Clonal variation in susceptibility of white birches (Betula spp.) to Mammalian and insect herbivores

Abstract

Resistance of small micropropagated plantlets and seedlings of white birch (Betula pendula Roth and B. pubescens Ehrh.) to hares (Lepus timidus L.), voles (Microtus agrestis L.) and weevils (Phyllobius and Polydrosus spp.) was determined. Field and cafeteria experiments were conducted over 2 yr period at several locations near Punkaharju Forest Research Station, Eastern Finland. There were significant differences among clones and seedlots (forest seed origins) in susceptibility to hares, voles, and weevils. One of the eight clones studied in detail was resistant to most tested agents (clone 39), whereas two clones were susceptible to each agent (clones 36 and JR/1). However, there was only one significant correlation (hare vs. Polydrosus weevil) among rankings of clones in susceptibility to different pests. Generally the differences among clones were similar in different experimental situations, indicating a genetic basis to variation in resistance. No difference in the susceptibility was observed between seedlots from natural forest and micropropagated plantlets from rapidly growing plus trees, suggesting that selecting for rapid growth did not compromise resistance as predicted by some theories.