Epidemiology of tomato spotted wilt virus in Chrysanthemum morifolium in South Korea and its management using a soil-dwelling predatory mite (Stratiolaelaps scimitus) and essential oils

Abstract

Tomato spotted wilt virus (TSWV) is one of most destructive viruses in vegetable and ornamental crop production worldwide. A greenhouse survey to determine the incidence of TSWV in Chrysanthemummorifolium Ramat. was conducted during the 2018 and 2019 growing seasons in South Korea. TSWV was detected using a double antibody sandwich-enzyme-linked immunosorbent assay, and positive results were confirmed using reverse transcription-polymerase chain reaction (RT-PCR). A total of 1569 chrysanthemum plants (70.77 %) tested positive for TSWV among 2217 symptomatic chrysanthemum plants collected from 16 greenhouses. In addition, 116 thrips (72.96 %; Frankliniella occidentalis Pergande) that contained TSWV were identified using RT-PCR from a total of 159 thrips collected from the greenhouses during the survey. A high incidence of viruliferous thrips may have played a role in TSWV occurrence in the chrysanthemum greenhouse. To develop a novel approach for thrips management, the effectiveness of a soil-dwelling predatory mite (Stratiolaelaps scimitus Berlese) and 45 essential oils (as bio-insecticides applied via foliar treatment) was assayed. Four essential oils (cinnamon oil, cinnamon bark oil, oregano oil, and thyme oil) were shown to be significantly toxic to eggs, larvae, and adults of F. occidentalis. For the combined treatment, individuals of S. scimitus (60/m²) were placed on the soil in the chrysanthemum greenhouses. Then, a mixture of the four essential oils was applied as foliar treatment at 4-day intervals. A very low incidence of thrips emerged as adults from the soil (1.2-8.5 %) in the combined treatment in the chrysanthemum greenhouses when surveyed twice per month, compared with the non-treated control or when conventional insecticide sprays were applied. The incidence of TSWV (0.93 %) in chrysanthemum treated with S. scimitus in conjunction with the mixture of four essential oils decreased significantly compared with that treated with chemical insecticides (32.05 %) and in the non-treated controls (84.85 %). Our findings contribute to the development of novel strategies to control TSWV disease in chrysanthemum plants; notably, the control of F. occidentalis using eco-friendly insecticides appears promising.

Keywords: Chrysanthemum morifolium; Essential oil; Management; Orthotospovirus; Thrips; Tomato spotted wilt virus.