Resistance evaluation of two-spotted spider mite in the genus Fragaria L.

Comparative resistance studies with two-spotted spider mite (Tetranychus urticae Koch) are only performed for wild species of Fragaria chiloensis and F. virginia, so far. In the present study we investigated the symptomatology in the genus Fragaria. 315 wild species accessions belonging to 20 species of the “Professor Staudt Collection” were evaluated. This living plant collection was cultivated in a greenhouse during which hot and dry summer conditions allowed the two-spotted spider mites to thrive. No insecticides were applied, allowing natural infestation to occur. The spider mites were observed on all plants in the collection. The degree of infestation was recorded on old and young leaves using a predefined nine-point scoring system. Symptoms occurred on all accessions without any exception, but with variable graduation especially on old leaves. These were infested at a much higher density than the young leaves. The young leaves showed fewer symptoms. For the first time, a comparative study of spider mite resistance in the genus of Fragaria was performed. Genetic resources of tolerance were described for some accessions of F. chiloensis, in contrast many accessions of F. cascadensis, F. chiloensis, F. moschata, F. vesca, and F. viridis showed severe phytophagous feeding symptoms. Further studies aiming on defined inoculation and resistance mechanisms need to be performed to assess useful accessions for further breeding.