Abstract
Increasing resistance against biotic and abiotic factors is an important goal of forest tree breeding. The aim of the present study was to develop a root rot resistance index for Scots pine breeding and evaluate its effectiveness. The productivity, branch diameter, branchiness, stem straightness, spike knots, and damage from natural infection of root rot in 154 Scots pine open-pollinated families from Latvia were evaluated through a progeny field trial at the age of 38 years. Trees with decline symptoms were sampled for fungal isolations. Based on this information and kriging estimates of root rot, 35 affected areas (average size: 108 m2; total 28% from the 1.5 ha trial) were delineated. Resistance index of a single tree was formed based on family adjusted proportion of live to infected trees and distance to the center of affected area. Heritability for resistance to root rot based on the value of this index, was high (0.37) and comparable to indices of growth traits. Correlations of family breeding estimates between resistance to root rot and the other traits were not significant, except for a weak, yet significant, positive correlation with diameter at breast height and branch diameter. Selection index including only growth traits (height and stem volume) had a negligible effect on damage by root rot. We detected a maximum genetic gain in resistance index of 33.7% when incorporating it into the selection index with positive gains for growth traits (6.5–11.0%). Two-stage selection with prior selection of the most resistant families was not superior to the use of selection index with only rot resistance included. Overall; rot resistance index appeared to be an effective tool in tree breeding for the selection of more resistant families, using the existing trials with natural (uncontrolled) infection
Highlights
Scots pine (Pinus sylvestris L.) is one of the most economically important tree species in the BalticStates and Scandinavia
For 149 trees, 28 different H. annosum genotypes were registered over a total area of 1.55 ha, and 35 affected areas of root rot obtained
There are no conifer species with genetically determined total resistance against the pathogen Heterobasidion spp. [6,7], estimated high heritability of resistance index (Table 1) suggests existing variation in the susceptibility of Scots pine to this fungus being strongly genetically controlled
Summary
In this region, it is regenerated primarily by planting, and most of all the plant material is a result of tree breeding; seeds for plant production are collected from seed orchards. It is regenerated primarily by planting, and most of all the plant material is a result of tree breeding; seeds for plant production are collected from seed orchards It is both relatively straightforward as well as important to improve a particular trait in significant portion of Scots pine stands. Scots pine breeding primarily had been focused on achieving gain in traits related to productivity (height, diameter, volume production), and frost hardiness in the northern part of the region. Little has been done in resistance breeding at practically applicable scale; the most prominent activities include selection
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