We have carried out restoring of some Latvian alfalfa genetic resources from seeds of accessions that did not germinate in soil at all. Two of them were repatriated from the N. Vavilov All-Russian Institute of Plant Industry (multiplied more than 40 years ago) and three from the Research Institute of Agriculture (Latvia) (multiplied 15-20 years ago). For germination of old seeds we used early elaborated in vitro culture conditions. Germination rate ranged 2-60%, depending from the genotype and seeds storage conditions. Plantlets with well developed roots and 2-3 leaves were planted in the substrate in small pots and grown in a greenhouse about a month, then replanted in the soil in field conditions and grown till the maturity. Restored accessions are available now for evaluation and involving in the alfalfa breeding programs.
Wood ash recycling can be a reasonable method for energy producers to decrease waste problems. Using wood ash as a fertilizer or liming material could improve soil macro and micronutrient content in peat soils. Therefore, the effect of wood ash on Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.) juvenile growth and nutrient content in the soil after spreading wood ash in medium to high doses before and after planting seedlings was investigated in peat forests in the Eastern part of Latvia. The aim of the study was to evaluate the effect of high doses of wood ash on soil properties and the growth of planted Norway spruce and Scots pine seedlings up to 10 years after experiment establishment. Wood ash was applied a year before planting seedlings in doses of 5 and 10 t ha−1 and right after planting in concentrations of 5, 10, 15, and 20 t ha−1. Changes in macronutrient content (i.e., phosphorus [P], and potassium [K]) and tree height and diameter at breast height were measured at one and 10 years after establishing the experiment. Fertilization one year prior to planting the seedlings exhibited a positive response on tree height and diameter growth compared to fertilization after the seedlings were planted. Soil samples from fertilized plots one year after establishment contained more P and K in the soil than the control plots. Wood ash application of the highest doses did not reach the overdose limit, as the tree growth (height and diameter at breast height) results of fertilized plots were similar to those of the control fields; therefore, no significant negative effect on tree growth was discovered.
Norway spruce is economically the most important tree species in Northern Europe; therefore, its productivity and vitality have key role in the forest management of this region. Tree height is directly linked to the productivity of the stand and is affected by growing conditions and tree genetics. Height increment in young stands determines the further development of the stand therefore, it is important to evaluate the effect of various factors on tree height growth during this stage and assess the possibilities to improve it with silvicultural measures and tree breeding. This doctoral thesis aims to assess the effect of microenvironmental conditions and genetics on the height increment of Norway spruce at a juvenile age in planted hemiboreal forests in Latvia. The doctoral thesis summarizes seven thematically linked scientific publications, and their results indicate the possibilities for substantial improvement of the growth of Norway spruce at a juvenile age. Tree height is considerably and significantly affected by the type of soil preparation and soil fertilization with wood ash a year before planting or by applying additional fertilizer during the planting process. Furthermore, the effect of these forest management measures lasts for at least the next 10 years. Providing favorable microenvironmental conditions considerably increases the proportion of spruces with lammas shoots, which in turn, increases the total height increment of these trees. A positive feedback loop exists between the presence of apical lammas shoots and the tree height increment, leading to increased tree height in young stands. The occurrence of lammas shoots and the intra-annual development of the height increment is genetically determined. Growth intensity (mm per day) for progenies from open-pollinated families of plus-trees with larger height increment culminated later in the season, had higher growth intensity at the active growth phase and remained high for a longer period.
Accessions with no germinating seeds are a common problem in plant gene banks and research institutions. Our goal was to elaborate and apply an in vitro method of germination and multiplication of old aged seeds of red and alsike clover and alfalfa. Eighteen clover and five alfalfa accessions were used for germination in vitro. Most of the accessions had produced seeds more than 20 years ago and the seeds did not germinate in soil. Seed pre-treatment with different concentrations of potassium permanganate, as well as addition of phytohormones, AgNO3 and activated carbon to germinating media were tested. Plantlets for all germinated accessions were obtained, even in the case when seeds were 44-year-old (alfalfa). Germination rate in vitro not always correlated with seed age and ranged from 2 to 72%. Pre-treatment with potassium permanganate was effective both for seeds sterilisation and germination stimulation. Most germinated seeds formed phenotypically normal seedlings with all organs. In vitro multiplication of obtained clover plants was performed. Best results were achieved by micropropagation of stem segments approximately 2 mm in length. Number of finally obtained plants depended not only on seed germination ability, but also on micropropagation ability in relation to genotype, and on acclimatization success in soil after in vitro cultivation
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