Supplementary UV-B Radiation Induces Fusarium Wilt of Spinach in a Glasshouse.

Abstract

The effects of supplementary UV-B radiation (290-320 nm, +UV-B) on the development of wilt disease of spinach (Spinacia oleracea) caused by the fungus Fusarium oxysporum f. sp. spinaciae were investigated under natural light condition in a glasshouse. The disease incidence in these plants greatly increased at low inoculum concentrations in soil inoculation experiments compared with plants without UV-B supplementation (-UV-B). In needle inoculation experiments with F. oxysporum f. sp. spinaciae, wilt occurred in plants under +UV-B as severely as in soil inoculation experiments. F. oxysporum f. sp. spinaciae was isolated from the roots of all wilted plants, as well as some symptomless plants in both soil inoculation and needle inoculation experiments. Re-isolation frequency under +UV-B was ca. 3.5 times higher than that of plants under -UV-B during the first three days of growth under UV-B supplementation. However, the re-isolation frequency in inoculated plants in both experiments irrespective of UV-B supplementation was over 80% by the end of both experiments. The results indicated that supplementary UV-B radiation incited disease development.