Browsing by discipline "Växtpatologi"
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(2009)Phytoplasmas are plant pathogenic phloem colonizing bacteria-like organisms. They can cause severe growth disorders in plants and thus weaken the productivity of crop plants or even kill them. Phytoplasmas have not caused any epidemics on crop plants in Finland and thus they have been little studied. The aim of this study was to find out if plants that have phytoplasma-like symptoms are actually infected by phytoplasmas. Plants with growth disorders were collected and their DNA was extracted. Phytoplasmal DNA was multiplied from the samples using PCR with phytoplasma-specific primers P1 and P7. The products were sequenced and compared with sequences available from databases. Phylogenetic trees were constructed to show the kinship between the phytoplasmas. In this thesis X-disease phytoplasmas were found from dandelion (Taraxacum spp. Weber), scentless mayweed (Tripleurospermun inodorum Schultz Bip.), creeping thistle (Cirsium arvense L.), alsike clover (Trifolium hybridum L.) and blueberry (Vaccinium myrtillus L.). Aster yellows phytoplasma was found from one red clover (Trifolium pratense L.). Data on phytoplasmas has not been published in other Nordic countries. In Lithuania phytoplasmas have been detected in several plant species such as raspberry (Rubus idaeus L.), sour cherry (Prunus cerasus L.), apple (Malus sp. Mill.), barley (Hordeum vulgare L.), oat (Avena sativa L.) and several other grasses that also grow in Finland. The climate change can increase the amount of vector insects in Finland, which will most likely help phytoplasmas spread more efficiently and cause diseases also on crop plants. The import of plants from other countries may enable the spread of new vector and phytoplasma species in Finland.
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(2008)Pectobacterium atrosepticum is a bacterium that is a causative agent of blackleg and soft rot of potatoes at temperate climate zone. The genome of P. atrosepticum was sequenced at 2004. Sequence revealed six vgrG genes, and five of them are predicted to encode for proteins having uncharacterized function. VgrG proteins are found to be secreted by a novel secretion system called type VI secretion. They are also suggested to be a part of the type VI secretion translocon. VgrG proteins are presumed to be cytotoxic to the hosts of pathogenic bacteria. A mutation in a vgrG gene attenuates virulence of a few human and animal pathogenic bacteria. The aim of this study was to find out the affect of vgrG genes to the virulence of P. atrosepticum. In this study, transcription of vgrG genes of P. atrosepticum was measured by a real-time reverse transcriptase PCR. P. atrosepticum was grown in a virulence gene inducing conditions. Most active vgrG genes were deleted by Red recombinase using method. Each mutant strain carried deletion in one of the active vgrG genes. Virulence of the mutant strains was assessed on potato tubers, according to their ability to rot tissue. Three vgrG genes were induced in bacteria when they grew in the host tissue. vgrG genes were most active in samples, which were taken from stems 96 hours after inoculation. One mutant strain was slightly more virulent (P = 0,0077). Two strains were slightly less virulent, but results were not statistically significant (P > 0,05). According to the profile of transcription, vgrG genes might be novel virulence genes. However, virulence essays did not support that possibility. In fact, one of the mutations increased the virulence of P. atrosepticum. It is possible that other vgrG genes cover the function of the deleted gene. There is no clear evidence that vgrG genes or the type VI secretion are novel virulence determinants of P. atrosepticum. Perhaps they have some other function in the active stage of the infection. Example, they might protect P. atrosepticum from competitive microbes in the rotten potato tissue.
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(2008)The causal agents of Potato scab, S. scapies, S. turbidiscapies and S. aureofaciens spoil the quality of tubers, slow down the formation of potato seedlings, increase the number of small sized tubers and therefore can have a significant impact on the potato harvest. Sometimes the technical methods applied in the potato farming are not effective enough and there are no chemical means available to prevent potato scab. In this work the properties of selected Finnish Actinomyces-isolates were studied from the point of view of biological control. Both potato scab forming and stains that do not cause visible signs of potato scab in tubers were selected for the study. The purpose was to study the ability of the stains to inhibit the growth of potato scab bacteria in different pH-conditions. In addition the ability of Streptomyces-strains to inhibit the growth of silver scurf, stem cancer and black scurf was studied. The competitive balance between different Actinomyces and fungal strains was tested on plates. Greenhouse tests were used to study the root infesting of Actinomyces strains. Streptomyces strains inhibited each others growth. This inhibition was not linked to scab. All strains tested prevented the growth of silver scurf and ps pathogens but strains S.griseoviridis ja 16IV turned out being especially effective in preventing. All strains grew in pH-conditions 5.5-8.0. An unknown Streptomyces strain 16IV did not grow well in pH 5.5 and S. turbidiscapies which is known to persist in acidic conditions grew well also in pH 8.0. All tested strains colonized potato root. The study showed that some of the isolates had potential for future studies in biological control. More research is needed to study the root colonization and the antagonism properties of selected strains in root conditions. The causal agents of Potato scab, S. scapies, S. turbidiscapies and S. aureofaciens spoil the quality of tubers, slow down the formation of potato seedlings, increase the number of small sized tubers and therefore can have a significant impact on the potato harvest. Sometimes the technical methods applied in the potato farming are not effective enough and there are no chemical means available to prevent potato scab. In this work the properties of selected Finnish Actinomyces-isolates were studied from the point of view of biological control. Both potato scab forming and stains that do not cause visible signs of potato scab in tubers were selected for the study. The purpose was to study the ability of the stains to inhibit the growth of potato scab bacteria in different pH-conditions. In addition the ability of Streptomyces-strains to inhibit the growth of silver scurf, stem cancer and black scurf was studied. The competitive balance between different Actinomyces and fungal strains was tested on plates. Greenhouse tests were used to study the root infesting of Actinomyces strains. Streptomyces strains inhibited each others growth. This inhibition was not linked to scab. All strains tested prevented the growth of silver scurf and ps pathogens but strains S.griseoviridis ja 16IV turned out being especially effective in preventing. All strains grew in pH-conditions 5.5-8.0. An unknown Streptomyces strain 16IV did not grow well in pH 5.5 and S. turbidiscapies which is known to persist in acidic conditions grew well also in pH 8.0. All tested strains colonized potato root. The study showed that some of the isolates had potential for future studies in biological control. More research is needed to study the root colonization and the antagonism properties of selected strains in root conditions.
Now showing items 1-3 of 3