Abstract:

Abstract: This paper investigated the tropism and its specificity of Alternaria alternata f. sp. phoenix, a pathogen of brown leaf spot of Phoenix sylveseris, to the leaf wounds of host and nonhost trees. The results showed that the germ tubes of the fungus had strong tropic growth toward the fresh wounds of hosts, but had little or no such directional growth to those of nonhosts. The existence and intensity of tropism of the pathogen were strongly associated with the recognition and successful infection to tested plants. Tropism of the fungus was affected by the distance between the wounds and spores, strong tropic response was observed within the range of 500 μm, and it decreased or even lost when the distance exceeded 1 000 μm. The freshness of wound is another major factor that affects the intensity of tropism, the fresh wound had stronger attraction to the fungal germ tubes, but the attraction of 24 hours old wound decreased dramatically, and the attraction almost lost when a wound was 48 hours or elder. The wounds of host tainted with non host leaf juice reduced their attraction, on the other hand, the wounds of non host tainted with host leaf juice increased their attraction. The fungus developed vigorously in host leaf extract liquids, but grew poorly in non host leaf extract liquids. The results of experiment demonstrated that there existed significant specificity of tropic growth of A. alternata f. sp. phoenix to wounds of hosts. Tropism is the first event in fungus-host recognition in this pathosystem and plays a crucial role in initiating a successful infection to host plants.

Key words: Key words: Alternaria alternata f. sp. phoenix, Phoenix sylveseris, tropism, recognition