International trade in plants, especially with potting substrates, is recognised as the main pathway of plant pathogen dissemination on a global scale. In the last 20 years, the wide use of internet commerce has become common in the nursery sector and, due to the nature of online sales, may be aggravating this risk. Oomycetes in the genera Phytophthora, Pythium and Phytopythium, cause a range of important plant diseases, responsible for serious economic and biological losses. This research focused on the detection of Oomycetes in imported potted ornamental plants in the UK and The Netherlands, including internet sales and asymptomatic plants. Isolation techniques and molecular protocols were developed to quantify pathogen load in ornamental plants, using TaqMan PCR and Next Generation Sequencing (NGS) to assess Oomycete diversity using a multi-locus approach. Survival of Phytophthora cinnamomi and Fusarium verticillioides was estimated in two commercial potting mixes used in ornamental plant production. Oomycetes were detected in all samples analysed with the NGS approach, with 38 Phytophthora spp. and 48 Pythium/Phytopythium spp. identified. Phytophthora ramorum, P. alni subsp. alni and P. cryptogea were common. TaqMan PCR quantification showed high numbers of Oomycetes in all samples, especially in substrates, followed by roots and baiting waters. During sampling by isolation, Pythium kashmirense was recovered from Viburnum plicatum, the first record of this species in the UK. The survival experiment showed that Fusarium verticillioides remained viable after 17 months, whereas Phytophthora cinnamomi was viable up to 7 months after inoculation. This work clearly demonstrated the widespread presence of Oomycete pathogens in the plants for planting pathway. Moreover, the protocols developed and findings of this work contribute greatly to the understanding of the potential for pathogens to spread in the international horticultural trade and may help to improve plant biosecurity protocols in the UK and Europe.

O controle de doenças em plantas geralmente é realizado com o uso de agroquímicos, que podem desencadear efeitos maléficos ao ser humano ou ao ambiente como um todo. Diversos trabalhos mostram o potencial de plantas medicinais no controle de fitopatógenos, tanto por sua ação fungitóxica direta, inibindo o crescimento micelial e a germinação de esporos, quanto pela capacidade de ativar o metabolismo de defesa das plantas, como o acúmulo de fitoalexinas, indicando a presença de moléculas com características elicitoras. Foram desenvolvidos dois experimentos na Universidade Tecnológica Federal do Paraná – Câmpus de Dois Vizinhos, com objetivos de avaliar o pontencial de preparados de Cavalinha (Equisetum sp.) na síntese de metabólitos de defesa em cotilédones de soja (Glycine max L.) e o efeito sobre o crescimento de Rhizoctonia solani, in vitro. O delineamento experimental utilizado para os experimentos foi inteiramente casualizado em esquema fatorial 3x5 resultante da combinação de três formas de extração (extrato alcoólico, infusão e maceração) e cinco concentrações (zero; 1; 10, 20 e 40%), com 4 repetições. No primeiro experimento foi avaliada a indução de fitoalexinas em cotilédones de soja em resposta aos derivados a base de cavalinha. Sementes de soja foram semeadas em areia autoclavada e mantidas em temperatura ambiente por 10 dias. Em seguida os cotilédones das plântulas foram removidos e na face abaxial destes foram aplicados os tratamentos. Após seguir os procedimentos metodológicos da técnica de extração, obteve-se via espectofotometria a quantificação da fitoalexina gliceolina, sendo então utilizados os cotilédones para quantificação da atividade da enzima fenilalanina amônia-liase (FAL) e o teor de fenóis totais. No segundo experimento foi avaliado o potencial fungistático dos preparados sobre Rhizoctonia solani. Em placas de Petri foram adicionados no meio de cultura BDA os preparados nas diferentes concentrações. Após a solidificação foi transferido para o centro de cada placa, um disco de micélio com Rhizoctonia solani. As placas foram incubadas sob alternância de fotoperíodo de 12 horas, em temperatura de 25oC. Os preparados de extrato alcoólico, infusão e maceração de cavalinha apresentam capacidade de indução das fitoalexinas gliceolinas em cotilédones de soja, bem como, ativam o metabolismo de compostos fenólicos. Entre os preparados, o extrato alcoólico e a maceração, se sobressaem sobre a infusão. Os preparados de extrato alcoólico, infusão e maceração de cavalinha em todas as suas concentrações inibem o crescimento do fungo Rhizoctonia solani, in vitro, sendo que o extrato alcoólico apresenta maior capacidade de supressão do crescimento micelial em comparação as demais formas de obtenção dos preparados. / Usually, the plant diseases control is accomplished with the use of chemicals products that can trigger harmful effects for the people or the environment. Several studies showed the potential of medicinal plants in the control of pathogens, either by their direct fungitoxic action, inhibiting the mycelial growth and spore germination, and by ability to activate the metabolism of plant defense, such as phytoalexin accumulation, indicating the presence of molecules with characteristics elicitoras. Two experiments were carried out in the Universidade Tecnológica Federal do Paraná - Câmpus Dois Vizinhos. The aims of these works were to evaluate the potential of "cavalinha" (Equisetum sp.) prepared in the defense metabolites synthesis of soybean cotyledons (Glycine max L.) and the effect on Rhizoctonia solani growth in vitro. The experimental design used for the experiments was completely randomized in factorial 3 x 5 (extract form x concentration), with four replications. The extract forms were alcoholic extract, infusion and maceration and the concentrations tested were zero, 1, 10, 20 and 40%. In the first experiment, the phytoalexins induction in the soybean cotyledons the according with "cavalinha" prepared was evaluated. Soybean seeds were sown in autoclaved sand and kept at room temperature for 10 days. After, the plantlets cotyledons were removed and on the surface of these the treatments were applied. Then, it followed the methodological procedures of extraction technique and it was obtained via spectrophotometry the phytoalexin glyceollin quantification. The cotyledons were then used to quantify of the enzyme phenylalanine ammonia lyase (PAL) activity and total phenols contend. In the second experiment was evaluated the potential fungistatic preparations on Rhizoctonia solani. The prepared with different concentrations was added in Petri dishes with PDA culture medium. After solidification was transferred to the center of each plate, a disc with Rhizoctonia solani mycelia. The plates were incubated alternating the photoperiod in 12 hour, at 25 °C temperature. The alcoholic extract, infusion and maceration "cavalinha" prepared present glyceolin induction of phytoalexins in soybean cotyledons, as well as it to activate the metabolism phenolic compounds. Among the prepared, the alcoholic extract and maceration forms were superior in relation the infusion form. The alcoholic extract, infusion and maceration "cavalinha" prepared using all over the concentrations inhibit Rhizoctonia solani growth in vitro. The alcoholic extract had a higher capacity to suppress mycelial growth compared to other forms of production preparations.

