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Browsing by Subject "dormancy"

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  • Kemppinen, Johanna (2017)
    Blackcurrant (Ribes nigrum L.) is a woody plant in cold regions and it adapts well for the Finland’s boreal zone. There were less than 600 companies farming blackcurrant and green currant in 2014 and the acreage was 1449 ha and the level of yield was over 1000 kg/ha. In year 2016, the number of companies were 544 and the acreage was 1435 ha and the level of yield less than 1000 kg/ha. There has been a pressure to reduce the high price of domestic blackcurrant, due to that the inexpensive imported berries have been taken more position in industry. The global warming can be a serious threat for the cultivation of blackcurrant in the future. There is a need for new cultivars of blackcurrant in Finland and the objective of this research was to examine the depth and reversal of on dormancy on various points of time and the resilience of winter. For the results the bud burst was monitored in quantity and temporal on forcing. The processing of release of dormancy in various temperatures and light conditions before the forcing was also included to the research. The cold hardiness was tested in temperatures, which was descending step by step in controlled sub-zero experiment. The results demonstrated that the bud burst was the lowest during the deepest dormancy in OctoberNovember and the largest in February, when the dormancy was already released. ‘Almiai’ and ‘Gagatai’ were the best cultivars, which were able to maintain the dormancy; in first forcing in October, bud burst 0 %. The bud burst was particularly substantial in February and ‘Ben Tron’ the bud burst was even 80 %. In October-November the time elapsed for bud burst was highest and least was in February with average of 10 days. The most optimal temperature in dormancy release was 0 ⁰C. On the cultivar ‘Mikael’ the bud burst was quicken in +18 ⁰C . The longer the processing time was, the shorter was the time for bud burst. The temperatures +12 ⁰C and +18⁰C were too high for dormancy release. In cold hardiness, the cultivars didn’t differ much from each other. The results demonstrate that the cultivars differ from each other in the depth of dormancy and release. ‘Almiai’ and ‘Gagatai’ maintained best their dormancy. These cultivars could be suitable options for farming in Finland. They were also winter hardiness. In the future, there should be breeding of blackcurrant cultivars, which adjust different kind of environments. Additionally, we should discover and breed cultivars, which have good resistant for winter and maintain dormancy, even though the temperatures are varying in winter.
  • Solarmo, Elina (2011)
    Potato virus Y (PVY) is currently the most yield and quality limiting pathogen of the cultivated potato (Solanum tuberosum L.) globally. While yield losses specific to PVY are hard to measure in presence of other pathogens they are estimated as 20 to 80 %. The most important way by which the virus spreads are virus-infected seed potatoes. High quality seed potato is very important for food, food industry and starch potato production. Visual inspection of the potato plants underestimates usually the real percentage of PVY infection. Laboratory tests provide more accurate results about the incidence of infections. The problem with testing PVY is that the virus cannot be detected reliably from samples taken from dormant tubers. Different treatments have been used to break dormancy of tubers e.g. chemicals (Rindite, bromoethane), plant hormones (gibberellic acid) and adjusted storage temperatures (cold and heat treatment). The results have varied a lot. In this thesis an experiment with oxygen-carbon dioxide (O2 40 %-CO2 20 %) treatment with different periods of time was used to end dormancy of potato tubers. The aim was to test whether the treatment could end dormancy of tubers earlier than normally and to see if the treatment has an effect on detection of PVY. One aim was also to test how reliably PVY could be detected from tuber and sprout samples compared with potato leaf samples which are normally used for virus testing. Results from the sprouting treatment were variable and could not be readily generalized. The treatment had no effect on the detection of PVY incidence. When the different plant materials were compared with each other, tuber material showed the lowest PVY percentage when compared to sprouts and leaves. Testing sprouts also underestimated the incidence PVY. The best material for testing PVY in potatoes were the leaf samples.
