Browsing by discipline "Kasvintuotantotieteet (kasvipatologia)"
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(2012)Bacterial soft rot is one of the most serious diseases affecting potatoes in fields and storages worldwide. Soft rot on potatoes and other crops are caused mainly by Pectobacterium atrosepticum, Pectobacterium carotovorum and several Dickeya species. The disease spreads via many ways and insects are suggested to be important agents in the epidemiology. Evolutionary and geological evidences suggest soil nematodes play essential roles in ecological processes including nutrients cycling, decomposition and disease suppression. Although some studies show that Pectobacteria can survive the digestive tract of the nematodes, it is unclear whether the soil nematodes can be vectors for transmission and dissemination of plant pathogenic bacteria. Moreover, the life span of C. elegans, a free-living and bacterial-feeding nematode, is limited when fed on Pectobacterium. How soft rot bacteria interact with C. elegans and how the nematodes respond to these bacteria are still unknown. Results of this study suggest that Pectobacterium could be disseminated via nematodes on potatoes, indicating that nematodes could serve as vectors in the dissemination of soft rot bacteria on crops. Through the bacterial transmission assay, Pectobacterium is proved to possess a better ability to persist with nematodes compared to E. coli. It seems that pectobacteria have some traits that provide this ability, so Pectobacterium mutants related to Pectobacterium-plant interaction were tested and the expressions C. elegans genes were measured using quantitative polymerase chain reaction (qPCR), aiming to find out genes playing a role in Pectobacterium-nematodes interaction. However, in this study most likely type VI secretion system, putative Flp/Tad-like pilus, flagella, full length lipopolysaccharides, quorum sensing or ExpAS two-component system are not necessary determinants for the interrelationship of Pectobacterium and nematodes.
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Kauran (Avena sativa L.) taudinkestävyys Fusarium culmorum- ja Fusarium langsethiae -sieniä vastaan (2013)Oat (Avena sativa L.) is a crop grown for feed and for food industry. It is the most used fodder plant after barley in Finland and is also exported. In 2011, oat was grown on 308 200 hectares in Finland and the average yield per hectare was 3390 kg. Several fungal and virus diseases cause remarkable crop losses in oats. Especially in the temperate zone, the most common disease is the head blight caused by Fusarium species. These fungi overwinter as mycelium or spores and produce mycotoxins. In Finland, F. culmorum is a common DON toxin producer and F. langsethiae is a T-2/HT-2 toxin producer in oats. Toxins affect the quality of oat yield and can make it unsuitable for use. Therefore, the amounts of mycotoxin allowed in cereals are stipulated by food safety authorities. This thesis was a part of MTT Agrifood Research Finland’s Hyötygeeni project. The aim of the research was to study resistance of eight oat cultivars to F. culmorum and F. langsethiae. Indicators of resistance were germination of the infested seeds, the proportion of infected seeds and the amounts of mycotoxins. The trials were made in greenhouse with artificial inoculations. The results indicated that four cultivars expressed similar levels of resistance to both Fusarium species. Three cultivars had better resistance to F. langsethiae than F. culmorum and only one cultivar had better resistance to F. culmorum than F. langsethiae. In future research, the results can be utilized in resistance breeding. Global warming will increase the risk of plant diseases. On that account importance of breeding will be emphasized.
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(2012)Caraway (Carum carvi L.) belongs to the plant family Apiaceae and is grown for its aromatic seeds. In the year 2011 caraway was grown on 20500 hectares in Finland. Most of it is located in Ostro-bothnia, Southern Ostrobothnia, Tavastia, Finland Proper and Uusimaa regions. The yield quality and quantity of caraway produced in Finland is good, hence making it a valuable export crop. However, the quality and quantity of caraway yield can be affected by plant pests, like weeds, insect pests and plant diseases. This thesis was part of research conducted within Superior Caraway Chain –project. The research aimed to survey the state of caraway cultivations and occurrence of plant pests. The main focus of this thesis was on plant diseases affecting caraway in Finland. Special interest was targeted on differ-ences in white mold occurrence and biodiversity of fungi colonizing caraway seeds within common cultivation areas in Finland. Also the possible effect of different soil preparation and yield drying methods on the fungal populations on caraway seeds were evaluated. The results indicated that white mold is quite common in Finnish caraway cultivations. However, it was noticed that the severity of the problem varies between different areas and harvest years. Infec-tion risk seemed to be bigger in the area of Ostrobothnia and in older caraway plantations (e.g. second harvest year). In addition to white mold also different kind of necrotic spots and lesions were detected from the stems and stem bases. It seems that the most important agents causing these symp-toms are Fusarium- and Mycocentrospora acerina- and possibly Alternaria- and Phoma complanata-fungi. These fungi were also detected on caraway seeds. Other common fungal pathogens isolated from the seeds were Aureobasidium-species and Botrytis cinerea. In addition to the pathogenic agents also many kind of saprophytic fungi that able to produce mycotoxins, were isolated from the seeds. Statistical analysis suggested that cultivation area, harvest year and different soil preparation and yield drying methods can significantly affect the occurrence of some fungal pathogens in cara-way seeds. In addition to white mold, many fungal pathogens and disease agents that may pose a possible threat to Finnish caraway cultivation in future were found. At least for now, the disease situation of cara-way is under pretty good control in Finland and instead of diseases, insect pests and weeds are more problematic and important agents causing yield loss on caraway cultivations in Finland.
