Opportunities to breed for broad mite resistance in Rhododendron simsii hybrids

Broad mites, Polyphagotarsonemus latus Banks, are a key pest in many ornamental plants including pot azalea, Rhododendron simsii hybrid. These minute mites (<200 µm) cause browning and curling of leaves and flowers leading to economic losses as damaged plants are unmarketable. Development of resistant cultivars might lead to a sustainable solution in controlling this pest. We studied the response upon a broad mite infestation in R. simsii by means of gene expression. Data showed the induction of the jasmonic acid defence pathway in response to a broad mite infestation. Furthermore, an oxidative stress response was observed in infested plants when compared to control plants. Scanning electron microscopy of leaf morphology in eight R. simsii cultivars with a known susceptibility for broad mites revealed the presence of different trichome types. Short trichomes with a sticky end were seen in resistant or more tolerant genotypes. The outcome of this study might provide new insights in breeding for resistance against this pest in azalea.