Survival of Fusarium oxysporum f. sp. lactucae on Crop Residue in Soil.

Abstract

Fusarium oxysporum f. sp. lactucae, the cause of Fusarium wilt of lettuce, can survive on crop residue in soil. Persistence of the pathogen over time will be influenced by the rate at which residue decomposes. We evaluated the effect of drying and fragmenting crop residue on the rate of decomposition and survival of F. oxysporum f. sp. lactucae. In a controlled experiment that represented optimal drying conditions, fragmenting and oven drying infested lettuce taproots at 30°C significantly reduced the frequency of recovery of the pathogen, compared with untreated tissue. However, in a field experiment, drying infested crop residue on the soil surface prior to incorporation did not significantly reduce survival of F. oxysporum f. sp. lactucae after 1 year. Regardless of treatment, there was not a significant decrease in soil inoculum density between 1 and 12 months after residue was incorporated. In a greenhouse experiment, fragmenting crop residue prior to incorporation in pathogen-free soil resulted in significantly higher inoculum densities of F. oxysporum f. sp. lactucae after 1 year. The increase in inoculum levels was associated with a faster rate of residue decomposition, which may be beneficial in the long run but not where lettuce will be replanted within the next year.