Cotton defense induction patterns under spatially, temporally and quantitatively varying herbivory levels

Authors: EISENRING, MICHAEL - Agroscope; MEISSLE, MICHAEL - Agroscope; HAGENBUCHER, STEFFAN - Agroscope; Naranjo, Steven; WETTSTEIN, FELIX - Agroscope; ROMEIS, JOERG - Agroscope

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2017
Publication Date: 2/21/2017
Citation: Eisenring, M.A., Meissle, M., Hagenbucher, S., Naranjo, S.E., Wettstein, F., Romeis, J. 2017. Cotton defense induction patterns under spatially, temporally and quantitatively varying herbivory levels. Frontiers in Plant Science. 8:234. doi: 10.3389/fpls.2017.00234.

Interpretive Summary: Plants have evolved a variety of mechanisms to defend themselves against herbivores, including a range of chemical defenses that can be activated only when the plant is attacked. These inducible defenses are important as they can minimize plant damage and influence management strategies to protect crop plants from insects. The optimal defense theory (ODT) predicts that plants allocate defense compounds to their tissues depending on its value and the likelihood of herbivore attack. We hypothesized that allocation of defense in cotton is consistent with ODT when plants are subjected to temporally, spatially and quantitatively varying damage by caterpillars. To quantify defenses we measured terpenoids, condensed tannins and the density of glands containing defensive compounds in cotton leaves. We found that cotton plants allocate most of their defensive compounds to the youngest leaves regardless of where the damage occurred, whereas defense induction in older leaves varied with damage location. In addition, the induced compounds could be found in newly formed young leaves up to 14 days after damage. Overall our results support the hypothesis that induced defense organization of cotton plants subjected to varying damage treatments supports ODT. These results could be useful to plant breeders and inform pest management decision-making.

Technical Abstract: The optimal defense theory (ODT) predicts that plants allocate defense compounds to their tissues depending on its value and the likelihood of herbivore attack. Whereas ODT has been confirmed for static damage levels it remains poorly understood if ODT holds true for defense organization of inducible plants under varying damage treatments. We hypothesized that allocation of inducible cotton (Gossypium spp.) defenses align with ODT when plants are subjected to temporally, spatially and quantitatively varying caterpillar (Heliothis virescens) damage. To quantify defenses we measured terpenoids, condensed tannins and gland densities in cotton leaves. Plants allocated most defenses to their youngest leaves regardless of damage location whereas defense induction in older leaves varied with damage location. For at least 14 days after damage termination plants reallocated defense resources from former youngest leaves to newly developed leaves. We observed a positive hyperbolic relationship between leaf damage area and produced defenses, indicating that plants are able to fine-tune their defense allocation. Overall our results support the hypothesis that induced defense organization of plants subjected to varying damage treatments supports ODT. However, factors like vascular architecture or chemical defense compound properties can limit predictions of ODT in some cases.