Tobacco necrosis virus (TNV) interfered with cucumber necrosis virus (CNV) replication in mixed infections. TNV inhibited both the initiation of CNV infections and subsequent CNV multiplication. Evidence of interference was found in qualitative evaluations of symptoms on a wide host range and by quantitative evaluations (lesion counts and incidence of systemic symptoms) on cucumber, cowpea, and bean. Fresh weight measurements similarly indicated antagonism in mixed infections. Some evidence of CNV interfering with TNV replication was found, in the form of a reduction in the occurrence of systemic symptoms. Photometric scanning of sucrose density gradient columns after centrifugation revealed that in mixed infections CNV reached only half the concentration attained in single infections while TNV was unaffected or even very slightly increased in concentration. This interference continued even when high temperatures greatly limited TNV replication. Only at 3° C, where its replication was barely detectable, did TNV have no effect on the CNV concentration attained. CNV did not significantly aid TNV replication at any temperature. In serial passage of mixed infections TNV quickly gained in concentration relative to CNV. Although CNV and TNV symptoms could not readily be distinguished from one another on most hosts, Phaseolus vulgaris var. Topcrop kept at 23 C and Chenopodium capitaturn kept at 18 C were established as reliable indicators of CNV and TNV respectively. One preparation from doubly infected tissue showed evidence of possible phenotypic mixing based on polyacrylamide gel electrophoresis and on reactions with antisera, although this could not be confirmed by infectivity tests. Through use of the antigen-antibody neutralization test, another virus preparation from doubly infected tissue gave evidence of possible genomic masking of TNV RNA in CNV coat protein. No evidence of possible genomic masking in the opposite direction was found. / Land and Food Systems, Faculty of / Graduate

Fusarium root rot is one of the most important diseases of pulse crops, with numerous Fusarium spp. comprising the disease complex. Fusarium solani and F. avenaceum have been reported to be major pathogens in the pea root rot complex, and all commonly grown varieties are susceptible. Greenhouse methods to evaluate peas for resistance to Fusarium root rot resulted in inconsistent disease severity across varieties. In 2015, F. avenaceum infested field plots were more heavily damaged based on emergence and yield than F. solani infested plots, and opposite trends were observed in 2016. Differences in root rot severity between years could be due to F. solani infestation causing more damage under warmer temperatures, while plots infested with F. avenaceum caused more damage under cooler temperatures. These results highlight the difficulties observed when screening for soil-borne pathogens, and the increased difficulties when a pathogen complex and changing environmental conditions are involved.

Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2008. / Full text also available online. Scroll down for electronic link.

Thesis (MScAgric (Plant Pathology))--University of Stellenbosch, 2005. / The genus Rhizoctonia includes important soilborne plant pathogens that can cause severe economic losses on a wide range of crops including cereal, canola, pasture and grain legume crops. Limited information is available on specific anastomosis groups (AGs), nuclear status, pathogenicity and cross-pathogenicity of Rhizoctonia isolates associated with each of these crops in the Western Cape province. Therefore, these aspects were investigated in this study, since information in this regard is crucial for the development of Rhizoctonia disease management practices.

3 pp. / Originally published: 2003 / True mistletoes are parasitic flowering plants with characteristic clumps of growth that are easily visible on the host plant. They reduce the growth of infected hosts, but it usually takes many years for true mistletoe infections to kill a mature tree or shrub. This article gives information about the disease cycle, the symptoms and prevention and control methods for true mistletoes.

Rhizoctonia solani, Pythium aphanidermatum, and Macrophomina phaseolina were isolated from Euphorbia lathyris grown in fields near Tucson, Arizona. R. solani occurred as a damping-off organism in the fall. P. aphanidermatum infected seeds, seedlings, and mature plants in laboratory and greenhouse tests. Although P. aphanidermatum was infrequently isolated from field plants in Arizona, it was a major pathogen of greenhouse plants growing at high temperatures in nonsterile soil. M. phaseolina was a major pathogen. Infection of E. lathyris roots occurred within 1 mo of an October 1980 planting, but symptoms were not significant until June. Sclerotia of this fungus ranged in numbers from 1 to 246 sclerotia/g field soil. Population densities of 0.2 sclerotium/g soil were sufficient to cause more than 90% plant death in field plots. Some plants infected with M. phaseolina were growing in an area newly cleared of native desert vegetation. Subsequently, M. phaseolina was found in uncultivated soils from four vegetative communities in southern Arizona at elevations from 600 to 2,000 m; the fungus also was recovered from roots of several symptomless native plants.

No description available.

Large amounts of industrial fertilizers are used to maximize crop yields. Unfortunately, they are not completely consumed by plants; consequently, this leads to soil pollution and negative effects on aquatic systems. An alternative to industrial fertilizers can be found in legume plants that provide a nitrogen source that is not harmful for the environment. Legume plants, through their symbiosis with soil bacteria called rhizobia, are able to reduce atmospheric nitrogen into ammonia, a biological nitrogen source. Establishment of the symbiosis requires communication on the molecular level between the two symbionts, which leads to changes on the cellular level and ultimately results in nitrogen-fixing nodule development. Inside the nodules hypoxic environment, the bacterial enzyme nitrogenase reduces atmospheric nitrogen to ammonia. Medicago truncatula is the model legume plant that is used to study symbiosis with mycorrhiza and with the bacteria Sinorhizobium meliloti. The focus of this work is the M. truncatula nodulation mutant nip (numerous infections and polyphenolics). The NIP gene plays a role in the formation and differentiation of nodules, and development of lateral roots. Studying this mutant will contribute knowledge to understanding the plant response to infection and how the invasion by rhizobia is regulated. Previous genetic mapping placed NIP at the top of linkage group 1 of the M. truncatula genome. A NIP mapping population was established with the purpose of performing fine mapping in the region containing NIP. DNA from two M. truncatula ecotypes A17 and A20 can be distinguished through polymorphisms. Positional mapping of the NIP gene is based on the A17/A20 genetic map of M. truncatula. The NIP mapping population of 2277 plants was scored for their nodulation phenotype and genotyped with flanking molecular genetic markers 146o17 and 23c16d, which are located ~1.5 cM apart and on either side of NIP. This resulted in the identification of 170 recombinant plants, These plants' DNAs were tested further with different available genetic markers located in the region of interest, to narrow the genetic interval that contains the NIP gene. Segregation data from genotyping analysis of recombinant plants placed NIP in the region between 4L4 and 807 genetic markers.