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(2014)Maize (Zea mays L.) is one of the most significant crops worldwide and the most common crop in Latin American countries. In Nicaragua, maize is produced mainly by small-scale farmers, who have no access to agrochemicals to control diseases. Fungi cause the majority of infectious diseases of maize. The two causal agents of the Tar spot complex do not cause major damage independently but together the oblicate parasite Phyllachora maydis Maubl. and the endophytic fungal Monographella maydis Müller & Samuels cause a lethal complex disease which causes significant yield losses in maize. The aim of this study was to determine the presence of the poorly known Tar spot disease in Nicaragua. The causal agents have been detected elsewhere in Latin American countries and now they are expected to occur also in Nicaragua, where 15 maize fields in three different municipalities (seven fields in Jalapa, one field in Pueblo Nuevo and seven fields in Nueva Guinea) were examined. Semi-structured theme interview was carried out to determine agricultural history and current situation of the maize fields. Twenty leaf samples from each field were collected randomly and the severity of Tar spot complex disease symptoms was estimated using a 9-grade scale. According to the prevalence of symptoms all seven fields from Jalapa were included in comparison of infection rate and the differences were tested by ANOVA and Tukey´s test. The fungal isolates in leaf samples were identified morphologically and isolated as pure cultures. The incidence of different fungal species in each area was examined by using logistic regression analysis. Risk odds-ratio was calculated by MedCalc calculator. To ensure the accuracy of morphological identification of the species, DNA from pure cultures was isolated with the CTAB-method. DNA was amplified with universal ITS (Internal Spacer Transcriber) primers ITS1 and ITS4, which copy the ITS1-, 5.8S- and ITS2 regions. ITS-regions of P. maydis were cloned in pGEM-T Easy vector and sequenced. All analyzed sequences were aligned with sequences of known species obtained from GenBank. In addition, ITS-regions of putative P. maydis and M. maydis isolates were annotated and their relationships in phylogenetic Neighbour-Joining analysis were determined with MEGA 5.2. The causal agents of Tar spot complex disease were tested for virulence by pathogenicity tests. Healthy maize leaves were used to determine the virulence of pathogens. Tests were carried out under laboratory conditions and repeated twice. Results suggested that Tar spot disease occurs in all sampled areas in Nicaragua and the prevalence of symptoms was affected by plant age, previous infections, nitrogen fertilization and the used maize varieties. The differences in incidence of symptoms in Jalapa were statistically significant. According the morphological and molecular identification, a total of 21 different fungi were observed in collected samples. The prevalence of species varied by region and regression analysis highlighted the occurrence of Xylaria sp. in Jalapa and Fusarium equiseti in Pueblo Nuevo. There is no previous evidence that Xylaria sp. could infect maize plants, however, the results suggested it is capable to infect maize as a secondary pathogen under favorable conditions. Sequence searches showed that ITS-sequences of P. maydis or M. maydis have not been added to GenBank previously. Phylogenetic analysis showed that both pathogens formed their own branch among the already known species. Results can be used when developing species-specific PCR primers to be used in seed inspection, predicting the spread of the disease, and studies on epidemiology, ecology and control of the fungal pathogens of maize in Nicaragua.
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(2012)The powdery mildew of strawberry (Podosphaera macularis) causes yield losses in both fields and under glass. The ability to resist the infection of powdery mildew is a desirable attribute in the breeding of new cultivars. The assessment of powdery mildew resistance of cultivars by laboratory tests would give tools to quickly separate resistant cultivars from susceptible in the process of plant breeding. The purpose of this study was to compare the powdery mildew resistance of strawberry cultivars demonstrated in laboratory and greenhouse tests, and to evaluate the methods used. In addition, it was tested in the F2 crossing populations of wild strawberry if the ability to resist powdery mildew could be genetically linked to a phenotypic character of runner production or the flowering habit. The ability to resist powdery mildew of the garden and wild strawberry was assessed in laboratory tests by inoculating detached leaflets of in vitro grown plants with conidia of powdery mildew, and incubating them in closed Petri-dishes with moist filter paper for two weeks. The symptoms of powdery mildew were assessed visually from the leaflets. Garden and wild strawberry plants were exposed to powdery mildew in the greenhouse, and the symptoms were assessed during an eight-week period. The detected differences between the garden strawberry cultivars were compared to the laboratory results. The differences between individual plants were observed in the F2 crossing populations of wild strawberry. The runnering/non-runnering trait and the flowering habit were also defined, and the connection of these traits to the powdery mildew resistance was tested. Runnering was observed from the plants in the greenhouse, and the flowering habit was determined in the laboratory with specific markers. The comparability between the laboratory and greenhouse tests of garden strawberry was poor. The variance in the laboratory data was great due to the difficulties in the controlling of the conditions, and the quality of the inoculum. Probably because of these problems the laboratory tests on the wild strawberry failed completely. In the greenhouse there could be seen differences between the individual plants of the F2 populations of wild strawberry. The differences were not able to be statistically linked to the habit of runner production or the flowering habit, but a hint of a weak connection could be observed between the runner production and the powdery mildew resistance. Stable conditions and the quality and freshness of the inoculum have a great role in the success of laboratory tests in assessing powdery mildew resistance. In the greenhouse the disease pressure should be kept limited, so that the differences in the resistance to powdery mildew can be assessed. The connection between the runner production and the powdery mildew resistance could be experimented in the future with a bigger test group.
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