Occurrence of tomato spotted wilt tospovirus in native flora, weeds, and horticultural crops

Abstract

Surveys to determine the incidence of tomato spotted wilt tospovirus (TSWV) in native plants, weeds, vegetables, and flowering ornamentals were done within or near horticultural properties in the Perth metropolitan area. Leaf or petal samples were tested for TSWV by enzyme-linked immunosorbent assay (ELISA). Samples from native plants and flowering ornamentals were also tested for impatiens necrotic spot tospovirus (INSV). Forty-two species of native plants were sampled from 17 sites. Of the 1590 plants sampled, only 1 plant of Calectasia cyanea (blue tinsel lily) was found to be infected. Weeds were sampled from 24 sites, and samples from 5543 plants in 45 species were tested. TSWV was found in 59 samples belonging to 16 different species from 8 sites. Among these, the highest virus infection levels at individual locations were in Arctotheca calendula (capeweed; 15%) and Sonchus asper (sowthistle; 32%). Vegetables were sampled from 28 sites, and samples from 3864 plants in 9 species were tested. TSWV was found in 309 samples from 22 sites. Those found to be infected were broad bean, capsicum, celery, chilli, eggplant, globe artichoke, lettuce, paprika, potato, and tomato. At individual locations, capsicum and tomato crops were sometimes 100% infected. Flowering ornamentals were sampled from 6 sites, and samples from 2698 plants in 16 species were tested. TSWV was found in 296 samples from 3 sites. Those found to be infected with TSWV were alstroemeria, calendula, Chinese aster, chrysanthemum, cosmos, dahlia, delphinium, gladiolus, snapdragon, statice, and zinnia. Highest incidences were in alstroemeria (32%), asters (81%), calendula (65%), chrysanthemum (30%), dahlia (28%), and statice (57%). No INSV was detected. In an infected calendula crop, TSWV infection declined sharply with distance from an aster infection source. Eight isolates of TSWV obtained from different weeds, vegetables, and flowering ornamentals differed widely in the severity of symptoms they induced in Nicotiana glutinosa, capsicum, and tomato. High incidences of TSWV were commonly associated with the presence of Frankliniella occidentalis (western flower thrips). Reservoirs of TSWV infection identified during the survey included infected planting stock and volunteer plants of vegetatively propagated flowering ornamentals, seedlings of vegetables previously infected in nurseries, old infected vegetable and flowering ornamental crops growing next to subsequently planted crops, and weeds. A control strategy involving the removal or avoidance of TSWV sources and vigilance to limit introduction of INSV on imported flowering ornamentals is discussed.