Effects of cis-Jasmone Treatment of Brassicas on Interactions With Myzus persicae Aphids and Their Parasitoid Diaeretiella rapae

Abstract

There is a need to develop new ways of protecting plants against aphid attack. Here, we investigated the effect of a plant defence activator, cis-jasmone (CJ), in a range of cultivars of Brassica napus, Brassica rapa and Brassica oleracea. Plants were sprayed with cis-jasmone or blank formulation and then tested with peach potato aphids (Myzus persicae Sulzer) (Hemiptera: Aphididae) and their parasitoid Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae). CJ treated plants had significantly lower aphid settlement than control plants in a settlement bioassay. Conversely, in a foraging bioassay, D. rapae parasitoids spent a significantly longer time foraging on CJ treated plants. Our results reveal that CJ treatment makes plants less attractive to and less suitable for M. persicae but more attractive to D. rapae in a range of brassica cultivars. It is likely that these effects are due to changes in volatile emission indicating activation of defence and presence of conspecific competitors to aphids but presence of prey to parasitoids. Increases in volatile emission were found in CJ induced plants but varied with genotype. Among the synthetic volatile compounds that were induced in the headspace of CJ treated brassica cultivars, methyl isothiocyanate, methyl salicylate and cis-jasmone were most repellent to aphids. These results build on earlier studies in Arabidopsis and show that tritrophic interactions are influenced by CJ in a wide range of brassica germplasm. The implication is that CJ is a promising treatment that could be used in brassica crops as part of an integrated pest management system.

Keywords: aphid; biological control; crop protection; induced defence; tritrophic interactions.

Figure 1

Adult Myzus persicae survival (Mean ± SE) out of the original 10 individuals after (A) 48 h and (B) 96 h in clip cages on six brassica cultivars (n = 10) treated with cis-jasmone or blank formulation (control). Brassica cultivars capped with “ns” do not show a significant difference between control and cis-jasmone treatment while asterisks denote differing levels of statistical significance: ^* < 0.05 and ^*** < 0.001 (generalised linear models with Poisson probability distribution).

Figure 2

Myzus persicae larviposition (Mean ± SE) after (A) 48 h and (B) 96 h in clip cages on six brassica cultivars (n = 10) treated with cis-jasmone or blank formulation (control). Asterisks denote differing levels of statistical significance: ^** < 0.01 and ^*** < 0.001 (generalised linear models with quasi-Poisson probability distribution).

Figure 3

Settlement of Myzus persicae (Mean ± SE) after 24 h on blank formulation (control) and cis-jasmone treated plants in a series of choice test bioassays (50 aphids released in each replicate; n = 10). Asterisks denote differing levels of statistical significance: ^** < 0.01 and ^*** < 0.001 (generalised linear models with either Poisson or quasi-Poisson probability distributions).

Figure 4

Mean total time spent foraging (Mean ± SE) by Diaeretiella rapae on blank formulation (control) and cis-jasmone treated plants (n = 10). Brassica cultivars capped with “ns” do not show a significant difference between control and CJ treatment while asterisks denote differing levels of statistical significance: ^* < 0.05 and ^** < 0.01 (two-sample t-tests).

Figure 5

Mean number (± SE) of mummified Myzus persicae on blank formulation (control) and cis-jasmone treated plants 15 days after exposure to Diaeretiella rapae for 2 h (n = 10). Brassica cultivars capped with “ns” do not show a significant difference between control and CJ treatment while asterisks denote differing levels of statistical significance: ^* < 0.05 and ^** < 0.01 (generalised linear models with either Poisson or quasi-Poisson probability distributions).

Figure 6

Behavioural responses of Myzus persicae females to volatiles from six brassica cultivars in an olfactometer bioassay. Individual aphids were given 12 min to make a choice between (A) one arm of blank formulation treated plants (BF—tween 80 and water) vs. three solvent diethyl ether (DEE) arms, (B) one arm of cis-jasmone treated plants (CJ) vs. three solvent control arms (DEE) and (C) two different treatment arms (BF, blank formulation treated plants and CJ, cis-jasmone treated plants) vs. two solvent arms (DEE). The shown values are mean time spent in arm ± SE (n = 10). For (A,B), brassica cultivars capped with “ns” do not show a significant difference between plant treatment while asterisks denote differing levels of statistical significance: ^* < 0.05, ^** < 0.01 and ^*** < 0.001 (paired t-test). For (C), different letters above bars indicate statistically significant differences between treatments (P < 0.05), based on Holm-Sidak method.

Figure 7

Behavioural responses of Myzus persicae females to eight synthetic chemical compounds. Individual aphids were given 12 min to make a choice between one arm containing a synthetic chemical compound vs. three solvent diethyl ether arms. The shown values are mean time spent in arm ± SE (n = 10). Synthetic chemical compounds capped with “ns” do not show a significant difference while asterisks denote differing levels of statistical significance: ^* < 0.05 and ^*** < 0.001 (paired t-test).

Figure 8

Total amount (mean nanograms plant⁻¹ h⁻¹ ± SE) of identified volatile organic compounds (VOCs) emitted from the six brassica cultivars with and without CJ-treatment. Asterisks indicate statistically significant differences: ^*** < 0.001 and ^* < 0.05 (paired t-test).

Figure 9

Principal Component Analysis (PCA) of the volatile compounds emitted by six brassica cultivars (i.e., Chinese kale, English Giant, pak choi, Samurai, Wesway, and Turnip Rutabaga) (n = 3). Score plot visualises the ordination of collected samples according to the first two PCs based on the quantitative values of emitted VOCs from different brassica cultivars with and without CJ-treatment, with the percentage of explained variation in parentheses. The ellipses show 95% confidence regions.