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Title: EVENTS OCCURRING AT COLLETOTRICHUM ORBICULARE INFECTION SITES ON WATERMELON

Author
item Russo, Vincent
item RUSSO, B - OKLAHOMA STATE UNIVERSITY
item CARTWRIGHT, B - OKLAHOMA STATE UNIVERSITY

Submitted to: Subtropical Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: At the point where hosts and microorganisms interact recognition must occur, and defenses must be overcome if fungi are to be successful pathogens. These activities can often be described with cytochemical methods and observed with microscopy. At inoculation sites the method by which Colletotrichum orbiculare colonizes living and dead watermelon (host) )leaves and dead onion (non-host) leaf-bases was studied. Spore germinatio was earlier on dead than on living tissues. There was no evidence of direct penetration through the cuticle, cell wall, or stomata using primary infection mycelia originating from appressoria. Host chemical defenses were apparently overcome since infection occurred and lesions were formed on living tissue. The method of colonization observed was different from that previously reported for a similarly appearing fungus that produces the same type of damage. This may be due to different methods of colonization used by races of the same fungal species. Since control methods are, in part, developed based on the biology of the pathogen it is important to know how that organism colonizes tissues.

Technical Abstract: There is insufficient information concerning infection and subsequent colonization of watermelon by the anthracnose fungus (Colletotrichum orbiculare). Observations of this interaction were made with bright-field, phase-contrast, and reflected- fluorescence microscopy on inoculated living and dead host and non-host (onion) tissue. Cytochemical tests were employed to interpret fungus and host responses. Spore germination on dea tissues was observed by 18 h, but was delayed an additional 6 h on living tissue. There was no evidence of direct penetration through the cuticle, cell wall, or stomata using primary infection mycelia originating from appressoria. There were no autofluorescent deposits below appressoria, but the hypersensitive response was observed in plant cells in living tissue. Phenolics and tannins were present in non-colonized host tissues. The method of colonization was different from that previously reported for the watermelon anthracnose fungus (C. lagenarium). It may be that races of th fungus use different colonization methods. Since control methods are, in part, developed based on the biology of the pathogen it is important to know how that organism colonizes tissues.