Detection of tospoviruses in bulbous crops and transmissibility by vegetative propagation

In dahlia visual selection on tomato spotted wilt virus (TSWV) is only possible to a limited extent. The unequal distribution of the virus in various plant parts during the growing and storage period caused problems in the development of a reliable test protocol. A serological test on tubers appeared to be the best: the tubers have to be stored for at least 1 month at 9°C and samples have to consist of at least three roots per tuber. 40-90% of the cuttings from TSWV-infected dahlia tubers appeared to be infected. Symptoms of TSWV in both gladiolus and iris cannot be distinguished from those caused by Impatiens necrotic spot virus (INSV). In iris a third (putative) tospovirus was detected, which is called iris yellow spot virus. In progeny-plants from infected iris and gladiolus no tospoviruses were detected. In Hippeastrum, Amaryllis and Nerine TSWV was detected in symptom-bearing leaves and also in the tunics connected with these leaves, but less frequent in other parts of the bulbs. This might explain the curing of the main bulbs after some years and the limited transmission of TSWV to the daughter bulbs.