Effects of Repeated Short-Duration Heating Cycles on Survival of Soilborne Plant Pathogens

Soil solarization is a nonchemical management tactic for soilborne plant pathogens. However, its effectiveness in temperate regions can be inconsistent because soil temperatures are elevated for short periods each day. Most solarization studies emphasize cumulative thermal thresholds or sustained daily maximum temperatures, providing limited insight into how repeated short-duration heating affects pathogen survival. This study quantified cyclic-heating effects on viability of four soilborne pathogens: Agroathelia rolfsii, Fusarium oxysporum, Rhizoctonia solani, and Sclerotinia sclerotiorum. Propagules were exposed in incubator experiments to repeated daily four-hour temperature cycles ranging from 34 to 54°C for up to 24 d, simulating diurnal soil temperatures observed during high-tunnel solarization in Kentucky. The experiment isolated biological consequences of repeated daily heating under standardized laboratory conditions. Viability was assessed by germination or growth following plating on quarter-strength acidified PDA. Increasing temperature and exposure duration reduced viability for all pathogens, but responses differed among species. Sclerotinia sclerotiorum was highly heat-sensitive and became nonviable within 3 days at ≥38°C. Rhizoctonia solani exhibited moderate sensitivity, with complete inhibition after 9 days at 46°C and 3 days at 50°C. Fusarium oxysporum maintained viability through 42°C, with a gradual decline at higher temperatures and complete mortality at 54°C. Agroathelia rolfsii was the most thermotolerant species, showing no significant reduction in germination until exposure reached 50°C, at which point complete inactivation occurred within 3 days. These results show that pathogen survival under solarization-relevant conditions is shaped by repeated short-duration heat cycles, underscoring the importance of temperature amplitude and exposure frequency when designing solarization strategies.