Further studies on Iris yellow spot tospovirus
Studies were done in Israel on the distribution of Iris yellow spot tospovirus (IYSV - EPPO Alert List) in its host plants, and on its transmission by thrips vectors. The known host plants of IYSV are Hippeastrum, onion (Allium cepa) and lisianthus (Eustoma russellianum). In Israel, IYSV is associated with a disease of onion called by the growers ‘straw bleaching’. The disease incidence can reach 50-60% in certain areas, leading to heavy losses in bulb production. Transmission studies showed that Frankliniella occidentalis is not a vector, but that Thrips tabaci can transmit IYSV from infected to healthy onion seedlings and leaf pieces. In the field, it was observed that population levels of T. tabaci were strongly related to disease incidence. It was also shown that the distribution of the virus within onion plants is uneven. Highest virus titres were found in inner leaves and near the bulb, but IYSV could not be detected in bulbs or roots of infected onions and Hippeastrum. In addition, no virus transmission could be obtained in the subsequent generations. Seeds harvested from infected onions did not transmit the virus to progeny plants. It appears that IYSV is not transmitted through seeds or bulbs, but by its thrips vector. The authors stressed that more studies on other natural hosts which could act as plant reservoirs in nature are needed to better understand the epidemiology of the disease.
Sources
Kritzman, A.; Lampel, M.; Raccah, B.; Gera, A. (2001) Distribution and transmission of Iris yellow spot virus.
Plant Disease, 85(8), 838-842.