Aragón Rodríguez, Sandra Milena

English

Tomato plants host multiple microbes able to colonize plant tissues endophytically without causing symptoms of infections. Whether these microorganisms living inside the plants co-exist completely undetected by the plant metabolism remains to be explored in detail. This research contributes to the understanding of the multitrophic interaction among tomato plants, fungal endophytes and the insect herbivores. We focused the research on three main topics (i) whether the studied fungi are able to colonize endophytically tomato tissues, (ii) which parameters are influenced by an endophytic colonization of the plants and (iii) whether endophytes are able to modulate the behavior of the insect herbivores on endophyte treated plants. The model evaluated here was composed by the three fungal endophytes Beauveria bassiana, Trichoderma koningiopsis and Metarhizium brunneum, the tomato plant Solanum lycopersicon (Mill.) as the host and two different insect herbivores, the aphid Myzus persicae and the polyphagous moth Helicoverpa armigera. Our aim was to evaluate the potential of three fungal species, B. bassiana, T. koningiopsis and M. brunneum to colonize endophytically plant tissues. In our research, we successfully achieved the establishment of the fungal entomopathogens B. bassiana and M. brunneum as well as the biocontrol agent T. koningiopsis in tomato plants with two different inoculation methods, seed and root inoculation. The colonization of plant tissues by B. bassiana when root inoculated was found to be higher in the leaves than in the stems, and almost no positive records of B. bassiana were found in the roots. While seed inoculated plants showed a higher colonization frequency in the roots than in leaves and stems. The colonization frequency observed in the plants treated with T. koningiopsis, was higher in the roots, than in the stems and leaves while M. brunneum was successful in colonizing root tissues, but the colonization of aboveground plant organs stem and leaves was achieved only in few samples. The effect of colonization with fungal endophytes on plant attributes was evaluated by i) comparing the headspace volatiles emitted by tomato plants (S. lycopersicon Mill) colonized with the endophytic fungi B. bassiana and T. koningiopsis  with those from non-treated plants, and those from plants with a dual application of an endophytic fungus and an insect attack caused by the aphid M. persicae, ii) by comparing the plant biomass, temperature and leaf chlorophyll content from tomato plants inoculated with B. bassiana, T. koningiopsis or M. brunneum compared to non-treated plants. On the basis of the tentative identifications and semi-quantitative assessments of compound amounts by the relative peak-area of the Total Ion Current (TIC), preliminary assignments of indicator compounds are suggested. For endophyte-free plant volatile profiles, one of the indicator compounds is the p-cymene. Endophytically inoculated tomato plant volatile profile is characterized by the release of α-pinene as the major indicator compound and the volatile profile of plants treated with endophyte and aphid attack is characterised by compounds such as β- caryophyllene, ascaridole and α-thujone. We observed that the Total Ion Current (TIC) peak area ratios of several sesquiterpenes, changed according to the treatment applied. The total plant biomass was significantly higher in those plants inoculated with T. koningiopsis while the total plant biomass of B. bassiana treated plants remains similar to control plants. The compounds p-cymene and α-pinene significantly reduced their TIC peak area when the plant was inoculated by the entomopathogenic fungi Beauveria bassiana. Thermal imaging captured with a heat-sensing camera revealed no significant differences in temperature profiles of leaves among treatments compared to the control plants. The leaf chlorophyll content measured in SPAD units showed that plants treated with B. bassiana had significant less chlorophyll content compared to non-treated plants and those treated with T. koningiopsis or M. brunneum. To determine if there is an endophyte modulation of plant-insect interactions, we evaluated i) the attraction of the aphid M. persicae towards tomato plants treated with the endophytes B. bassiana and T. koningiopsis compared to non-treated plants and, ii) the oviposition preference of the polyphagous moth H. armigera when offered tomato plants inoculated with B. bassiana, T. koningiopsis or M. brunneum simultaneously. With the aphid M. persicae, the host plant selection was tested in multiple choice experiments under laboratory and greenhouse conditions, using five different odor sources (i.e. B. bassiana strains EAB 04/01 Tip (Bb1), Bv 061 (Bb2) and Bb1022 (Bb3); T. koningiopsis strain Th003 and non-treated plants) simultaneously. We observed that winged aphids can discriminate between treated and non-treated tomato plants with more specimens attracted to blends emitted by tomato plants treated with the entomopathogenic endophytic fungi B. bassiana Bb1 compared to the non-treated plants under laboratory and greenhouse conditions. 
In a multiple choice set up, we offered one plant from each of the six different treatments (i.e., B. bassiana Bb1, Bb2 and Bb3; T. koningiopsis Th003, M. brunneum and non-treated plants) to one female of H. armigera for oviposition preference, and the number of eggs laid on the plant surface was registered after 24 hours. We observed that H. armigera had less preference to oviposit on those plants treated with Bb1. While no significant differences were found in the other treatments compared with the control

Georg-August-University Göttingen

How entomopathogenic endophytic fungi modulate  plant-insect interactions

https://ediss.uni-goettingen.de/bitstream/11858/00-1735-0000-0023-3E6B-1/1/Sandra_Aragon_Dissertation_How%20entomopathogenic%20endophytic%20fungi%20modulate%20plant%20insect%20interaction.pdf

How entomopathogenic endophytic fungi modulate plant-insect interactions

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Georg-August-University Göttingen