Cumulative effect of needle cast on Scots pine saplings

Premature needle cast, affecting the needles on one-year old shoots, thus shrinks the size of green crown of Scots pines, and can cause reduction of increment or even death of trees, especially during first years of their growth. Aim of our study was to evaluate the lasting impact of pathological needle cast to young Scots pines and its implications for tree breeding. Assessment of needle cast damages in 5 grade scale and measurements of height were done repeatedly in Scots pine open pollinated progeny trial, consisting of 65 families, located in central part of Latvia. Proportion of saplings with different level of needle cast damage differed significantly between the years of impact: severely damaged were 51%, 30% and 17% of saplings in growing seasons 4, 5 and 6, respectively. Both the needle cast damage grade at current growing season, as well as height of the sapling before the needle cast infection (at the end of the third growing season) had a significant effect on its grade of needle cast damages in the next growing season. Cumulative level of needle cast damages at the age 4 to 6 years had significant negative effect on height of the saplings at the age of 12 years both at individual tree and family mean level, as well as on survival. Selection of best growing families in such trial would also lead to selection of genotypes least affected by the disease.