Suppression of spinach Fusarium wilt by intercropping with Allium plants

Abstract

Intercropping with Welsh onion and Chinese chive was evaluated as a means to reduce the incidence of Fusarium wilt on spring-summer spinach caused by Fusarium oxysporum f. sp. spinaciae (FOS). In preliminary experiments (i.e., plant box experiment and container experiment), intercropping spinach with Welsh onion and Chinese chive suppressed development of spinach Fusarium wilt. Particularly, intercropping with Welsh onion yielded stronger suppression. Subsequently, at two commercial spinach fields in Takayama City, Gifu Prefecture, during the first cultivation season after soil fumigation, Welsh onion and Chinese chive were intercropped on the ridge shoulders along the sides of rain shelters where FOS often survives. As a result, both intercropping systems effectively reduced the incidence of spinach Fusarium wilt (44 to 100% reduction) up to 5 months post fumigation. F. oxysporum was detected from soils in the ridges of plots with spinach-Chinese chive intercropped at a level similar to that in plots with only spinach, and soil populations of F. oxysporum in spinach-Welsh onion intercropped plots were undetectable during cultivation. These results suggest that intercropping with alliums, particularly Welsh onion, on ridge shoulders along the sides of rain shelter after soil fumigation can effectively reduce the incidence of Fusarium wilt on spring-summer spinach.