Alternaria brassicicola is the causal pathogen of Alternaria sooty spot in broccoli. A. brassicicola can survive on cabbage plant residue left on the soil surface for approximately 23 weeks (Humpherson-Jones, 1989). In this study, we investigated its transmission via broccoli residue after harvest and confirmed that A. brassicicola survived on the residue. When broccoli was grown in a greenhouse inoculated with broccoli residue infected with A. brassicicola, Alternaria sooty spot occurred in the florets and inoculated isolate were detected. These findings suggest that the residue serve as a source of infection for subsequent broccoli crops. The broccoli plant fragments (leaf, floret, leaf stalk and stem) infected with A. brassicicola were left on the soil surface or buried in the soil. Conidia were stably detected for up to 90 days in A. brassicicola–infected broccoli plant fragments left on the soil surface. Conversely, conidia were barely detected in plant fragments other than leaves after 30 days when buried in the soil. It was thought that aerobic conditions on the soil surface were necessary for the survival of A. brassicicola.

Sweet potato stem rot is caused by Fusarium oxysporum f. sp. batatas (Fob), a major soil-borne pathogen, and the recent emergence of benomyl-resistant isolates has raised concerns about its spread. In this study, endophytic bacteria were isolated from sweet potato seedlings grown in organic field soil in pots. Among six isolates, strain IUJS5 strongly and reproducibly suppressed Fob infection. Identified as Burkholderia sp., IUJS5 colonized seedlings and inhibited Fob mycelial growth in dual culture, forming clear inhibition zones. These results indicate that IUJS5 suppresses stem rot through antifungal activity, suggesting its potential as a biocontrol agent for sweet potato stem rot.