Within-plant distribution of induced resistance in apple seedlings: rapid acropetal and delayed basipetal responses |
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Authors: | Bettina Gutbrodt Karsten Mody Raphaël Wittwer Silvia Dorn |
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Institution: | (1) ETH Zurich, Institute of Plant, Animal and Agroecosystem Sciences, Applied Entomology, Schmelzbergstrasse 9/LFO, 8092 Zurich, Switzerland; |
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Abstract: | Induction of plant resistance by herbivory is a complex process, which follows a temporal dynamic and varies spatially at
the within-plant scale. This study aimed at improving the understanding of the induction process in terms of time scale and
within-plant allocation, using apple tree seedlings (Malus × domestica) as plant model. Feeding preferences of a leaf-chewing insect (Spodoptera littoralis) for previously damaged and undamaged plants were assessed for six different time intervals with respect to the herbivore
damage treatment and for three leaf positions. In addition, main secondary defense compounds were quantified and linked to
herbivore feeding preferences. Significant herbivore preference for undamaged plants (induced resistance) was first observed
3 days after herbivore damage in the most apical leaf. Responses were delayed in the other leaf positions, and induced resistance
decreased within 10 days after herbivore damage simultaneously in all tested leaf positions. Chemical analysis revealed higher
concentrations of the flavonoid phloridzin in damaged plants as compared to undamaged plants. This indicates that herbivore
preference for undamaged apple plants may be linked to phloridzin, which is the main secondary metabolite of apple leaves.
The observed time course and distribution of resistance responses within plants contribute to the understanding of induction
processes and patterns, and support the optimal defense theory stating young tissue to be prioritized. Moreover, induced resistance
responses occurred also basipetally in leaves below the damage site, which suggests that signaling pathways involved in resistance
responses are not unidirectional. |
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