Past work on inducible resistance has focused on leaves, although recent work has focused on tissues like roots and sometimes flowers. Less is known how these compounds affect florivores and whether a plant's response in flowers may depend on the presence of active anthocyanin pathways. We aim to answer the question whether inducible resistance compounds in wild radish, Raphanus sativus, can affect florivores and if this effect is mediated by the anthocyanin content of the flower.
In our first experiment we looked within a single population of R. sativus to see if different maternal lines induce resistance to florivores. Seeds from four lines were randomly assigned to a control (no damage) or damage treatment. Damage consisted of allowing a neonate Spodoptera exigua larva to feed on the first true leaf until half of the area was consumed. Control plants received only a cage. To assay levels of resistance we allowed a neonate S. exigua larva to feed on petals for 10 days.
In a second experiment we used seeds from fourteen different R. sativus populations across Northern California to increase the breadth of genotypes tested. Using the same methods as in the first experiment, we tested whether induction depended on whether the plant produced white (anthocyanin free) or purple (anthocyanin-containing) flowers.
Results/Conclusions
In the first experiment, we found that in one maternal line the larvae from the experimental plants weighed significantly less that larvae from control plants, but there were no differences between the treatments for the other three lines. In the second experiment we found a significant damage treatment by petal color interaction such that larvae from experimental plants weighed less than control larvae, but only in the white-flowered plants.
These results demonstrate that leaf damage can induce resistance in flowers. This effect can depend on the genotypes or flower color. Surprisingly, and in contrast to previous work, inducibility was stronger in white flowers than in purple flowers. Induced resistance in flowers may be adaptive if the same types of herbivores damage leaves and flowers in R. sativus and if damage to flowers affects pollination. Alternatively, induced resistance may be side-effect of induced resistance in leaves, since R. sativus leaves are highly inducible by prior leaf damage. We know from observation that the same herbivores can attack flowers and leaves, but thus far no experiments have been performed to determine if florivory can affect pollination in this system.