4.3. Effect of transgenes conferring enhanced pathogen resistance on the interaction with symbiotic fungi in rice

Microbial diseases cause substantial losses to crops. In order to reduce yield loss the development of novel breeding strategies is urgently needed. Transgenesis has been recognized as a powerful approach to enhance disease resistance. However, the designs of transgenic plants often target resistance to foliar pathogens without considering effects on root interactions. Frequently, pathogens are capable of infecting multiple plant organs and tissues. For the rice blast fungus Magnaporthe oryzae for instance, it was shown that the fungus efficiently invades not only leaves but also roots, causing disease in either case. The fungal infection structures differ considerably between leaf and root invasion and involve different independent genetic components in the fungus. Root associations also include beneficial microbial interactions such as the ancestral arbuscular mycorrhizal (AM) symbiosis. This symbiosis is an integral component of most terrestrial ecosystems and more than 80% of the vascular plants enter into this association including most crop species. Understanding the effects of transgenes conferring enhanced resistance to pathogens on the AM symbiosis is of utmost ecological importance.