Preference of Japanese field voles (Microtus montebelli) for apple rootstock genotypes: Correlations with bark characteristics

Along with the expansion of dwarfing apple rootstocks in Japan, damage through bark-eating by the Japanese field vole (Microtus montebelli Milne-Edwards, 1872) in apple orchards has increased. The most prevalent cultivar, JM7, in particular, is highly susceptible to vole gnawing. Hence, it is a pressing task to reduce vole damage to apple rootstocks by developing and introducing a new dwarfing rootstock cultivar that is less susceptible to voles. In order to achieve this, it is critical to elucidate which rootstock characteristics underlie vole preference. Preferences of the Japanese field vole among seven apple rootstocks were examined by a cafeteria experiment using ten voles. Voles showed a clear preference for the JM7 cultivar. Nutrient and morphological analyses of these rootstocks revealed that voles preferred to eat rootstocks which were poor in total phenolics, rich in nitrogen, and had low edible ratios of shoots. Among the tested seven rootstocks, JM7 was richest in nitrogen, and poorest in total phenolics. Our results indicate that future breeding projects on vole-resistant dwarfing apple rootstock genotypes should aim to develop a cultivar that is rich in total phenolics and poor in nitrogen, while keeping the advantageous traits of the JM7 rootstock, such as high productivity, and ease of propagation by hardwood cutting.