Scots pine (Pinus sylvestris) is Latvia's most economically important tree species. It accounts for 38% of the total forest area of Latvia. One of diseases affecting P. sylvestris is root rot caused by the fungus Heterobasidion annosum, which causes large economic losses. There is some evidence of Scots pine trees with higher levels of resistance but no absolutely resistant tree clones have been described so far. Many genes encoding peptides and proteins with direct or indirect antifungal activity have been described in various plant species, but only few of them have been studied in conifers. In our study we have utilised various approaches to research genetic aspects of Scots pine resistance to H. annosum. Here we present our initial results. Initially, H. annosum infection was determined in 300 trees and in a subset of twenty seven trees representing fifteen families (progeny of one mother tree) infection levels were quantitatively characterised. Candidate-genes were selected based on previously published research. Gene copy number variation (CNV) analyses were performed on selected samples. Copy number variation polymorphism was detected for a gene encoding a thaumatinlike protein analogues of which are described as potent antifungal proteins in other plants. As increased gene copy number can lead to increased gene product amounts in cells it is possible that an increased copy number of thaumatin-like protein is beneficial to the pine tree in respect to resistance against H. annosum and other pathogens. Further experiments need to be performed to investigate this in more detail.

It is essential to have information on the tree biomass due to the fact that it is an important ecosystem pool for reporting changes in carbon stocks of forests and increased attempts to diversify the energy sources. In Latvia, comparatively few studies have focused on this topic so far. Our study was conducted on two 36 - 38 years old Norway spruce plantations. Detailed stem analysis of 39 trees was performed, and biomass of the above-ground tree components was determined. We analyzed tree and clone-level biomass distribution, biomass relations with tree dimensions and dependence on the genetic factors. The mean total biomass (kg d.w.) of all analyzed sample trees was 131.4 ± 10.58 kg, the mean biomass of stem 85.9 ± 6.98 kg, the mean biomass of dead branches 8.3 ± 0.82 kg, the mean biomass of living branches 23.5 ± 2.34 kg and the mean biomass of needles 13.7 ± 1.22 kg. On average, 66.1% of biomass was allocated to the stem, 6.4% to the dead branches, 17.4% to the living branches and 10.1% to the needles. The biomass of the analyzed trees positively correlated with all tested tree parameters - DBH, tree height, stem volume. Typically, with increasing tree parameters total biomass and stem biomass increased rapidly but branch and needle biomass increased slowly. Significant differences of tree dimensions were detected between the clones, and the differences in total biomass and stem biomass were clearly correlated with the differences in tree dimensions over clones. No significant impact of the clone was found specifically on the tree biomass or its distribution.

Survival, growth (height, diameter at breast height, stem volume, yield) and quality (thickest branch up to 2 meters of tree height, branchiness, and stem straightness in grades) of phenotypically selected Scots pine plus-tree progenies from different regions in Latvia at the age of 32 years have been analyzed. The material was planted in 4 tests in different forest types (Cladinoso-callunosa, Vacciniosa, Hylocomyosa, and Oxalidosa) in Kalsnava, Eastern part of Latvia. Average number of trees per family varied from 11 to 21 (survival 18-35%). Mean height for Scots pine at the age of 32 years was 14.2 -16.3 m, coefficient of variation -10-17%, diameter at breast height - 13.1-17.7 cm, 24-32%, stem volume 0.1-0.2 m**3, 49-64%, diameter of thickest branch at up to 2 meters of tree height - 1.3-1.7 cm, 23%. To secure ability for detection of significant (alpha=0.05) family differences, average number of trees number per family at evaluation age should be at least 24. Narrow sense individual tree heritability (h**2) was 0.11 for stem volume, 0.09 for diameter at breast height, and 0.07-0.11 for diameter of thickest branch up to two meters of tree height.

The effect of different fertilizer backgrounds on the potato yield and its chemical composition of different varieties, destined for processing into chips, was investigated at the Elmininkai Research Station of the Lithuanian Institute of Agriculture in 2000. The investigation showed, that potato tuber yield depended on fertilization and genetic characteristics of the potato variety. The most productive potatoes of the following varieties were: early Voke (20,6-36,0) t ha*[-1) and medium late Saturna (27,0-35,4 t ha*[-1)).

Evaluation of virulences of Blumeria graminis f.sp. hordei was started in Latvia in 1981, first in the Baltic States. Until 1994 the observations were carried out only in the central part of Latvia - Salaspils. As the climatic factors and the used barley varieties in various parts of Latvia are different, in 1995 we started regular observations of the particularities of the genetic structure of the pathogen population also in Daugavpils. The aim of this investigation was to detect particularities of the genetic structure of the pathogen population in different parts of Latvia in 1996-2000.