Piperonylic acid (PA) treatment induces systemic plant resistance
against plant-parasitic nematodes, without negative effects on plant
growth and development
Foliar PA pre-treatment enhanced resistance to the root-knot nematodeMeloidogyne incognita, as evidenced by a reduced number of galls
28 dai (-56%, P < 0.001), an effect that showed no
dose-dependence over the tested concentration range (100 - 1000 µM;Figure 1a ). PA also induced resistance against the rice
root-knot nematode M. graminicola at 14 dai (-40%, P <
0.001; Figure 1b ). As PA is not acutely toxic to M.
incognita or M. graminicola (Table 1 ), reduced
susceptibility is likely due to induced resistance (IR) rather than
direct toxicity. Our data suggest a conservation of PA-IR between dicots
and monocots.
To verify that PA-IR is not triggered by an unknown off-target effect of
PA, we tested whether two other previously described C4H inhibitors,
4-Propynyloxybenzoic acid and 3-(4-Pyridyl)-acrylic acid (Schochet al. 2002), also induced resistance against M.
graminicola in rice (see Supplementary Figure S1 ). Since these
two inhibitors induced the same resistant phenotype as PA, despite their
very different chemical structures and inhibition mechanisms (Schochet al. 2002), it is highly likely that C4H inhibition is indeed
the root cause of PA-IR.
Since IR may have negative effects on plant growth and development, the
effect of weekly foliar PA treatment at concentrations ranging from 100
- 1000 µM on tomato growth was investigated. No effect on leaf area,
shoot dry mass or root length was seen (P = 0.97, P = 0.71 and P = 0.45,
respectively; Figures 1c-e ). 300 µM was chosen as the standard
dose for all following experiments.
The efficacy of PA-IR against root-knot nematodes was validated in a
greenhouse naturally infested with M. incognita and M.
javanica. Soil samples taken before the trial contained 14 000 J2s per
liter of soil, indicating a severe infestation.
The effect of PA on plant health and yield was evaluated, and its effect
on root-knot nematode disease severity was compared to both an untreated
control and the commercial nematicide Cedroz. Both PA and Cedroz reduced
disease severity, as indicated by plant gall index (P = 0.042 and P =
0.025 respectively, Figure 1f ). By the end of the trial,
untreated plants showed a mean gall index (± SEM) of 8.1 ± 0.4, versus
6.3 ± 0.3 in PA-treated plants and 4.6 ± 1.1 in Cedroz-treated plants.
Neither treatment significantly affected cumulative yield (PA: +13%, P
= 0.77; Cedroz: +34%, P = 0.21 – Figure 1g ). No phytotoxicity
or growth reduction was observed with any treatment.
Piperonylic acid treatment enhances tomato resistance to the
foliar pathogens Botrytis cinerea and Pseudomonas syringae.
Foliar PA treatment enhances resistance against two foliar pathogens,B. cinerea R16 (Figure 2a-c ) and P. syringaeDC3000 (Figure 2d ). PA treatment increased the percentage of
resistant interactions with B. cinerea from 34% in the control
to 64% (P = 0.014), and inoculation sites also exhibited higher
Fv/Fm (and thus higher photosynthetic
efficiency) in PA-treated plants (+11%, P = 0.018). In an experiment
with higher disease pressure, PA pre-treatment still reduced B.
cinerea disease pressure (3% resistant interactions in mock-treated
plants versus 34% in PA-treated plants, P < 0.001;Supplementary Figure S2a ) and again increased
Fv/Fm (+20%, P = 0.003;Supplementary Figure S2b). Reduced B. cinerea disease
severity was also observed in a greenhouse experiment with strawberry
(Fragaria x ananassa Duchesne ‘Elsanta’), shown in