2024 Volume 90 Issue 4 Pages 243-252
Diaporthe destruens, which causes foot rot disease of sweet potato, is transmitted to seed tubers, so it is important to use healthy seed tubers for seedling production. To develop effective technology for disinfecting seed tubers using vapor heat, we first generated a nitrate non-utilizing (nit) mutant strain, Mn04, of D. destruens, using a chlorate-containing medium. Mn04 had typical morphology and pathogenicity but was deficient in nitrogen utilization. To test the heat tolerance of Mn04, α-spore suspensions were treated with heated water for different durations (0–18 min) and temperatures (43°C, 46–49°C). The number of colonies decreased at 46°C or higher, but not at 43°C; higher temperatures killed spores more rapidly, and 0.72–2.85 min were required to reduce the number of survivors by 90% at each temperature (D) from 46°C to 49°C. To determine the minimum vapor heat conditions needed to kill D. destruens in tubers, we inoculated 20 apparently healthy tubers with Mn04, incubated them at 20°C for 2 days, then treated them with vapor heat at different temperatures for different durations. Tubers were then plated on selective medium to reisolate Mn04. D. destruens was not reisolated when the vapor temperature was 47°C for more than 110 min or 48°C for more than 100 min. From 210 samples treated with vapor heat at 48°C for 100 min, Mn04 was reisolated from only 7. Thus, the heat resistance of D. destruens strain Mn04 did not decrease at 43°C, but decreased at 46°C or higher, whereas vapor heat at 48°C for 100 min disinfected apparently healthy sweet potato tubers inoculated with Mn04 strain by more than 93.8% (P < 0.05).
