Differential performance and parasitism of caterpillars on maize inbred lines with distinctly different herbivore-induced volatile emissions.

Plant volatiles induced by insect feeding are known to attract natural enemies of the herbivores. Six maize inbred lines that showed distinctly different patterns of volatile emission in laboratory assays were planted in randomized plots in the Central Mexican Highlands to test their ability to recruit parasitic wasps under field conditions. The plants were artificially infested with neonate larvae of the fall armyworm Spodoptera frugiperda, and two of its main endoparasitoids, Campoletis sonorensis and Cotesia marginiventris, were released in the plots. Volatiles were collected from equally treated reference plants in the neighbourhood of the experimental field. The cumulative amount of 36 quantified volatile compounds determined for each line was in good accordance with findings from the laboratory; there was an almost 15-fold difference in total emission between the two extreme lines. We found significant differences among the lines with respect to the numbers of armyworms recovered from the plants, their average weight gain and parasitism rates. Average weight of the caterpillars was negatively correlated with the average total amount of volatiles released by the six inbred lines. However, neither total volatile emission nor any specific single compound within the blend could explain the differential parasitism rates among the lines, with the possible exception of (E)-2-hexenal for Campoletis sonorensis and methyl salicylate for Cotesia marginiventris. Herbivore-induced plant volatiles and/or correlates thereof contribute to reducing insect damage of maize plants through direct plant defence and enhanced attraction of parasitoids, alleged indirect defence. The potential to exploit these volatiles for pest control deserves to be further evaluated

Average quantities (in ng; mean ± s.e; n = 12) of volatiles compounds collected in the field from the headspace of infested maize plants belonging to six different inbred lines.

<p>The compounds are arranged in order of increasing retention time. Identifications based on mass spectra (MS) alone must be considered tentative. When an authentic standard was available, retention time (RT) served as additional criterion. For comparative purposes, coefficients <i>r</i> (Pearson product moment correlations) and the respective probabilities <i>p</i> are given for correlations with average amounts of volatiles (n = 6) obtained from collections carried out in a six-arm olfactometer (means of log-transformed values).</p

Overview of the numbers of insects and their status after collection (begin) and after rearing out (end).

a<p>originating from earlier infestations of other plants or from natural infestation as judged from size comparison with the other caterpillars; excluded from assessment of performance parameters, i.e. recovery rate and biomass.</p>b<p>excluded from the calculation of parasitism rates.</p>c<p>included in the calculation of parasitism rates as unparasitized.</p

Correlation coefficients <i>r</i> (Pearson product moment correlations) between 6 maize inbred lines for the different parameters assessed in the field, i.e. the mean values shown in Figure 3.

<p>Bold numbers indicate a significant correlation (Fisher’s r to z <i>p</i><0.05).</p

Arrangement of the experimental plots with the 6 maize inbred lines.

<p>The enlargement shows the generalized location of the plants that were infested with <i>Spodoptera frugiperda</i> larvae inside the plot, the actual pattern being somewhat variable among the plots depending on the availability of suitable plants. The six plots to the left and the bigger plot with plants of the variety “Delprim” were used for volatile collections.</p

PeroxiBase: A class III plant peroxidase database

International audienc

Prokaryotic origins of the non-animal peroxidase superfamily and organelle-mediated transmission to eukaryotes

Members of the superfamily of plant, fungal, and bacterial peroxidases are known to be present in a wide variety of living organisms. Extensive searching within sequencing projects identified organisms containing sequences of this superfamily. Class I peroxidases, cytochrome c peroxidase (CcP), ascorbate peroxidase (APx), and catalase peroxidase (CP), are known to be present in bacteria, fungi, and plants, but have now been found in various protists. CcP sequences were detected in most mitochondria-possessing organisms except for green plants, which possess only ascorbate peroxidases. APx sequences had previously been observed only in green plants but were also found in chloroplastic protists, which acquired chloroplasts by secondary endosymbiosis. CP sequences that are known to be present in prokaryotes and in Ascomycetes were also detected in some Basidiomycetes and occasionally in some protists. Class II peroxidases are involved in lignin biodegradation and are found only in the Homobasidiomycetes. In fact class II peroxidases were identified in only three orders, although degenerate forms were found in different Pezizomycota orders. Class III peroxidases are specific for higher plants, and their evolution is thought to be related to the emergence of the land plants. We have found, however, that class III peroxidases are present in some green algae, which predate land colonization. The presence of peroxidases in all major phyla (except vertebrates) makes them powerful marker genes for understanding the early evolutionary events that led to the appearance of the ancestors of each eukaryotic group

Overview of the parameters assessed for six maize inbred lines arranged in order of increasing total volatile emission.

<p>A-C) plant parameters; D-F) performance of the herbivore <i>Spodoptera frugiperda</i>; G-I) parasitism; J-L) natural infestation with herbivores and potential predators; n = number of plants; N = number of arthropods.</p

Total volatile emission of the six maize inbred lines according to collections conducted in the laboratory (six-arm olfactometer) as compared to collections carried out in the field (<i>r</i> = 0.92, <i>p</i> = 0.0093).

<p>Total volatile emission of the six maize inbred lines according to collections conducted in the laboratory (six-arm olfactometer) as compared to collections carried out in the field (<i>r</i> = 0.92, <i>p</i> = 0.0093).</p

Principal component analysis (PCA) of herbivore-induced volatile emission and of other plant parameters.

<p>A) Biplots of a PCA of the 36 volatile compounds (for identity see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0047589#pone-0047589-t001" target="_blank">Table 1</a>) released by the individual maize plants. B) PCA of the average values for each line of the volatiles pooled into seven groups and of the other variates (A, B, D–L as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0047589#pone-0047589-g003" target="_blank">Fig. 3</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0047589#pone-0047589-t003" target="_blank">Table 3</a>).</p