  • Sjöblom, Robin (2020)
    In winter plants are exposed to harsh winter conditions with low temperatures being one of the major challenging factors. Traditionally winter has been considered a period unfavourable for plant growth and activity, but newer findings reveal higher levels of activity than previously assumed possible. Adaptations to different winter conditions are observed between species but also within species between populations which can be expressed in differing phenology between populations. Dormancy is a widespread phenomenon in the plant kingdom with major importance in plant evolution. Dormancy is considered to be present in seeds and buds of a wide spectre of plant groups, but asexual reproductive units like bulbils have been thought to lack the ability to undergo the phenomenon of dormancy. Findings suggest that a dormancy-like phenomenon can also be present in bulbils. Allium oleraceum is a bulb forming geophyte with a widespread distribution in Europe that grows on many differing habitats. The predominate form of reproduction in the species is the vegetative formation of bulbils. The wide distribution has led to adaptation to different environmental conditions, furthermore the species displays six levels of polyploidi partially differing in traits like ecology. The differences between cytotypes are regional and there are large intracytotytpic variations. In Finland tetra- and pentaploid populations have been reported, differing in their distribution patterns. The Finnish cytotypes exhibit differences in morphology but there is also evidence for ecological differences between the cytotypes. In addition, there is an atypical tetraploid population which differ significantly morphologically from other tetraploid populations. The objective of this master’s project was to examine the growth of bulbils from three different origins of Allium oleraceum. Another objective of the experiment was to give information on differences between the cytotypes in Finland, tetra- and pentaploids, but also the atypical tetraploid cytotype. Furthermore, I investigated whether the bulbils exhibit a dormancy-like phenomenon, with a special focal point on dormancy according to Vegis’ theory (1964). Earlier findings have shown considerable capability of growth during winter in Allium oleraceum, which is also examined in this project. The experiment included collected bulbils from two localities. Tetra- and pentaploid bulbils were collected from a mixed population of both cytotypes in Tvärminne, Hangö, and tetraploid bulbils were also collected from the atypical tetraploid population on Sveaborg, Helsingfors. Growth experiments were done outside and in growth chambers with controlled temperature and light conditions. The bulbils were planted outside in early autumn. Of each origin one group was kept outside during the entire winter, one group was put in growth chambers in December and one group was put in growth chambers in February to examine the effect of differing winter length on growth. During the experiment, the timing of growth onset in bulbs and leaf growth was followed up. The origins included in this project exhibited considerable differences. The pentaploid cytotype from Tvärminne had bulbils of greater size than the tetraploid cytotypes, between which there was only an indication of a difference. For the bulbils from the atypical tetraploid population growth onset took place early in the autumn and the vast majority of the bulbils started growing in a short period of time. For the two origins from Tvärminne the growth onset took place later and a considerable number of bulbils started growing in the spring. The tetraploid cytotype from Tvärminne exhibited earlier growth onset and a higher share of bulbils started growing in the autumn than the pentaploid cytotype from Tvärminne. In the growth chambers the differences between the three origins were not as obvious but the two cytotypes from Tvärminne were affected by the timing of the experiment more than the atypical tetraploid cytotype from Sveaborg. The observed differences between the origins in the experiment are thought reflect the different distribution patterns of the cytotypes and could hence be adaptations to different conditions. The atypical tetraploid population could be of Central European origin which would mean that it could have adaptations to mild winters which would explain the big difference between this origin and the two other origins. Between the two experiments in the growth chambers significant differences were observed. The growth was considerably greater in February than in December for all origins, especially in the midmost temperatures. The observed differences between the two experiments signifies that bulbils of Allium oleraceum exhibits a dormancy-like phenomenon and according to Vegis’ theory. In contrary to earlier findings, only little growth was observed during winter. The lack of considerable growth could be explained by the thick snow cover which made the amount of light that reached the plants very low which then led to little growth. The results from this project suggest that there are differences between the three different origins of bulbils included. Further studies are needed to find out if the observer differences are adaptations to local conditions or if there are differences on a higher level between the Finnish cytotypes.