The impact of climatic and genetic factors on needle cast damage, as well as relationship between the degree of damage and survival and growth of trees was evaluated in the study. The analysis was done in two series of experiments, both established in two locations in Latvia (central and eastern part). Needle cast damage (in 5 grade scale) as well as the height and height increment, diameter of root collar and survival of trees were assessed. Results suggest that the degree of needle cast damage was influenced by the genetic, as well as climatic factors, and also their interaction. The average degree of needle cast damage in experiment of open-pollinated families was 4.7 ± 0.01 in central and 4.6 ± 0.03 in eastern Latvia; in the experiment of control-crossed families it was 4.6 ± 0.02 in central and 3.4 ± 0.04 in eastern Latvia. The impact of genetics on the needle cast damage degree was statistically significant (p is less than 0.05), and this effect was observed when any of growth traits (diameter, height or height increment) was used as a covariate in analysis. Results suggest the potential to select more resistant families, since the genetic correlation of grade of the damage between locations was significant (r = 0.40 - 0.72) and therefore improve also the growth of trees, since the grade of the damage had a negative correlation with growth traits both at provenance and family mean level (r = -0.69 and r = -0.42; p is less than 0.01).

Recent studies have demonstrated the occurrence of different needle cast (Lophodermium spp.) species in young Scots pine Pinus sylvestris L. stands in different regions of Latvia. The impact of these fungi has been known also historically, but is predicted to increase in future due to climate changes that are forecasted to have a positive impact on presence and vigour of various species of fungi. The aim of the study was to characterize the needle cast damage in young Scots pine stands in central Latvia. Material was collected in 12 Scots pine stands at the age of 3 to 26 years in 28 plots with a total area of 8.1 ha in the middle of two consecutive growing seasons (years 2012 and 2013). The impact of disease was visually assessed using a 5 grade scale, depending on the proportion of damaged (brown) one-year old needles. Incidence of damaged trees (P, %) and damage intensity (R, %) was calculated and used to characterize the occurrence and severity of the infection in the stands as well as its link to other stand parameters. Damage incidence (ranging from 20 to 100%), as well as the intensity (from 4 to 35%) was slightly (incidence-also significantly) higher in 2013 in comparison to 2012; correlation between those two parameters was strong in both years (r = 0.94 and r = 0.84, respectively). The stand age, density (ranging from 1200 to 6900 trees haE-1) and tree height did not significantly correlate with the damage incidence or intensity. Forest type (Hylocomiosa or Myrtillosa mel.) was not a significant factor, too.

Scots pine (Pinus sylvestris L.) is one of the most widespread coniferous species in boreal zones and it has a considerable economic importance in the Baltic countries. The impact of fungi on Scots pine has been known also historically, but it is predicted that it will increase in future due to climate changes that will have a positive effect on incidence and vitality of various species of fungi. The aim of the study was to characterize the occurrence of Lophodermium spp. in young stands of Scots pine in Latvia. Needle samples were collected from young pine stands (aged 1 – 14 years) located in all regions of Latvia. DNA extraction from needles was done using modified CTAB protocol, presence of Lophodermium in total extracted DNA was detected using a PCR method. Meteorological data – air temperature and precipitation – were obtained from all 34 observation stations of the Latvian Environment, Geology and Meteorology Centre. The presence of Lophodermium spp. was detected in all surveyed stands, and occurrence differences between the western and eastern regions were significant (p = 0.004). The occurrence of Lophodermium spp. in the eastern and western regions was affected by the meteorological conditions in autumn and winter of the previous years, as well as differences in the given years’ air temperature and precipitation. In 2016, the eastern region of Latvia had a higher May−August precipitation and, to a lesser extent, temperature, which correlated with a higher occurrence of Lophodermium spp.