Odor uniformity among tomato individuals in response to herbivore depends on insect species.

Plants produce specific volatile organic compound (VOC) blends in response to herbivory. Herbivore-induced blends may prime the plant for future attack or attract carnivorous insects; these responses have been considered adaptive for plants. If herbivores differentially modify the VOC emission among individuals within a group of plants they feed upon, then plant responses to herbivores will not only produce specific blends but also variation in odor among individuals, i.e. individuals smell the same, then having a uniform odor. We investigated the VOC emission variation or uniformity among tomato individuals (Solanum lycopersicum L. cv. Castlemart) in response to moderate wounding by (1) nymphs of the psyllid Bactericera cockerelli (Sulc.) (TP); (2) Lepidoptera chewing-feeding larvae of Fall Armyworm (Spodoptera frugiperda Smith) (FAW) and (3) of Cabbage Looper (Trichoplusia ni Hübner) (CL), and (4) mechanical damage (MD). We used a ratio-based analysis to compare the fold-change in concentration from constitutive to induced VOC emission. We also used size and shape analysis to compare the emission of damaged and non-damaged individuals. Aside of finding herbivore-specific blends in line with other studies, we found patterns not described previously. We detected constitutive and induced odor variation among individuals attacked by the same herbivore, with the induced odor uniformity depending on the herbivore identity. We also showed that the fold-change of VOCs from constitutive to induced state differed among individuals independently of the uniformity of the blends before herbivore attack. We discuss our findings in the context of the ecological roles of VOCs in plant-plant and plant-carnivore insects' interactions

Volatile organic compound blend profile (relative concentration) emitted by three selected tomato individuals before (black bars) and after (white bars) different damage treatments.

<p>Footnote of Figure 4. Bars represent the concentration percent of each compound in a blend relative to the sum of the absolute concentration of all compounds in that blend. VOCs: 3-hexanol (1), α-pinene (2), o-cymene (3), β-myrcene (4), (+)-4-carene (5), α-phellandrene (6), α-terpinene (7), <i>p</i>-cymene (8), β-phellandrene (9), nonanal (10), and decanal (11)..</p

Volatile organic compounds absolute concentration fold-change from the constitutive to the induced state emitted by Castlemart tomato plants under different damage treatments.

<p>Footnote of Figure 3. The absolute concentration is the abundance of single volatiles in the blend calculated from peak areas in chromatograms. Damage treatments: TP, tomato psyllids; CL, Cabbage looper caterpillar; FAW, Fall armyworm caterpillars; MD, Mechanical damage. Bars represent the fold-change of individual tomato plants within treatments. Spaces without bars indicate lack of change or a fold-changes smaller than 1 (see Table S1).</p

Linear discriminant analysis of the absolute (A) and relative (B) concentration of non-damaged (black points) and damaged (white points) Castlemart tomato individuals.

<p>Footnote of Figure 5. Data of non-damaged individuals (30 plants assigned to each treatment) was pooled for comparison with the induced VOC concentration by each treatment. For visual purposes, we extracted the coordinates of individuals before and after each type of damage. Thus, each plot represents the discrimination of damaged individuals against themselves before and after damage. The first three linear discriminant of the absolute and relative VOC concentration accounted for at least 90% of the variation. Damage treatments: TP, Tomato psyllid nypmhs; CL, Cabbage looper caterpillars; FAW, Fall Armyworm caterpillars; MD, mechanical damage.</p

Absolute concentration (mean ± SD of peak area) of volatile organic compounds emitted by Castlemart tomato plants before (black bars) and after (white bars) damage treatments.

<p>Footnote of Figure 2. Peak absolute concentration represents the abundance of a single volatile in the blend. Damage treatments: TP, tomato psyllids (n=9); CL, Cabbage looper caterpillars (n=8); FAW, Fall armyworm caterpillars (n=6); MD, Mechanical damage (n=7). Asterisks indicate significant differences in the absolute concentration of volatile emissions before and after damage (paired-t test or Wilcoxon test at <i>P</i>=<0.05).</p