Data from: Fungal volatiles influence plant defence against aboveground and belowground herbivory

Plants have evolved resistance traits that negatively affect attackers,
and tolerance traits that sustain plant growth despite herbivore damage.
These mechanisms often co-occur in a mixed-defence strategy, balancing
resistance and tolerance. These plant defences can be enhanced upon
interaction with soil microorganisms. Here, we investigated the effects of
volatiles emitted by soil-borne fungi on plant defence to insect
herbivory, and on plant phenology. We exposed roots of Brassica rapa
plants to volatiles emitted by four soil-borne fungi. As a proxy of plant
resistance, we assessed the performance of Pieris brassicae, a caterpillar
feeding on leaves and inflorescences, and of Delia radicum, an insect root
herbivore. As a proxy of plant tolerance, we compared growth of
volatile-exposed plants challenged with or without insects. Additionally,
we assessed the effects on plant phenology by recording bolting time and
by counting the number of buds and flowers. Plant exposure to fungal
volatiles differentially affected plant resistance to above- and
belowground herbivory. Performance of P. brassicae caterpillars differed
between the fungal volatile-exposed plants but were variable between
experimental batches. In contrast, the effects of fungal volatiles on D.
radicum performance was predominantly negative, indicating an increased
plant resistance. Despite root consumption by D. radicum, root dry weight
remained unchanged in infested plants compared with uninfested ones,
irrespectively of the volatile exposure, suggesting compensation for the
tissue loss, sometimes at the cost of undamaged aboveground tissues. When
B. rapa plants were attacked by P. brassicae caterpillars, only exposure
to volatiles of some fungi led to compensation for the loss of aboveground
tissues consumed by the caterpillars, which differed between leaves and
inflorescences. Furthermore, bolting was accelerated in response to
volatiles of some fungi, resulting in more buds and flowers, which
suggests a potential enhancement of plant fitness. Our data show that
fungal volatiles can modulate the mixed-defence strategies of B. rapa
plants, balancing plant resistance and tolerance to above- and belowground
herbivory. These effects may be variable and were fungus-specific.
Ultimately, plant fitness may be enhanced upon root exposure to fungal
volatiles.