Direct trade-off between cyanogenesis and resistance to a fungal pathogen in lima bean (Phaseolus lunatus L.)
Article first published online: 28 OCT 2009
© 2009 The Authors. Journal compilation © 2009 British Ecological Society
Journal of Ecology
Volume 98, Issue 1, pages 226–236, January 2010
How to Cite
Ballhorn, D. J., Pietrowski, A. and Lieberei, R. (2010), Direct trade-off between cyanogenesis and resistance to a fungal pathogen in lima bean (Phaseolus lunatus L.). Journal of Ecology, 98: 226–236. doi: 10.1111/j.1365-2745.2009.01591.x
- Issue published online: 11 DEC 2009
- Article first published online: 28 OCT 2009
- Received 12 May 2009; accepted 11 September 2009 Handling Editor: Fergus Massey
- Colletotrichum gloeosporioides;
- direct defence;
- multiple defence syndrome;
- plant–pathogen interaction;
- plant resistance;
- polyphenol oxidase;
1. Plants are simultaneously attacked by multiple herbivores and pathogens. While some plant defences act synergistically, others trade-off against each other. Such trade-offs among resistances to herbivores and pathogens are usually explained by the costs of resistance, i.e. resource limitations compromising a plant’s overall defence.
2. Here, we demonstrate that trade-offs can also result from direct negative interactions among defensive traits. We studied cyanogenesis (release of HCN) of lima bean (Fabaceae: Phaseolus lunatus) and effects of this efficient anti-herbivore defence on resistance to a fungal pathogen (Melanconiaceae: Colletotrichum gloeosporioides).
3. Leaf tissue destruction by fungal growth was significantly higher on high cyanogenic (HC) lima bean accessions than on low cyanogenic (LC) plants. The susceptibility of HC accessions to the fungal pathogen was strongly correlated to reduced activity of resistance-associated polyphenol oxidases (PPOs) in leaves of these plants. LC accessions, in contrast, showed high PPO activity, which was correlated with distinct resistance to C. gloeosporioides.
4. Experimentally applied, gaseous HCN reduced PPO activity and significantly increased the size of lesions caused by C. gloeosporioides in LC leaves.
5. Field observations of a wild lima bean population in Mexico revealed a higher infection rate of HC compared to LC plant individuals. The types of lesions observed on the different cyanogenic plants in nature were similar to those observed on HC and LC plants in the laboratory.
6. Synthesis. We suggest that cyanogenesis of lima bean directly trades off with plant defence against fungal pathogens and that the causal mechanism is the inhibition of PPOs by HCN. Our findings provide a functional explanation for the observed phenomenon of the low resistance of HC lima beans in nature.