Wild relatives of Chrysanthemum as sources of resistance against the thrips Frankliniella occidentalis

Abstract Chrysanthemum is one of the most important ornamental crops worldwide. Cultivation of C hrysanthemum is affected by infestations of thrips, of which in Europe Frankliniella occidentalis is the most important species. Although genetic variation for thrips resistance in Chrysanthemum cultivars has been observed, no strong thrips resistance has been successfully introduced in breeding programmes. Crop wild relatives can be sources of resistance traits, but information on the thrips-resistance level of wild species in the Chrysanthemum genus or of species in the related genus Artemisia is not yet available. Therefore, we screened 47 accessions from 23 Chrysanthemum species and related genera in whole plant assays for thrips population build-up and in leaf-disc assays for larval development and survival. We identified several wild Chrysanthemum and Artemisia accessions on which population build-up was reduced, survival was low, and development of larvae was inhibited. On five highly resistant accessions, larvae were impaired in their development at the first larval stage (L1), effectively interrupting the life cycle of thrips. Next, we investigated the possible role of T-shaped and glandular trichomes in thrips resistance and found a positive correlation between arrested development in the L2 stage and higher density of T-shaped trichomes. However, not all the resistant accessions showed higher trichome density, suggesting that the latter accessions contain other resistance mechanisms. The identified resistant and susceptible wild relatives of Chrysanthemum may be used in further studies to elucidate the mechanism and the genetics of thrips resistance, and resistant accessions could be used as sources of thrips resistance in Chrysanthemum breeding programmes.