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Epidemiological Conditions Promoting Rhizopus Soft Rot and Fusarium Root Rot of Sweetpotato
A. C. SCRUGGS (1), L. M. Quesada-Ocampo (1). (1) North Carolina State University, Raleigh, NC, U.S.A.

Sweetpotato production is limited by many postharvest diseases including Rhizopus soft rot (RSR) and Fusarium root rot (FRR). However, little is known about the epidemiological conditions that promote RSR and FRR. The effects of temperature (13, 23, and 29°C), relative humidity (75, 85, 95%), and inoculum level (3-, 5-, and 7-mm diameter mycelia plugs) on disease progression of RSR and FRR were investigated in controlled growth chamber studies. Six wounded, ‘Covington’ sweetpotatoes were inoculated with an actively growing mycelia plug of <i>Rhizopus</i> <i>stolonifer,</i> <i>Fusarium solani, </i>or<i> F. proliferatum, </i>and incubated in the dark at the desired temperature and humidity<i>. </i>Control roots were included and the experiment was repeated twice. Disease progression was recorded for RSR and FRR as percent decay and lesion diameter, respectively, for two weeks. Sporulation on infected roots was also recorded. Area under the disease progress curve (AUDPC) values were calculated and subjected to an ANOVA. Significant differences were observed for RSR and FRR across the temperature, humidity, and inoculum level treatments. Disease progression of RSR and FRR was consistently higher at 29°C, 95% humidity, and 7 mm inoculum level as compared to lower temperatures, humidities, and inoculum levels. These findings will contribute in providing accurate recommendations to growers so that environmental conditions in storage and curing facilities may be optimized to reduce postharvest diseases.

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