CLONAL VARIATION IN SUSCEPTIBILITY OF WHITE BIRCHES (BETULA SPP) TO MAMMALIAN AND INSECT HERBIVORES

Resistance of small micropropagated plantlets and seedlings of white b irch (Betula pendula Roth and B. pubescens Ehrh.) to hares (Lepus timi dus L.), voles (Microtus agrestis L.) and weevils (Phyllobius and Poly drosus spp.) was determined. Field and cafeteria experiments were cond ucted over 2 yr period at several locations near Punkaharju Forest Res earch Station, Eastern Finland. There were significant differences amo ng clones and seedlots (forest seed origins) in susceptibility to hare s, voles, and weevils. One of the eight clones studied in detail was r esistant to most tested agents (clone 39), whereas two clones were sus ceptible to each agent (clones 36 and JR/1). However, there was only o ne significant correlation (hare vs, Polydrosus weevil) among rankings of clones in susceptibility to different pests. Generally the differe nces among clones were similar in different experimental situations, i ndicating a genetic basis to variation in resistance. No difference in the susceptibility was observed between seed lots from natural forest and micropropagated plantlets from rapidly growing plus trees, sugges ting that selecting for vapid growth did not compromise resistance as predicted by some theories.