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Poster: Biology & Disease Mgmt: Mycology


Evaluating isolate aggressiveness of Fusarium oxysporum f.sp. niveum in Florida
T. SANCHEZ (1) (1) University of Florida, U.S.A.

Fusarium wilt, caused by Fusarium oxysporum f. sp. niveum, is a major soil borne disease of watermelon with limited host resistance available. Understanding isolate aggressiveness is important for variety selection and other management strategies. Pathogenicity tests of 72 isolates collected from 10 Florida counties were conducted to examine their aggressiveness on the variety Black Diamond under greenhouse settings. Seedlings were inoculated with a conidial suspension using a root dip method. Aggressiveness was measured by the percentage of wilted plants and AUDPC for incidence, over a 4 week period after inoculation. Significant (P<0.05) differences between isolates were found using ANOVA. Based on wilted plants, isolates were characterized into 4 aggressiveness levels; not aggressive, weak, medium and severe (0%, 1-32%, 33-67% and 68-100% wilt respectively). It was observed that 33.3% of the isolates were not aggressive, 15.3% weak, 25.0% medium, and 26.4% severe. Quantitative diversity indices (Simpson’s = 0.27 and Shannon entropy H’ = 1.35) indicate that these aggressiveness levels are highly diverse in Florida, and that no single level was dominant. Characterizing the aggressiveness is a necessary step for race determination, as well as the assessment of various integrated management strategies. Further research is presently being conducted that evaluates the efficacy of current integrated management strategies on isolates with a severe aggressiveness rating.