Soil fertility alters susceptibility of young clonal plantlets of birch (Betula pendula) to a dipteran stem miner

Abstract

Larvae of Phytobia betulae Kangas (Diptera: Agromyzidae) mine within the differentiating xylem tissue near the vascular cambium of birch trees. These larvae start in the canopy and move toward the base of the stem, leaving permanent brown tunnels in the wood. The aim of this study was to test whether young clones of European white birch (Betula pendula Roth) exhibit differences in susceptibility to Phytobia, whether altered growth media (soil fertility) and the subsequent growth reaction affect the susceptibility of birch to Phytobia, and whether there is genotype × environment interaction. Soil fertility levels of 2-year-old micropropagated plantlets of nine birch clones were manipulated in two experiments. The growth and size of the plantlets were measured and the density of Phytobia was estimated from larval tunnels (pith flecks). Phenotypic variation (nutrient effect) influenced the occurrence of Phytobia. Phytobia densities were significantly higher on plantlets grown at high soil fertility levels than on plantlets with the lowest soil fertility level. Clonal effects were detected in only one experiment. In general, Phytobia favoured birch clones with larger diameters.