäße in Stamm und Wurzel. Für die Landwirtschaft ist die Erforschung der Interaktionen zwischen Pflanzen und dem pathogenene Pliz von großer Bedeutung um mögliche Angriffspunkte zur Pilzbekämpfung zu finden. Diese Arbeit fokussiert sich auf zwei spezifische Gene in Verticillium dahliae, die für die Pathogenität des Pilzes eine Rolle spielen. Des Weiteren wurde die Gen­Regulation in Verticillium longisporum durch Analyse eines Transkriptoms untersucht. Die Studie hat zum Ziel die hohe Anpassung des Pilzes an die Bedingungen innerhalb des vaskulären Systems der Wirtspflanze zu zeigen, in dem dem saprophytischen Pilz nur eine limitierten Menge an Nährstoffe zugänglich ist. Das untersuchte V. dahliae Protein VdThi4 ist Teil der Thiamin Biosynthese (Vitamin B1). Dieses Mitochondriell lokalisierte Protein ist mit seinen weiteren Funtktionen in den DNA Reparaturmechanismus und die zelluläre Antwort auf oxidativen Stress (induziert durch ROS) eingebunden. Das Fehlen des Proteins führt im Pilz zum Verlust der pathogenen Eigenschaften auf der Wirtspflanze Solanum lycopersicum. Neben Proteinen wichtiger Stoffwechselwege spielen sekretierte Proteine eine große Rolle bei der Wirtsinfektion. Solche Proteine sind der Erste Kontakt zwischen Pathogen und Wirt und werden von beiden Seiten abgesondert. Infektionsversuche an S. lycopersicum zeigten, dass der Pilz das membrangebundene V. dahliae Protein VdPa14_2 für die Wirtspflanzeninfektion benötigt. Dieses Protein scheint die Resistenz gegen oxidativen Stress in der Zelle zu verringern in der Synthese schwarzen Melanins involviert zu sein. Für die Infektion von Wirtspflanzen und die Pathogenität benötigt V. dahliae viele verschiedene Proteine aus verschiedenen Stoffwechelwegen, wie die analysierten Proteine VdThi4 und VdPa14_2, die in der Zelle verschiedene Funktionen haben, aber beide für die Pathogenität des Pilzes benötigt werden. Um ein umfassenderes Bild der Interaktion zwischen Pilz und Pflanze zu bekommen, wurde die Genregulation in V. longisporum untersucht. Hierfür wurde ein Transkriptom erstellt. Es wurden sowohl die spezifisch- als auch die gleich-regulierten Transkripte während der in situ Kultivierung des Pilzes in Xylem­Saft aus Brassica napus, sowie der in vitro Kultivierung in simuliertem Xylem medium (SXM) untersucht. Beide Medien stellten sich während der Analyse als grundverschieden heraus. Das SXM stellt hingegen früherer Annahmen keine Simmulation der in vivo Konditionen innerhalb des vaskulären Systems einer Pflanze dar.