Cultivar susceptibility and stress hormone response in raspberry [Rubusideaus) to two-spotted spider mite (Tetranychus urticae)

摘要

The two-spotted spider mite (Tetranychus urticae) is a common pest on raspberry (Rubus ideaus), especially when cultivated under cover. In three experiments we studied susceptibility to spider mite in six raspberry cultivars: 'Carmina', 'Esperanza', 'Maravilla', 'Polka', 'Riviera' and 'Tulameen'. Individual leaves of long cane plants were inoculated with 10 spider mites. The first two experiments showed the lowest number of spider mites on 'Carmina' and 'Riviera' and the highest on 'Polka' and 'Maravilla'. In the third experiment the lowest number of mites were found on 'Carmina' and the highest number on 'Tulameen' and 'Polka'. Two raspberry cultivars: 'Carmina' (resistant) and 'Maravilla' (more susceptible) were chosen to study the response of stress hormones upon spider mite infestation. Both cultivars were grown as a dense crop in a greenhouse and inoculated with spider mites to establish one treatment with high infestation and one with low infestation. During four weeks, number of mites (adults, nymphs, larvae and eggs) were counted and leaf samples were taken for LC-MS/MS analysis of the stress hormones salicylic acid (SA) and jasmonic acid (JA). Leaf samples taken at the start of the experiment (week 0) served as a control before infestation. For both genotypes and for both infestation levels, the concentrations of SA did not differ significantly either before or after infestation. Notably, the JA concentrations dropped in both cultivars and for both infestation levels, to levels up to tentimes lower at 7 days post inoculation (dpi). Only in 'Maravilla' the level of JA increased again at 28 dpi in the low and high infestation level, although only in the high infestation level spider mite numbers were decreasing. It is known that JA levels often increase as a response to herbivores like spider mites. However, spider mites also can interfere with the stress response in the plant by influencing stress hormone levels. Therefore it is probable that for the tested raspberry cultivars the decrease of the JA levels is due to defence suppression caused by the spider mites.