AN ANTI-HYDROTACTIC RESPONSE AND SOLID-SURFACE RECOGNITION OF GERM TUBES OF THE RICE BLAST FUNGUS, MAGNAPORTHE-GRISEA

Magnaporthe grisea, the causal agent of rice blast disease, differenti ates an appressorium to penetrate through the host cuticle with an inf ection peg elaborated from the appressorium, Similar reaction is obser ved on various synthetic substrata, By using a hardness-adjustable mat erial, Hycel A-342, the correlation between appressorium formation and substratum hardness was evaluated, The results suggested that substra tum hardness played an important role in triggering appressorium forma tion of M. grisea. Furthermore, growth orientation of germ tubes was c oerced by the hydrophobicity of the contact surfaces, When conidia ger minated at the interface of two differently hydrophobic phases, the ge rm tubes grew preferentially towards the more hydrophobic phase, Mutag enesis studies suggested that loss of this anti-hydrotactic behavior i mpaired appressorium formation, Since water is a pre-requisite for ger mination, we propose that the anti-hydrotactic response initiates atte mpted penetration into the plants by germ tubes, then triggers appress orium formation by the surface hardness.