Characterization of trichome morphology and aphid resistance in cultivated and wild species of potato

Trichomes are specialized epidermal structures that protect plants from abiotic and biotic stresses. Cultivated potato (Solanum tuberosum) is known to have both glandular and non-glandular trichomes. However, the criteria for trichome type classification have not been studied in detail. In addition, there is a poor understanding of the types of trichomes that exist in wild potato species. Here, the morphology and density of trichomes were compared between a representative cultivated potato variety and 17 wild potato species using Cryo Scanning Electron Microscopy (CryoSEM). Based on trichome morphology, the cultivated variety and each of the wild species were seen to have two glandular and two non-glandular trichome types. We classified the eighteen potato species into four groups using trichome type and density criteria. Groups I and II represented species with a higher density of glandular or non-glandular trichomes, respectively, on both abaxial and adaxial leaf surfaces. Group III represented species with a higher density of non-glandular trichomes on abaxial leaf surfaces alone. Group IV represented species with an overall lower trichome density on both abaxial and adaxial leaf surfaces, but which was formed of both glandular and non-glandular types. Honey dew spots were quantified following infestation with the aphid Macrosiphum euphorbiae to test whether trichome composition is associated with resistance to aphid feeding. Fewer honey dew spots were observed in the Group I representative species S. berthaultii and S. hougasii compared to that in species from other groups. Furthermore, correlation coefficient analysis showed that honey dew spot number was negatively associated with glandular trichome density. These results imply that glandular trichomes play an important role in aphid resistance and thus can be used for developing insect-resistant potato.